Table of Content

25 December 2022, Volume 43 Issue 24
Food Chemistry
Effect of Glycation with Different Reducing Saccharides on Conformation and Antioxidant Activities of Ultrasonic Pretreated α-Lactalbumin
BU Dan, TU Zongcai, LIU Guangxian, HU Yueming, WANG Hui
2022, 43(24):  1-6.  doi:10.7506/spkx1002-6630-20211014-143
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Ultrasonic pretreated α-lactalbumin (α-LA) was glycated with D-glucose, D-mannose and D-allose under dry heat treatment at 55 ℃ for 6 h, separately. The molecular mass, grafting degree, particle size, secondary structure, tertiary structure and antioxidant activity of glycated α-LA were investigated. The results showed that the structure and antioxidant activity of α-LA were affected by glycation, and ultrasonic pretreatment promoted the glycation reaction. Among these reducing sugars, α-LA modified with D-allose exhibited the lowest relative content of free amino acids, highest degree of glycation and largest increase in antioxidant activity, and ultrasonic pretreatment could enhance the antioxidant activity of α-LA. The enhanced glycation extent and the conformational changes of α-LA may contribute to the increase in the antioxidant activity of α-LA. Ultrasonic assisted glycation is a promising method to improve the functional properties of α-LA.
Differences in Thermal Degradation and Rheological Properties of Alkali-Soluble Pectin Fraction in Two Kinds of Lotus Rhizome with Different Textures
DUAN Ruibing, LI Jie, LIU Jihong, YAN Shoulei
2022, 43(24):  7-15.  doi:10.7506/spkx1002-6630-20220301-002
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In this study, sodium carbonate-soluble pectin fraction (NSF) from two kinds of lotus rhizome with different textures (mealy and crunchy) were evaluated for differences in thermal degradation and its relationship with rheology. After heat treatment at different temperatures, primary structure analysis and nanostructure observation of NSF showed that the thermal degradation degree of NSF from Miancheng lotus rhizome (mealy) was greater than that of NSF from Lulin Lake lotus rhizome (crunchy). The chain of NSF from Lulin Lake lotus rhizome was star-shaped (long branched chain), while the chain of NSF from Miancheng lotus rhizome was mostly short, straight. For both of them, the chain length and height decreased and so did the branching degree after heating. Additionally, the consistency decreased significantly. The pseudoplasticity of NSF from Miancheng lotus rhizome increased slightly, while that of NSF from Lulin Lake lotus rhizome decreased. The chain length, chain height and branching degree of NSF were closely related to the consistency, and the branching degree and the proportion of chains of different lengths (molecular mass distribution) contributed greatly to the difference in pseudoplasticity. Therefore, there was a close relationship between the structure and the rheological properties of NSF, and the difference in thermal degradation of NSF was related to the texture difference between mealy and crunchy lotus rhizome. This study provides a theoretical basis for understanding the relationship between the thermal degradation of NSF and the texture (processing and maturity) of fruits and vegetables.
Cryoprotective Effect and Mechanism of Fish Scale Gelatin on Surimi Myofibrillar Proteins
ZHU Shichen, YU Jiehang, JIN Yan, DING Yuting, ZHOU Xuxia, YANG Qing, WEI Zhengpeng, WANG Jinmei
2022, 43(24):  16-24.  doi:10.7506/spkx1002-6630-20220119-192
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The cryoprotective effects of adding different concentrations (0.5%, 1% and 2% (m/m)) of fish scale gelatin on frozen-thawed surimi were investigated in terms of the molecular structure myofibrillar proteins and gel properties. After eight cycles of freezing and thawing, the solubility, sulfhydryl content and Ca2+-ATPase activity of myofibrillar proteins with 1% fish scale gelatin decreased by 49.2%, 17.4% and 31.2%, less than those in the control group without fish scale gelatin (69.8%, 26.6%, and 49.4%), respectively. The increase in surface hydrophobicity and carbonyl content was inhibited more by 1% fish scale gelatin (42.7% and 229.9%) than by commercial anti-freezer (159.4%). Meanwhile, adding fish scale gelatin obviously inhibited the deterioration of the rheological properties and gel properties of surimi during freeze-thaw cycles. Furthermore, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and differential scanning calorimetry (DSC) indicated that fish scale gelatin could inhibit myofibrillar protein degradation by interacting hydrophobically with the side chain of myofibrillar proteins as well as inhibiting ice crystal growth.
Effect of Extrusion Temperature on Functional and Structural Properties of Extruded Rice Protein and Glucose Conjugates
HUO Jinjie, XU Yan, WANG Na, WANG Peng, ZHU Minpeng, ZHANG Yifan, GAO Yuzhe, XIAO Zhigang
2022, 43(24):  25-32.  doi:10.7506/spkx1002-6630-20211003-009
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In order to develop a rapid and efficient method for the industrial production of rice protein-glucose conjugates, rice protein was extruded and then subjected to the Maillard reaction with glucose. Herein, rice protein was extruded at different temperatures (80, 90, 100, 110, 120 and 130 ℃) and then conjugated with glucose for 30 minutes at pH 10.5. We analyzed the effect of different extrusion temperatures on the functional properties (solubility, emulsification activity index (EAI) and emulsion stability index (ESI)) and structural properties of extruded rice protein and glucose (ERPG) conjugates and characterized ERPG conjugates using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Compared to native rice protein and glucose (NRPG) conjugate, the degree of glycosylation (DG) of ERPG conjugate prepared with rice protein extruded at 90 ℃ was the highest, and the solubility of ERPG conjugates prepared with rice protein extruded at 90–120 ℃ decreased. The EAI, ESI and surface hydrophobicity of ERPG conjugates prepared with rice protein extruded at 80–90 ℃ increased, while those of ERPG conjugates prepared with rice protein extruded at 100–130 ℃ slowly decreased. The FTIR results showed that ERPG conjugate had higher contents of α-helix, β-turn and random coil and a lower content of β-sheet than NRPG. The SDS-PAGE indicated that the protein was aggregated into larger particles by extrusion. Under SEM, ERPG conjugates exhibited more disordered structure with irregular fragments.
Effect of Temperature on Color, Physicochemical Characteristics and Antioxidant Activities of Ovalbumin-Glucose System under Alkaline Condition
TAN Ji’en, YAO Yao, WU Na, XU Mingsheng, ZHAO Yan, LIU Huiping, TU Yonggang
2022, 43(24):  33-41.  doi:10.7506/spkx1002-6630-20211010-092
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This study was conducted to investigate the effect of temperatures (4, 25 and 37 ℃) on the color, physicochemical characteristics and antioxidant activities of ovalbumin-glucose system during the Maillard reaction induced by alkali. The results showed that with increasing either incubation time or temperature, the color of ovalbumin-glucose system was deepened, and the contents of brown products and fluorescent compounds increased gradually; the content of intermediate products increased at 4 and 25 ℃, but increased at first and then decreased at 37 ℃ with increasing reaction time. Likewise, the pH increased at first then decreased. Fourier transform infrared (FTIR) spectroscopic analysis showed that ovalbumin was conjugated with glucose. Amino acid analysis suggested that the serine, histidine and cysteine residues in ovalbumin had relatively high reactivity, and the cysteine residue had the highest reactivity among them. The antioxidant activity of the reaction product from ovalbumin-glucose system was significantly improved compared with their physical mixture, but it slightly decreased with incubation time.
Preparation and Stability Analysis of Soy Protein Isolate-High Methoxyl Citrus Pectin-Gallic Acid Pickering Emulsion
XU Xinyu, YANG Hujun, JIA Bin, ZHANG Huimin, ZUO Feng
2022, 43(24):  42-51.  doi:10.7506/spkx1002-6630-20210929-353
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In this study, a protein-polysaccharide-polyphenol complex was prepared from soybean protein isolate (SPI), high methoxyl citrus pectin (HMCP) and gallic acid (GA). The preparation conditions were optimized by using one-factor-at-a-time method and orthogonal array design. Furthermore, a Pickering emulsion was prepared with this complex and characterized for rheological properties, particle size and distribution, zeta potential and emulsion stability. The results showed that the maximum absorbance of 3.082 was observed for the emulsion containing the complex prepared at pH 4.5 and 35 ℃ using 40 mg of gallic acid. Under these conditions, SPI, HMCP and GA were most tightly bound. The Pickering emulsion with an oil volume fraction (φ) of 0.7 had the best elasticity and viscosity, and formed a dense gel network structure. Its zeta potential and average droplet size were (?54.08 ± 2.74) mV and (220.36 ± 7.13) nm, respectively. The Pickering emulsion showed weaker creaming and smaller droplet size at 4 ℃ than 25 ℃, which was more conducive to maintaining the emulsion stability. With the increase of heat treatment temperature, the creaming degree of the emulsion increased gradually. At φ values of 0.7 and 0.8, the droplet size was not affected by temperature. Freezing destroyed the interface of the emulsion. With increasing either φ value or freezing time, the creaming phenomenon became more obvious, greatly reducing the stability of the emulsion. With the increase of pH, the creaming phenomenon became more obvious. When the emulsion system pH was close to 4, the droplet size was the smallest and the droplet size distribution was relatively uniform. High concentration of salt ions destroyed the degree of binding of the complex, caused droplet aggregation and obvious creaming, and reduced the stability of the emulsion.
Effect of Sodium Salt Substitute on the Functional Properties of Liquid Whole Egg
TONG Ping, ZANG Feng, HOU Yuliang, CHEN Hongbing, GAO Jinyan
2022, 43(24):  52-59.  doi:10.7506/spkx1002-6630-20211201-012
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In order to explore the feasibility of replacing sodium chloride with potassium chloride or magnesium chloride to improve the functional properties of liquid whole egg (LWE), the effects of different concentrations of sodium chloride (0.2, 0.4, 0.8 and 1.6 mol/L), potassium chloride (0.2, 0.4, 0.8 and 1.6 mol/L) and magnesium chloride (5, 10, 20 and 40 mmol/L) on the physicochemical and functional properties of LWE were evaluated. The results showed that the functional properties of LWE were significantly affected by the addition of salt. After adding 0.8 and 1.6 mol/L potassium chloride, the foam stability was increased by 21.4% and 21.6%, respectively. After adding 20 and 40 mmol/L magnesium chloride, the emulsion stability was increased by 14.7% and 24.1%, respectively, and the protein solubility by 12.7% and 13.8%, respectively. In addition, the water-holding capacity and elasticity of LWE gels were not damaged after adding 40 mmol/L magnesium chloride, and the gel hardness was significantly increased. Meanwhile, 40 mmol/L magnesium chloride caused little change in the color of LWE and no significant change in its pH. In conclusion, magnesium chloride has the potential to replace sodium chloride to improve the functional properties of LWE. These results will provide a theoretical basis for adding sodium salt substitute into LWE.
Preparation and Physicochemical Properties of Phenolic Acid-Citrus Pectin Copolymers by Free Radical-Mediated Grafting
YANG Hujun, ZUO Feng, WANG Kun, XU Xinyu, ZHANG Huimin, JIA Bin
2022, 43(24):  60-66.  doi:10.7506/spkx1002-6630-20220301-018
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In this study, phenolic acid-citrus pectin copolymers was prepared by a free radical-mediated grafting method, and their structure and physicochemical properties were analyzed and compared. The results showed that among five phenolic acid-citrus pectin copolymers, the grafting rate was syringic acid-citrus pectin copolymer was the highest, (74.2 ± 1.38) mg/g, followed by gentisic acid-citrus pectin copolymer, (67.24 ± 1.55) mg/g. Compared with pectin, the molecular mass distribution of the graft copolymers was more homogeneous and decreased significantly. The molecular masses of gentisic acid-citrus pectin and syringic acid-citrus pectin copolymers decreased from (109.98 ± 0.05) kDa to (65.11 ± 0.02) and (39.83 ± 0.05) kDa, respectively, the degrees of esterification increased from (51.62 ± 1.46)% to (70.83 ± 1.64)% and (72.73 ± 2.18)%, respectively, the contents of galacturonic acid increased from (39.18 ± 1.08)% to (52.42 ± 1.36)% and (53.88 ± 1.19)%, respectively, and the solubility increased from (39.34 ± 1.08)% to (54.40 ± 1.36)% and (59.87 ± 1.21)%, respectively. In addition, through Fourier transform infrared spectroscopy and scanning electron microscopy, it was found that the monosaccharide type of phenolic acid-citrus pectin copolymer was identical to that of pectin, and phenolic acid was mainly covalently grafted onto the molecular chain of citrus pectin, resulting in a decrease in its thermal stability, and causing the structure of citrus pectin to change from rough, dense, blocky to flaky with a relatively smooth surface.
Preparation, Physicochemical Properties and Structural Characterization of Chondroitin Sulfate from Tilapia Processing By-Products
ZUO Gege, ZHONG Saiyi, CHEN Jing, XU Minfeng, CHEN Jianping, LI Rui, LIU Xiaofei, SONG Bingbing, JIA Xuejing
2022, 43(24):  67-73.  doi:10.7506/spkx1002-6630-20211013-119
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In this study, chondroitin sulfates were prepared from tilapia processing by-products (head, backbone, fin and tail) by two-step enzymatic hydrolysis followed by precipitation with cetane pyridine chloride. Their physicochemical properties and structural characteristics were analyzed by ultraviolet (UV) spectroscopy, cellulose acetate electrophoresis, infrared spectroscopy and high performance liquid chromatography (HPLC). The results showed that fish heads and tails mainly contained type C chondroitin sulfate (Δdi6S) at levels of 46.10% and 41.01%, respectively; fish backbones and fins mainly contained type A chondroitin sulfate (Δdi4S) at levels of 71.86% and 69.59%, respectively. The decreasing order of the purity of chondroitin sulfates from these body parts was heads (90.37%), tails (83.33%), backbones (59.76%), and fins (52.01%). Monosaccharide composition analysis showed that chondroitin sulfates from fish heads, backbones, fins and tails were mainly composed of glucuronic acid, glucose and galactosamine in different proportions, and their number-average molecular masses were 51 422, 18 402, 19 481 and 76 371, respectively. The types and composition of chondroitin sulfate extracted from different body parts were significantly different. Chondroitin sulfates extracted from tilapia heads and tails were similar to that from shark cartilage, and thus may have the potential to replace chondroitin sulfate from shark cartilage.
Ball Milling Combined with Alkaline-Assisted Enzymatic Extraction Improved the Physicochemical and Functional Properties of Soluble Dietary Fiber from Herba Lophatheri
FAN Hua, LIU Fuguo, WANG Yutang, LI Yinxia, LIU Xuebo
2022, 43(24):  74-82.  doi:10.7506/spkx1002-6630-20220301-013
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Soluble dietary fiber (SDF) was extracted from Herba Lophatheri by enzymatic extraction, ball milling-assisted enzymatic extraction, alkaline-assisted enzymatic extraction, and ball milling combined with alkaline-assisted enzymatic extraction. The yield of SDF was determined, the four SDFs were characterized by high performance liquid chromatography (HPLC), nano-laser particle size analyzer, rheometer, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and differential scanning calorimetry (DSC), and their water-holding capacity, oil-holding capacity, and antioxidant activity were analyzed and compared. The results suggested that all SDFs had the typical structure of polysaccharides and the same crystal types as cellulose, but their monosaccharide composition and microstructure were different. SDF extracted by ball milling combined with alkaline-assisted enzymatic extraction had the highest yield ((30.03 ± 1.03)%) and water-holding capacity ((4.86 ± 0.1) g/g), high viscosity, and the lowest zeta potential ((?22.83 ± 1.95) mV). Besides, it had a loose porous structure, and potent 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging activity ((49.40 ± 0.93)%), indicating strong water-binding capacity, antioxidant activity, and gel-forming capacity.
Synthesis and Evaluation of Sweet Dihydrochalcone Derivatives from Naringin
LI Zhihao, HUANG Baohua, ZHEN Weicong, ZHOU Jinlin, LU Yujing
2022, 43(24):  83-92.  doi:10.7506/spkx1002-6630-20220317-197
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Naringin was hydrolyzed in hot alkali solution to obtain phloracetophenone-4’-β-neohesperiodoside as an intermediate product for the synthesis of 13 dihydrochalcone glycosides by Claisen Schmidt condensation and O-Michael addition with several benzaldehyde derivatives, where methyl, methoxy, hydroxyl or halogen atoms were introduced into the B ring, followed by catalytic hydrogenation. The structures of these dihydrochalcone glycosides were confirmed by 1H and 13C nuclear magnetic resonance (NMR). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was used to investigate their cytotoxic effects on HK2 cells. The survival rate of HK2 cells was more than 80%, indicating no obvious cytotoxicity. Sensory evaluation showed that of the 13 compounds, seven were sweet, five were not sweet and one was bitter. An electronic tongue equipped with sweetness sensors was used to detect the sweetness values of reference substances and the 13 dihydrochalcone glycosides. The results were basically consistent with the sensory evaluation. The correlation analysis between the structures of the dihydrochalcone glycosides and their sweetness showed that the sweetness of dihydrochalcone derivatives with neohesperisyl at position 4 on the A ring was greatly affected by the substituent groups at positions 3’ and 4’ of the B ring. The seven sweet dihydrochalcone glycosides had no substituent at positions 2’ to 6’of the B ring or were connected with OH, F or Cl. Methyl and methoxyl groups were not the key groups contributing to the sweetness.
Effects of Extraction Methods on the Structural and Functional Characteristics of Dietary Fiber from Auricularia cornea var. Li.
WANG Siqi, WANG Jiajia, LI Bozheng, GUO Wanchun, LIU Xuejun
2022, 43(24):  93-101.  doi:10.7506/spkx1002-6630-20211028-324
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Insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) from Auricularia cornea var. Li. were extracted by alkaline or enzymatic extraction. Our aim was to compare the effects of the two extraction methods on the structural, physicochemical and functional properties of dietary fiber. Scanning electron microscopy (SEM) analysis showed that dietary fiber extracted by enzymatic extraction method had a looser and more complex structure. Fourier transform infrared spectroscopy (FTIR) indicated that all samples showed the characteristic absorption peaks of sugar. X-ray diffraction analysis (XRD) showed that enzymatically extracted dietary fiber had lower crystallinity. Thermogravimetric analysis (TGA) demonstrated that alkaline extracted dietary fiber had higher stability. Enzymatically extracted dietary fiber had water-holding capacity of 10.68?20.79 g/g, oil-holding capacity of 2.05?3.72 g/g, swelling power of 2.85?12.14 mL/g, glucose content of 4.92?7.95 μg/g and cholesterol-adsorbing capacity of 3.89?8.19 mg/g, which were significantly higher than those of dietary fiber extracted by alkaline method, and it had a stronger inhibitory effect on α-amylase (45.43%?66.71%) and pancrelipase (21.50%?36.52%). These results reveal that the dietary fiber of A. cornea var. Li. can be used as a functional food ingredient. This study provides a theoretical basis for further exploring the nutritional value of A. cornea var. Li..
Effect of Safflower Seed Oil Emulsion Loaded with Resveratrol on the Quality of Nemipterus virgatus Surimi Gel
SONG Chunyong, HONG Pengzhi, ZHOU Chunxia, ZHONG Tanjun, LIU Lu
2022, 43(24):  102-109.  doi:10.7506/spkx1002-6630-20211017-178
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In order to improve the quality of surimi products, the effects of safflower seed oil emulsion (10 mL/100 g) loaded with resveratrol on the gel properties, microstructure and oxidative stability of Nemipterus virgatus surimi gel were investigated, and the effects of resveratrol addition at different levels (0.1%?0.3%) on the quality of surimi gels were compared. The results showed that the whiteness, water-holding capacity and bound water content of N. virgatus surimi gel were increased by adding safflower seed oil emulsion, together with an improvement in the texture characteristics and a decrease in the cooking loss percentage (P < 0.05). In addition, the pore size of the three-dimensional network structure of the gel was reduced. The distribution of oil droplets in the gel matrix with safflower seed oil emulsion was not uniform, the average diameter of oil droplets was great than 2.0 μm, and the oxidation of oil increased with storage time (P < 0.05). Furthermore, after adding safflower seed oil emulsion loaded with resveratrol, the whiteness and water-holding capacity were significantly increased together with a decrease in the cooking loss percentage (P < 0.05) and a significant enhancement in the texture and oil oxidation stability of the gel (P < 0.05). Resveratrol still had strong antioxidant activity in the surimi gel matrix. Resveratrol could contribute to the emulsification of safflower seed oil, making fine oil droplets be evenly distributed in the gel matrix, and the interaction between resveratrol and proteins in surimi promoted the formation of gel networks. The average diameter of oil droplets in the emulsion with 0.3% resveratrol was less than 1.5 μm, and the three-dimensional network structure of the gel with 0.3% resveratrol exhibited the smallest pore size and a uniform and dense spatial hierarchy. Therefore, safflower seed oil emulsion loaded with resveratrol could improve the gel characteristics of N. virgatus surimi and enhance the oxidative stability of the gel, which will be useful for the development of new surimi products.
Effect of Pathway Configurations on the Synthesis of 2’-Fucosyllactose in Escherichia coli
LIANG Shanquan, ZHANG Dengya, YANG Shaoqing, HE Zi, LIU Dan, JIANG Zhengqiang
2022, 43(24):  110-116.  doi:10.7506/spkx1002-6630-20220602-016
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The de novo synthesis pathway of 2’-fucosyllactose (2’-FL) was established in Escherichia coli BL21 Star (DE3) in this study. The β-galactosidase gene lacZ M15 and the uridine diphosphate (UDP)-glucose lipid carrier transferase gene wcaJ were knocked out using the CRISPR/Cas9 gene editing system. The effects of three different pathway configurations, viz., operon, pseudo-operon, and monocistronic on the synthesis of 2’-FL were explored. The results showed that the concentration of 2’-FL produced in shake flasks was 0.34 g/L after overexpression of the de novo synthesis pathway related genes in E. coli BL21 Star (DE3). The concentration of 2’-FL was increased to 1.26 g/L by deleting the lacZ M15 and wcaJ genes. The highest concentration of 2’-FL of 1.92 g/L was observed in strain BS-7 when regulated by the operon expression. Fed-batch fermentation of strain BS-7 accumulated 14.04 g/L 2’-FL with a productivity of 0.59 g/(L·h) and a lactose conversion rate of 63%, respectively. This study suggested that lower gene expression levels not only increased 2’-FL production, but also could improve the conversion efficiency of substrate in engineered E. coli.
Purification, Physicochemical Properties, and Mimotope Peptide Prediction of Tropomyosin from Antarctic Krill (Euphausia superba)
WANG Shan, LIU Yao, LIU Kexin, ZHANG Shuqi, LIN Songyi, SUN Na
2022, 43(24):  117-128.  doi:10.7506/spkx1002-6630-20220223-184
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Tropomyosin (TM) from Antarctic krill (Euphausia superba) was extracted, purified, and identified by mass spectrometry, and its thermal stability, pH stability and digestive stability were studied. Meanwhile, sequence homology analysis, spatial structure homology modeling, and allergen mimotope peptide recognition were carried out using bioinformatics. The crude protein was extracted, thermally treated to remove impurities, precipitated at the isoelectric point and purified by salting-out. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of the purified protein showed only one clear band with molecular mass near 32 kDa. The target protein was identified as TM (Euphausia superba) by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis and UniProt database search. The molecular mass of the protein was 32.6 kDa and the peptide coverage was 97%. The results of homology analysis and physicochemical properties showed that TM from Antarctic krill was a highly conserved protein, and its sequence homology with those from 26 crustacean species ranged from 88% to 98.2%. TM from Antarctic krill had strong stability to heat, acid, alkali and gastric juice digestion, but poor stability to intestinal juice digestion, and was easily degraded by trypsin and chymotrypsin to produce low-molecular-mass peptides. Eight mimotope peptides (EAQNKETNAKADKADDEVH, DLERSEERLN, TKLAEASQAADESER, EADRKYDE, ERAEERAEAG, VSEEKANQREEAYKEQI, RSVQKLQKEVDR, VNEKEKYKGI) in Antarctic krill TM were finally predicted and identified by five bioinformatics tools including DNAStar Protean, AntheProt, BepiPred 1.0 server, ABCpred server, and Immunomedicine Group, and mapped in the spatial structure. This study provides a scientific basis for the accurate prediction and identification of mimotope peptides in TM from Antarctic krill and the development of hypoallergenic products.
Gas Chromatography-Time-of-Flight Mass Spectrometry for Analysis of Metabolites in Large Yellow Croaker Roe Sauce during Rapid Fermentation
ZHOU Jing, ZHANG Huadan, HUO Yuming, LEI Cailing, DU Xiping, LIANG Peng, CHENG Wenjian, CHEN Lijiao
2022, 43(24):  129-137.  doi:10.7506/spkx1002-6630-20220226-227
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In order to understand the differences and changes of metabolites in large yellow croaker roe sauce during rapid fermentation, samples were collected over a fermentation period of 30 days and analyzed for metabolite composition by gas chromatography-time-of-flight mass spectrometry (GC-TOF-MS). Multivariate statistical analysis was performed on the obtained data, and the differential metabolites were selected based on statistically significant difference at P ≤ 0.05 and the variable importance in the projection (VIP) of the first principal component (PC1) ≥ 1 in the orthogonal partial least squares-discriminant analysis and were analyzed by hierarchical agglomerative clustering. The results showed that a total of 46 differential metabolites were identified, including 10 sugars, 9 alcohols, 7 of amino acids, 6 organic acids, 4 esters and 3 aldehydes, 1 fatty acid, and 6 other compounds. These metabolites were involved in the metabolic pathways of valine, leucine and isoleucine biosynthesis, protein digestion and absorption, galactose metabolism, ammonia acyl-tRNA biosynthesis, glycine, serine and threonine metabolism, glucosinolate biosynthesis, citric acid cycle, amino acid biosynthesis, shikimic acid-based biosynthesis of alkaloids, inositol phosphate metabolism, and biosynthesis of unsaturated fatty acids. Fifteen significantly differential metabolites were identified included amino acid metabolites involved in multiple metabolic pathways. The results of this study provide a theoretical basis for the industrial production of large yellow croaker roe sauce.
Effect of Phospholipase A1 Auxiliary Protein PlaS of Serratia marcescens on the Cell Membrane of Host Bacteria and Its Subcellular Localization
ZHOU Jie, WU Zhenghao, LI Chuang, LIU Qingtao, ZHANG Huimin, WANG Zhou, LIU Yan, XUE Zhenglian
2022, 43(24):  138-144.  doi:10.7506/spkx1002-6630-20220302-024
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To prove that the phospholipase A1 accessory protein PlaS of Serratia marcescens has a significantly disruptive effect on the cell membrane of Escherichia coli BL21 (DE3) during heterologous expression, changes in cell membrane properties were explored, their effect on cell membrane fatty acids was identified by gas chromatography-mass spectrometry (GC-MS), and subcellular localization was observed by laser confocal microscopy. The results showed that after the heterologous expression of PlaS, the inner and outer membrane permeability of the host bacterium was significantly increased, and cell membrane fluidity and surface hydrophobicity were severely decreased, indicating loss of cell membrane functions; the saturation degree of fatty acids was decreased, that is, the relative contents of straight-chain saturated fatty acids and trans-monounsaturated fatty acids in fatty acids were reduced, and the relative contents of cis-monounsaturated fatty acids were increased. Moreover, membrane rigidity was enhanced, membrane fluidity was reduced, and the cell membrane components and structure were abnormal, so that the cells could be susceptible to death. Laser confocal microscopy showed that significant fluorescence was observed in the host cell membrane. In summary, the heterologous expression of the membrane protein PlaS in E. coli disrupts the structure and function of the host cell membrane and exhibits growth inhibition, which will provide support for further research on the mechanism of PlaS inhibition and its functional development.
Differences in Enzymatic Properties between Mannanases from Aspergillus fumigatus (AfMan5A) and Rhizopus microsporus (RmMan134C) and Their Synergy in the Degradation of Polysaccharides
LIU Xue, LU Haiqiang, WANG Yuyin, TIAN Hongtao, GU Xinxi
2022, 43(24):  145-153.  doi:10.7506/spkx1002-6630-20220105-030
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This study aimed to analyze the differences in the enzymatic properties of mannanases from Aspergillus fumigatus HBHF5 (AfMan5A, belonging to the GH5 family) and Rhizopus microsporus GZHF10 (RmMan134C, belonging to the GH134 family), and to explore their potential to synergistically degrade polysaccharides when used in combination. The results showed that the enzymatic properties of AfMan5A and RmMan134C were quite different. The optimum temperature and pH of AfMan5A were 60 ℃ and 6.0, respectively, while those of RmMan134C were 35 ℃ and 5.0, respectively. Cu2+, Zn2+, Mn2+ showed inhibitory activity against both enzymes, while Mg2+, Fe3+ and Li+ could promote the activity of AfMan5A, but slightly inhibit the activity of RmMan134C. RmMan134C exhibited a broader spectrum of substrates than AfMan5A, and the best substrate for both of them was konjac glucomannan. Furthermore, they did not synergistically act on mannan-based substrates but showed a good synergistic effect in the degradation of microcrystalline cellulose, with a synergy coefficient of 6.1. This study analyzed the difference in properties of GH5 and GH134 family mannanases and the synergistic effect of degrading polysaccharides, and provided a certain theoretical support for the further application and promotion of mannanases.
Differences in Microbial Diversity and Metabolites in Naturally Fermented and Starter Culture-Fermented Mutton Sausages
TIAN Haiyong, SU Wei, MU Yingchun, JIANG Li, ZHAO Chi
2022, 43(24):  154-163.  doi:10.7506/spkx1002-6630-20211221-247
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To explore the effects of fermentation methods on the microbial communities and metabolites in dry fermented mutton sausages, the differences in the microbial communities and metabolites in naturally fermented and starter culture-fermented mutton sausages were analyzed by high-throughput sequencing and metabolomics, and the correlation between microbial communities and significantly differential metabolites (SDM) was investigated. The results showed that inoculated fermentation had obvious effect on the microbial community of mutton sausages. At the genus level, Leuconostoc, Rahnella, Brochothrix and Debaryomyces were dominant during natural fermentation, and Leuconostoc, Brochothrix, Psychrobacter, Pediococcus, Debaryomyces and Penicillium were dominant during inoculated fermentation. Inoculate fermentation increased the types and contents of flavor substances, especially esters and amino acids. Based on multivariate statistical analysis, 29 volatile metabolites and 16 non-volatile metabolites that significantly differed between the natural and inoculated fermentation groups were identified (fold change (FC) > 2, variable importance in the projection (VIP) > 1, P < 0.05). Besides, correlation analysis showed that seven bacterial genera (Leuconostoc, Brochothrix, Pediococcus, Psychrobacter, Enterococcus, Rahnella and Staphylococcus) and seven fungal genera (Debaryomyces, Penicillium, Aspergillus, unspecified_Aspergillaceae, unspecified_Capnodiales, unspecified_Capnodiales, Rhizopus and unspecified_Basidiomycota) were regarded as core microorganisms (| r | > 0.8, P < 0.05).
Bacterial Community Succession during Long-Term Fermentation of Shrimp Paste and Its Effect on Formation of Biogenic Amines
DENG Yijia, WANG Rundong, ZHANG Yuhao, LI Xuepeng, JI Guangren, LI Jianrong
2022, 43(24):  164-173.  doi:10.7506/spkx1002-6630-20220306-076
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Sensory characteristics, the succession of bacterial communities and the contents of six biogenic amines during long-term fermentation (1, 2, 3 and 8 years) of shrimp paste were investigated by sensory evaluation, high-throughput sequencing and high-performance liquid chromatography (HPLC), respectively. Results showed that the color of shrimp paste turned dark brown, the L* value declined and the b* value increased then declined, and the grainy mouthfeel disappeared along with the prolongation of fermentation time. Meanwhile, the shrimp-like and ammonia-like smell decreased, and umami taste reached the maximum after two years of fermentation. The bacterial flora detected in shrimp paste comprised 600 species belonging to 894 genera in 42 phyla, with the dominant phyla being Firmicutes and Proteobacteria, and the dominant genera being Tetragenococcus, Psychrobacter, Pseudomonas, Enterococcus, Lactobacillus and Roseovarius, and the bacterial diversity reached a peak after two years of fermentation. The types and contents of biogenic amines in shrimp paste gradually increased as fermentation progressed. Putrescine, cadaverine, histamine, tyramine, spermidine and spermidine were detected in all samples after eight years fermentation. Pearson correlation analysis showed that histamine had a significantly positive correlation with Devosia (P < 0.05), but a significantly negative correlation with Bacillus, Ralstonia, Photobacterium and Staphylococcus (P < 0.01). Putrescine had a significantly positive correlation with Ralstonia (P < 0.01), buta significantly positive correlation with Pseudomonas, Roseicyclus and Sulfitobacter (P < 0.05). Acinetobacter was positively correlated with cadaverine (P < 0.01). The study provides a theoretical basis for screening functional strains and controlling biogenic amines in shrimp paste.
In Vitro Colonic Fermentation Characteristics of Chemically Crosslinked High-Amylose Maize Starches and Their Regulation Mechanism on Gut Microbiota
LIU Junkai, WANG Shaokang, GU Zhipeng, FU Xiong, HUANG Qiang, ZHANG Bin
2022, 43(24):  174-181.  doi:10.7506/spkx1002-6630-20220112-112
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In this study, we used high-amylose maize starch as the raw material to prepare chemically crosslinked starches with different crosslinking degrees employing sodium trimetaphosphate (STMP), phosphorus trichloride oxide (POCl3) or epichlorohydrin (EOH) as the crosslinker. The in vitro fermentation characteristics of the crosslinked starches with fecal microorganisms were investigated and the effect of the crosslinked starches on the intestinal microbiota in vitro was evaluated. Results showed that the fermentation rate of the crosslinked starches decreased with increasing amount of crosslinker used. All these crosslinked starches increased the relative abundance of beneficial bacteria including Roseburia and Ruminococcus. Compared to STMP and POCl3, EOH crosslinking more effectively inhibited the fermentation rate of starch, and promoted butyric acid production.
Microbial Community Succession and Quality Change of Commercial Low-Salt Shrimp Paste during Fermentation
BAN Yuhan, WANG Liwen, YANG Bingbing, MA Aijin, SANG Yaxin, SUN Jilu
2022, 43(24):  182-191.  doi:10.7506/spkx1002-6630-20210930-373
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In order to improve the fermentation process of the emerging commercial low-salt shrimp paste, this study systematically analyzed the changes in the major quality indicators during the fermentation process. High-throughput sequencing technology was used to analyze the microbial community diversity and composition. The results showed that during the fermentation of shrimp paste, the pH, malondialdehyde (MDA) content, total volatile basic nitrogen (TVBN) content, amino acid nitrogen content, moisture content, salt content and biogenic amine content fluctuated in the range of 7.19–6.90, 3.09–5.56 mg/kg, 44.81–175.05 mg/100 g, 1.42–1.63 g/100 g, 59.19%–62.40%, 11.02%–12.04% and 0–113.29 mg/kg, respectively. The MDA content increased and then subsequently decreased. The contents of amino acid nitrogen, TVBN and biogenic amines all showed an increasing trend. At the middle and late stages of fermentation, the bacterial diversity indexes decreased significantly, and the fungal diversity indexes decreased slowly. At the early stage of fermentation (0–7 days), Streptococcus and Lactobacillus were the dominant bacterial genera. During the middle and late periods (34–145 days), Tetragenococcus was the dominant bacterial genus and was differential between the three stages of fermentation. Trichosporon was the dominant fungal genus at the early stage of fermentation. At the middle stage, Candida and Alternaria became the dominant genera. At the late stage, Candida became the dominant genus, and no significantly differential fungal genera were found between the three fermentation stages. The Spearman correlation heat map showed that compared with the fungus genera, the bacterial genera had a higher correlation with the physiochemical indicators, indicating that the bacterial community was dominant in the fermentation process. Tetragenococcus was positively correlated with the TVBN, amino acid nitrogen, and MDA contents; Streptococcus was significantly negatively correlated with the content of biogenic amines. Starting from the 64th day, the quality indicators and microbial community of the shrimp paste remained basically stable, suggesting that shortening the fermentation time can be considered as an option to improve the fermentation process. These results provide a theoretical basis for improving the fermentation process of low-salt shrimp paste.
Gas Chromatography-Mass Spectrometry-Based Metabolomic Analysis of Differential Muscle Metabolites in Giant Salamander (Andrias davidianus) Meat during Cold Storage
JIN Wengang, ZHAO Ping, LIU Junxia, LAN Afeng, CHEN Dejing, PEI Jinjin, GAO Ruichang
2022, 43(24):  192-201.  doi:10.7506/spkx1002-6630-20220218-140
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In order to establish the correlation between physicochemical indexes and muscle metabolites in giant salamander meat during cold storage, differential metabolites between giant salamander muscle stored for different periods (0, 2, 4 and 8 days) at 4 ℃ were analyzed by gas chromatography-mass spectrometry (GC-MS) non-targeted metabolomics combined with multivariate statistical model. The results showed that the composition of metabolites in giant salamander muscle refrigerated for 8 days was significantly different from those stored for 0, 2 and 4 days. According to partial least squares-discriminant analysis (PLS-DA) and variable importance in projection (VIP) (VIP ≥ 1, P < 0.05 in t-test), 69 differential metabolites were identified including organic acids and their derivatives (21), amino acids and their derivatives (14), sugars and their derivatives (7), nucleotides and their derivatives (10), amines and their derivatives (6), and other compounds (11). According to the hierarchical cluster heatmap, the giant salamander meat samples could be divided into three groups: early (days 0–2), middle (day 4) and late stages (day 8). Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the important metabolic pathways during the cold storage of giant salamander meat were purine metabolism, aminoacyl-tRNA biosynthesis, glyoxylic acid and dicarboxylic acid metabolism, pyruvate metabolism and the tricarboxylic acid cycle. Metabolic pathway mapping and Pearson’s correlation analysis showed that L-lysine, L-serine, L-isoleucine, L-methionine, pyruvic acid, succinic acid, glycine could be used as potential markers for the change in meat quality of giant salamander.
Component Analysis
Changes in Key Aroma Components of Fresh Milk Fan during Storage
WANG Yadong, HAN Haoying, HAN Zhaosheng, WANG Rongxue, WANG Jiao, YANG Zhijie, CAO Yanping, WANG Bei
2022, 43(24):  202-209.  doi:10.7506/spkx1002-6630-20220127-285
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The changes in the volatile flavor composition of fresh milk fan during storage were analyzed by solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS), gas chromatography-olfactometry (GC-O) and descriptive sensory evaluation. A total of 70 volatile flavor compounds were detected, and 19 characteristic flavor compounds identified by GC-O were accurately quantified, and their odor activity values (OAV) were calculated. Sixteen of these compounds with OAV greater than 1 were identified as key aroma components. The sensory properties, key aroma components and storage time of milk fan were analyzed by partial least squares (PLS). The results showed that the storage period of milk fan could be divided into three stages. The first stage was the first day, and the sensory quality of milk fan was the highest at this stage, which may be related to the high content of ester components such as ethyl acetate and ethyl hexanoate. The second stage comprised the fourth and seventh days. At this stage, milk fan had mild sensory quality and the characteristics of wine aroma, which may be related to the content of ethyl butyrate. The third stage comprised the 11th and 15th days, where the sensory quality of milk fan was the worst, and the contents of all esters and lactones except for delta-decalactone decreased with storage time.
Evolution of Fatty Acid Composition, Volatile Flavors and Bioactive Ingredients of Coffee Oil during Coffee Bean Roasting
DONG Conghui, DONG Wenjiang, CHENG Jinhuan, HU Rongsuo, HE Hongyan, CHEN Xiao’ai, LONG Yuzhou, HUANG Jiaxiong, CHEN Gang, CHEN Jianfei
2022, 43(24):  210-222.  doi:10.7506/spkx1002-6630-20220302-023
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In this study, the physicochemical properties, fatty acid composition, volatile components and bioactive ingredients of oil from Arabica coffee beans from Yunnan roasted for different periods were systematically investigated. The results showed that as the degree of roasting increased, the color of the oil deepened, the acid value showed an increasing trend from 1.60 to 3.75 mg/g, the iodine value decreased from 142.04 to 83.12 mg/100 g, the anisidine value first increased and then decreased, ranging from 3.40 to 16.26, and the saponification value decreased slightly but not significantly. A total of 11 fatty acids were identified, the most predominant being linoleic acid, whose content ranged from 43.06% to 64.39%, followed by stearic and palmitic acids with contents ranging from 12.67% to 27.55% and oleic acid in the range of 9.03% to 17.20%. The effect of roasting degree on the type of fatty acid was not significant, but there were some differences in the content of fatty acid. A total of 25, 33, 36, 53, 54, 59, 64 and 58 volatile components were identified in oils from coffee beans roasted to eight different degrees from JQ to FZ, respectively. The major volatile components were furans, pyrazines, ketones and pyrroles, whose type and content showed a decreasing trend. The contents of bioactive ingredients including kahweol, α-tocopherol, γ-tocopherol and δ-tocopherol decreased, while the total phenolic content increased continuously from 7.75 to 15.96 mg/100 g. The results of this study provide a theoretical basis and technical support for the fine and deep processing and high-value utilization of coffee beans.
Comparison of Differences in Aroma Components among Vitis vinifera L. cv. ‘Tannat’ Grapes Grafted onto Different Rootstocks
HAN Xiao, YANG Hangyu, CHEN Weikai, WANG Yu, WANG Jun, HE Fei
2022, 43(24):  223-231.  doi:10.7506/spkx1002-6630-20220216-108
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In the present research, the effects of grafting onto six rootstocks including ‘1103P’, ‘140R’, ‘101-14’, ‘3309C’, ‘SO4’ and ‘Beta’ on the accumulation of aromatic compounds in ‘Tannat’ (Vitis vinifera L.) grapes from the 2016 and 2017 vintages were studied by using gas chromatography-mass spectrometry (GC-MS). The results showed that the effect of different rootstocks on grape aroma was more significant for the 2016 vintage. ‘1103P’ could significantly increase the content of C6/C9 compounds in ‘Tannat’ grapes and free hexanol, (Z)-3-hexenol, (E)-2-hexenal and 1-hexanal were the characteristic C6/C9 compounds; ‘140R’ was beneficial to the synthesis of esters in ‘Tannat’ grapes, while ‘3309C’ showed a tendency to reduce the contents of C6/C9 compounds, esters and volatile phenols in ‘Tannat’ grapes. Both ‘Beta’ and ‘SO4’ increased the content of terpenes in ‘Tannat’ grapes from both vintages, and ‘SO4’ also could significantly increase the content of C13-norisoprenoids in ‘Tannat’ grapes, with the characteristic ones being free (E)-β-damasone and (Z)-β-damasone. The research results provide a reference for the selection and application of the grafting rootstocks for ‘Tannat’ grapes in practical production.
Rapid Determination of Seven Water-Soluble Vitamins in Starch-Fortified Foods
NIU Canjie, YE Sudan, HU Yuxia, WANG Fengjun, LING Yun
2022, 43(24):  232-238.  doi:10.7506/spkx1002-6630-20220206-009
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A method using high performance liquid chromatography with diode array detector and fluorescence detector (HPLC-DAD-FLD) was established to simultaneously analyze seven water-soluble vitamins in starch-fortified foods. The sample was hydrolyzed by amylase at 60 ℃ for 45 min and ultrasonically extracted after pH adjustment. Chromatographic separation was carried out by gradient elution using 5 mmol/L sodium dodecyl sulfate solution containing 0.1% phosphoric acid adjusted to pH 3.0 with triethylamine as mobile phase A and acetonitrile as mobile B. Vitamin B1, niacin and nicotinamide were detected at maximum UV absorption wavelengths. Good linearity was observed for all analytes with correlation coefficients (r2) of 0.999 6–0.999 9. The recoveries for spiked samples were 90.5%–102.5%, the limits of detection (LODs) were 0.01-0.08 mg/100 g, and the limits of quantitation were 0.025–0.26 mg/100 g. The developed method is rapid, efficient and suitable for the simultaneous determination of the seven vitamins in bulk starch-fortified foods.
Effect of Roasting Degree on Physicochemical Indexes and Flavor Components of Cold Brew Coffee
TANG Wenxiao, XIAO Ying, JIANG Tianning, JIANG Feng, ZHU Jing, ZHOU Yiming
2022, 43(24):  239-248.  doi:10.7506/spkx1002-6630-20220211-058
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In this study, light, medium, and dark roasted Catimor coffee beans from Yunnan, China and Sumatra Indonesia were selected to compare the differences in the extract concentration, extraction efficiency, titratable acid, total phenols, total sugar, caffeine, trigonelline, chlorogenic acid, antioxidant activity and volatile components of cold and hot brew coffee. Principal component analysis (PCA) was carried out to explore the effect of roasting degree on the physicochemical indexes and flavor components of cold brew coffee. The results showed that with the increase of roasting degree, the extract concentration and extraction efficiency of cold brew coffee increased significantly, and the levels of titratable acid, total phenols, total sugar, trigonelline, chlorogenic acid, and antioxidant activity decreased significantly (P < 0.05). Cold brew coffee had higher extract concentration, extraction efficiency and total sugar levels than hot brew coffee, while the levels of titratable acid, total phenolic content, and antioxidant activity were significantly lower than those of hot brew coffee (P < 0.05). The headspace solid phase microextraction combined with gas chromatography (HS-SPME-GC-MS) analysis showed that the content of volatile components in light roasted coffee was significantly lower than that in medium roasted coffee, and dark roasted coffee had the highest number and amount of volatile components. Furthermore, PCA could distinguish between cold and hot brew coffee, and the contribution rate of volatile components was quite different between them. 2-Butanone, 2-butenal and other substances responsible for floral aroma had a higher contribution rate to cold brew light roasted coffee, while compounds contributing to roasted nut-like aroma including 2-methylpyrazine and furfuryl alcohol had a higher contribution rate to hot brew light roasted coffee. 2,6-Diethylpyrazine, ligustrazine and other compounds contributing to roasted nut-like aroma had a higher contribution rate to both cold and hot brew middle roasted coffee. 2-Vinylfuran, methylfurfuryl mercaptan, 2,5-diethylpyrazine, and furfuryl methyl sulfide had a higher contribution rate to cold brew dark roasted coffee, and cresol and 1-methylpyrrole had a higher contribution rate to hot brew dark roasted coffee. Compared with hot brew coffee, roasting degree had a greater impact on the antioxidant capacity and volatile components of cold brew coffee.
Analysis of the Effects of Different Storage Methods on the Flavor of Onion-Covered Nang, a Baked Flatbread, by Gas Chromatography-Ion Mobility Spectrometry
Gulnazar SIREYIL, HUANG Wenshu, BAI Yujia, FENG Zuoshan, Aygul ALIM
2022, 43(24):  249-257.  doi:10.7506/spkx1002-6630-20220208-030
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In this study, gas chromatography-ion mobility spectrometry (GC-IMS) was used to analyze the volatile substances of onion-covered Nang under six different storage conditions, including low-temperature storage, room temperature storage, vacuum storage at room temperature, oxygen-free storage at room temperature, aseptic storage at room temperature, and oxygen-free and aseptic storage at room temperature. The results showed that 66 volatile flavor compounds were identified from onion-covered Nang, including 9 alcohols, 4 ketones, 18 aldehydes, 4 esters, 3 furans, 1 acid and 27 unrecognized compounds. As storage time increased, the content of volatile aldehydes in onion-covered Nang stored at low-temperature and vacuum remained basically unchanged, while the content of volatile aldehydes showed a decreasing trend under the other storage conditions. Principal component analysis (PCA) and Euclidean distance analysis showed that the types and concentrations of volatile substances on day 0 of low-temperature storage were relatively close to those under the other storage conditions, and the positions of the data points in the PCA plot were gathered together, indicating that the change of volatile substances was not obvious under low-temperature storage conditions. This study can provide useful information for understanding the flavor change of onion-covered Nang during storage.
Analysis of Volatiles in Commercially Available Polylactic Acid Straws Using Fourier Transform Infrared Spectroscopy and Gas Chromatography-Mass Spectrometry
ZHANG Zhurui, YANG Qinghua, TONG Xing, WANG Zhiwei, HU Changying
2022, 43(24):  258-265.  doi:10.7506/spkx1002-6630-20220302-029
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Commercially available straw samples were collected for compositional analysis by Fourier transform infrared (FT-IR) spectroscopy, and the non-targeted analysis of volatile compounds in the straw samples was performed by gas chromatography-mass spectrometry (GC-MS). The compounds were identified using retention index, the National Institute of Standards and Technology (NIST) mass spectral library and mass spectrometry-data-independent acquisition (MS-DIAL) deconvolution, and relevant databases were used for traceability analysis and to identify compounds of safety concern. The results showed that the samples were all found to comprise PLA alone or mixed with poly(butyleneadipate-co-terephthalate) (PBAT) and poly(butylene succinate) (PBS) in different proportions. Totally 41 volatile substances were detected by GC-MS, and 173 volatile substances by headspace GC-MS (HS-GC-MS), mainly plastic additives and pesticides and detergents that may originate from raw materials, and the safety of some substances should be of concern. The results of GC-MS and HS-GC-MS were complementary to each other, which is beneficial for more accurate analysis of volatile substances. This study provides a basis for the analysis and safety risk assessment of volatile substances in commercially available PLA straws.
Correlation Analysis of Moisture Content and Aroma Quality in the Scenting Process of Jasmine Tea
YE Qiuping, YU Wen, ZHENG Shizhong, ZENG Xinping, CHEN Fei, HAO Zhilong
2022, 43(24):  266-272.  doi:10.7506/spkx1002-6630-20220322-265
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In order to explore the migration of moisture and the variation in aroma components during the scenting of jasmine tea, tea samples before scenting, before heat release, before flower pick-out and after drying were analyzed for water distribution by low-field nuclear magnetic resonance (NMR), and the composition and content of aroma components in these samples were determined by headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS). The results showed that the moisture content of jasmine tea was significantly different at different stages of scenting, and all tea samples except tea base before scenting exhibited the signal peaks of bound water, immobilized water and free water. Bound water was the major water state, and the proportion of peak area of bound water tended to increase initially and then decrease, and was higher than that before scenting. The proportion of peak area of immobilized water decreased first and then increased, and was lower than that before scenting. The?proportion of peak area of free water was the lowest and not found before scenting, and presented a trend of first decreasing and then increasing during scenting. A total of 75 aroma components were identified in the jasmine tea scenting process, including alcohols, esters, alkenes and aldehydes. The aroma released from jasmine flowers was adsorbed by tea, so the content of aroma components increased in jasmine tea after drying. Among them, the content of esters was the highest (9.721 μg/g), followed by alcohols (3.854 μg/g), and alkenes (3.377 μg/g), and the number of alkenes was the largest (26). The score for aroma quality of jasmine tea increased, then decreased and increased again during scenting, and was higher than that before scenting, which was more suitable than aroma index for evaluating the aroma quality of jasmine tea. Correlation analysis showed that the peak areas of bound water and immobilized water had a positive correlation with the relati contents of alcohols, and the peak area of free water had a significantly negative correlation with the contents of esters but a significantly positive correlation with the contents of alkenes. The results provide a theoretical basis for enriching the knowledge about the aroma adsorption mechanism of jasmine tea and regulating the processing parameters of jasmine tea.
Effects of Various Drying Methods on Volatile Composition of Stropharia rugosoannulata by Headspace-Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry
QIN Yuchuan, WU Deping, WANG Liling, FANG Ru, HE Liang, WANG Yanbin, QIAN Hua, LIU Bentong
2022, 43(24):  273-280.  doi:10.7506/spkx1002-6630-20220216-109
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The volatile composition of fresh, freeze-dried and oven-dried Stropharia rugosoannulata was analyzed by headspace-solid phase microextraction-gas chromatography-mass spectrometry. The results showed that 3-octanone, nerolidol and hexanal were the major flavor substances in fresh S. rugosoannulata, accounting for 68.25%, 13.12% and 1.40% of the total volatiles, respectively, and the flavor activity values of these compounds were 142.63, 162.39 and 11.71, respectively. High temperature caused loss of the flavor substances of S. rugosoannulata and the production of alkanes and other volatile components. The freeze-dried sample had the best preserved morphology, but some volatile components such as alkene and ketone were seriously lost due to the high vacuum. The volatile profile of the sample dried by hot air at 30 ℃ was the most diverse, and 58 compounds were identified, including aldehydes, alkenes, alcohols, esters, pyrazines, furans and other flavor compounds. 1-Decene, cyclododecane, 2-amyl furan, 4,6-dimethylpyrimidine, 2-undecane ketone and schisterol accounted for 17.17%, 6.58%, 5.97%, 5.74%, 5.62% and 5.58% of the total volatiles, respectively. The results of this study are of great significance for understanding the difference in the volatile composition of fresh and dried S. rugosoannulata and guiding the deep processing of S. rugosoannulata.
Determination of Cysteine Content by Supramolecular Polymer-Based Dual Wavelength Resonance Light Scattering Spectroscopy
LIU Yi, YUAN Li, YUAN Jiayi, CHU Wen, MA Weixing
2022, 43(24):  281-286.  doi:10.7506/spkx1002-6630-20220328-352
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A new method for the determination of cysteine by single-wavelength and dual-wavelength resonance light scattering spectroscopy with malachite green was established. The reaction conditions of the cysteine-malachite green system were optimized. The results showed that in borax-sodium hydroxide buffer solution, malachite green combined with boric acid to produce resonance light scattering, and two strong resonance light scattering peaks appeared at wavelengths of 285 and 338 nm; after adding cysteine, the resonance light scattering became more intense, and the intensity of resonance light scattering increased with the increase of cysteine concentration. The difference between the intensity of resonance light scattering at 285 and 338 nm displayed a linear relationship with cysteine concentration in the range of 0.10–0.60 mg/L, with limits of detection of 10.7 and 13.3 μg/L, respectively. The limit of detection of the dual-wavelength superposition method was 3.23 μg/L. When applying this method to detect cysteine in hepatoprotective agent and soy sauce, the relative standard deviations (n = 6) were within 3%, which meets the requirements of quantitative analysis.
Influence of Manual Picking and Management on Chemical Composition of Raw Pu-erh Tea
QU Yanyan, YANG Zijia, LI Jun, LI Zhen
2022, 43(24):  287-295.  doi:10.7506/spkx1002-6630-20220716-187
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In this study, mass spectrometry-based metabolomics was used to analyze the chemical composition of raw Pu-erh tea made from the fresh leaves of the large-leafed tea cultivar picked from an abandoned tea plantation where manual picking and management have been resumed. It was found that manual picking and management resulted in a significant increase in the contents of theanine, glutamic acid, both responsible for the fresh and brisk taste, and total amino acids, and also increased the contents of umami-enhancing alkaloids and catechins responsible for the sweet aftertaste of Pu-erh tea, thereby improving the taste and quality of the tea. Chemical analysis showed that manual management did not significantly change the total polyphenol content or antioxidant capacity outside cells of the tea. However, cytotoxicity and antioxidant activity tests showed that the inhibitory effect on the proliferation of cancer cells (U2OS) and the antioxidant capacity inside cells were enhanced by manual management. Manual picking and management had little effect on the contents of inorganic ions, total phenols or caffeine of the tea, indicating manual intervention had no significant influence on the physiological status of the plants. This study may provide a theoretical basis for the study of the quality of raw Pu-erh tea.
Safety Detection
A High-Speed Raman Imaging Method for the Detection of Adulteration in Milk Powder Using Self-encode Shrinkage Neural Network
XIA Qi, HUANG Zhixuan, BAO Lei, BU Hanping, CHEN Da
2022, 43(24):  296-302.  doi:10.7506/spkx1002-6630-20211130-378
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In this study, we proposed a high-speed Raman imaging method for the identification of adulterants in milk powder. In this method, a novel self-encode shrinkage neural network (SSNN) was developed to extract intrinsic information from the low signal-to-noise ratio Raman image with short integration time. Thereafter, multivariate regression models for quantitating the adulterant content in milk powder accurately were developed with the SSNN filtered Raman images. The coefficient of determination (R2) of these quantitative models for various adulterated samples was above 0.95. Through this method, a sample region size of 50 mm × 50 mm could be scanned with Raman imaging technique within two minutes, 30 times faster than traditional Raman imaging method. These satisfactory results demonstrate that this method can successfully meet the demand of milk powder adulteration detection in practice and can be used to detect adulteration in other non-homogeneous food systems.
Construction of Bionic Skin Electrochemical Sensor and Its Application for Detection of Egg Albumin
LIU Bing, CAO Hanwen, JIANG Donglei
2022, 43(24):  303-309.  doi:10.7506/spkx1002-6630-20220607-072
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According to the hierarchical structure of the human skin, bionic skin microtissue with epidermal layer and subcutaneous tissue layer, which can simulate the reaction of the skin to food allergens, was bioprinted with human skin fibroblasts and RBL-2H3 cells and was used to construct a bionic skin electrochemical sensor by combined use of polypyrrole modification and rapid electrochemical detection technology. The results showed that the sensor could identify egg albumin well, and the linear range was 0.5–2.5?μg/mL. A linear regression equation was fitted as follows: y = 4.45C + 14.24, with a correlation coefficient (R2) of 0.998, and the detection limit of this method was 0.19?μg/mL. The successful construction of the electrochemical sensor shows the possibility of applying biological 3D printing technology to prepare multi-cell composite bionic structures.
Identification of the Age of Luzhou-Flavor Base Baijiu by Gas Chromatography-Mass Spectrometry Fingerprinting and eXtreme Gradient Boosting Machine Learning
LIU Qingru, MENG Lianjun, ZHANG Xiaojuan, ZHAI Weiji, CHAI Lijuan, LU Zhenming, XU Hongyu, WANG Songtao, ZHANG Suyi, SHEN Caihong, SHI Jingsong, XU Zhenghong
2022, 43(24):  310-317.  doi:10.7506/spkx1002-6630-20211129-354
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In order to identify the age of Luzhou-flavor base baijiu, headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to create a fingerprint of the volatile composition of Luzhou-flavor base baijiu, and the eXtreme Gradient Boosting (XGBoost) algorithm was used to establish a regression model. Feature selection was conducted via a combination of variable importance evaluation using the extremely randomized trees, and F_regression and mutual_info_regression in the sklearn feature selection module. The coefficient of determination (R2) of the proposed regression model was 0.987, demonstrating good predictive reliability. This study provides a new idea for the identification of baijiu age.
Quantification of Bovine-Derived Ingredients in Meat Products by Duplex Droplet Digital Polymerase Chain Reaction
XIONG Suyue, LI Jiapeng, LI Jinchun, WEI Yixuan, XU Suigen, LIU Ruixi, CHEN Xi, WANG Shouwei, QU Chao, QIAO Xiaoling
2022, 43(24):  318-324.  doi:10.7506/spkx1002-6630-20211123-289
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One typical way of meat adulteration is by adding low-priced meat ingredients into high-priced meat products. In this study, a duplex droplet digital polymerase chain reaction (ddPCR) method was developed to accurately identify bovine-derived ingredients in meat products. By analyzing the single-copy β-actin gene sequences of 14 animal species, bovine-specific primers and probes as well as universal primers and probes for animal-derived ingredients were designed to develop a duplex ddPCR system. The formula to calculate the relationship between the mass of bovine-derived ingredients (M, mg) and the number of copies of specifically amplified genes (C, copies/μL) was established as follows: M = 0.033C + 2.37. The results of this method for mixed meat samples containing a known amount of beef and different beef cuts basically agreed with the actual values. Moreover, the relative copy number was helpful to judge whether beef products could be adulterated with non-bovine-derived ingredients. The developed method was successfully applied to detect the adulteration of commercial beef products. We believe that this method will provide technical support for the quantitative detection of adulterated beef products and grading and identification of meat mixtures from different animal specices.
Determination of 24 Mycotoxins in Milk by Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry
DING Xueyan, SHAO Ruiting, ZHANG Hanlu
2022, 43(24):  325-334.  doi:10.7506/spkx1002-6630-20220207-016
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A method was developed for the multi-residue determination of 24 mycotoxins including aflatoxin B1 (AFB1), AFB2, AFG1, AFG2, AFM1, ochratoxin A (OTA), zearalanone, zearalenone, α-zearalanol, β-zearalanol, α-zearalenol, β-zearalenol, T-2 toxin, HT-2 toxin, fumonisin B1 (FB1), FB2, FB3, deoxynivalenol (DON), 3-DON, 15-DON, alternariolmethylether, alternariol, tentoxin and tenuazonic acid in milk by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The sample was extracted with 80% aqueous acetonitrile, the extract was purified by matrix solid-phase dispersion (MSPD) extraction and blown to dryness under nitrogen, and the residue was re-dissolved in 1 ml of 50% aqueous acetonitrile (V/V) and analyzed by UPLC-MS/MS. An acquity UPLC HSS T3 (2.1 mm × 100 mm, 1.8 μm) reversed-phase column was used for the separation with gradient elution. Detection was performed under the multiple reaction monitoring (MRM) mode using electrospray ionization. The correlation coefficients (R2) for all analytes were greater than 0.985, the recoveries for spiked samples ranged from 71.0% to 123.0%, and the relative standard deviation (RSD) was less than 10%. The developed method has the advantages of simple operation, good repeatability, high sensitivity and low impurity interference and can be used for the determination of the 24 mycotoxins in milk.
Classification Method for Mee Tea Grades Based on Olfactory Visualization Technology
DING Yuhan, GE Dongying, JING Lei, Muhammad SHAHZAD, JIANG Hui
2022, 43(24):  335-341.  doi:10.7506/spkx1002-6630-20220331-383
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A rapid and accurate method for the classification of Mee tea grades based on olfactory visualization technology was proposed. First, 12 different porphyrin indicators which were found to have an obvious chromogenic effect in the preliminary experiment were selected to develop a color-sensitive gas sensor array. The sensor array was then used to test different grades of Mee tea infusion, and the characteristic images were acquired and analyzed by principal component analysis (PCA) for dimensionality reduction. The obtained PCA results with different dimensionalities were used as input variables to establish a classification model for Mee tea grades using support vector machine (SVM). Finally, three swarm intelligence algorithms, firefly algorithm (FA), gray wolf optimization (GWO) and cuckoo search (CS), were used to optimize the penalty factor (c) and the kernel function parameter (g) of the SVM model. Results showed that the classification accuracy of the original SVM model for the test set was 80% with 12 principal components needed, and increased after optimization with each of the three algorithms. The classification accuracy of the model optimized by CS was 93.3%, and the number of principal components needed was reduced to 6. Accordingly, olfactory visualization technology can be used to classify Mee tea grades, and the model performance can be enhanced and the classification accuracy can be improved by swarm intelligence optimization algorithms significantly.
Oxidized Carminic Acid for the Detection of Iron Ions in Mushroom
LIU Lanxiang, LI Xiang, TANG Baoshan, TAN Rui, XU Juan, MA Jinju, ZHANG Hong
2022, 43(24):  342-348.  doi:10.7506/spkx1002-6630-20220623-255
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In order to further develop the application of carmininc acid (CA) for fluorescence detection, oxidized carminic acid (OCA), which is water soluble and emits blue fluorescence, was synthesized in one step by an ethanol-assisted hydrothermal method using carminic acid as the raw material and potassium periodate as the oxidant. Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis showed that the structure of OCA contained conjugated aromatic rings and a large number of oxygen-containing functional groups, and transmission electron microscopy (TEM) and dynamic scattering light (DLS) indicated an average particle size of approximately 7.5 nm. Optical tests showed that the fluorescence emission of OCA appeared in the range of 380–620 nm, the maximum excitation wavelength was 336 nm, and the maximum emission wavelength was 445 nm. OCA showed excellent fluorescence stability in solutions at pH 1–9 and in different salt solutions containing anions. UV-visible absorption spectroscopy showed that its maximum absorption peak appeared at 225 nm. OCA had good selectivity for iron ions, which led to a significant decrease in its fluorescence intensity. The percentage of decrease in the fluorescence emission peak integrated area, (S0–S)/S0, showed a good linear relationship with the mass concentration of iron ions in the range of 11.2–56.0 mg/L, and the limit of detection was 2.5 mg/L. Applying an OCA-based fluorescent sensor to detect the content of iron ions in mushrooms, the recoveries of this method was 95.3%–110.4%, with relative standard deviation (RSD) between 2.3% and 4.6%, indicating that the fluorescence detection method is reliable.
Detection of Guar Gum in Adulterated Livestock Meat by High Performance Liquid Chromatography-Mass Spectrometry
GUO Chao, CHEN Chao, LI Huichen, WANG Zhen, XU Ruolin, ZHAO Wentao, LI Yingying, GUO Wenping, ZHANG Zhaohui
2022, 43(24):  349-356.  doi:10.7506/spkx1002-6630-20220129-298
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This study proposed a high performance liquid chromatography-mass spectrometry (HPLC-MS) method for the determination of guar gum in adulterated livestock meat. The samples were enzymatically hydrolyzed by β-mannanase, added with acetonitrile to precipitate protein, and then centrifuged. The supernatant was purified on a neutral alumina column, detected using a liquid chromatography-tandem mass spectrometer, and quantified by external standard method. The results showed that the linear range for guar gum was 0–2 g/kg, the correlation coefficient was above 0.99, the limit of detection (LOD) was 0.030 0 g/kg, the limit of quantification (LOQ) was 0.100 g/kg, and the recoveries ranged from 85.4% to 109.8%, with relative standard deviations (RSDs) between 1.5% and 9.3%. The developed method has the advantages of simple pretreatment, clear detection indexes and high sensitivity, and can be used as an effective method for detecting added guar gum in livestock meat.
Determination of Nine Cannabinoids in Foods by Solid Phase Extraction Combined with Gas Chromatography-Mass Spectrometry
TANG Qingqiang, XIA Linbing, CAO Dan, YANG Fang, WU Chundeng, XUE Kunpeng
2022, 43(24):  357-364.  doi:10.7506/spkx1002-6630-20220331-385
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In this study, an analytical method based on gas chromatography-mass spectrometry (GC-MS) was developed for the determination of nine cannabinoid compounds in foods such as olive oil, pork and bread. The samples were extracted with methanol or acetonitrile, and the extract was purified on a solid phase extraction column. The target compounds were separated on an Agilent HP-5MS column. The instrument was operated using an electrospray ionization source (EIS) in the selected ion monitoring (SIM) mode. The external standard method was used for quantification. This method showed good linearity in the concentration range of 10–500 μg/L with correlation coefficients greater than 0.999 2. The limits of detection (LOD, RSN = 3) and limits of quantification (LOQ, RSN = 10) of the developed method were 1–15 and 2.5–50 μg/kg. The average recoveries of the nine cannabinoids from negative samples of different matrices spiked at LOQ, 2 × LOQ and 10 × LOQ concentrations ranged from 65.2% to 117.9%, with relative standard deviations (RSDs) between 2.0% and 12.7%. This method is very sensitive, fast, highly applicable, and useful for the detection of cannabinoid residues in foods.
Authenticity Identification of Geographical Indication Mutton Based on Mineral Element Fingerprint
QI Jing, LI Yingying, JIANG Rui, ZHANG Chen, ZHANG Shunliang, GUO Wenping, WANG Shouwei
2022, 43(24):  365-370.  doi:10.7506/spkx1002-6630-20220227-237
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This study proposed a technique for identifying the authenticity of geographic indication mutton based on mineral element fingerprint combined with one-class modeling strategy. The results showed that the contents of mineral elements in the meat of Yanchi Tan sheep, Balikun Kazak sheep and Sunit sheep under the protection of geographical indication had fingerprint characteristics. In the one-class modeling strategy, only real sample sets were collected for modeling to identify the real samples from a variety of fraud samples. The soft independent modeling of class analogy (SIMCA) model based on each of the geographical indication mutton samples had excellent performance, with an identification accuracy of 100% for the test samples. Therefore, mineral element fingerprint combined with one-class modeling has a wide application prospect in the field of authenticity identification of geographical indication mutton.
Differences in Pollution Levels of Harmful Esters in Infant Formula Powder and Its Ingredient Oils
ZHANG Ni, ZHOU Jing, HU Shoujiang
2022, 43(24):  371-377.  doi:10.7506/spkx1002-6630-20211123-285
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A gas chromatography-mass spectrometry (GC-MS) method for the detection of 3-chloropropyl alcohol ester, 2-chloropropyl alcohol ester and glycidyl esters in oils and milk powder was established and applied for the detection of ester pollutants in vegetable oils and infant formula powder. Meanwhile, the differences in the pollution levels of three harmful esters in different vegetable oils were analyzed, and the correlation with the fat content of milk powder was studied. Among the vegetable oils commonly used in infant formula ingredients, palm oil had the highest pollution level, followed by rapeseed oil, soybean oil, corn oil and edible vegetable oil blend, and sunflower seed oil, coconut oil, walnut oil, flax seed oil had lower pollution levels. The pollution levels of 1,3-dioleic acid-2-triglyceride palmitate (OPO) and edible vegetable oil blend (containing OPO) were the lowest. Totally 88.4% of the 95 infant formula powder samples were found to contain 3-monochloropropane-1,2-diol ester (3-MCPDE) at concentrations of ND?0.231 mg/kg, with an average of 0.070 4 mg/kg and a median value of 0.064 5 mg/kg. 2-MCPDE was detected in 42.1% of the samples at concentrations of ND?0.034 mg/kg. The detection rate of GE was 2.1% at concentrations of ND?0.019 mg/kg. The 3-MCPDE content in 10.5% of the samples exceeded the EU limit of 0.125 mg/kg. There was a significantly positive correlation between the total amount of the three ester pollutants and the fat content in milk powder, with a Pearson correlation coefficient of 0.453. In order to protect the safety of infants, infant formula manufacturers should carefully select raw oils and reduce the pollution of harmful esters in infant formula powder as much as possible under the premise of ensuring nutritional health.