The nanoparticle formation between bovine serum albumin (BSA) and anthocyanin (ACN) was characterized using scanning transmission electron microscope (STEM) and nanoparticles size analyzer. The anthocyanin-binding capacity of BSA was studied by ammonium sulfate salting-out method. DPPH and ABTS radical scavenging capacities and release characteristics in both simulated intestinal fluid (SIF) and simulated gastric fluid (SGF) systems were investigated for oxidation stability of BSA-bound anthocyanin system. The results showed that both BSA and anthocyanin-bound BSA could be self-assemble and form nanoparticles in phosphate buffer (pH 7.4), and the particle size (15–20 nm) of the anthocyaninbound BSA was smaller than that of the BSA (30–35 nm). The molar binding ratio between BSA and antocyanin was 1:10. The DPPH radical and ABTS+· scavenging abilities of BSA-bound anthocyanin were significantly stronger than those of unbound anthocyanin. There was no significant difference in stability between unbound anthocyanin and BSA-bound anthocyanin in SGF system, while significant difference in SIF system was observed. The content of unbound anthocyanin decreased by approximately 70% after 6 hours; however, no significant change was observed for BSA-bound anthocyanin. BSA revealed remarkable stabilizing effect on anthocyanin oxidation.
The effect of glycosylation treatment coupled with dynamic high-pressure microfluidization (DHPM) on emulsifying properties and structure change of β-lactoglobulin (β-Lg) was investigated. The results showed that glycosylation treatment coupled with DHPM obviously improved the emulsifying capacity and emulsion stability of β-Lg. The emulsifying activity index (EAI) of β-Lg subjected to glycosylation treatment in the presence of high pressure at 0, 40 and 120 MPa were 136.3, 168.1 m2/g and 177.9 m2/g, respectively. The emulsifying stability index (ESI) of β-Lg subjected to glycosylation treatment was 52.3 min. With increasing the pressure up to 40 MPa and 120 MPa, the ESI of β-Lg treated by glycosylation were increased to 56.4 min and 59.0 min, respectively, indicating the structural change of β-Lg due to the combinatorial treatment of DHPM and glycosylation. This structural change was characterized as increased molecular weight, sulphydryl (—SH) content, reduced surface hydrophobicity (Ho), changed secondary structure, and unmasked amino acids in the tertiary structure after the combinatorial treatment of DHPM and glycosylation. These results revealed that the conjugation with galacto-oligosaccharides (GOS) changed the structure of β-Lg, which contributed to the increase of surface hydrophilic groups of β-Lg and resulted in the improvement of emulsifying properties.
The effects of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as crosslinking reagents on the structure and properties of zein films were investigated to find ways to improve the tensile strength and elongation and reduce the water vapor permeability and moisture absorption. Results showed that films prepared with 90% ethanol as the solvent and 0.06 g of EDC/g zein or 0.06 g of NHS/g zein exhibited the best properties. The tensile strength, elongation, water vapor permeability, moisture absorption and weight loss were 83 MPa, 5.5%, 2.5 × 10-8 (g·m)/ (m2·h·Pa), 39.4% and 3.6%, which were increased by 97.6%, 57.1%, reduced by 43.2% and 24.4%, and enhanced by 20.0% compared to those without added cross-linking reagent, respectively, and the static water contact angle of the experimental samples was 67.4°, indicating the film surface to be hydrophobic. In addition, the surface of zein films containing EDC and NHS was arranged orderly and closely as smaller uniform spherical aggregates as observed using atomic force microscope (AFM)
The safe use of printing materials for food packaging is a major area of investigation. The hazardous substances like plasticizers in printing inks can migrate into the food through the packaging material. However, there have been few studies reporting the migration kinetics of the the plasticizers to food from ink. In this study, a novel method was developed for the study of migration of plasticizers from the printing inks through paper to milk powder at 100, 70, 50 ℃ and 25 ℃, respectively and for different contact times ranging from 5 min at 100 ℃ to 40 days at 25 ℃. The inks were offset printed by simulating the real situation, hadwhich has never been used in migration research. The plasticizers investigated included the commonly used dibutyl phthalate (DBP), bis(2-ethylhexyl) phthalate (DEHP), di-n-octyl phthalate (DOP) and a new type of the environmentally-friendly plasticizer, acetyl tributyl citrate (ATBC). Gas chromatography coupled with flame ionization detector (GC-FID) was used for the determination of ethanol extracts of these plasticizers from both printed paper and milk powder. The results showed that the paper did not provide an appropriate barrier against the migration of the plasticizers from printing inks. The maximum migration of DBP and ATBC reached almost 67.8% while that of DEHP and DOP was about 6.7%. The contact time, the temperature and the properties of the compounds are the factors affecting the real mass transfer.
This study illustrated multiple potential factors influencing actomyosin dissociation, including internal factors(AMP, IMP, ADP, ATP, Ca2+, and PO4 3-) and external factors (marinated with NaCl or with different phosphate salts).Actomyosin was extracted from duck breast muscle and the protein composition was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western-blot analysis. Results: The density of actin bands was increased significantly when the actomyosin was treated with 8, 16 mmol/L AMP or IMP or with 25–50 mmol/L PO4 3- at 4 ℃, whereas treatment with 8, 16 mmol/L ADP or with 0.1–5 mmol/L Ca2+ did not result in a significant change in actin band densities.These results suggest that marinating duck muscle with different salts has no significant effects on actomyosin dissociation.
Factors such as pH and mixing ratio for influencing the complex of sugar beet pectin and gelatin were studied. The total concentration of sugar beet pectin and gelatin was fixed at 0.1 g/100 mL. At a certain mixing ratio, the mixed system was acidified by gluconolactone, and the turbidity, light scattering intensity and hydrodynamic radius of the system were determined. Through exploring featured pHs, the phase boundaries were determined and a pH-composition phase diagram was established. The turbidity was measured using UV-Vis spectrophotometer, and light scattering intensity and hydrodynamic radius were tested using Zetasizer Nano-ZS apparatus. Based on the phase diagram and microscopic observation, no interaction was found between sugar beet pectin and gelatin at higher pH levels, while intramolecular and subsequently intermolecular soluble complexes were formed due to further acidification. At low pH levels, insoluble molecular complexes were developed and the system became unstable.
Potassium chloride was used to partially replace sodium chloride (20% – 60%) in dry-cured meat from pig hindquarters and its effect on physical, proteolysis and sensory properties in dry-cured meat was investigated. The results showed that partial replacement of NaCl from 0 to 60% by KCl in dry-cured meat did not significantly affect the proteolysis index and peptide nitrogen, amino acid nitrogen and alanyl aminopeptidase (AAP) activity. Also, the sensory analysis of final products with 40% or lower replacement did not reveal an obvious difference (P > 0.05). When 40% NaCl was replaced by KCl, the NaCl content was only 3.14% in final products without impact on proteolysis and sensory properties, suggesting that the optimal replacement level is 40%.
In this study, wheat flours from three cultivars (lines) with different gluten strengths were used to investigate the effects of adding different amounts of gluten and starch on wheat rheological properties and starch pasting property by using the method of separation and recombination. The results showed that with increasing addition of gluten, dough stability and farinograph quality number (FQN) increased, while peak viscosity, through viscosity, final viscosity, break down, and setback decreased. Moreover, with the increasing level of added starch, dough stability and FQN decreased, whereas peak viscosity, through viscosity, final viscosity, breakdown, and setback increased. Little effects of different amounts of gluten and starch on dough moisture absorption and starch gelatinazation temperature were found. The same general tendency existed in each quality parameter of wheat flour with different gluten strengths, but the amplitudes of variation were different.
Non-enzymatic browning easily takes place during thermal treatment of peach juice. Browning degree and the colour parameter L* are usually used as indexes to evaluate non-enzymatic browning. The indexes during thermal processing at different temperatures 80, 90 ℃ and 100 ℃ for peach juice were investigated. The results showed that with increasing temperature, the browning degree was increased by 0.185, 0.221 and 0.276, whereas the L* value was decreased by 4.22, 5.74 and 7.53, respectively. Both the chroma value and Hue angle were gradually decreased. The browning index (BI) was increased as the temperature increased. Various kinetic models including zero-order kinetic, first-order kinetic and combined kinetic models were employed to fit the experimental data. The results showed that the combined kinetic model was a better one for describing the dynamic changes in browning degree and colour value, as compared to the other two models (R2> 0.823). Furthermore, the declined vitamin C content during thermal processing could be accurately described by the zeroorder kinetic model (R2>0.894). Meanwhile, the combined kinetic model (R2>0.905) could properly express the gain of 5-hydroxymethylfurfural contents. The relationship between 5-hydroxymethylfurfural and browning degree was satisfactorily fitted by means of quadratic model (R2>0.940) at three different temperatures.
The relationships between the changes in chemical parameters of bamboo shoots (Dendrocalamus latiflorus), including titratable acidity, moisture content, salt concentration, protopectin content, cellulose content, lignin content, and hardness were investigated and compared during the pickling process. Meanwhile, the vascular bundle tissue of bamboo shoots was observed under a scanning electron microscope. It was found that there were highly positive correlations between such chemical parameters as titratable acidity, salt concentration, ethanol insoluble (AIS) content, protopectin content and cellulose content and hardness of bamboo shoots. Besides, the microstructure of vascular bundle tissue of bamboo shoots was obviously altered during pickling.
A comparative study was conducted on muscle physical and chemical qualities of Polyodon spathula, the hybrid sturgeon H. dauricus♀ × A. schrencki♂ and Aristichthys nobilis. The results showed that flesh content in A. nobilis was significantly higher than in two other sturgeon species (P < 0.05). The muscle protein content of P. spathula was not different from that of the hybrid and A. nobilis (P > 0.05), and we further found that the hybrid was significantly lower than A. nobilis (P < 0.05). Crude fat was significantly more abundant in P. spathula as compared to that of A. nobilis (P < 0.05), although both species showed no significant difference from hybrid sturgeon (P < 0.05). A. nobilis contained significantly higher amounts of ash than the other sturgeon species (P < 0.05). The fatty acid profiles in these three fish species were found to consist of three saturated fatty acids (SFAs) and six unsaturated fatty acids (UFAs), and the UFA content in hybrid sturgeon was higher than in P. spathula and A. nobilis (P < 0.05). The content of mono-unsaturated fatty acids (MUFAs) in P. spathula was significantly higher than in hybrid sturgeon and A. nobilis (P < 0.05) and the contents of poly-unsaturated fatty acids (PUFAs) were significantly different among the three species (P < 0.05) and the decreasing order was hybrid sturgeon > P. spathula > A. nobilis. Similarly, the contents of highly unsaturated fatty acids (HUFAs) were significantly different among them (P < 0.05), showing a decreasing order of A. nobilis > hybrid sturgeon > P. spathula. The atherogenic index (AI) in P. spathula was significantly lower than that observed for A. nobilis (P < 0.05), and the thrombosis index (TI) in P. spathula and hybrid sturgeon was significantly lower than that of A. nobilis (P < 0.05). The cooked meat yield of hybrid sturgeon was significantly lower than that of A. nobilis(P < 0.05), whereas the collagen content was significantly higher than that of A. nobilis(P < 0.05). Both juice loss and water loss in P. spathula were significantly lower than those of hybrid sturgeon and A. nobilis (P < 0.05). Fat loss and muscle fiber diameter were not significantly different between P. spathula and hybrid sturgeon (P > 0.05), but fat loss in P. spathula and hybrid sturgeon was significantly lower than in A. nobilis (P < 0.05), while muscle fiber diameter was significantly higher than that of A. nobilis (P < 0.05). No significant difference in muscle hardness was found between P. spathula and A. nobilis (P > 0.05), but the values of both species were significantly lower than that of hybrid sturgeon (P < 0.05); in addition, adhesiveness, cohesiveness, resilience and shear force in hybrid sturgeon were significantly higher than those observed for A. nobilis (P < 0.05). Springiness in P. spathula was significantly higher than that of A. nobilis (P < 0.05). Chewiness was significantly different among the three species, and the descending order was hybrid sturgeon > P. spathula > A. nobilis. The hardness of cooked meat from hybrid sturgeon was significantly higher than that of A. nobilis (P < 0.05); as for cohesiveness and resilience, P. spathula was significantly higher than hybrid sturgeon and A. nobilis (P < 0.05). Springiness in P. spathula was significantly higher than that found in A. nobilis (P < 0.05). Gummines and chewiness in P. spathula were significantly higher than those of A. nobilis (P < 0.05). Shear force was significantly lower in P. spathula compared to A. nobilis (P < 0.05). Moreover, muscle tenderness of P. spathula was significantly lower than that of A. nobilis (P < 0.05), and hybrid sturgeon was in the middle. However, no significant differences in juiciness, greasiness or flavor were found among the three species. In conclusion, the flavor and IT/AT in P. spathula are relatively better, similar to hybrid sturgeon, indicating health benefits; the contents of protein and other nutrients such as HUPA in A. nobilis are higher or close to the ideal patterns, suggesting its higher nutritional value and better tenderness.
Objective: To isolate and identify the chemical constituents from the flowers of Chinese Fringetree (Chionanthus retusa Lindl et Paxt). Methods: The chemical constituents were isolated and purified by sequential column chromatographies on silica gel, Sephadex LH-20 and semi-preparative HPLC, and their chemical structures were elucidated by spectroscopic methods. Results: A total of ten compounds were obtained and they were chemically identified as quercetin-3-methyl ether-7-O-α-L-arabinofranosyl(1→6)-β-D-glucopy–ranoside (1), eriodictyol-7-O-β-D-glucoside (2), acacetin-7-O-α-L-rhamnopyranosyl (1→6)-β-D-glucopyranoside (3), myricetin-3-O-β-D-glucopyranoside (4), luteolin-7- O-β-D-glucoside (5), kaempferol-3-O-β-D-glucoside (6), and luteolin (7), myricetin (8), apigenin (9), and quercetin (10), respectively. Conclusions: The compounds 1 through 6 were identified for the first time in the flowers of this plant, which have been reportedly to possess potent antioxidant capacity.
Objectives: The objectives of this study were 1) to analyze the in vitro antioxidant capacities of the four major functional components including polysaccharides, flavonoids, carotenoids and vitamin C (VC) in goji berries (Lycium barbarum); 2) to investigate the percentage contributions of these major antioxidant substances to the total antioxidant capacity of goji; and 3) to explore the in vitro antioxidant mechanism. Methods: The total antioxidant capacity was evaluated by ferric reducing antioxidant power (FRAP) assay and DPPH, ABTS and hydroxyl radical scavenging assays. Results: Flavonoids contributed over 96% to both free radical scavenging capacity and FRAP of goji berries with smaller than 4% contribution from VC, while the antioxidant capacities of high concentrations of goji polysaccharides (642.7170 mg/L) and carotenoids (109.9280 mg/L) were too low to be detected. Conclusion: Goji flavonoids play a leading role in the total antioxidant capacity of fresh goij berries.
The texture, microstructure and color of bamboo shoots (Dendrocalamus latiflorus) after pickling with different salt concentrations were investigated and compared with those of the unprocessed one in order to evaluate the effect of pickling on the edible quality of bamboo shoots. The results showed that textural characteristics such as hardness, cohesiveness and chewiness decreased obviously after pickling process. Meanwhile, different salt concentrations significantly influenced hardness whereas their effect on cohesiveness and chewiness were not obvious. The scanning electron microscope images of bamboo shoots revealed that the parenchyma cells obviously shrank and cell gap increased, and parts of parenchyma cells were damaged after pickling process. In addition, compared to those of fresh bamboo shoots, the lightness degree of pickled bamboo shoots decreased whereas yellowness degree increased, and the total color differences significantly changed. The research results may provide a reference for industrial production and eating quality control of pickled bamboo shoots.
In this study, 5 mg/L ozone was used as an oxidant to treat glutinous rice. After ozone treatment, glutinous rice flour was produced and corresponding starch was prepared. Results showed that the pasting viscosity of oxidized glutinous rice flour and corresponding starch was increased with increasing ozone treatment time, whereas the hot paste stability and aging resistance were slightly weakened but the cook properties did not show an obvious change. As the oxidation time prolonged, the carboxyl content was increased. Moreover, the carbonyl content initially increased and then decreased with increasing oxidation time. The Fourier transform infrared spectroscopy (FT-IR) analysis revealed that hydroxyl group was firstly oxidized to carbonyl groups at C2, C3 and C6 in glucose units of starch, and then carboxyl groups, but at the same time the C—O—C linkages were not broken.
The effect of chitosan addition on the color, mechanical properties and barrier properties of soybean protein isolate (SPI) composite packaging materials was evaluated. The composite packaging materials showed the best properties when the ratio of chitosan to SPI was 1:1. The tensile strength of the composite packaging materials increased, while the elongation at break, water vapor permeability and oxygen permeability decreased. Moreover, the color turned slightly yellow within the range of consumer acceptance. The formation of ether linkage or C-N bond between SPI and chitosan could be the major reasons for the improvement of these properties.
Maillard reaction products from whey protein peptide (WPP-MRPs) were prepared from alcalase hydrolysates of whey protein and glucose. The antioxidant activity of WPP-MRPs and the influences of temperature, pH, light condition, metal ions and H2O2 on their activity were investigated. The results showed that the total reducing power, hydroxyl radical scavenging activity and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging activity of WPPMRPs increased in a concentration-dependent manner. Furthermore, WPP-MRPs remained strong antioxidant activity when heated at 90–100 ℃. The antioxidant activity at alkaline condition was stronger than at acidic or neutral conditions. Meanwhile, the antioxidant activity decreased sharply in the presence of sunlight, H2O2 or metal ions such as Cu2+, Fe2+ or Fe3+.
The solubility, swelling power, transparency, settlement curve, freeze-thaw stability, aging value, gel strength and viscosity of starch from grain amaranth K112 (Amaranthus cruentus L.) seeds were analyzed and compared with those of starches from corn, cassava and sweet potato. The results indicated that the starch content in grain amaranth seeds was 62.49%, in which amylose accounted for about 6.12%. The solubility, transparency and settling velocity of grain amaranth starch were lower whereas the swelling power was higher as compared with those of starches from three other crop plants. This starch had poorer freeze-thaw stability, intermediate gel strength and lower viscosity.
This study aimed to analyze the electronic absorption spectral acquisition and characteristics of three carotenoids in dacanoic acid reverse micelle solvents. In the present study, tetrahydrofuran, acetone and ethanol were selected to separately construct decanoic acid reverse micelles. After lycopene (acyclic hydrocarbon), β-carotene (cyclic hydrocarbon) and zeaxanthin (cyclic hydroxyl compound) were dissolved in each solvent, the electronic absorption spectra of the solutions were acquired over the wavelength range of 300-550 nm. The spectral characteristics were consequently assessed. Data from these investigations suggested that a slight shift in the maximum absorption wavelength (λmax) of all three carotenoids were observed in decanoic acid reverse micelle solvents, in comparison with those in decanoic acid. A bathochromic shift was seen with cyclic carotenoids and a hypsochromic shift was seen with acyclic carotene. Additionally, an increased polarity of the added organic solvents could result in a reduced absorption coefficient (A1% 1 cm).
In order to analyze the genetic diversity of indigenous wine yeasts and the differences between indigenous isolates and commercial wine yeast strains, genetic variability of 28 isolates from Jingyang, Shaanxi Province and 18 commercial strains was analyzed using four microsatellite markers (ScAAT1, YOR267C, C11 and YPL009C). Meanwhile, genetic parameters were also analyzed by PopGen32. Forty-six strains were amplified by four microsatellite prime pairs, and generated a total of 66 polymorphic bands with 16–18 alleles for each locus. The average polymorphism information content (PIC) of all strains at four loci was 0.862 3, suggesting that all the four SSR loci were hypervariable. Forty-six strains gave 39 different patterns with a discriminatory power of 98.94%. The heterozygosity was observed as 0.478 3–0.658 5. These results indicate that indigenous wine yeasts and commercial yeasts have high levels of genetic diversity, and both have unique alleles. Both kinds of strains have clear clustering boundary in the phylogentic tree.
With glsA1 in BJ3-2 as the homologous sequence, glutaminase gene glsA2 with high activity was targeted and integrated into the Bacillus subtilis BJ3-2 chromosome by constructing a single-exchange integrative vector. A recombinant strain BJ3-2A2 was obtained with good genetic stability. The results of detection showed that glutaminase activity in the recombinant strain was 3.36 times higher than that in the original strain BJ3-2. The amino acid contents in douchi fermented with BJ3-2A2 and the original BJ3-2 were measured, and the results showed that glutamate content in fermentation products from the recombinant strain was increased by 12.8% as compared to that observed with the original strain. All the analyses show that B. subtilis BJ3-2 is transformable as a RecE+ strain and that glutaminase gene glsA2 can be highly expressed in the BJ3-2 chromosome, thus improving the flavour of douchi.
The survival of Lactobacillus casei LC2W and the bacterial communities in cheddar cheese were analyzed by using selective media and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method during the ripening period of 180 days at 6 ℃. Results demonstrated that SBM and MSE selective media could not objectively reflect the dynamic changes of various microorganisms in the cheese due to the poor selectivity. The population of the starters Streptococcus thermophilus and Lactococcus lactis decreased significantly, while the population and species of the non-starter Lactobacillus significantly increased during the ripening period. L. casei LC2W survived well in the cheese and retained its viability at > 1 × 108 CFU/g even after 180 days ripening. It is concluded that cheddar cheese can be an effective vehicle for delivery of L. casei LC2W and that PCR-DGGE technology combined with traditional culturedependent methods can be more suitable for cheese microflora analysis.
Fourteen strains of suspected lactic acid bacteria were isolated from 7 naturally fermented pickle juices gathered from Daqing, Heilongjiang Province. 16S rDNA was extracted from each of these bacterial strains using a bacterial genomic DNA extraction kit. The species were identified by DNA sequencing, homology analysis and phylogenetic tree. The results indicated that the all 14 strains belonged to lactic acid bacteria, including 4 strains of Lactobacillus curvatus (HD12-1, HD13-5, HD14-1 and HD15-1), 1 strain of Lactobacillus brevis (HD18-2), 3 strains of Lactobacillus sakei (HD12-2, HD13-1 and HD16-5), 1 strain of Leuconostoc mesenteroides (HD18-3), and 5 strains of Lactobacillus plantarum (HD14-3, HD15-2, HD16-2, HD17-3 and HD17-4). Among these strains, 6 strains, including HD12-1, HD13-1, HD14-1, HD15-1, HD16-2 and HD16-5, were able to grow at pH 2.5, 3.0 or 3.5, with a survival rate above 2% at pH 3.0.
The formation and regeneration of the protoplast from Asperigillus niger with high yield of acid-stable α-amylase was Optimized using single factor experiments, Plackett-Burman design and response surface method. The optimum conditions for protoplast formation and regeneration were as follows: A. niger aged at 72h, spore concentration at 7.5×106 CFU/mL, hydrolysis with 10 g/L snailase, 10 g/L cellulose and 10 g/L lysozyme under 37℃, pH 6.8 for 2 h, and 0.85 mol/L mannitol for stabilization of osmotic pressure. At this condition, the rate of protoplast formation and regeneration reached 86.92% and 42.67 %, rescpectively.
A cryoprotectant composed of skim milk powder, sucrose and glycerol for vacuum lyophilized spore power of Aspergillus niger was developed and its formulation was optimized by one-factor-at-a-time and uniform design. By regression analysis of the experimental data, the optimal cryoprotectant formulation (per 100 mL of cryoprotectant) found to consisted of 6.43 g of skim milk powder, 13.03 g of sucrose, and 6.88 g of glycerol. The predicted survival rate of spore with the addition of the optimized cryoprotectant after freeze-drying was 88.82%, which was close to the actual value of 87.03%.
In this paper, the effects of initial medium pH and feeding of the substrates glucose and phenylpyruvic acid (PPA) on the production of phenyllactic acid (PLA) by Lactobacillus paracasei W2 in a 7.5 L fermentor were studied. The results indicated that all three factors generated corresponding effects on cell growth and PLA production. Two substrate feeding strategies, intermittent feeding of PPA and continuous feeding of both glucose and PPA were performed and the initial medium pH was set to 6.5. After 36 h of fermentation under these conditions, PLA production reached 1.148 g/L and 2.121 g/L, respectively, and the conversion rate of PPA reached 62.19% and 47.2%, respectively. In addition, in comparison with fedbatch fermentation, the PLA yield was enhanced by 41.72% and 161.53%, respectively.
Nineteen samples of Tibetan fermented dairy products were collected from eight pasturing areas and a polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method was established to investigate the biodiversity of lactic acid bacteria in Tibetan fermented dairy products. After total DNA was extracted from dairy samples by a commercial kit (Tiangen DP326), the V3 region of the 16S rRNA gene was amplified by nested PCR and touchdown PCR, and the PCRamplified products were subjected to DGGE electrophoresis. All bands were excised from the gel and sequenced, and the species of strains were identified and a phylogenetic tree was constructed. NTsys 2.10e software was used to analyze the similarity of band profiles. Results showed that the microbial flora of lactic acid bacteria in Tibetan fermented dairy products was composed of Lactobacillus paracasei, Lactobacillus helveticus, Lactobacillus fermentum, Lactobacillus crispatus, Lactobacillus delbrueckii, Lactobacillus buchneri, Lactococcus raffinolactis, Leuconostoc mesenteroides, Lactobacillus plantarum, Pediococcus pentosaceus, Lactococcus lactis and Streptococcus thermophilus. Therefore the conclusion is drawn that Lactobacillus delbrueckii is the dominant species in most of the samples, and it simultaneously distributes in all eight pasturing areas. This study has successfully established a PCR-DGGE method to investigate the biodiversity of lactic acid bacteria in Tibetan fermented dairy products.
The production of cellulaes from tea seed (Camellia oleifera) cake with a minimized content of residual tea saponin of 0.917% as obtained by ultrasonic extraction method was studied in solid-state fermentation by mixed strains of Neurospora crassa with Issatchenkia oriental, Trichoderma reesei, Trichoderma vivide or L. plantarum. The activities of cellobiohydrolase 1 (C1), β-1,4-endoglucanase (Cx) and β-glucosidase (β-G) and filter paper activity (FPA) in fermentation supernatants were determined to explore their synergistic action on enzymatic hydrolysis of cellulose. The enzyme activity of C1 from Neurospora crassa combined with Trichoderma vivide was increased by 51.09% compared with that obtained from single-strain fermentation by Neurospora crassa; meanwhile, the combination of both strains resulted in prolonged secretion of cellulases, and the FPA activity reached 2.782 U/g after 96 h. The cellulose was degraded by 64.19% and 61.59% in tea seed cake fermented for 10 days by Neurospora crassa mixed with Trichoderma reesei and Trichoderma vivide, respectively. The overall tendency of the enzyme activities was an increase with increasing the inoculum size irrespective of fermentation with Neurospora crassa alone or combined with other strains. However, the cellulase activities were declined at higher inoculum sizes surpassing 9 mL/100 g of Neurospora crassa when inoculated alone. These results indicate that Neurospora crassa is able to cooperate with Trichoderma reesei and Trichoderma vivide respectively to degrade cellulose.
16S rRNA analysis was employed to investigate the microbial populations in putrefactive surface layer during leaf mustard pickling process. The microbial diversity and dynamics were assessed by Shannon-Weaver, Chao, ACE, Simpson, rarefaction analysis and similarity coefficient. All 16S rRNA gene sequences retrieved from brine samples with pickling for 7, 22 d and 60 d were assigned to Vibrio, Halomonas, Pseudoalteromonas, Shewanella, Marinomonas, Geobacillus, Pseudomonas, Psychrobacter, Cobetia, Oceanobacillus, Pantoea and Lactobacillus. Among these genera, the dominant bacterium during the pickling process was pathogenic Vibrio and its number in these three samples was 45.8%, 74.2% and 44.9%, respectively. The spoilage bacteria such as Pseudoalteromonas, Shewanella and Pseudomonas were mainly observed on day 7, and the number of Lactobacillus, Cobetia and Halomonas was gradually increased with the pickling process. The community similarity coefficient was decreased to 0.4064 from 0.5131 and then increased to 0.8168. The results indicated that the bacterial succession was associated with the pickling process and such succession is responsible for the spoilage of leaf mustard and the production of some noxious ingredients. These results provide a useful guidance for quality and safety control of pickled leaf mustard.
In order to explore the combinatorial induction of recombinant dextransurase experssion in E. coli by isopropyl β-D-1-thiogalactopyranoside (IPTG) and lactose, a mixture of IPTG and lactose was added to the cell culture to induce the expression of recombinant dextransurase. Based on the optimal culture medium, IPTG concentration and the amount of lactose added, bacteria concentration and induction time revealed significant impacts on the enzyme activity. The results showed that the optimal concentrations of IPTG and lactose were 0.1 mmol/L and 2.5 g/L, respectively, and optimal induction time was 4 h at 25 ℃. Under these culture conditions, the activity of dextransucrase could reach up to 40.44 U/mL. The combinatorial induction of recombinant E. coli dextransurase by IPTG and lactose was feasible, greatly reducing the dosage of IPTG and industrial production costs.
Based on the metabolic utilization of trimethylamine oxide (TMAO), six common food spoilage microorganisms (S. aureus, E. aerogenes, E. faecalis, E. coli, L. monocytogenes and S. enteritidis) were classified by analyzing their effects on physicochemical properties of PCA medium containing TMAO. Subsequently, TMAO metabolites were analyzed by using non-suppressed ion chromatography and identified mainly as trimethylamine. Finally, different physical and chemical indicators (pH, conductivity, turbidity and TMA content) of the culture medium were plotted against culture time. The generation of TMA can affect the conductivity and pH of the medium, and this effect has a significant difference depending on the bacterial species.
Pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-dependent GDH, EC1.1.5.2), which catalyzes the conversion of D-glucose to gluconic acid, is an important enzyme in the production of gluconic acid by fermentation or enzymatic method. The aim of this study was to clone and characterize the gene enconding PQQ-dependent GDH from Gluconobacter suboxydans. Primers were designed based on the conserved region of the PQQ-attaching sites, and the entire gdh gene was obtained by thermal asymmetric interlaced-PCR (TAIL-PCR). The gene was then sequenced and analyzed by bioinformatics methods. The sequence analysis suggested that its coding region consisted of 2268 bp nucleotides encoding 755 amino acids. The deduced amino acid sequence showed a high level of similarity to the PQQ-dependent GDH of Gluconobacter oxydans. The molecular weight of the encoded protein was 81.72 ku with an isoelectric point of 5.14. The bioinformatic analysis suggested that its second structure consisted of 18.41% alpha helix, 16.16% extended strand and 65.43% random coil and its N-terminal contained five transmembrane domains locating in the region between amino acid residues 1 and 140. This study indicates that TAIL-PCR provides a simple and efficient method for the cloning of the unknown genes. The bioinformatic analyses of GDH provide a foundation for further investigation on the characteristics and catalytic mechanism of GDH and its potential applications in gluconic acid production.
A bacterium numbered as ZN-14 with the ability for efficient oxidization of xylitol to L-xylulose, a rare ketopentose, was isolated and purified from soil samples, through primary isolation and secondary screening. We have employed this isolated strain for the production of L-xylulose from xylitol by a resting cell reaction at 37 ℃ and pH 9.0. After 24 h, L-xylulose was produced at a yield of 26.62% when 20 g/L xylitol was utilized as the precursor. The strain was identified as Bacillus megaterium, based on the sequence analysis of 16S rDNA and the general morphological and biochemical characteristics.
Objective: To explore the effects of a polysaccharide from Ganoderma atrum (PSG-1) on cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), inositol triphosphate (IP3)/Ca2+ and diacylglycerol (DAG)/protein kinase C (PKC) signaling pathways in peritoneal macrophages of S-180 tumor-bearing mice. Methods: A tumor-bearing mouse model was established by inoculating mouse sarcoma S-180 cells into BALB/c mice; peritoneal macrophages were collected from the S-180 tumor-bearing mice, then cultured in vitro and treated with PSG-1 at various concentrations. The IP3, DAG and cAMP levels in cell culture supernatant were measured by ELISA. The intracellular Ca2+ content was assayed by a flow cytometric method. The PKA and PKC protein expression in macrophages was determined by Western blotting. Results: PSG-1 in the concentration range of 20–160 μg/mL stimulated the production of IP3, DAG and cAMP in the macrophages from S-180 tumor-bearing mice, increased the intracellular Ca2+ content, and increased the protein expression of PKA and PKC. Conclusion: PSG-1 can exert anti-tumor activity in peritoneal macrophages of S-180 tumor-bearing mice through the activation of cAMP/PKA, IP3/Ca2+ and DAG/PKC signaling pathways.