The aim of the present study was to investigate the characteristics of Mozzarella cheese made from milk containing different somatic cell count (SCC) at zero (0 cells/mL, after microfiltration), low (300000 cells/mL) and high (600000 cells/mL) levels. Analyses for cheeses included composition recovery and proteolysis, free fatty acid, free oiling off, meltability, texture and sensory after 1, 15, 30, 45, 60 days of storage. SCC did not significantly affect (P > 0.05) composition recovery. There were no significant differences in physicochemical characteristics between LSCC and HSCC cheeses, However, microfltration treatment significantly affected physicochemical characteristics of Mozzarella cheese. SCC below 600000 cells/mL was not among the important factors affecting Mozzarella cheese during 60 days of storage.
Effects of heating conditions, including setting temperature, setting time and heating method on the gel properties were investigated by texture analysis and determinations of whiteness, water-holding capacity, microstructure, TCA-soluble peptides content, protein solubility. Results showed that heating temperature, time and method all had a significant effect on the gel properties of horse mackerel surimi. The optimum condition for processing horse-mackerel surimi was a two-step heating method with setting at 30 ℃ for 5 h (or at 40 ℃ for 4 h) and then heating at 90 ℃ for 20 min, which resulted in the formation of high compacted and uniformed three dimensional network structure observed under scanning electronic microscopy (SEM). Horsen mackerel surimi gel showed a structure with aggregates of sparse packed spherical proteins, arranged in clusters when setting at 50-70 ℃, which indicated the modori phenomena occurred.
In order to evaluate antioxidant activity in vitro of procyanidins from pericarp of four cultivars (Baila, Feizixiao, Nuomizi, Huaizhi) of litchi (LPPC), superoxide anion radical, hydroxyl radical and hydrogen peroxide scavenging assays were carried out using pyrogallo-luminol, ferrous sulfate-Luminol-hydrogen peroxide and Luminol-hydrogen peroxide systems, respectively. In addition, copper sulfate-phen-VC-hydrogen peroxide-DNA system was used to determine the preventing effect of LPPC against DNA damage. Results showed that among the litchi cultivars, Baila LPPC possessed the best scavenging potency against superoxide anion and hydrogen peroxide and Feizixiao LPPC indicated the most efficient hydroxide radical scavenging ability and DNA damage preventing effect. In conclusion, procyanidins from pericarp of different litchi cultivars acted different antioxidant effects in different chemiluminescence systems.
Basic compositions contributing to turbidity of pearl oyster protein hydrolysates were investigated. Results showed that turbid materials were mainly composed of 54.3% crude protein and 26.1% ester. SDS-PAGE pattern confirmed that peptides with small molecular size were the major components of turbid materials; amino acid analysis revealed that hydrophobic amino acids in turbid materials were 42% and higher than the content in hydrolysates. SDS analysis exhibited more effective to dissolve turbid materials than guanidine hydrochloride, urea and sodium chloride. Moreover, particle size distribution analysis showed that SDS treatment could significantly reduce the particle size of turbid materials. Average particle size of turbid materials was reduced to 97.9 nm from 1954.3 nm in turbid materials at the concentration of 8% during SDS treatment. All of these investigations suggested that turbid system was formed by large molecular peptides through hydrophobic interaction. In contrast, lipids had little effect on the turbidity of hydrolysates.
The binding reaction of caffeic acid with bovine serum albumin (BSA) was studied using fluorescence spectroscopy. Caffeic acid quenched the fluorescence of BSA through a static process. The primary binding pattern between caffeic acid and BSA included electrostatic and hydrophobic interaction, and the latter was identified to be the main force under physiological condition. It was found that caffeic acid was located near the Tyr residue region of site I in BSA by competing binding experiment using warfarin and ibuprofen as site markers by fluorescence spectra. The distance between the donor (BSA) and receptor (caffeic acid), r0, was obtained to be 3.64 nm according to Forster's non-radiative energy transfer theory. In addition, the effect of caffeic acid on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy.
Young leaves of L.bararum and L.chinense with different geographical origins were compared for differences in main active compounds, such as polysaccharides and total flavonoids. Among geographical populations of each species and between the two species, no significant differences in contents of polysaccharides and total flavonoids were seen, respectively. While the content of polysaccharides in young leaves of L.chinense were significantly higher than that of L.bararum. Hence, L.chinense leaves were a potential source for medicinal food. Science there were significant differences in contents of polysaccharides and total flavonoids within the same geographical population of each species, it is of great interest to develop good varieties by interstrain breeding.
Fruits of 25 litchi varieties were used as materials to study fruit quality, major components, physical-chemical parameters, soluble protein, total phenols and total antioxidant capacity. Results indicated that significant differences of juice rate, contents of total soluble solids and total acids, edible pulp rate, and sugar/acid ratio in fruits of different litchi varieties were observed. Huidonghongyan exhibited the highest juice rate and Tianyan the lowest, which were 70.76 % and 32.77 %, respectively. The highest content of total soluble solids was observed in Shuijingqiu to be 19.57 %; in contrast, the lowest content of total soluble solids in Jianjianghongnuo was 12.00 %. In addition, obvious differences in polyphenol oxidase (PPO) and peroxidase (POD) activities, and color stability were also observed in different litchi varieties. PPO activity was ranged from 0 to 35.00 U and POD activity from 15.3 to 6013 U. The color difference (ΔE) was ranged from 0.39 to 17.20 at 30 ℃ and from 1.64 to 38. 42 at 100 ℃. Preliminary evaluation indicated that Huidonghongyan, Nuomici, Yuanzhi, Heiye, Zhongshanzhuangyuanhong and Baitangyin were excellent litchi varieties for litchi juice and litchi wine making.
PSE (pale, soft, exudative) meat myofibrillar protein reveals much lower solubility and poorer gel properties when compared with that of normal meat (red, firm and non-exudative, RFN). Our objective was to evaluate effects of phosphates on gel properties of porcine myofibrillar protein. PSE and RFN porcine longissimus muscles were used as experimental materials and effects of sodium hexametaphosphate (SHMP), sodium pyrophosphate (SPP) and sodium tripolyphosphate (TPP) on myofibrillar protein solubility, sol turbidity and gel properties were evaluated. Results showed that all the three kinds of phosphates evidently affected myofibrillar protein solubility and aggregation and gel strength. PSE gel formed with the addition of 0.25% TPP and RFN gel formed without the addition of TPP had approximate gel strength. In conclusion, phosphates could improve sol system environment so as to enhance sol and gel properties.
A HAAKE rheometer was employed for the rheological characterization of soybean β-conglycinin-dextran mixed gels in this study. Results showed that β-conglycinin-dextran mixture had a higher elastic modulus than single β-conglycinin. With the same molecular weight dextran, the elastic modulus of mixed gel increased with increasing dextran concentration; similarly, with the same concentration dextran, the elastic modulus of mixed gel increased with increasing molecular weight of dextran. The elastic modulus of β-conglycinin-dextran mixture in 0.25 mmol/L phosphate buffer (pH 7.6) was higher than that in 0.5 mmol/L phosphate buffer (pH 7.6); while, the initial gel formation temperature of β-conglycinin-dextran (the same molecular weight dextran, the same dextran concentration) mixture in the first buffer was less than that in the second buffer, namely, Tp0.25 < Tp0.5.
Antibacterial activity of rape bee pollen extract was investigated using Oxford cup method. Results indicated that 0.5% formic acid extraction fraction from ethanol extract of rape bee pollen exhibited strong antibacterial activity. Minimum inhibitory concentrations (MIC) of formic acid extraction fraction against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus subtilis were 25, 50, 50 mg/mL and 100 mg/mL, respectively. HPLC analysis showed that bioactive components with antibacterial activity in formic acid elution fraction were weakly polar substances.
In this study, change of isoflavone contents and compositions in sufu (fermented tofu) during pre-fermentation and salting was investigated. Results indicated that total content of isoflavones exhibited a gradual decrease during pre-fermentation and salting. The loss of isoflavones was mainly attributed to tofu preparation and salting process. The compositions of isoflavone were altered during pre-fermentation and salting, which revealed an increase of aglycones such as daidzein and genistein, and a corresponding decrease of glucosides such as daidzin and genistin. Total content of isoflavones in sufu treated with less than 10% salt was higher than that of sufu treated with 15% salt.
Five commercially available Vicia villosa Roth honeys were evaluated for contents of total phenolic acid and total flavonoids, reducing power and DPPH radical scavenging activity. Results indicated that the content of total phenolic acid in the samples theoretically equivalent to that of catechin varied from 9.323 to 21.982 mg/100 g honey, and the content of total flavonoids theoretically equivalent to that of rutin from 0.842 to 2.295 mg/100 g honey. All the honey samples exhibited some antioxidant activity in a dose-dependent manner. A positive correlation was observed between total phenolic acid content and DPPH radical scavenging activity or reducing power. This demonstrated that the antioxidant activity of these honeys may be inked to the total phenolic acid content. In addition, total flavonoids content had no obvious correlation with total phenolic acid content, reducing power or DPPH radical scavenging activity.
In order to make more effective use of fish waste materials, acid-soluble and pepsin-soluble collagens (ASC and PSC) were extracted from swim bladders of grass carp and properties of ASC and PSC were investigated. The yields of ASC and PSC were 4.7% and 11.1%, respectively, on the basis of dry weight. UV spectra of ASC and PSC from grass carp exhibited the maximum absorption peak at 230 nm. Amino acid profiles of ASC and PSC revealed that contents of hydroxyproline and proline were 16.87% and 17.55%, respectively. SDS-PAGE patterns indicated that both ASC and PSC were composed of at least two different α-chains (α1 and α2), which was similar to porcine type I collagen. The denaturation temperatures (Td) of ASC and PSC were 33.0 ℃ and 34.8 ℃, respectively, about 3 - 4 ℃ lower than that of porcine skin collagen (37 ℃). These results suggested that collagens from swim bladders of grass carp had potential as an alternative or a supplementary source of collagen from land vertebrates being used in different fields for industrial purposes.
This study was conducted to test main nutritional components of milk from Henan dairy goat (DG) and its hybrid goat (HG) during early lactation. Results showed that dry substance content reached the maximum, 24.14 g/100 g and 26.17 g/100 g at 1 and 2 days post-lactation in DG and HG, respectively, and then decreased with prolonged lactation time; likewise, fat content reached the climax, 6.32 g/100 g and 5.38 g/100 g at 5 days and 4 days post-lactation, respectively, and then exhibited a descending trend. For both DG and HG, milk lactose content displayed a general ascending trend during early lactation. Protein content in DG milk was elevated gradually during 5-day colostrum-producing period, and then basically trended to be stable later; in contrast, protein in DG milk exhibited a trend to first decrease and then basically keep stable. Ash content in both milk was first decreased in early lactation stage and then fluctuated around a fixed value. Calcium content was basically kept stable over the whole tested lactation period. There was a slight increase in phosphorus content in early lactation stage followed by a fluctuated decrease. It was concluded that the main nutritional components of both milk changed with lactation time and the changes were closely related to feeding management and nutritional condition control for dairy goats.
With the aim of achieving an in-depth understanding of effect of ultra-high hydrostatic pressure treatment on limonene in navel orange juice, a mathematical model describing the relationship between limonene content and three treatment parameters, such as pressure(100-500 MPa), temperature (20-40 ℃) and treatment time (10-20 min) was created using Box-Behnken central composite design combined with regression analysis, and interactive effects of the three variables on the dependent variable were then evaluated using response surface methodology (RSM). This model was found to be significant (P< 0.0001) with a regression coefficient of 0.9938 and an adjusted regression coefficient of 0.9858. The predicted values of limonene content were in good agreement with the experimental values. This demonstrated the reliability of the created model in predicting limonene content in navel orange juice subjected to ultra-high hydrostatic pressure treatment under different conditions.
Fruits of 18 longan cultivars were analyzed for physical and chemical parameters, total antioxidant capacity, soluble protein and total phenolics. Results showed that there were remarkable differences in fruit juice rate, contents of total soluble solids and total acids, edible pulp rate and ratio of sugars to acids of tested longan cultivars. Fruit juice rate ranged from 36.02% to 55.74%, and the highest was exhibited in Shuiyan cultivar (55.74%) and the lowest in Hualuguangyan (36.02%).Total soluble solids content ranged from 11.3% to 21.77%, and the highest was exhibited in Baihuamu (21.77%) and the lowest in Qingkebaoyuan (11.3%). Besides, notable differences were also observed in PPO and POD activities and color stability of these longan cultivars. PPO ranged from 0 to 6.6 U, and POD from 72.7 to 1816.7 U. Longan fruits exposed to 30 ℃ and 100 ℃ revealed a total color difference (ΔE) value ranging from 0.24 to 3.68 and from 7.62 to 63.53, respectively. It was preliminarily evaluated that Shixia, Chuliang, Baihuamu, Hualuguangyan and Shuangzimu were excellent cultivars for longan juice and longan wine making. Among these longan cultivars, Shuangzimu and Qingkebaoyuan exhibited the highest and lowest total antioxidant capacity of 20.39 mmol/L and 3.73 mmol/L, respectively. Soluble protein content was fluctuated in the range of 45.82 (Jiluanyan) to 88.8 mg/L (Shixia). The highest total phenolics content valued at 749.95 mg/L was observed in Hualuguangyan, and the highest at 13.02 mg/L in Jiluanyan.
In this study, in vitro adsorption process of low density lipoprotein (LDL) onto macroporous resin was investigated. Lipoprotein from calf serum was used as the material to conduct adsorption experiments by 3 kinds of macroporous resins. The optimal resin was screened in terms of adsorption capacity towards LDL. Results indicated that macroporous resin D113 exhibited the highest adsorption capacity. Meanwhile, dynamic adsorption process was also described using a mathematical mode, which could well fit experimental data. Therefore, this model will provide practical reference for further research of LDL adsorption.
Different storage-age Pu-erh tea (1, 5, 10 years) infusion (8 g/L) sweetened with sucrose 50 g/L was filtrated and inoculated with kombucha culture for 8-day fermentation at 28 ℃. The fermentation broth was dynamically analyzed for microbial population, pH, tea polyphenols, total acidity, protein and biomass as well as high-boiling-point substances. Results showed that there were no obvious differences in microbial population, pH values, etc. between Pu-erh and green or black tea infusion fermented by kombucha culture. Therefore, Pu-erh tea infusion was an excellent matrix for kombucha fermentation. Added together, 35 non-volatile components (mainly including 14 alcohols and 13 acids) were identified by GC-MS in different storage-age Pu-erh tea infusion fermented by kombucha for 3, 4, 6, 7 days and 8 days. Alcohols were detected with the most frequencies at the initial fermentation stage (0-4 days), and acids were dominant later. Citric acid, nonahexacontanoic acid, l-(+)-ascorbic acid, 2, 6-dihexadecanoate, etc. were detected in the maturation period (the 7th day), which may be the crucial constituents in favor of health in fermented Pu-erh tea infusion by kombucha.
In order to investigate the changing trend of microorganisms in shellfish, total number of bacteria and coliform in 3 species of shellfish such as Ruditapes philippinarum, Chlamys farreri and Solen gouldii Conrada stored at -18, 4, 15 ℃ and 22 ℃ for different periods were determined. Results indicated that an obvious decrease in total number of bacteria in shellfish stored at -18℃ for more than 24 h was observed; in contrast, no obvious change in shellfish stored at other temperature conditions for 12 h or at 4 ℃ for 24 h was observed. Moreover, a positive correlation between total number of bacteria and coliform group in shellfish stored at 22 ℃ was also observed. Taken together, the original status of microorganisms present in shellfish can be remained for a longer period of time at the environmental condition of 0 ℃.
Thermodynamic adsorption characteristics of Chaenomeles sinensis polyphenols onto NKA-9 resin were studied. Results showed that adsorption equilibrium data obtained within the temperature range of 298-308 K and concentration range of 20-40 mg/mL could be well fitted by the Langmuir-type and Freundlich-type isotherm equations and the adsorption was favorable type. Meanwhile, the changes of enthalpy, free energy and entropy were measured. It was indicated that the adsorption was an endothermic process.
An acidic polysaccharide with antioxidant activity was obtained from Prunella vulgaris Linn through sequential steps of water extraction and alcohol precipitation, then decolorization and deproteinization by HZ-820-type unpolar resin adsorption, and finally purification. 3-Hydroxydiphenyl-sulfuric acid and barium chloride-gelatin turbidimetric methods were used to determine contents of galacturonic acid and sulfate in the polysaccharide, and the results were (58.85 ± 0.46)% and (7 ± 0.52)%, respectively. Ultraviolet and infrared (IR) spectral analyses indicated that the monosaccharide composition of the polysaccharide consisted of galacturonic acid, xylose, glucose, rhamnose, and galactose and it belonged to the nonglycoprotein family. Moreover, this polysaccharide revealed strong scavenging activities against hydroxyl free radicals and DPPH free radicals.
The rheological properties and their mathematical models of four kinds of cassava modified starches by esterification and cross-linking, acetylation, oxidation and pregelatinization, respectively, were investigated to understand the regular flow. Along with this, the correlation of rheological properties of cassava modified starches and gel properties of silver carp surimi was also analysed. Results showed that the four kinds of starches were all pseudoplastic fluid in aqueous solution. The Arrhensius equation could accurately describe the influence of temperature on flow behavior of cassava modified starches. The more the flow properties of aqueous solution of cassava modified starches were far away from Newton fluid and the bigger the viscosity coefficient became, the better the surimi gel properties became.
In order to explore the effect of addition of oat flour on quality properties of pork sausages, the textural attributes of pork sausages containing oat flour were assessed by sensory evaluation and instrumental determination (texture profile analysis, TPA), and correlation analysis was conducted among the assessment results by the two approaches. Meanwhile, the water-holding capacity (WHC) of compound sausages was also determined. Results indicate that the compound sausages had an excellent texture and overall acceptability when oat flour was at 14% addition level. Hardness obtained from TPA was significantly (P < 0.05) correlated with sensory hardness (r = 0.898) and cohesiveness obtained from TPA significantly (P < 0.05) correlated with sensory hardness or springiness (r = -0.863, -0.825). WHC of compound sausages was slowly increasing with increasing level of added oat flour, ranged from 94.33% to 94.83%. However, WHC did not increase obviously when the addition level was beyond 17%. It was nferred that oat flour added to sausages may help improve WHC of compound sausages. Therefore, compound oat flour sausages with good acceptability, texture and WHC could be made from meat added with oat flour in an appropriate proportion.
With the aim of revealing the differences in mechanical and barrier properties and protein structure of soy proteinisolate edible films produced at different thermal treatment temperatures and correlation between them, this study was conducted. Films produced at 90 ℃ showed the best mechanical and barrier properties. The difference in protein structure was evaluated in terms of disulfide bond content, hydrophobic value and main secondary structures including alpha-helix and beta-sheet. It was demonstrated that disulfide bond content and alpha-helix presented a positive correlation with mechanical and barrier properties of the films, which were negatively correlated with hydrophobic value.
Effect of plasticizers on properties of carboxymethyl cellulose (CMC) and methyl cellulose (MC) films was studied, and the mechanism was discussed through scanning electron microscopic (SME), infrared spectrometric and X-ray diffractometric observations. Results showed that 0.2% glycerol added exhibited a good plasticizing effect on CMC films, while, for MC films, the optimal plasticizer was polyethylene glycol at a concentration of 0.4%. The effect of plasticizers on film properties depended on the material-plasticizer compatibility.
According to the mass transfer mechanism, the extraction process of grape seed procyanidins could be described with the concentration of procyanidins. In the present study, a kinetic equation was established on the basis of mass equilibrium. In order to evaluate the equation, experiments for extracting procyanidins from grape seed with ethanol under different temperatures were carried out. The relationship between balance concentration of procyanidins and extraction temperature was obtained by fitting experimental data. Additionally, the important kinetic parameters were calculated using Arrhenius equation and the apparent activation energy for extraction process was calculated to be 2.08×104 J/mol. The results of verification experiment showed that the presented kinetic equation could describe the extraction process of grape seed procyanidins and the extraction process accorded with diffusion theories. This kinetic equation can provide a good theoretical base for further study on extraction of grape seed procyanidins.
A certain amount of nitrite residue was kept in meat products during preparation processing. In order to investigate the change of nitrite in different meat products during preparation and storage, three kinds of meat products such as manor ham, Australia beef and lilac burned chicken were used as the materials to track the change of nitrite content and optimize critical preparation processing and storage. Meanwhile, nitrite content of poultry products in market was also investigated. Results indicated that nitrite content of meat products exhibited an obvious descending trend during thermal treatment. In addition, nitrite content in refrigerated meat products exhibited faster decrease than that of frozen meat products with the same package condition. However, currently available poultry products in market were generally low in nitrite content so that a negative impact to the inhibition of Clostridium botulinum was observed. Therefore, these investigations can provide a good academic base for studying the change of nitrite content in meat products during preparation processing and storage as well as a great guidance to design optimal addition amount of nitrite in meat products during preparation.
Corn gluten meal was hydrolyzed by proteolysis with alkaline protease and the refined hydrolysate was then separated and purified by Sephadex G-15 and G-10 column chromatographic and preparative HPLC methods. With α-tocopherol as a positive control, the hydrolysate and its fractions were evaluated for antioxidant activity by DPPH radical scavenging assay, linoleic acid auto-oxidation inhibition assay, ferric reducing/antioxidant power (FRAP) assay and superoxide anion scavenging assay based on pyrogallol auto-oxidation method. Results revealed that fraction II eluted from Sephadex G-10 column exhibited the highest antioxidant activity, a relative molecular mass distributed in range of 400 to 700 D detected by MS and an amino acid composition mainly consisting of glutamic acid, alanine, leucine, histidine, proline and phenylalanine.
This study was designed to examine effects of gelation temperature and CaCl2 level on Ca2+-induced cold gelation of whey protein. Results showed that low gelation temperature and increased CaCl2 concentration were in favor of the formation of clear gel. Gels formed at 0, 10 or 20 ℃ exhibited an increase in hardness with increasing CaCl2 concentration. In addition, a sharp increase was observed in the water-holding capacity of gels formed at 0 or 10 ℃ when the CaCl2 concentration was increased from 20 to 40 mmol/L. With the exception of gels formed at 0 ℃ with 20 mmol/L CaCl2, lower temperature resulted in higher gel strength and water-holding capacity. Therefore, temperature and CaCl2 concentration are both key factors affecting cold gelation of whey protein.
In the present study, vital wheat gluten (WG) was comminuted into 8 different meshes using a jet mill, and effect of comminution degree on physico-chemical and functional properties of WG was examined. Results showed that with decreasing particle size, there was an obvious decrease in moisture content in WG and the water absorbing capacity exhibited an ascending trend below 500 mesh and a descending trend between 900 mesh and 500 mesh and held the line approximately above 900 mesh. Whiteness, foaming properties, emulsifying properties, water holding capacity and oil holding capacity had different increases as particle size decreased. Therefore, ultrafine comminution can improve some properties of VWG and the improvement in physico-chemical and functional properties varies with comminution degree.
In order to enhance the foam stability of green draft beer, barley lipid transfer protein 1 (LTP1) encoding DNA sequence from Hordeum vulgare was modified to construct yeast Saccharomyces cerevisiae expression plasmid YEp181-KAMLC of barley LPT1 using the plasmid YEplac181. The expression of barley LTP1 was regulated by alcohol dehydrogenase promoter (ADH1 promoter) and terminator cytochrome C terminator (CYC1) of Saccharomyces cerevisiae, and the matured form of barley LTP1 was secreted under the lead of α-mating factor 1 signal peptide. Fermentation for 132 h at 30 ℃ gave a yield of barley LTP1 as high as 29.45 mg/L.
Simple sequence repeats (SSRs) were investigated in 12144 qualified ESTs downloaded from Nucleotide ESTs database of Lentinula edodes in NCBI. There were 359 SSRs in all the ESTs sequences of Lentinus edode, which were composed of 243 di- (67.69%), 114 tri- (31.76%), 1 penta- (0.28%) and 1 hexa- (0.28%) nucleotide SSRs. The estimated frequency of SSRs was approximately 1 SSR per 33.8 ESTs. Total length of SSRs was 7727 kb, accounting for about 2.94% of total ESTs sequences. In addition, we selected 100 ESTs sequences in Lentinus edodes and designed 100 primer pairs for EST-SSR markers, of which 20 were arbitrarily selected and synthesized. Selection and investigation of these primers were performed with 4 wild-type strains of Lentinula edodes. There were 16 primer pairs characterized by clear and stable target bands, of which 11 presented genetic diversity. Our findings indicated that these Lentinula edodes EST-SSRs markers developed in this study were useful and effective.
Four Lactobacilli stains were isolated and screened from traditional fermented dairy products dairy tofu popular in Inner Mongolia. According to phenotypic, physiological-biochemical and API tests, the strains were all identified as Lactobacillus plantarum and named C2, C8, C15, and C21, respectively. The negative staining method was used to observe their capsules, and the results indicated that except strain C2, all the others produced capsular polysaccharides and the capsules could be seen by using optical microscopy. The 48 h growth and exopolysaccharide-producing ability of the four strains were analyzed. It was found that all these strains exhibited a gradually increasing exopolysaccharides production during 48 h culture, and strain C21 produced the highest amount of exopolysaccharides.
Double enzyme hydrolysis was used to prepare peptides from corn gluten meal. In order to maximize degree of hydrolysis (DH), crucial hydrolysis parameters were optimized. Results showed that a maximum DH of 80.97% was obtained by optimized sequential hydrolysis for 1.5 h using protease alkaline at 55 ℃ and pH 8.5 with 5 g/100mL substrate concentration and 4% enzyme dose followed by 1.5 h using papain at pH 7.5 with 3.5% enzyme dose, which was significantly higher that obtained by single enzyme hydrolysis.
In order to exploit new carbon and nitrogen sources for Hericium erinaceus, effects of kind and amount of carbon and nitrogen sources on the content of polysaccharide in harvested mycelia and broth of Hericium erinaceus after 35-day liquid submerged fermentation. The phenol-sulfuric acid method was used to determine polysaccharide content. Results showed that the optimal carbon and nitrogen sources were starch and soybean dregs for polysaccharide production in Hericium erinaceus mycelia, respectively, and the content of polysaccharide was as high as 162.17 mg/g when the amounts of starch and soybean dregs were 4.0% and 1.5%. In conclusion, starch and soybean dregs are the optimal choices of carbon and nitrogen sources for polysaccharide production in Hericium erinaceus due to low cost and broad source, which will have a promising popularilization prospect in practical production.
According to sensory evaluation and acidity determination, 6 Lactobacilli strains (4-1, 4-7, B-2, E-1, E-5, J-2) were selected from 109 isolated from spontaneously fermented yak yoghurt samples from western Sichuan plateau. The fermentation characteristics of these strains, including growth curve, acid production, fermented yoghurt viscosity, acetaldehyde synthesis were compared. Along with this, the phylogenic analysis based on 16S rDNA sequence was performed. Results showed that maximum growth was observed in the strains cultured for 14 h in MRS medium or 8 h in 10% skim milk at 42 ℃, and the acidity of yoghurt fermented with each of them reached the Chinese national standard of GB2746—1999 for yoghurt, and the viscosity and acetaldehyde amount were in the ranges of 1050-4900 mPa·s and 15.11-26.64μg/mL, respectively. Strains E-1 and E-5 revealed weaker acid-producing ability during cold storage when compared with other four strains. The highest values of viscosity and acetaldehyde amount of yoghurt fermented with each strain appeared on the 5th and 2nd day of cold storage. Furthermore, only slight change was observed in the viscosity of yoghurt fermented with strains E-1 or E-5. The highest acetaldehyde content in yoghurt fermented with strains J-2 or E-5 was observed on the 3rd day of cold storage, while that in yoghurt fermented with other four strains alone on the 2nd day. Homology analysis of 16S rDNA gene sequence indicated that there was a homology above 99% among strains 4-7, E-1 and E-5 and these strains and L.plantarum strains were included in the same branch of phylogenetic tree based on 16S rDNA gene sequence. Strain J-2 belonged to the L.paracasei family, and exhibited a homology of 97.6% to the representative stain of this family, L. paracasei SM63 (AJ441107 ). There was a homology of 99% between strains 4-1 and B-2, which were included in the L. fermentum branch. All these results showed that strains E-1 and E-5 had a good potential as starters for yoghurt production..
In order to achieve an in-depth development of konjac fly powder, the technology for preparation of angiotensin- I-converting enzyme (ACE) inhibitory peptides by hydrolyzing this resource was studied. The optimum protease and the optimum hydrolysis conditions were determined for maximizing ACE inhibitory activity in vitro of konjac fly powder hydrolysate. Results showed that alkaline protease was the optimum protease to hydrolyze konjac fly powder protein. The optimum conditions for alkaline protease-catalyzed enzymolysis were as follows: substrate concentration 2.25%, temperature 50 ℃, enzyme concentration 3500 U/(g substrate), and pH 8.0 for a hydrolysis duration of 270 min. Under the optimum conditions, the ACE inhibitory ratio of konjac peptides with a yield of 12.70% was 95.69%. After freeze drying, konjac peptides powder with yellowy color and an IC50 of 0.80 mg/mL was obtained, which comprised 52.67% peptides and 62.30% protein. In conclusion, the developed enzymolysis technology is feasible for the preparation of ACE inhibitory peptides with high biological activity from konjac fly powder.
Freshly-prepared crude polyphenol oxidase (PPO) from chayote was enzymologically characterized in the present study. Results showed that the optimal reaction pH and temperature for this enzyme were 7.5 and 30 ℃, respectively, and substrate concentration was positively correlated with enzyme activity. This enzyme could quickly catalyze the oxidation of pyrogallic acid as a substrate, but exhibited relatively low catalysis activity towards catechol, hydroquinone and resorcinol. The activity of this enzyme was inhibited by vitamin C, citric acid, sodium tetraborate, magnesium chloride and EDTA-2Na in decreasing order. With increasing concentration, there was an increase in inhibitory effects of vitamin C and citric acid against enzyme activity.
Fusion between protoplasts from Cordyceps sinensis and Cordyceps militaris subjected to heat and ultraviolet inactivations, respectively, was studied. In order to maximize fusion rate, five crucial fusion conditions were optimized using orthogonal array design. A maximum fusion rate of 2.74 × 10-5 was achieved through 20 min fusion at 35 ℃ under the promotion of 40% PEG and 0.08 mmol/L CaCl2 (pH 7). Besides, the genetic relationships among the parent and fusant strains were quested by morphologic observation, rivalry experiments and RAPD-PCR identification.
Crude phenoloxidase (PO) was extracted from Portunus trituberculatus and characterized biochemically. This enzyme exhibited an optimal pH of 8.2 and temperature of 55 ℃ for catalyzing the oxidation of pyrocatechol as a substrate. Optimal enzyme stability was observed in the ranges of pH 7.8-8.4 and 25-40 ℃. Browning reaction catalyzed by this enzyme obeyed the Michaelis-Menten equation. The values of Km and Vmax at 30 ℃ and pH 7.2 were calculated to be 0.531 mol/L and 0.049 A530nm/min, respectively. Twelve inhibitors tested all had a certain inhibitory effect against this enzyme, among which phytic acid was the strongest inhibitor, followed in turn by sodium metabisulfite, L-cysteine, oxalic acid and ascorbic acid.