Abstract:It has been reported that Lactobacillus gasseri produces a variety of bacteriocins that inhibit a few kinds of food pathogenic bacteria, but there are few researches on how bacteriocins affect the interaction between Lactobacillus gasseri and the intestinal microecology. This study utilized the in silico prediction of bacteriocin operon, antibacterial experiment with six strains of food-borne pathogenic bacteria as indicators and liquid chromatograph mass-spectrometer/mass spectrometer analysis to prove that Lactobacillus gasseri FNMGHLBE6L1, FNMGHLBE20L5 and FHNFQ16L5 produced different bacteriocins. Through the animal experiments, the effects of three bacteriocin-producing Lactobacillus gasseri strains on the intestinal microecology of the mice were investigated. The diversity and profile of the gut microbiota were dramatically influenced by all three strains of Lactobacillus gasseri, and the level of colonic interleukin-1β was also significantly decreased. In summary, the gut microbiota was significantly affected by bacteriocin-producing Lactobacillus gasseri, and the variations in effects among strains were associated with their bacteriocin production. This study could serve as a guide for future research on the relationship between various bacteriocin-producing Lactobacillus gasseri and the gut microbiota.

Abstract:Sand washing is a traditional step in bean paste processing, resulting in resource waste and pollution. The author determined the impact of different cooking methods, including conventional pressure cooking, high-pressure cooking, conventional pressure steaming, and high-pressure steaming on the nutritional components, hardness, water absorption rate and gelatinization degree of the adzuki bean, as well as on the particle size distribution, rheological properties, texture, sensory analysis, and consumer acceptability of the bean paste. The results showed that after treated with 4 different cooking methods, mass fractions of tannin and saponin decreased by 27.32%~53.01% and 26.45%~51.21%, respectively , with the most severe loss of active ingredients occurring in high-pressure cooking. High-pressure cooking caused rapid gelatinization of adzuki beans, while high-pressure steaming resulted in a slower change in gelatinization degree due to the low water absorption rate of (5.74±0.53)%. The average particle size of conventional pressure steamed bean paste was the largest, reaching (230.00±16.09) μm. Texture and sensory evaluation results showed that the steamed bean paste exhibited smaller adhesiveness (-665.42~-657.30 g·s), stronger chewiness (819.64~822.03), and more pronounced bean particle graininess (6.75~6.88). The high-pressure-cooked bean paste scored (6.32±0.80) points in the preference rating, and the consumers considered it as delicate in texture and moderate in viscosity and hardness. Therefore, the development of whole bean paste is feasible, and high-pressure cooking is more suitable for whole bean paste processing.

Abstract:To evaluate the antibiotic resistance of lactic acid bacteria in fermented foods and their transmission risk, this study was conducted to isolate and identify lactic acid bacteria from commercially available yogurt and kimchi, to identify their antibiotic resistance phenotypes by disk diffusion method, to analyze multi-antibiotic resistance, and to identify their antibiotic resistance genotypes by PCR. A total of 62 strains of lactic acid bacteria including 9 different species were isolated from 40 samples. Most of the strains were multi-antibiotic resistant from the yogurt origin. The resistance rates of yogurt-derived Lactobacillus to five antibiotics, including kanamycin, were higher than those of kimchi-derived strains, while the resistance rates of kimchi-derived Lactobacillus to gentamicin and streptomycin were above 40%. The results of antibiotic-resistant genotype identification showed the detection rate of tetM gene was the highest at 16.12%. The detection rates of fivegenes in yogurt sample isolates were higher than kimchi samples. The results of plasmid conjugation transfer showed that the tetracycline resistance gene tetM could be transferred to the recipient bacterium EC600 from two yogurt-derived strains. Overall, this study was conducted to assess the antibiotic resistance and transmission risk of lactic acid bacteria in commercially available fermented food, it can provide theoretical basis for ensuring the safety of fermented food.

Abstract:Rice starch has the advantages of small particles, high whiteness, and low allergenicity, but the difficulty in extraction, as well as its high cost, limits the wide application of rice starch in the food industry. The authors used three varieties of rice as raw materials and optimized the extraction conditions of alkali and protease to investigate the effects of different extraction processes on the structural and physicochemical properties of rice starches. The results showed that the protein residual rate in the alkali-extracted rice starches ranged within 0.65%~1.35% under the conditions of 0.20% alkali mass concentration, solid-liquid ratio of 1 g∶5 mL, and reaction duration of 4 h. The protein residual amount in the protease-extracted rice starches ranged from 0.58% to 0.82% with protease of 0.50%(mass fraction) at 45 ℃ under pH 4.0 for 4 h. The rice starches displayed irregularly polyhedral granules with a diameter ranging from 4 to 8 μm. Compared to the alkali-extracted rice starches, the protease-extracted rice starches had a more prominent polyhedral structure. The relative crystallinity of alkali-extracted rice starch was 22.93%~43.58%, slightly lower than that of protease-extracted rice starch (28.00%~43.81%). The solubility of rice starch (at the temperature of 90 ℃) was 3%~15% higher than that of rice flour, and the swelling power was 8%~20% higher. Meanwhile, protease-extracted rice starch exhibited higher solubility and swelling power. Furthermore, compared to rice flour, rice starch showed stronger gel properties. The hardness of rice flour gels, alkali-extracted rice starch gels, and protease-extracted rice starch gels were in the range of -7.16~275.96 g, 55.09~368.43 g, and 62.37~373.45 g, respectively.

Abstract:In order to detect the polymorphisms of κ-casein and α_s1-casein gene in yak milk from seven different pastures in certain areas of Qinghai province, the effect of gene polymorphisms on cheese coagulation characteristics was analized. Yak milk somatic cells were extracted, and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis technique was used to extract DNA for PCR amplification and enzymatic digestion, followed by gene typing based on electrophoresis bands. Yak milk proteins were also extracted and high-performance liquid chromatography(HPLC) was used to analyze the chromatographic profiles of various samples compared to the standard samples, with a focus on peak time and peak shape for gene typing. The rheological characteristics during coagulation for different genotypes of yak milk were determined by rheometer. Cheese coagulation time was recorded, and cheese yield was calculated. The results showed that there were three genotypes for the κ-casein gene in yak milk, i.e., type AA, AB and BB. The analysis of the three genotypes and coagulation characteristics showed that the A allele was favorable in terms of coagulation time. Similarly, for the α_s1-casein gene in yak milk, three genotypes (AA, AB, and BB) were also identified. The analysis of the coagulation time, cheese yield, maximum dynamic viscosity, and maximum shear rate revealed that the B allele was favorable. The above results suggest that both κ-casein and α_s1-casein of yak milk in seven Qinghai farms have gene polymorphisms. The A allele in κ-casein and B allele in α_s1-casein are the main effective genes affecting the coagulation characteristics of yak milk.

Abstract:To realize the on-demand controlled release of natural plant essential oil cinnamaldehyde (Cin) and to address the application limitations caused by its high volatility and photothermal sensitivity, cinnamaldehyde was modified with chitosan(CS) as a reactant. A pH-sensitive cinnamaldehyde-chitosan Schiff base derivative(Cin-CS) was synthesized through the reaction of amino and aldehyde groups at different molar ratios. The structure and surface morphology of the samples were characterized by Fourier transform infrared spectrum and scanning electron microscope. The pH response behavior of Cin-CS was explored in various pH buffer solutions and in high humidity environment with different volume fractions of CO₂. And the preservation effects of Cin-CS on bananas were studied. Results showed that the graft saturation was achieved when the molar ratio of amino and aldehyde groups was 4∶1. The presence of imine bonds in the structure indicates successful grafting. With the decrease of pH of buffers solutions and the increase of CO₂ concentration and time, the cumulative release rate of Cin-CS gradually increased, which achieved the effect of responsive release and sustained release. The application of Cin-CS in banana fresh-keeping showed that it could delay the increase of weight loss rate, slow down the decline of hardness and soluble solids, thereby confirming that Cin-CS has a certain fresh-keeping effect.

Abstract:5-Ketofructose(5-KF) has a similar sweet taste quality as D-fructose, and cannot be metabolized by humans, giving it a low caloric value. These properties illustrate 5-KF can become a potential candidate for a non-nutritive natural sweetener. In this study, the 5-KF producing strain was constructed via overexpression of membrane-bound fructose dehydrogenase gene from Gluconobacter japonicus in Gluconobacter oxydans. By screening different expression hosts, expression vectors and promoters, the engineered strain QT-10 which can efficiently synthesis 5-KF was obtained. The fed fermentation process was optimized in a 3 L fermenter. Finally, 650 g/L D-fructose could be completely transformed in 82 h with continuous fructose-feeding strategy, and up to 608 g/L 5-KF was reached with the yield of 94.6% and the space-time yield of 7.41 g/(L·h).

Abstract:In order to identify the key components affecting the taste quality of oyster sauces, 15 commercially available products were analyzed in this study. With the aid of quantitative descriptive analyses, the differences in taste of oyster sauces were compared. The flavor peptides composition, amino acid nitrogen mass fraction as well as the composition and mass fraction of free amino acids and flavor nucleotides were examined. The correlation between taste and physicochemical indicators of oyster sauce was determined by partial least squares regression(PLSR) and Pearson's method. The results showed that the key components affecting the taste quality of oyster sauces included the mass fraction of amino acid nitrogen, inosine monophosphate, the composition of flavor peptides ,the mass fraction of glycine and glutamate. The amino acid nitrogen mass fraction(R=0.707) and the peptide with a relative molecular weight of 500~1 000 (R=0.681) showed a highly significant positive contribution to the sauce. A positive correlation was established between the oyster flavor and glycine mass fraction, while the freshness perception was impacted by the mass fraction of glutamate and inosine monophosphate. This study can provide scientific basis for the construction of an evaluation system for the taste quality of oyster sauce.

Abstract:To explore the optimal selenium-tolerant strains in Pleurotus ostreatus and determine the culture conditions and mycelial characteristics, four kinds of Pleurotus ostreatus were screened by solid culture and liquid fermentation. Pleurotus djamor was selected to culture selenium-enriched mycelium. The enzymatic activity indicators and the in vitro antioxidant activities of mycelial proteins and polysaccharides were determined. The results determined Pleurotus djamor as the best selenium-tolerant species. The optimal culture conditions were as follows: shaking speed of 150 r/min, pH 6.5, temperature of 25 ℃, and selenium concentration of 5.0 mg/L. Compared with the conventional mycelium, the selenium-enriched mycelium promoted the activities of PPO, POD and SOD, improved the stress resistance of mycelium. The selenium-enriched mycelium and its polysaccharides and proteins had strong scavenging ability to DPPH, superoxide anion radical and hydroxyl radicals. Finally, the effect of selenium-enriched mycelium of Pleurotus djamor on the survival rate of Caco-2 cells was investigated, and it was found that the selenium-enriched mycelium could inhibit the survival rate of Caco-2 cells. The selenium-enriched liquid fermented mycelium of Pleurotus djamor has been preliminarily determined with high physiological activity, which could be considered as a selenium supplement.

Abstract:The effects of five commercial heat treatments including pasteurization (LTLT at low temperature long-time, HTST at high temperature short-time), UHT (Ultra-high temperature), spray drying (SP), and retort sterilized (RS) on the secondary structure of goat milk protein, the degree of oxidation, and the accumulation of Maillard reaction products were studied. The damage degree of goat milk protein caused by different heat treatments was LTLT, HTST

Abstract:In the present study, bovine legs were selected as the raw material, and the mixed bacteria of Pediococcus pentosaceus and Pediococcus lactis were used as the starter based on the pre-experimental screening, and the fermentation process of conditioned steak was optimized by the response surface method. Using the unfermented conditioned beef steak marinated at low temperature for 10.00 h as the control group, the effects of different treatments on the pH value, texture, color, and flavor of the steak were investigated, and the sensory quality of steak was evaluated using a fuzzy comprehensive evaluation method. The results showed that the optimal process conditions of mildly-fermented conditioned steak were 0.015% fermentation dose, 10.00 h fermentation time, and 31.5 ℃ fermentation temperature. Compared with the unfermented condi- tioned steak, the pH value, hardness and chewiness of the mildly-fermented conditioned steak were significantly reduced (P<0.05), and the values of L^*, a^*, and b^* as well as the sensory score significantly increased (P<0.05). After fermentation, the types of esters, aldehydes, ketones, olefins, and other compounds in the mildly-fermented conditioned steak increased by 0.4%, 3.0%, 0.7%, 0.5%, and 0.7%, respectively. In summary, mild-fermentation may improve the tenderness and flavor of steak, enhance product quality, and provide a theoretical basis for the innovative research on tenderization and provide a theoretical basis for the innovative research on the tenderization of steak and fermented steak products.

Abstract:Hydrolyzed wheat protein was analyzed by basic physicochemical components, relative molecular mass distribution, and amino acid composition. The peptide composition and sequence were identified by LC-MS/MS. The results showed that the total protein mass fraction of hydrolyzed wheat protein was (80.53±8.06)%, with the relative molecular mass mainly below 2 000 and a mass fraction of essential amino acids approximately 52.4%. Eight peptides were identified by Q3 scanning, PIS scanning, and MRM quantification, including leucyl-glutamine(LQ), valanyl- glutamine(VQ), isoleucyl-isoleucine(II), leucyl-leucine(LL), alanyl-isoleucine(AI), valanyl-leucine(VL), leucyl-methionine(LM) and isoleucyl-methionine(IM), with mass fractions of 385.0, 32.5, 30.0, 122.8, 8.9, 5.9, 134.9, 147.0 μg/g, respectively. These peptides may exhibit functional activities in vivo and serve as the material foundation for the application of hydrolyzed wheat protein in nutritional health food.

Abstract:To enhance the utilization of walnut meal, walnut protein was enzymatically hydrolyzed by trypsin and the purified hydrolysates were separated to analyze the antioxidant peptides. The preparation conditions were optimized by using superoxide anion free-radical scavenging as the main indicator. The purified components were sequenced by LC-MS/MS and the peptides were screened by docking binding energy and protein stability index. Under optimum hydrolysis conditions, the superoxide anion free-radical scavenging rate of hydrolysate was 26.57%. Altogether four hydroly- sate fractions were separated by Smartdex G-50, among which, the hydrolysate, namely D-4 displayed the highest scavenging rate at the same concentration. The sequence of D-4 component was identified and R.AGIQFPVG.R was presumed to be the main bearer of antioxidant activity, as determined by virtual computer screening. Through molecular docking with lipoxygenase, it was found that R.AGIQFPVG.R was able to form hydrogen bonds with inactive center of lipoxygenase with a binding energy of -21 933.85 J/mol. The docking results showed that R.AGIQFPVG.R bound to the lipoxygenase inactive site via Glu186, indicating that the peptide acted mainly as a non-competitive inhibitor. This study conducted an enzymatic hydrolysis of walnut meal to prepare antioxidant peptides to provide a reference research for the screening of natural antioxidants.

Abstract:This study utilized gas chromatography-ion mobility spectrometry (GC-IMS） and gas chromatography-mass spectrometry (GC-MS) to investigate the volatile components of tarragon. The results indicated that essential oil accumulation was a gradual process during the growth and development of tarragon on the southern slope of the Tianshan mountains. The detection results of GC-IMS showed that tarragon leaves contained 35 volatile organic compounds (VOCs) with carbon chains ranging from C₂~C₁₀ , mainly including 6 terpenes, 12 aldehydes, 4 alcohols, 1 furan, 3 esters, 5 ketones, and 4 other substances, with significant differences among them. The detection of GC-MS identified 54 volatile organic compounds in tarragon essential oil, with carbon chains ranging from C₇~C₃₂ , including 16 terpenes, 12 alcohols, 9 esters, 4 phenols, and 2 aldehydes etc. GC-MS detected a relatively large number of species with higher relative molecular weight. The complementary use of GC-MS and GC-IMS technologies can provide comprehensive information on the volatile components of tarragon, offering new research perspectives for the development, utilization, analysis and detection of tarragon and its essential oils.

Abstract:This study systematically compared the effect of high concentration (10~5 000 mg/L) and low concentration(2.5~50.0 mg/L) of calcium lignosulfonate on the yield of biomass and three high-value products by using mixotrophic Phaeodactylum tricornutum growth in shake flasks with an aim to determine the optimal dose and effect. The results showed that at the optimal concentration of calcium lignosulfonate (10 mg/L), the biomass yield reached to 281.32 mg/(L·d). Additionally, the yields of fucoxanthin(Fx), eicosapentaenoic acid(EPA) and chrysolaminarin(Chrl) were 4.41, 10.60 and 57.24 mg/(L·d), respectively, which were 9.98%, 1.92%, and 7.27% higher than that in the control group. Notably, the yields of Fx and Chrl significantly increased (P<0.05). The author developed a novel mixotrophic culture model with the addition of calcium lignosulfonate, which was able to achieve a simultaneous yield enhancement of the three high-value products in mixotrophic Phaeodactylum tricornutum, providing a new technical support for improving the large-scale cultivation efficiency and application value of Phaeodactylum tricornutum.

Abstract:In order to investigate the structure-function relationship of soybean protein isolate enzymatic hydrolysate(SPIH) under different enzymatic hydrolysis time, the hydrolysis of soybean protein isolate(SPI) was evaluated by measuring the degree of hydrolysis and the mass fraction of polypeptide. The relationship between structure and function was characterized by Fourier transform infrared spectroscopy, endogenous fluorescence spectroscopy, surface hydrophobicity, emulsification, and antioxidant capacity. The results showed that the hydrolysis degree of SPI increased with the prolonged enzymatic hydrolysis duration, while the mass fraction of polypeptide initially increased and then decreased over the duration of enzymatic hydrolysis. Moreover, as the enzymatic hydrolysis time increased, protein unfolding occurred. The protein structure gradually unfolded after enzymatic hydrolysis at 2 h, leading to a red shift in maximum absorption wavelength and enhanced fluorescence intensity. In addition, the secondary structure of SPI was changed by enzymatic hydrolysis, with the β-fold area fraction reaching its peak at 2 h. The surface hydrophobicity, emulsification, antioxidant capacity, ζ-potential and the particle size of the SPIH emulsion were all optimized at 2 h of enzymatic hydrolysis. This study provides the theoretical basis for understanding the changes in structural and functional properties of SPI under different enzymatic hydrolysis durations, thereby expanding its applications in the food industry.

Abstract:To investigate the effects of different molding techniques on the main chemical components of white peony tea, Fu'an Dabai was used as the raw material and the withered leaves with different moisture content (40±1)%, (35±1)%, and (30±1)% were light rolled (QR) or tidied (LT) referring to the traditional white tea processing technology. The main chemical components of tea samples were detected and analyzed by ultra-high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-QqQ-MS) and headspace solid-phase microextraction combined with gas chromatography time-of-flight mass spectrometry (HS-SPME-GC-TOF-MS). The results showed that the sensory quality score of white peony tea with different molding techniques decreased with the decrease of moisture content in the withered leaves. At the same moisture content, the QR molding was superior to the LT molding. The total contents of amino acids and catechins of white peony tea after molding(QR, LT) were significantly lower than those in traditional white peony tea (CK)(P<0.05), while the total sugar content and the relative contents of aldehydes were significantly higher than those in traditional white peony tea (P<0.05). Tea soup of white peony tea with high moisture content (40±1)% and gently kneaded withered leaves exhibited better freshness, thickness, and sweetness, along with a noticeable sweet floral aroma. Overall, the white peony tea molded with high-moisture(40±1)% withered leaves had better comprehensive quality. QR could facilitate the formation of sweet flower fragrance, while LT could be more conducive to the development of delicate fragrance flavor, providing a technical reference for improving the flavor and quality of white peony tea through molding techniques.

Abstract:Yeast β-glucan is a type of polysaccharide that is difficult to dissolve in commonly used solvents such as water, acids, and alkalis. Traditional preparation methods are complex, cumbersome, and often result in low product yield or impurities, causing difficulties in industrialization. In this study, an alkaline method combined with dimethyl sulfoxide(DMSO) was used to explore and optimize the production process of yeast β-glucan. The results showed that under the conditions of 0.7 g/dL NaOH at 80 ℃ for 2.6 hour alkaline treatment, the highest impurity removal rate was 71.84%. Separation and purification of β-glucan were accomplished under the conditions of the solid-to-liquid ratio of 30 mg∶1 mL and 80% volume fraction of DMSO at 80 ℃ for 30 minutes, resulting in a β-glucan product with a purity of 95.84%. The product was identified by thin-layer chromatography and Fourier-transform infrared spectroscopy, and the product was indicated as β-glucan composed of glucose monomers. Moreover, Anti-inflammatory experiments showed that this product had a certain biological activity. The study aimed to simplify production processes, scale up production, improve product quality, and provide a theoretical reference for industrialized production.

Abstract:In order to analyze the changes in volatile compound profiles of Pixian broad bean-chili paste (BCP) during koji making, moromi fermentation and post fermentation as well as to reveal the predominant volatile compounds in BCP and their origins, a systematic analysis of volatile compounds were carried out in BCP, its ingredients (broad bean cotyledon BBC, and fresh chili FCL) and semi-finished products (broad bean koji BKJ, pickled chili PCL, and broad bean moromi BMR). Through HS-SPME-GC-MS method, there were altogether 73 volatile compounds from all the studied samples(such as 6 hydrocarbons, 11 alcohols, 8 carbonyls, 8 heterocycles, 13 terpenoids, 18 esters, 6 acids, and 3 miscellaneous compounds). Total volatile contents of the ingredients were relatively low, showing (19.64±3.84) μg/g and (7.84±1.30) μg/g (an equivalent of 4-methyl-2- pentanol as an internal standard) in BBC and FCL, respectively. Many volatiles in BBC, FCL and BKJ were not found in BCP, indicating that their volatile profiles were not strongly related to those in the final products. Total volatile contents in broad bean moromi (BMR) and pickled chili (PCL) increased evidently to (82.42±17.63) μg/g and (49.71±8.06) μg/g after fermentation. Larger proportion of terpenoids and alcohols were found in PCL, indicating linalool, phenyl-ethanol, 2-methoxy-3- isobutyl pyrazine etc. as the key flavor compounds. More heterocyclic compounds, carbonyls and acids were detected in BMR, indicating phenylethanol, 1-octene-3-ol, phenylacetaldehyde etc. as the key flavor compounds. Total volatile contents in BCP were further increased (exceeded 100 μg/g) with esters as the most abundant compounds. Key flavor compounds of BCP included ethyl laurate, phenyl-ethanol, linalool etc. With the extension of post fermentation, changes in total volatile compounds, volatile composition and key flavor compounds in BCP were relatively low, indicating that they tended to be stable at this stage. Moreover, FCL was the main origin of terpenoids in BCP. Heterocyclic compounds and 4-ethyl-guaiacol were contributed mostly by BMR, while esters were formed in the post-fermentation stage.