Abstract:Formate dehydrogenase(FDH) is one of the most effective enzymes for NADH regeneration and is extensively utilized in the food, pharmaceutical and chemical industries. However, wild-type FDH often suffers from low enzyme activity and poor catalytic efficiency, resulting in lower product conversion and hindering industrial production. In order to obtain FDH with improved catalytic performance, FDH from Candida boidinii was used as a template and HOTSPOT WIZARD v3.1 was employed for three-dimensional structure simulation and prediction. And 2 mutants, P68G and Q197K, were constructed. In comparison to the wild type, they exhibited 11% and 33% higher enzyme activity, respectively. The improved activity was attributed to the replacement of the phenyl ring on the side chain of residue P68G by hydrogen, reducing steric hindrance for formate substrate entry, while the mutation of the side chain amide group in Q197K to aminobutyl enhanced the flexibility of the enzyme. However, these 2 mutations negatively affected the thermal stability of FDH. Hence, a cysteine mutation was introduced at position I239 to form a disulfide bond with C262, thereby enhancing the thermal stability. Ultimately, the mutant strain CbFDH Q197K/I239C was obtained, which exhibited remarkable improvement in thermal stability, displaying a 31% increase in enzyme activity compared to the wild-type and a 45% increase compared to I239C. This study demonstrates that the activity and thermal stability of FDH could be enhanced through semi-rational protein structure prediction, providing a reliable theoretical foundation for the efficient construction of FDH with stable performance and strong reducing power.

Abstract:To investigate the biosynthesis pathway of exopolysaccharides (EPS) in Bifidobacterium longum A17, the authors relied on the whole-genome sequencing, and EPS synthesis-related genes were annotated and subjected to homology analysis using eggNOG-mapper, KEGG, GO data annotation, and local sequence alignments. According to the homology analysis, an A17 eps gene cluster consisting of 19 genes with a length of approximately 20 kb was obtained. The synthesis pathway of the precursor glyconucleotides of EPS was predicted, and the key gene pgm involved in the pathway was found and heterologously expressed. The eps gene cluster is responsible for the synthesis of eps monomer repeat units and the subsequent EPS synthesis process related to the export. In the EPS precursor glyconucleotide synthesis pathway, Bifidobacterium longum A17 utilizes glucose and lactose to form 2 precursor glyconucleotides, UDP-Gal and UDP-Glc. Among them, pgm encodes 1→6 glucose phosphomutase, whose production and activity are enzyme related to EPS synthesis.

Abstract:Cyclodextrin glycosyltransferase (CGTase) can generate cyclodextrin by cyclization reaction; however, the production is limited in natural bacterial strains, which results in high costs for cyclodextrin production. Thus, the authors aimed to enhance the expression of CGTase by heterologous expression and fermentation optimization strategies. First, the cgt gene derived from Bacillus xiaoxiensis STB08 was inserted into the plasmid pET-20b(+) and expressed in the host strain Escherichia coli BL21(DE3). After 96 h of fermentation in a suitable culture medium, the extracellular enzyme activity reached 34.66 U/mL. Subsequently, the fermentation conditions were optimized by changing the dissolved oxygen and adding a certain final concentration of Ca²⁺, which led to an increase in enzyme activity to 66.86 U/mL and 83.15 U/mL, respectively. Furthermore, the synergistic effect of dissolved oxygen and Ca²⁺ increased the enzyme activity to 105.69 U/mL, representing a 204.93% improvement compared to that before fermentation optimization. Finally, the mechanism of dissolved oxygen and Ca²⁺ addition on the fermentation level was studied by protein localization analysis and flow cytometry. The results showed that the lower dissolved oxygen could reduce the formation of inclusion bodies in recombinant E. coli, with higher cellular activity observed at lower dissolved oxygen levels. However, the excessively low dissolved oxygen resulted in insufficient cell density to meet the needs of normal bacterial growth and metabolism. The addition of Ca²⁺ could reduce the formation of inclusion bodies and provide good cellular protection. Therefore, the synergistic effect of dissolved oxygen and Ca²⁺ ensured a high growth concentration of bacteria, and Ca²⁺ increased cell permeability and protected the cells, resulting in a significant increase in viable cell count. This study improved the soluble expression of CGTase in E. coli, providing a new strategy and method for its industrial production, as well as serving a reference for the fermentation optimization of the related enzymes.

Abstract:Fruits and vegetables are perishable at high temperature, making it vital to cool them down rapidly and transport them through the cold chain circulation immediately after harvest. The authors aimed to study the effects of different distribution methods on the nutrition and quality of fruits and vegetables, using lettuce, cucumber, grape, and mango as the research objects. After precooling, the samples were refrigerated and distributed in both semiconductor refrigerated cabinets and propane refrigerated cabinets for 24 hours, and compared with the non-refrigerated samples distributed at normal temperatures. Sensory evaluation and nutrient analysis were conducted. The results showed that the sensory evaluation of fruits and vegetables under propane refrigerator distribution, semiconductor refrigerator distribution and normal temperature distribution were 8.3~8.7, 8.2~8.6 and 7.1~8.0 ℃, respectively. The rates of weight loss ranged from 0.23% to 2.67%, 0.28% to 2.21% and 0.97% to 4.88%, respectively. Propane refrigerated cabinets provided optimal quality and minimal weight loss in the refrigerated distribution of fruits and vegetables, with lettuce, cucumber, grape, and mango having VC contents of 1.09, 1.48, 5.65, and 5.54 mg/100 g respectively; soluble solids contents of 3.4, 4.17, 16.2, and 15.44 mg/g respectively; soluble protein contents of 0.021, 0.027, 0.091, and 0.11 mg/g respectively; and the highest retention of nutritional components. The carbon emissions per unit mass of fruits and vegetables distributed by propane and semiconductor refrigeration were measured at 65.4 g/kg and 300 g/kg, respectively. The carbon emissions from propane refrigerated cabinets were lower than those from semiconductor refrigerated cabinets.

Abstract:To compare the sterilization effectiveness and impact on storage quality of fresh-cut lotus root between plasma-activated water(PAW) and commonly used preservatives(L-ascorbic acid, sodium hypochlorite), this study investigates the effects of PAW on browning, phenolic substances, and reactive oxygen species metabolism in fresh-cut lotus root. The ‘Elian 5’ lotus root cultivar was chosen as the research subject, with distilled water treated as a blank control. The fresh-cut lotus root samples were soaked in PAW, L-ascorbic acid solution, or sodium hypochlorite solution for 10 minutes, followed by storage at 4 ℃ for 12 days. Various relevant indicators were measured during the storage period. The results showed that all 3 treatments could effectively maintain the storage quality of lotus root. Among them, PAW exhibited the best antibacterial effect and moisture retention, while L-ascorbic acid could better delay the decline of hardness and VC content in lotus root. Furthermore, PAW could effectively reduce the accumulation of reactive oxygen species in fresh-cut lotus root by maintaining higher levels of reactive oxygen species metabolism enzyme activity, preserving the integrity of cell membrane structure. Simultaneously, it inhibited the activity of peroxidase, inducing the accumulation of phenolic substances, ultimately slowing down the browning process. In conclusion, PAW can effectively maintain the storage quality of fresh-cut lotus root, inhibit microbial growth and browning, and has broad application prospects in the field of sterilization and preservation of fresh-cut lotus root.

Abstract:Compared to liquid yogurt, freeze-dried yogurt blocks offer greater convenience for consumption. The development of freeze-dried soy-based yogurt blocks introduces new product varieties to plant-based yogurt. This study investigated the effects of pre-freezing temperature and mixing temperature on the textural characteristics and viability of lactic acid bacteria in soy-based freeze-dried yogurt blocks, while the properties of freeze-dried dairy-based yogurt blocks were compared with those of freeze-dried soy-based yogurt blocks. The results revealed that the eutectic temperature and glass transition temperature of soy-based yogurt freeze-dried mixture were -9.04 ℃ and -30.73 ℃, respectively, which were comparable to those of dairy-based yogurt mixtures. It was found that higher pre-freezing temperatures resulted in looser and more fragile product texture along with lower viability of lactic acid bacteria. Conversely, excessively low temperatures of pre-freezingreduced bacterial viability and led to structural collapse due to the narrow water vapor sublimation channels. Ultimately, a pre-freezing temperature of -25 ℃ was determined to be suitable. Increasing the mixing temperature could slightly increase the viability of lactic acid bacteria in freeze-dried yogurt blocks without significantly affecting the product texture. Although dairy-based yogurt blocks exhibited higher bacterial viability, freeze-dried soy-based yogurt blocks showed comparable viability of Lactobacillus and Bifidobacterium after 30 days of storage. The viability of Lactobacillus and Bifidobacterium in freeze-dried soy-based yogurt blocks was higher without nitrogen-filled packaging.

Abstract:In order to explore a high-efficient method to promote the enzymatic hydrolysis of Procambarus clarkia with multi-mode ultrasound, the dual-frequency probe ultrasound and tri-frequency divergent ultrasound were used to pretreat Procambarus clarkii in this study, and the promotion effects of multi-mode ultrasonic pretreatment on the enzymatic hydrolysis of Procambarus clarkii were comparatively investigated. Through the single factor experiments, the optimal frequency mode of the dual-frequency probe ultrasonic equipment was found to be 20/28 kHz in the sequential mode, while that of the three-frequency divergent ultrasonic equipment was 20/40 kHz in the sequential mode. On this basis, the response surface experiment with three factors and three levels was carried out to optimize the ultrasonic pretreatment conditions and to establish a corresponding regression equation. The optimization experiment was conducted to obtain the best ultrasonic pretreatment conditions. The optimal pretreatment conditions of the dual-frequency probe ultrasonic equipment were determined, including the use of 250 W ultrasonic power, treatment time of 10 minutes, and temperature of 35 ℃. As a result, the degree of hydrolysis of Procambarus clarkii reached 38.98%. Similarly, the tri-frequency ultrasonic equipment achieved an optimal hydrolysis rate of 46.12% under the optimal conditions of 250 W ultrasonic power, 40 minutes duration, and 40 ℃. The experimental results showed that multi-mode ultrasound could effectively improve the enzymatic hydrolysis effect of Procambarus clarkii.

Abstract:To achieve the double-win of economic and environmental benefits, how to increase the degradation rate of protein in the wastewater and to reduce the odor substances that generated during the fermentation process in the treatment of the wastewater of potato starch processing were studied. The aerobic Pseudomonas bryophyta and anaerobic Serratia marcescens were mixed at a low temperature (15 ℃) and the fermentation conditions were optimized by single factor and response surface methodology. Results showed that the optimum processing conditions were: the inoculum amount 1.98%, mass ratio of Pseudomonas bryophyta to Serratia marcescens 1:2, fermentation time 48 h, the protein degradation rate was 65.32% in this condition. Compared with the group without fermentation, ammonia nitrogen content decreased by 51.05%, and the phosphate content increased by 18.67%. Volatile malodorous substances such as indole, hydrogen sulfide and 3-methylindole were undetectable, so was the biogenic amines such as cadaverine, histamine, tryptamine, tyramine, spermine, and spermidine. Moreover, the content of growth hormones like indole acid-valine methyl ester and indole acetic acid oxide increased during fermentation, which was beneficial to the germination of cucumber seeds. The fermentate method proposed can economically solve the problem of wastewater treatment of potato starch processing at low temperature environment, and provide a certain basis for subsequent volarization of fermented potato wastewater.

Abstract:The byproduct of yolk immunoglobulin, freeze-thaw egg yolk pellet (FYP), was used as raw material to prepare low-fat egg yolk powder and egg yolk oil with desirable functional properties and quality through enzymatic hydrolysis and subcritical extraction, aiming to realize the comprehensive utilization of egg yolk resources. Initially, denatured FYP was subjected to enzymatic hydrolysis with alcalase, and the improvement of functional properties were investigated. Subsequently, subcritical extraction was employed to obtain low-fat egg yolk powder and the byproduct(egg yolk oil). The extraction process was optimized primarily based on the residual oil rate of low-fat egg yolk powder. Propane was selected as the extraction solvent, and the optimal extraction conditions were determined to be at extraction temperature of 35 ℃, pressure of 1.5 MPa, extraction time of 120 minutes, and solid-to-liquid ratio of 1 g∶7 mL. Furthermore, the solubility and emulsification of low-fat egg yolk powder were analyzed. The results demonstrated that the solubility and emulsifying capacity of low-fat egg yolk powder increased with an increase in enzyme dosage, while the residual oil rate decreased significantly. At the enzyme dosage of 1 000 U/g, the residual oil rate of the low-fat egg yolk powder reached 15.50%. However, further increasing the enzyme dosage led to a decrease in oil extraction efficiency. Therefore, the optimal enzyme dosage was determined to be 1 000 U/g, where the low-fat egg yolk powder has reduced fat content and desirable solubility and emulsifying properties.

Abstract:To obtain soybean yoghurt with enhanced physiological activity, this study investigated the effect of soybean germination on the fermentation characteristics of soymilk by lactic acid bacteria and the physiological activity and flavor of soymilk. The results showed that within the initial 72 h, the content of trichloroacetic acid-soluble nitrogen and free amino acids in soybean significantly increased (P＜0.05) with the germination time. The fermentation characteristics of lactic acid bacteria-germinated soymilk were significantly improved, resulting in the duration to reach the fermentation endpoint (pH 4.5) shortened from 7.2 h to 5.0 h. Additionally, the titratable acidity increased from 42.18 °T to 66.56 °T, accompanied by an increase in the content of lactic acid and citric acid. Germination also reduced the hardness of lactic acid bacteria-fermented soymilk, resulting in a smoother texture. After 72 h of germination, lactic acid bacteria-fermented soymilk exhibited increased physiological activity with a 19.83 mg/hg increase in γ-aminobutyric acid content, a 115.02% increase in isoflavone glycosides, and significant enhancements in DPPH, ABTS, and hydroxyl radical scavenging rates(P<0.05). On the other hand, germination led to a noticeable increase in off-flavor compounds in soy milk. Considering the combined effect of germination on physiological activity and flavor, soybean yoghurt was prepared using soybeans germinated for 36 h. The influence of 4 direct inoculation fermentation agents on the flavor and sensory quality of soy yogurt was evaluated. The results showed that soy yogurt fermented with Agent A had the lowest content of off-flavor compounds and the best sensory quality.

Abstract:In order to establish a rapid detection method for carrot components in complementary foods for infant and young children using isothermal real-time fluorescence, specific primers for loop-mediated isothermal amplification (LAMP) were designed and synthesized based on the carrot ITs1-5.8 SRNA-ITS2 gene sequence. The specificity and sensitivity of the method were verified by DNA from common crop and white radish with different carrot mass ratios. Different cultivars of carrot seeds were selected to verify the applicability of the method, and its practicality was tested through pre-packaged food. The results indicated that the established method exhibited strong specificity without cross-reactivity with other species. It can detect the composition of carrot as low as 0.01% mass ratio within 1h, demonstrating high sensitivity. It is suitable for the detection of different carrot cultivars with a wide range of application. The method proved to be fast and accurate when validated with actual samples. This method offers simplicity, cost-effectiveness, real-time synchronization of intelligent data interpretation, and accurate and rapid visualization of results. Therefore, it can be used for the rapid detection of carrot components in complementary foods for infant and young children, providing a technical basis labeling management and food safety supervision in complementary foods for infant and young children.

Abstract:In order to explore the differences in molecular structure and characteristics of rice starch from different varieties of rice in Ningxia, the starch was extracted using the alkaline method. The crystal structure, crystallinity, molecular order, and gelatinization properties of rice starch from 21 different varieties in Ningxia were detected and analyzed through X-ray diffractometer (XRD), rapid viscosity analyzer (RVA), and Fourier transform infrared spectrometer (FTIR). The results showed that all rice starch molecules had an A-type structure. Different varieties of rice exhibited variations in crystallinity and molecular order, with ‘Ninggeng 28’ having the highest crystallinity at 32.96%. ‘Rice 3’ displayed characteristic absorption peaks at 1 748 cm-1 and 2 852 cm-1 in the infrared spectrum. All RVA curves of rice starch exhibited the trend of increase initialy, followed by a decrease, and increase later. Among them, ‘Ninggeng 41’ had the higher viscosity but poor thermal stability and shear resistance, while‘843’ had low viscosity and ‘Tianjiangyou 169’ showed good thermal stability and shear resistance. The varieties 'Ninggeng 41', 'Daohuaxiang 4', and 'Ningxiang' demonstrated elevated levels of retrogradation. The results could provide a theoretical basis for the classification and fine processing of different rice varieties in Ningxia.

Abstract:The authors summarized the national food safety supervision sampling results for quick-frozen foods from 2016 to 2020, as well as the inspection status of 7 quick-frozen food manufacturing enterprises from 2018 to 2020, aiming to analyze the situation of quick-frozen food supervision sampling and identify the main food safety issues. A total of 208039 batches of quick-frozen food were sampled and inspected nationwide from 2016 to 2020, with a compliance rate of over 99.2%. The overall situation of quick-frozen food safety is stable, with the main issues identified during the inspection process being microbial contamination, the excessive use of additives beyond permissible limits, and elevated peroxide values. The regulatory authorities are advised to develop comprehensive sampling plans and ensure that production enterprises and testing organizations to fulfill their respective responsibilities, and to safeguard food safety together.