Abstract:Adipic acid, as the monomer for manufacturing polymers such as nylon, fiber and plastics, has broad applications in food, pharmaceutical, plastics, and chemical industries. At present, low-level yield of adipic acid generated from food feedstocks was mainly due to the carbon atom loss. To tackle this issue, an artificial adipic acid biosynthesis pathway for obtaining the highest theoretical adipic acid yield from palmitic acid was designed and constructed. Then, cell utilization for fatty acids was improved by enhancing endogenous β -oxidation pathway and introducing heterogenous ω -oxidation pathway. Furthermore, various strategies of system metabolic engineering were used for further optimizing adipic acid biosynthesis pathway. Finally, the optimal recombinant strain Escherichia coli AA0304 produced 1.32 g/L adipic acid by optimizing fermentation conditions. Therefore, this synthetic platform could lay a good foundation for the production of high-value chemicals from waste oleaginous feedstocks.

Abstract:In order to explore the inactivation mechanism of Bacillus subtilis spores by high-pressure thermal sterilization (HPTS) combined with different mass concentrations of Nisin, the spore survival rate, nucleic acids leakage, inner membrane permeability and spore composition changes after treatment were studied by plate counting, ultraviolet spectrophotometry, flow cytometry and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The results showed that the disinfectant effect of HPTS combined with Nisin was higher than that treated by HPTS alone. The spore survival rate decreased by 6.30 after 20 min under 550 MPa at 75 ℃ combined with 500 mg/L Nisin. It was found that the permeability and damage of spore inner membrane increased, and the content leakage amount increased, while spore nucleic acid, peptidoglycan, cell wall and other components changed. HPTS combined with Nisin treatment could effectively destroy the water permeability barrier of inner spore membrane, change the structure of spore membrane lipid, nucleic acid and polysaccharide, reduce the resistance of spore, affect the metabolism of spore and inactivate the spore. This study provided a theoretical basis for HPTS combined with Nisin to inactivate Bacillus subtilis spores, promoting the application of HPTS in food processing.

Abstract:Pea protein was used to prepare Maillard reaction products (MRPs) through enzymatic hydrolysis and further thermal reaction with sugars. Taking the degree of hydrolysis(DH) and solid dissolution ratio as the indices, the optimal conditions of pea protein peptides preparation was determined as follows: 4 h hydrolysis with 3 500 U/g substrate protamex protease and then 4 h hydrolysis with 400 U/g substrate aminopeptidase. The components with relative molecular weight less than 1 000 in hydrolysates was 91.60%, and 90.83% of the total amino acids were peptides, which were mainly small peptides. The effects of initial reaction pH (6.4, 7.4 and 8.4) on the color and flavor of MRPs derived from pea peptides were further investigated. The results showed that the higher pH caused the stronger browning degree. The results of electronic tongue analysis and human sensory evaluation showed that the addition of 0.5% MRPs into the solution with 0.5% salt could enhance the saltiness, umami and kokumi. Comparing to the salt solution, the saltiness and umami with the addition of MRPs were increased by 41.03% and 303.39%, respectively. When the initial pH increased from 6.4 to 8.4, the saltiness increased by 57.30% and the umami increased by 36.48%, at the meanwhile, kokumi and volatile flavor compounds were also increased significantly.

Abstract:Aspergillus flavus is one of the main contaminants in corns during storage, which directly affects the quality and safety of food and feed. The biological control by microorganisms and their metabolites has a wide range of practical application value. In this study, the SG17 strain obtained from previous screening was preliminarily identified as Streptomyces sp. strain through morphological observation, physiological and biochemical detection, and 16S rRNA sequence analysis. The dural culture method showed that this strain had a broad-spectrum antibacterial effect on various pathogenic fungi such as Aspergillus flavus. The inhibition rate of SG17 was (41.24 ± 0.32)% when the crude extracts were further treated at 100 ℃ for 60 min, decreasing by 16% compared with that of the control group. After 15 days storage at room temperature, the antibacterial rate was (25.95±0.68)% and retained about 50% activity, showing good thermal stability and environmental adaptability. The germination of Aspergillus flavus spores could be effectively inhibited by 50 μg/mL of antibacterial crude extract. Furthermore, the growth of Aspergillus flavus on corns could be significantly inhibited by 100 μg/mL antibacterial crude extract, and the antifungal rate remained above 80% after 14 days of continuous culture, which suggested high application value.

Abstract:Starch adhesives have attracted more and more attention in the fields of paper making, wood processing, textile, architecture and so on because of its green and eco-friendly features. The oxidized starch was mixed with sodium carboxymethyl cellulose (CMC) and sodium lauryl sulfate (SDS) was added. Their effects on the properties of adhesive were studied in this paper. The results showed that with the increase of CMC proportion, the freeze-thaw stability, initial viscosity and adhesion of the adhesive increased gradually, however, the peeling strength and drawing degree changed insignificantly. Finally, the optimal ratio of starch to CMC was 85∶15. With the mass fraction of SDS added from 0.5% to 1% to 1.5%, the initial viscosity, adhesion and freeze-thaw stability of the adhesive increased at first and then decreased, and the drawing degree insignificantly changed. Finally, 1% mass fraction was determined as the optimum SDS content.

Abstract:Cordycepin (3’-deoxyadenosine), which is the core bioactive ingredient of Cordyceps militaris, has various biological activities, such as anti-tumor, anti-bacterial, anti-virus and immunity enhancement. However, the content of cordycepin in Cordyceps militaris is low and the strain of Cordyceps militaris is easily degenerated. It is urgent to breed high-yield and high-quality Cordyceps militaris strains. In this study, Cordyceps militaris CM17 strain with high yield of cordycepin and Cordyceps militaris ZGCM strain with high yield of fruiting bodies were used as the parents. The ascospore monospora strain with MAT1-1 genotype was isolated from ZGCM and the conidia monospora strain with MAT1-2 genotype was isolated from CM17. Hybridization between the strains of single spore with different MAT genotype was studied through cross-breeding. A new strain ZA10-C4 with high yield of fruiting bodies and high content of cordycepin was successfully obtained through molecular identification and biological characteristics screening. The yield of cordycepin in hybrid strain ZA10-C4 was as high as (12.82±0.85) mg/g in fruiting bodies, which was 4.33 times higher than that of parent strain ZGCM. And ZA10-C4 maintained the characteristics of ZGCM with high yield of fruiting bodies. At the same time, an improved rapid gene extraction and labeling method was used to identify the MAT gene of spore strain and hybrid strain, which improved the efficiency of breeding.

Abstract:In order to reduce the environmental pollution and resource waste of discarded crayfish shells, crayfish shells and D-gluconic acid solution with 50% mass fraction were used as raw materials to prepare human calcium supplement, i.e., calcium gluconate, by ultrasonic-assisted method. The effects of particle size of crayfish shell powder, gluconic acid amount, liquid-to-material ratio, ultrasonic time, reaction temperature and ultrasonic power on the yield of calcium gluconate were studied. The response surface experiment was optimized based on the single factor experiment. The results showed that the optimal process conditions were 4.68 mL of 50 % D-gluconic acid, 30∶1 of liquid-to-material ratio, and 32.1 min of ultrasonication under 45 ℃. The yield of calcium gluconate was 86.38%, which was close to the predicted value of 86.85%. Compared with other non-ultrasonic assisted preparation methods, this yield was increased by 10%. Ultrasonic assistance could increase the yield of calcium gluconate prepared from crayfish shells, and the yield of ultra-finely pulverized crayfish shell powder increased by 3.28% compared with that of the crude crayfish shell powder. The solubility of prepared calcium gluconate at different pH values was much higher than that of the calcium in crayfish shells, with higher absorption and utilization rate, providing the possibility for further use as a human calcium supplement. Crayfish shells were used as a calcium source to prepare calcium gluconate, which could improve the comprehensive utilization of crayfish shells and provide technical reference for reducing environmental pollution and achieving cleaner production.

Abstract:The effects of different processing methods on the extraction and physicochemical properties of pectin from Akebia trifoliata peel were investigated to improve the extraction rate and pectin quality. Pectin was extracted by acid method from the unprocessed Akebia trifoliata peel powder and the peel powder was further processed by stir-frying, sand-making, vinegar-making and wine-making methods, and the structure of pectin was characterized. The extraction rate of pectin, content of galacturonic acid, esterification degree, emulsifying activity, emulsifying stability and antioxidation were determined. The extraction yield, galacturonic acid content and antioxidant activity of vinegar-making pectin were the highest, reaching 19.53%, 83.51% and 82.95%, respectively. The first two indexes were 5.90% and 6.41% higher than those of unprocessed pectin, respectively. The processing method order from high to low were vinegar-making>wine-making> sand-making>stir-frying according to the extraction rate of pectin and the content of galacturonic acid. The esterification degree of vinegar-making pectin (82.26%) was close to that of unprocessed pectin (82.51%), and its emulsifying activity and stability were also higher, reaching 89.23 m2/g and 160.15 min, suggesting the processing method order from high to low was vinegar-making>wine- making>stir-fryingg>sand-making. The pectins prepared by different processing methods were characterized by FT-IR, XRD and SEM, and their structural properties were basically consistent with the characteristics of pectin. Vinegar-making method could significantly improve the extraction rate of pectin and the galacturonic acid content, effectively keeping the quality of pectin extracted from Akebia trifoliata peel.

Abstract:Flavor is an important factor in the evaluation of rice quality. The instant rice for airline catering was studied to improve the rice flavor after sterilization under high temperature and high pressure, aiming to approach the flavor of freshly cooked rice. The results showed that the addition of 1% white vinegar, 1% peanut oil and 0.5% trehalose (mass fractions) could significantly inhibit the decline of rice flavor caused by high temperature and high pressure. After two-stage autoclaving, it could be stored and transported at ordinary or low temperature. The electronic nose was sensitive to the changes of main volatile components in instant rice, and could be used for the non-destructive analysis of volatile components in rice. PCA analysis could distinguish the different storage time of rice.

Abstract:This study aimed to explore the effect of cultivars and seasons on the biochemical components variation of Camellia sinensis var. assamica in Yunnan, providing a theoretical basis for the selection of cultivars and seasons of tea harvesting and processing. Five cultivars of Camellia sinensis var. assamica cv. Yunkang 10, Camellia sinensis var. assamica cv. Yunkang 14, Camellia sinensis var. assamica cv. Xueya 100, Camellia sinensis var. assamica cv. Foxiang 2 and Camellia sinensis var. assamica cv. Zijuan were used in this study. One bud and two leaves of new shoot were collected and steamed in spring, summer and autumn, respectively. The seasonal variation of main biochemical components of five cultivars was investigated, including water content, water extract, tea polyphenols, amino acids, and caffeine. The biochemical components of different tea varieties were measured and compared. The results showed that the content of total catechin of Camellia sinensis var. assamica cv. Zijuan was higher than other cultivars, and its epigallocatechin contents was significantly higher than that of other cultivars. The highest content of water extract and catechin quality index were observed in Camellia sinensis var. assamica cv. Yunkang 10. The content of amino acid in spring tea was the highest, which was even higher than the threshold of famous qualified green tea. The contents of water, caffeine, catechin(C) and the total of catechin in summer tea were significantly higher than those in other seasons. The content of polyphenols in tea collected in autumn was the highest, while the total contents of amino acids and catechin were significantly lower than those in other seasons. The biochemical components of tea showed significant differences among different cultivars and different seasons. The suitability of tea processing can be studied according to the differences of biochemical components and combined with the practice.

Abstract:With the rise of milk tea beverage industry, the demand of powdered oils in the ready-to-sell beverage industry has gradually increased. The emulsification of powdered oils is one of the important factors affecting the application of milk tea. Therefore, the commercial typical powdered oil exclusively used in milk tea, i.e., non-dairy creamer (NDC), was studied. The emulsification of NDC was investigated by particle size analysis and microstructure observation, and the emulsion stability was further detected by Tubiscan analyzer. The results showed that NDC-1 and NDC-2 had smaller particle size (0.261 μm and 0.229 μm, respectively) and uniform distribution of emulsion droplets, with good emulsion stability at 60 ℃ (the stability index (TSI24 h) of NDC-1 emulsion was 1.05 at 60 ℃ for 24 h). On this basis, milk tea was prepared using powdered oils. It was found that NDC-1 and NDC-2 milk tea had better texture and smooth taste, which provided a theoretical basis for the application of powdered oils in milk tea.

Abstract:In order to improve the quality of fresh glutinous rice flour, fresh glutinous rice was treated with L-ascorbic acid and the optimum condition was studied by response surface methodology based on the single factor experiment. The effect of treated glutinous rice flour on the sensory qualities of cooked frozen glutinous rice dumplings was evaluated. The results showed that the optimal technological condition for L-ascorbic acid treatment of glutinous rice was 0.039% mass fraction of oxidant for 48 h at 60 ℃. Under the optimum condition, the peak viscosity, trough viscosity, final viscosity and retrogradation value of glutinous rice flour increased, and the peak viscosity increased by 81.5% compared with that of the original glutinous rice flour. The hardness, viscoelasticity, chewiness of rice dumplings and the sensory score increased, and the transmittance (%) of rice dumpling soup (expressed by paste turbidity) decreased, indicating that L-ascorbic acid treatment could significantly enhance the peak viscosity of fresh glutinous rice flour and improve the sensory quality of quick-frozen glutinous rice dumplings.

Abstract:Pumpkin seed is a high-quality plant protein resource and an important oil crop with dual-purpose of medicine and food. This article reviews several deep-processed products of pumpkin seeds and their comprehensive utilization, including pumpkin seed snack food, pumpkin seed protein and peptide products, pumpkin seed oil, pumpkin seed powder, etc., aiming to provide a theoretical basis for the development of new pumpkin seed series products.

Abstract:Biogenic amines widely existed in some foods, especially in fermented foods, which have certain hidden danger of food safety. In order to obtain biogenic amines degrading strains used in fish sauce and other fermentation products, non-biogenic amines producing strains were primarily screened from the natural fermentation fish sauce by double-layer chromogenic medium method, which was re-screened by high-performance liquid chromatography (HPLC) method to obtain a strain MZ5 with high efficiency of histamine degradation. The strain was identified as Pichia kudriavzevii, and the strain showed high histamine degradation activity in the range of 10~200 mg/L histamine concentration, 0~5% volume fraction of ethanol, pH 5~7 and 0~8 g/dL NaCl. The histamine degradation rate was 98.61% at the initial histamine mass concentration of 50 mg/kg and pH 7. Pichia kudriavzevii had good tolerance to ethanol, pH and salt concentration, and could be used as the fermentation preparation. This study could provide a research basis for the development of biological amine degradants in fermented food.