Abstract A chitosan-based edible coating was prepared by incorporating γ-polyglutamic acid and curcumin. The physical, mechanical and antimicrobial properties of the chitosan/γ-polyglutamic acid/curcumin edible coating were characterized. Furthermore, the effect of chitosan/γ-polyglutamic acid/curcumin edible coating on the shelf-life of fresh beef was investigated. The γ-polyglutamic acid and curcumin incorporation greatly improved the performance of chitosan coating, including coating formation and antimicrobial activity. After the application of coating, the chitosan/γ-polyglutamic acid/curcumin edible coating had a good protection effect on the color of beef and was conducive to prolonging the shelf life of beef with good quality compared to pure curcumin edible coating. These results revealed that application of chitosan/γ-polyglutamic acid/ curcumin edible coating will be a good way to preserve freshness of fresh beef.

Abstract Comparsion of the effects of the chilling (4 ºC), superchilling (-2 ºC) and frozen (-18 ºC) storage on microbial spoilage and bacterial community structure of fresh beef was evaluated by high-throughput sequencing technology in this study. The results indicated that storage temperature can significantly affect the degree of microbial spoilage and bacterial community structure of fresh beef during storage. At the species level, the primary dominant bacterial species in beef samples was Pseudomonas fragi with relative abundance of 37.78% followed by Myroides phaeus and Brochothrix thermosphacta with 10.95% and 4.64%, respectively, at the beginning of storage. Both superchilling and frozen storage can effectively inhibit the growth of P. fragi, while the chilling storage failed to demonstrate strong inhibition for growth of P. fragi. Similar result was found for Myroides phaeus. The chilling, superchilling and frozen storage can not effectively inhibit the growth of Brochothrix thermosphacta and Acinetobacter johnsonii. The difference of microbial spoilage in beef stored in three kinds of storage may be related to the difference of the bacterial community structure and the formation of dominant spoilage bacteria. These results revealed that superchilling and frozen storage can effectively inhibit the formation of dominant spoilage bacteria, resulting in a good freshness preservation.

Abstract In order to explore the distribution and transfer of lead elements in soil and rice in the five regions of Chahayang, Wuchang, Fangzheng, Xiangshui and Jiansanjiang in Heilongjiang Province, and analyze the impact of rice intake on human health, the samples were tested by ICP-MS. Modeling the lead-element transfer in the soil-rice system, using the Nemero comprehensive pollution index method and the health risk assessment model to evaluate the lead pollution status of rice in the study area and its health risks to adults and children. The results showed that the average content of lead in rice in the study area was Chahayang 0.02 mg/kg, Wuchang 0.03 mg/kg, Fangzheng 0.017 mg/kg, Xiangshui 0.023 mg/kg and Jiansanjiang. 0.024 mg/kg did not exceed the lead content limit specified by China's National Food Hygiene Standard (0.2 mg/kg); Based on the prediction model of heavy metal lead content, pH value, and organic matter in the soil, the transfer of lead elements in the soil-rice system of Chahayang, Fangzheng, Xiangshui, and Jiansanjiang rice fields can be significantly described, with R2 values ranging from 0.224 to 0.419; Both the pollution index and the comprehensive pollution index in the study area were less than 1, which belong to the non-pollution category. The health risk index of heavy metal lead for adults and children in all five regions is lower than the maximum acceptable risk level recommended by USEPA, and there is no risk of causing cancer.

Abstract The study aimed to improve polysaccharide-based packaging to extend the shelf life of fresh produce; a composite film with antimicrobial function was developed and tested. The packaging film is a blend of agar, a film-forming substrate; carrageenan, as a reinforcing agent; glycerol, as a plasticizer; and Nisin, an antimicrobial agent. The film was evaluated for its antibacterial, mechanical, and barrier properties at different humidity levels, using fresh-cut watermelon as the test food material. The film effectively inhibited the growth of Staphylococcus aureus and Listeria monocytogenes. Under relative humidity of 20%, 50%, and 90%, the tensile strength of the antibacterial film containing 0.28% Nisin was 23.08 ± 0.65, 16.09 ± 1.73, and 6.52 ± 0.56 MPa, respectively, and the film also had excellent barrier and heat-sealing properties. The packaging test using fresh-cut watermelon sealed in the antibacterial film containing 0.28% Nisin, under controlled atmosphere storage at either 4 °C or 20 °C, effectively inhibited microbial colonization in the melon and slowed the deterioration of the fruit, as indicated by measures of hardness, weight loss, and soluble solids. This method can extend the shelf life of fresh-cut fruit and provide a reference for further research on polysaccharide-based protective film for fresh produce.

Abstract In this study, the effects of the starter culture Lactobacillus sakei on pH, the total lactic acid concentration, nitrite depletion and histamine reduction of chili sauce were investigated. The nitrite concentration in the CPN sample was significantly lower (p < 0.05) than that of the CPS sample (as control), and decreased by 30.87%.The putrescine and histamine concentration in starter culture inoculated chili sauce were significantly lower (p < 0.05) than that of the control sample, and were decreased by 38.08% and 49.88%, respectively. These results revealed that L. sakei could be used as a potential starter culture for nitrite depletion and biogenic amines reduction of chili sauce with good sensory attributes.

Abstract In this study, the effects of the starter culture Lactobacillus sakei on microbial quality and the bacterial community diversity of chili sauce were investigated. In starter culture inoculated chili sauce (CPN sample), Lactobacillus spp. was predominant bacteria with 86.08% of the relative abundance on the 30th day of fermentation. Meanwhile, the spoilage organisms and pathogenic bacteria, including Staphylococcus spp., Enterobacter spp., Pseudomonas spp. and Neorhizobium spp. were nearly undetectable in starter culture inoculated chili sauce. In contrast, Lactobacillus spp. and Weissella spp. were predominant bacteria, and trace Pseudomonas spp. and Neorhizobium spp. were still detectable at the end of fermentation in the spontaneous fermentation (CPS sample). These results revealed that L. sakei could be used as a potential starter culture for the microbial quality improvement.

Abstract Changes in bacterial community composition and bacterial counts of chilled pork during storage at 4 °C were unraveled by culture-dependent method and culture-independent method. Physical and chemical analyses including drip loss, total volatile basic nitrogen (TVB-N), pH, and surface color were also performed to estimate its quality and shelf life. A total of 37 phyla, 575 genera and 843 species were identified in all samples by high-throughput sequencing technology during 10 days’ storage. At the phylum level, Proteobacteria and Firmicutes were the dominant phylum. At the genus level, Pseudomonas spp., Acinetobacter spp., Pantoea spp., Brochothrix spp. and Raoultella spp. were the dominant genera with their average relative abundance above 5%. In addition, 12 species with average relative abundance more than 1% were found. These dominant bacteria were main pathogenic or spoilage bacteria, and seriously affected the quality of chilled meat. Based on the results of total viable counts (TVC), TVB-N level and sensory evaluation, the shelf life of chilled pork stored at 4 °C was no more than 3 days. Through the analyses of the TVC and the microbial community structure during the spoilage of chilled pork, the main microorganisms causing spoilage were revealed, which will guide significance for further control microbial quality of chilled pork.

Abstract Comparative efficacy of sodium lactate and Natamycin as preservative against discoloration and spoilage of fresh beef stored at 4 °C were evaluated. Fresh beef was treated with 3 g/L sodium lactate and Natamycin, respectively, and sterilized physiological saline was used as negative control. The spoilage of beef samples was monitored by pH, total volatile basic nitrogen (TVB-N), discoloration, sensory analysis and bacterial quality which were determined by culture-dependent and culture-independent analyses. The acceptable shelf life of fresh beef treated by sodium lactate and Natamycin reached 6 days and 4 days, respectively. Whereas, the control sample was acceptable for 3 days. The two kinds of preservative were conducive to hygiene levels improvement. Lactobacillus spp. and Weissella spp. sharply displaced the Ralstoni spp. with high potential spoilage and became the predominant bacteria, and the proliferation of Serratia spp. as the representatives’ genus of psychrotrophic Enterobacteriaceae were completely controlled in the preservative treated samples. Sodium lactate displayed a remarkable efficacy against discoloration and spoilage of chilled beef, resulting in shelf life extension by 3-4 days. Natamycin has a remarkable antibacterial efficacy but a little efficacy against discoloration. Thus, sodium lactate is more suitable for freshness promotion of chilled beef.

Abstract Sodium lactate contribution on color stability of chilled beef was evaluated by proteomics analysis combined with the relative Mb content and NADH/ NAD+ ratio. The sodium lactate exhibited a remarkable efficacy against discoloration of chilled beef and showed a desirable color appearance for 6 days, while the control showed an undesirable color appearance on the 3rd day. Based on the significance analysis of protein interaction network, 12 proteins responsible for color stability of chilled beef treated by sodium lactate have been identified, which participated mainly in redox systems, metabolic enzymes, oxidoreductase, structural proteins and heat shock proteins. The proteins were correlated with NADH regeneration. Thus, we suggest that the color stability promotion may attribute to the role of in the regeneration of NADH by sodium lactate treatment.

Abstract The efficacy of sodium lactate combined with Natamycin against discoloration and spoilage of beef stored at 4 °C was evaluated. The beef was treated with 3 g/L sodium lactate combined with 3 g/L Natamycin, and 3 g/L sodium lactate treatment and 3 g/L Natamycin treatment were performed as control. The spoilage of beef samples was monitored by pH, total volatile basic nitrogen (TVB-N), discoloration, sensory analysis and microbial quality. Sodium lactate exhibited a remarkable efficacy against discoloration together with antibacterial efficacy against spoilage. Natamycin has no contribution to delaying discoloration but displayed a remarkable antibacterial efficacy. These results revealed that sodium lactate combined with Natamycin was more conducive to hygiene levels improvement. In the sample treated by sodium lactate combined with Natamycin, Lactobacillus spp. and Weissella spp. sharply displaced the Ralstoni spp. with high potential spoilage and became the predominant bacteria, and the proliferation of Serratia spp. as the representatives’ genus of psychrotrophic Enterobacteriaceae were completely controlled. As a result, the acceptable shelf life of beef treated by sodium combined with Natamycin reached 7 days. While the acceptable shelf life of beef treated by sodium lactate and Natamycin was 6 and 4, respectively.

Abstract The effect of super-chilled storage (-2 °C) on shelf life and quality of beef was investigated, compared with chilled (4 °C) and frozen (-18 °C) storage. The pH value, color, TVB-N, water-holding capacity, total viable counts (TVC) and sensory evaluation were used to evaluate the freshness, shelf life and quality of beef. These results indicated that the fresh beef stored in super-chilled condition demonstrated better pH and color stability compared to chilled storage, and exhibited better water-holding capacity and sensory score compared to frozen storage. Based on the TVB-N level and TVC, the super-chilled storage was conducive to prolong the shelf life of beef with good quality. The super-chilled storage is a good way to preserve freshness of fresh beef. In conclusion, this work provides data for the preservation of fresh beef which will benefit the meat industry.

Abstract Fresh beef was treated with 3 g/L sodium lactate (Group SL) and the fresh beef without treatment was sampled as negative control (Group C). Based on the comprehensive analyses of pH, color and glycolytic rate, sodium lactate usage exhibited a better pH and color stability, which is conducive to maintaining the meat quality. The Group SL had lower glycogen content and higher lactate content than that of Group C. Meanwhile, the Group SL had significantly higher (p < 0.05) lactate dehydrogenase and hexokinase activity than that of Group C druing chilled storage. Moreover, NADH/NAD+ ratio in Group SL maintained at a stable level with a range from 0.54 to 0.68 during chilled storage. In contrast, Group C showed a high NADH/NAD+ ratio which indicated insufficient reducing activity. These results revealed that the sodium lactate treatment had a positive relationship with glycolytic rate and promoted the increase of glycolysis rate. These results may be partially explained the reason why sodium lactate usage can promote color stability via increase of glycolysis rate.