Soybean protein isolate (SPI) was used as raw material to prepare antioxidant peptides through ultrasound-assisted enzymatic hydrolysis in this study. SPI hydrolysate was separated by ultrafiltration into peptides with different molecular masses, whose antioxidant activity was evaluated by measuring the scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)(ABTS) cation radicals and hydroxyl radicals, as well as using the ferric reducing antioxidant power (FRAP) assay. The amino acid composition was analyzed, and peptides with high antioxidant activity were identified. Molecular docking was used to elucidate their antioxidant mechanisms. The results showed that peptides with a molecular mass of < 3 kDa exhibited the strongest DPPH, ABTS cation and hydroxyl radical scavenging capacity, as well as the highest FRAP(P < 0.05). Amino acid composition analysis revealed that the peptides contained higher levels of hydrophobic and antioxidant amino acids, which were positively correlated with their antioxidant activity. By liquid chromatography-tandem mass spectrometry (LC-MS/MS), 1217 unique peptides were identified, and 10 potent antioxidant peptides (activity score > 0.90) were selected from them. Molecular docking indicated that these peptides had low binding energy (-9.7 to-7.2 kcal/mol) with kelch-like ECH-associated protein 1(Keap1), primarily exerting antioxidant activity through hydrogen bonds and hydrophobic interactions. This study provides theoretical and technical support for the high-value utilization of soybean protein resources and the development of natural antioxidant peptides.

The present study aimed to explore the effect of inoculated fermentation on the quality of fermented beef sausage. A mixed culture was used to prepare fermented beef sausage, and naturally fermented sausage was also prepared as a control. The quality of fermented sausage was evaluated by measuring its physicochemical parameters such as pH, color, texture and nitrite residue. Furthermore, the antioxidant activity of peptides in fermented sausages were investigated by measuring their scavenging capacities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, 2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical and hydroxyl radicals. The results showed that the pH and brightness of fermented beef sausages decreased significantly with fermentation time (P < 0.05). Nitrite residue was significantly reduced to be within the allowable range of the national standard (P < 0.05). On the 21st day, the pH of inoculated fermented sausage was significantly lower than that of the control group (P < 0.05), while the opposite was observed for hardness, springiness and chewiness (P < 0.05). The results of peptide measurement and sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) showed that compared to the control group, the peptide content of inoculated fermented sausage increased, and so did the ABTS cation radical and DPPH radical scavenging activities of peptides (P < 0.05). Therefore, the quality of fermented beef sausage was greatly improved by inoculation with the mixed starter, and the polypeptide content and antioxidant activity were also increased.

Salt-baked chicken was prepared with a low-sodium salt mixture containing 52% sodium chloride, 30% potassium chloride, 8% calcium lactate and 10% yeast extract (m/m) as a low-sodium (LS) group, and with 100% sodium chloride as a control group. The effect of the low-sodium salt formulation on the physicochemical and microbiological quality of salt-baked chicken was explored during storage. The results showed that pH of salt-baked chicken first rose and then fell with storage time. Total sulfhydryl content and sensory score from fuzzy mathematics decreased. Total volatile basic nitrogen (TVB-N) content, thiobarbituric reactive substances (TBARS) value and total colony number increased. At day 0 of storage, coliform and pathogenic bacterial count complied with the national hygienic standard for cooked meat products GB 2726-2016, but exceeded it at day 30. pH, TVB-N content, TBARS value and total colony number were always higher in the LS group than the control group, whilst the opposite was true for the degree of fat and protein oxidation. However, the color parameters a* and b* values and sensory score were not significantly different between the two groups (P > 0.05). TVB-N and total number of colonies indicated that the salt-baked chicken from LS group had severe deterioration during the same storage period. High-throughput sequencing showed that the most dominant bacterial phylum in salt-baked chicken was Firmicutes, and the most dominant bacterial genus in both groups were Serratia and Paeniclostridium. In summary, the application of the lowsodium salt formulation can inhibit fat and protein oxidation in salt-baked chicken while having no significant effect on its color or sensory quality and no negative effect on its safety. Neither of the groups is fit for consumption after 20 days of storage.

In order to systematically explore the effect of starter on the antioxidant activity of peptides from fermented sausage, the in vitro antioxidant activity of crude peptides extracted from naturally and starter fermented sausage were assessed. The results showed that the peptides from starter fermented sausage had a stronger ability to chelate metal ions and scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radicals, which increased by 13%, 10% and 20%, respectively, compared with the control group, while the 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging capacity was weaker than that of the peptides from naturally fermented sausage. Furthermore, the in vivo antioxidant activity of the peptides from starter fermented sausage was evaluated using a mouse model of D-galactose-induced aging. The results of growth performance showed that the crude peptides could promote the growth of mice and increase visceral indices. Moreover, the crude peptides significantly increased the activities of various antioxidant enzymes in the mouse serum and liver tissue including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) as well as total antioxidant capacity (T-AOC) and reduced malondialdehyde (MDA) content, restoring the antioxidant capacity to normal and even higher than normal levels. This study has shown that the crude peptides from starter fermented sausage have outstanding antioxidant activity, and thus can provide another option for the development of protein-derived antioxidant peptides.

Fermented sausages were manufactured with Staphylococcus simulans NJ201 as a starter, and naturally fermented sausages were used as a control. The pH, color parameters, texture, peroxide value (POV) and thiobarbituric acid reactive substances (TBARS) value, protein carbonyl content, total sulfhydryl content, and volatile flavor composition in fermented sausages were measured to explore the effect of S. simulans NJ201 on the quality and oxidative stability of fermented sausages. The results showed that inoculation with S. simulans NJ201 significantly lowered the pH value of fermented sausage during its fermentation and maturation (P < 0.05), and improved the color and the texture characteristics. The POV, TBARS value and protein carbonyl content of the inoculated group were significantly lower than those of the control group (P < 0.05), whereas the sulfhydryl content was significantly higher than that of the control group (P < 0.05). The number and amount of volatile flavor substances in the inoculated group were higher than those in the control group. In summary, inoculation with S. simulans NJ201 can improve the taste and enhance the flavor of fermented sausages, effectively inhibit fat oxidation and protein oxidation and increase the oxidative stability of fermented sausages.

In order to investigate the effects of thermal processing methods on the quality and oxidation characteristics of pork, boiled, microwaved, roasted, or deep-fried pork loin was evaluated for quality indicators such as cooking loss, color, shear force, texture, basic chemical composition, odor and taste and oxidation indicators such as protein carbonyl content and thiobarbituric acid reactive substance (TBARS) value. The results showed that compared with the control group (raw pork), the quality and oxidation characteristics of cooked pork samples were significantly different. The decreasing order of cooking loss rate during different thermal treatments was roasting > microwave > deep-frying > boiling; protein and ash contents were positively correlated with cooking loss, while water content was negatively correlated with cooking loss. The most significant color changes were found in deep-fried pork, whose elasticity, cohesiveness and shear force were significantly different compared with the other treated groups. Protein carbonyl content was significantly higher in microwaved pork than the other treated groups (P < 0.05). Roasted pork exhibited the highest TBARS value. Electronic nose results showed an increase in the content of volatile flavor substances after thermal processing, and electronic tongue results indicated that the umami intensity of deep-fried pork was the highest. The results of this study can provide reference for the selection of pork thermal processing methods.

To explore the effect of functional starter cultures on the quality, flavor and antioxidant activity of fermented fish sausage, we prepared fermented fish sausage by inoculation with a cocktail of the functional starter culture strains Lactobacillus plantarum CD101 and Staphylococcus simulans NJ201 or natural fermentation as a control, and we measured the pH, texture, color difference, antioxidant capacity, volatile flavor substances and free amino acids of the prepared samples. The results showed that inoculation with functional starter culture could rapidly reduce the pH of fish sausage during fermentation and improve the stability and safety of the sausage; improve the hardness and chewiness, and enhance the brightness and color, thereby making the sausage have better quality; significantly increase the scavenging capacity of sausage-derived peptides against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical cation and hydroxyl radical, contributing to improving the antioxidant activity of sausage-derived peptides; and increase the contents of ketones, esters and other flavor substances, enriching the flavor of the sausage and making it have a stronger sweetness and fruity aroma. Moreover, inoculation with functional starter culture promoted the release of free amino acids from the sausage, which was conducive to enhancing the nutritional properties, antioxidant capacity and flavor of the sausage.

In this study, sauced beef was prepared by three different cooking processes: ultrasonic-assisted stepwise cooking (CF), stepwise cooking (F) and traditional cooking (CT). In order to investigate changes in the flavor substances of sauced beef during different cooking processes, the effect of the three cooking processes on the flavor of sauced beef were analyzed from the perspective of the Maillard reaction. Absorbance at 294 nm (A_{294 nm}) and 420 nm (A_{294 nm}), which can reflect the amount of Maillard reaction products (MRPs) formed in the middle and late stages, respectively, were measured. The results showed significant differences in A_{294 nm} between the CF and CT groups at 0.5 h of cooking (P < 0.05), but no significant differences between the CF and CT groups at 2 and 4 h (P > 0.05). A_{294 nm} and A_{420 nm} were significantly higher in the F group than in the CT and CF groups at 0.5 and 4 h. The CF group had the highest fluorescence intensity. Protein secondary structure analysis indicated an increase in the relative content of β-sheet and a decrease in the relative content of α-helix in the CF and F groups compared with the CT group; α-helix unfolding led to the exposure of intramolecular hydrophobic groups, thereby increasing the surface hydrophobicity and fluorescence intensity. Ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) identified 103, 167, and 200 differential metabolites in the CT, F, and CF groups, respectively, and a large number of amino acids, dipeptides, nucleosides, and heterocyclic compounds were produced in the CF group; gas chromatography-mass spectrometry (GC-MS) results showed that CF and F promoted the production of volatile flavor substances in sauced beef. The above results indicated that both cooking processes could promote the Maillard reaction and consequently improve the flavor of sauced beef.

In this study, marinated beef tendon was subjected to sous-vide cooking under different combinations of temperature and time. Traditional high-temperature stewing was used as a control. The cooked meat was digested in vitro and the digest was added to an in vitro absorption model based on Caco-2 cells to simulate the absorption process. The effects of different temperature-time combinations on the protein absorption of sous-vide cooked beef tendon were determined by measuring the protein absorption products. The results showed that sous-vide processing increased the absorption of free amino acids and peptides especially those with small molecular mass of 300-500 Da. Sous-vide cooking at 60 ℃ favored the absorption of myosin and actin, while sous-vide cooking at 80 ℃ favored the absorption of collagen. Compared with the other treatment groups, sous-vide cooking at 60 ℃ for 8 h resulted in the occurrence of significantly more essential amino acids and antioxidant amino acids as well as more small-molecular-mass peptides and specific bioactive peptides in the absorbed products, showing higher nutritional levels.

In this study, we aimed to investigated the effect of mixed cultures on improving the physiochemical properties, flavor and antioxidant activity of peptides of fermented mutton sausage. The physicochemical indexes such as pH, color and texture, as well as the types and contents of free amino acids and volatile flavor substances in fermented mutton sausage prepared with mixed culture of Lactobacillus plantarum CD101 and Staphylococcus simulans NJ201 and naturally fermented sausage as a control were measured, and the scavenging ability of peptides extracted from the sausages against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cationic radicals and hydroxyl radicals were tested. The results showed that the mixed culture was able to rapidly reduce the pH of fermented mutton sausage during fermentation, improve its safety, enhance its brightness, color, hardness and chewiness, thereby improving its quality. Moreover, the mixed culture increased the total amount of free amino acids, the types and contents of volatile flavor substances and consequently enhanced the flavor of fermented mutton sausage, as well as significantly increased the radical scavenging capacity of peptides from fermented mutton sausage. In conclusion, inoculated fermentation could significantly improve physicochemical properties, flavor and antioxidant capacity of peptides from fermented mutton sausage. This study can provide a theoretical basis for the industrial production of fermented meat products.