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In this study, antioxidant peptides derived from sheep hemoglobin were prepared from fresh sheep blood. Sephadex G-25 chromatography, DEAE Sephadex A-50 chromatography, reverse phase high performance liquid chromatography (RP-HPLC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were used to separate, purify, and identify peptides from the hydrolysate of sheep hemoglobin. The antioxidant activity of the obtained peptides was evaluated by their free radical scavenging capacity, stability against simulated gastrointestinal digestion and protective effect on H2O2-induced oxidative injury in Caco-2 cells. The results indicated that three novel antioxidant peptides, Ala-Tyr-Glu-Val-Asp (AYEVD), Phe-His-Thr-Met-Glu (FHTME) and Ser-Phe-Met-Tyr-Glu-Lys (SFMYEK), were purified and identified from the hydrolysate, with molecular masses of 595.60, 663.74 and 803.92 Da, respectively. Among them, AYEVD had the strongest scavenging capacity to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, and AYEVD showed stronger antioxidant activity after simulated gastrointestinal digestion. In addition, AYEVD inhibited H2O2-induced oxidative injury in Caco-2 cells, significantly reduced the accumulation of reactive oxygen species (ROS), suppressed early cell apoptosis and the formation of malondialdehyde (MDA), and increased the activity of intracellular antioxidant enzymes. Therefore, this study could provide a theoretical basis for the application of novel antioxidant peptides from sheep hemoglobin in functional foods.

Oat β-glucan (OG) was used to replace salt in mutton mince at levels of 0%, 0.4%, 0.8%, 1.2% and 1.6%. To determine the appropriate level of OG replacement, the cooking loss, water-holding capacity (WHC), water distribution and content, color, gel strength, texture, secondary structure of myofibrillar protein, scanning electron micrograph (SEM) of mince samples with 2.0% salt, 0.4% OG + 1.6% salt, 0.8% OG + 1.2% salt, 1.2% OG + 0.8% salt and 1.6% OG + 0.4% salt were measured. The results showed that with increasing level of OG replacement, the cooking loss of mutton mince gels decreased first and then increased gradually, while the WHC showed the opposite trend. A significant decrease in the WHC was observed when 1.6% OG was added (P 0.05). The secondary structure of myofibrillar protein in the gel with high levels of OG replacement (> 0.8%) was similar to that in the control (P > 0.05), and the SEM image showed more loose structure with increased porosity. Through correlation analysis and principal component analysis (PCA), it was found that the synthetic score of the gel with 0.4% OG was higher than that of the other groups, which could ensure further reduction of salt intake while maintaining the gel quality of mutton mince.

An improved screening procedure was developed for the detection of amino acid decarboxylase-positive microorganisms (especially lactic acid bacteria and Enterobacteria). Monolayer culture and double layer colour development methods for the detection of amino acid decarboxylase-positive lactic acid bacteria and Enterobacteria were established. Biogenic amine-positive bacteria strain was isolated directly from the samples. The applicability and detection level of the designed medium were quantitatively evaluated by the confirmation of the amine-forming capacity using an HPLC procedure, while tyrosine decarboxylase and lysine decarboxylase genes were detected by PCR with specific primers. The screening method showed a good correlation with the chemical analysis and molecular detection. Enterobacter aerogenes, Enterobacter cloacae, Escherichia coli, Enterococcus faecium, and Enterococcus faecalis were obtained from traditional Chinese sausage. The isolation and screening of amino acid decarboxylase-positive lactic acid bacteria and Enterobacteria can be carried out simultaneously by the improved method.