The effects of high-temperature heating, repeated freezing and thawing, and ultraviolet (UV) irradiation on the acceleration of lipid oxidation in pork backfat were compared. Changes in the acid value (AV), free fatty acid (FFA) content and composition, peroxide value (POV), thiobarbituric acid reactive substances (TBARS) value, lipid oxidation products (LOP) and microbial load of pig backfat were measured to obtain the most suitable accelerated lipid oxidation method. The results showed that high-temperature heating treatment was the most effective way to promote lipid oxidation, increasing the POV from (0.0083 ± 0.00) to (0.0530 ± 0.00) g/100 g and the TBARS value from (0.24 ± 0.01) to (0.65 ± 0.00) mg/kg. Repeated freezing-thawing treatment increased the POV from (0.0180 ± 0.00) to (0.0347 ± 0.00) g/100 g and the TBARS value from (0.13 ± 0.00) to (0.25 ± 0.00) mg/kg, and UV irradiation increased the POV from (0.0081 ± 0.00) to (0.0198 ± 0.00) g/100 g and the TBARS value from (0.07 ± 0.00) to (0.21 ± 0.00) mg/kg. No microorganisms were detected in the high-temperature heating treatment. In the repeated freezing-thawing and UV irradiation treatments, the number of microorganisms gradually increased with the number of freezing-thawing cycles or irradiation time. This does not rule out the influence of microbial growth on lipid oxidation. Therefore, high-temperature heating treatment is the most suitable method to accelerate lipid oxidation among these three methods.

To explore the effects of starter cultures with antioxidant activity on the quality of Cantonese sausage, this study used pork frozen at -20 ℃ for 0, 3, 6 and 9 months to make Cantonese sausages (denoted respectively as 0E, 3E, 6E and 9E) employing a mixed-strain starter culture of Lactiplantibacillus plantarum L52, Pediococcus pentosaceus L256, Staphylococcus xylosus S56 and S. xylosus S236 (L52: L256: S56: S236 = 5:10:2:3, V/V), all having antioxidant potential. Uninoculated sausages were also produced as controls and designated as 0C, 3C, 6C and 9C, respectively. The changes of microbial counts, sensory quality and physicochemical indexes were analyzed during sausage processing. Results showed that prolonged freezing time inhibited the growth of some microorganisms in pork. At the middle stage of fermentation, the numbers of lactic acid bacteria and Staphylococcus were significantly higher in the experimental group than in the control group (P < 0.05). Prolonged freezing time of pork meat reduced the sensory quality of sausages, and the sensory quality of the experimental group was better than that of the control group. The overall sensory score of 9E (71.85 points) was significantly higher than that of 9C (59.60 points). The pH and water activity (a_w) of the experimental group were lower than those of the control group. Prolonged freezing time of pork meat led to a higher degree of oxidation of sausages. After drying, the thiobarbituric acid reactive substances (TBARS) value, carbonyl group value (CGV) and protein carbonyl content of 6E were 29.66%, 26.32% and 23.72% lower than those of 6C (P < 0.05), and the protein sulfhydryl content was 40.36% higher than that of 6C (P < 0.05). Compared with 6C, the intensity of the bands in the ranges of 18-27 and 27-55 kDa, corresponding respectively to sarcoplasmic and myofibrillar proteins, were significantly enhanced in 6E. The total content of biogenic amines was 25.15% lower in 3E than in 3C. The total content of ethyl esters was significantly higher in 9E (8.81 μg/kg) than in 9C (2.91 μg/kg) (P < 0.05). The results showed that the four-strain cocktail of lactic acid bacteria and Staphylococcus could improve the antioxidant activity, eating quality and safety of Cantonese sausages.

Fermented foods are rich in protein and free amino acids, which are decarboxylated by microbial amino acid decarboxylase to produce biogenic amines. Excessive ingestion of biogenic amines poses a threat to human health. Tyramine, a biogenic amine having high toxicity, is present in fermented foods in large quantities, so developing safe and effective methods to control tyramine is of practical significance for improving the safety of fermented foods. In this article, the physiological functions, harms and limit standard of tyramine in fermented foods are described with an emphasis on the formation mechanism and control methods of tyramine, so as to provide theoretical references for further improving the safety of fermented foods.