Effect of reuterin addition before and after fermentation on yogurt quality

Reuterin, a nonprotein, broad-spectrum antibacterial substance produced by Limosilactobacillus reuteri through glycerol fermentation, exhibits potential as a biological preservative in dairy products. The work aimed to investigate the effect of adding various concentrations of reuterin (9.125, 18.25, and 36.5 mM) on yogurt quality, both before and after the addition of the starter culture. The study also examined the inhibitory efficacy of reuterin against preinoculated Staphylococcus aureus in yogurt. The results showed that prefermentation reuterin supplementation markedly altered yogurt properties, including red-shifted redness values, elevated pH, reduced titratable acidity, decreased lactic acid bacteria viability, and lower apparent viscosity, compared with the control group. Furthermore, SDS-PAGE results demonstrated that reuterin also reacted with casein in yogurt, which might lead to the conversion of casein monomers into oligomers at 42°C for 6 h. All these changes exhibited concentration dependence. Conversely, postfermentation reuterin addition did not markedly alter yogurt color and mitigated postacidification by suppressing lactic acid bacteria proliferation during refrigeration (4°C, 28 d). Reuterin also inactivated S. aureus, shortening the time required to reduce bacterial counts in yogurt below the detection limit by 3 to 9 d. However, high-concentration reuterin weakened the intensity of casein electrophoretic bands, impaired the rheological properties of yogurt, and induced densification of the casein gel network structure. Notably, yogurt supplemented with low-concentration reuterin postfermentation most closely resembled the control group in quality. These findings suggest reuterin is unsuitable for prefermentation use, while its postfermentation application at low concentrations holds promise as a yogurt biopreservative.