Thermosonication combined with ε-polylysine (TSε): A novel technology to control the microbial population and significantly improve the overall quality attributes of orange juice

At present, most commercial orange juice still uses high temperature-long time thermal treatment (HTLT) to prolong its shelf life. However, HTLT treatment can have many negative effects on the overall quality of juice. Therefore, it is of great significance to explore novel non-thermal sterilization techniques to produce high-quality orange juice. In this study, we compared the inactivation effects of thermosonication (TS), TS combined with epsilon-polylysine (TS epsilon), TS combined with nisin (TSN) and HTLT on the bactericidal effects of natural microflora in orange juice. On this basis, the effects of TS epsilon and HTLT treatments on the comprehensive quality characteristics of orange juice were further explored. The results showed that TS epsilon and HTLT treatments had better effect on controlling the number of microorganisms and inactivating endogenous enzymes, and epsilon-polylysine showed a significant synergistic lethal ability (p < 0.05) to the total bacterial count and yeast in orange juice. With HTLT treatment, sterilization is not achieved because Alyciclobacillus spores are not inactivated, and it could be replaced by inactivation or pasteurization when the Alyciclobacillus are high. In addition, TS epsilon treatment maintained sensory quality, which was significantly better in TS epsilon-treated juice compared to HTLT-treated juice. Moreover, TS epsilon treatment markedly enhanced or strongly retained the functional substances of orange juice. The contents of polyphenols and carotenoids increased by 12.53% and 36.46%, respectively, while the antioxidant activities of ORAC, DPPH, and FRAP increased by 53.27%, 14.42%, and 7.26%, respectively. Additionally, the retention rate of ascorbic acid was as high as 85.42%. Therefore, as a novel non-thermal inactivation microbial technology, TS epsilon treatment contributes to the improvement of organoleptic quality and functional characteristics of orange juice.

Automated summary

Currently, the common high temperature-long time thermal treatment used in commercial orange juice negatively affects the quality. Therefore, exploring new non-thermal sterilization techniques to produce high-quality orange juice is significant. The study compared the effects of thermosonication, thermosonication combined with epsilon-polylysine, thermosonication combined with nisin, and high temperature-long time treatment on the microflora in orange juice. Based on the results, the combination of thermosonication and epsilon-polylysine treatment showed better control of microorganisms and inactivation of endogenous enzymes, while maintaining sensory quality and functional characteristics of orange juice.