Changes in the Microbial Content and Quality Attributes of Carrot Juice Treated by a Combination of Ultrasound and Nisin During Storage

The objective of the article was to study the effects of ultrasound (US) and 80 ppm nisin-assisted US (US + nisin) on the inactivation of microorganisms and the nutritional quality of fresh carrot juice. Fresh carrot juice was exposed to HT (60 °C, 10 min), US, and US + nisin at 271 W and 30 °C for 10 min since the treatments had a similar microbial inactivation effect. Results showed that nisin exhibited an additional inactivation effect on the total aerobic bacteria (TAB) with US, while having no obvious effect on the yeast and mold (YM). The TAB was increased by 2.56, 2.20, and 4.28 log 10 cycles, while the YM was increased by 4.67, 4.75, and 6.84 log 10 cycles in carrot juice treated by US, US + nisin, and HT, respectively, after 20 days’ storage at 4 °C, indicating that US + nisin had a better post-inhibition effect on TAB than US and HT. Moreover, no significant changes occurred in the total suspended solids (TSS), viscosity, turbidity, or color, while carotenoid content was increased by 22.4%, 34.6%, and 21.4% in the carrot juice treated by US, US + nisin, and HT, respectively. In conclusion, the study ascertained that US + nisin is able to ensure both the microbial safety and the quality of carrot juice more effectively than HT alone.