Preparation and evaluation of ozone micro-nano bubbles ice for Litchi precooling.

Ozone (O) is an effective agent for post-harvest fruit preservation against diverse microorganisms. In this study, a cost-effective ozone micro-nano bubbles ice (O-MNBI) was prepared, characterized, and subsequently used to precool litchi. The optimal protocols for O-MNBI production were as follows: water (2 °C, pH = 7) was pumped into a micro-nano O bubble generator for 10 min aeration treatment. The water was then contained in a box and immersed in the supercooled NaCl solution (-20 °C) to form O-MNBI. The microscope image confirmed that the sizes of the ultrafine bubbles were predominantly less than 100 μm. The stable release duration of O was 168 h. Litchi precooled by O-MNBI for 20 min exhibited significantly (p < 0.05) elevated L*, a*, b* values, reduced total microbial colony count, respiration rate, relative conductance, and stable total soluble solids, thereby maintaining superior color and qualities. This study could provide a promising alternative to conventional ice-water precooling of litchi.