Non-thermal Treatment of Postharvest Strawberry and Establishment of Its Optimal Freezing Condition

Abstract

To secure the microbial safety of frozen strawberries, they were treated with the combined solution of aqueous chlorine dioxide and acetic acid prior to freezing and the effects of different freezing methods (at ?20°C in a freezer, at ?70°C in a gas nitrogen convection chamber, and at ?196°C in liquid nitrogen) on the quality changes of strawberries were examined. Regarding the color of frozen strawberries, there were negligible changes among freezing treatments. In contrast, vitamin C content and sensory evaluation scores of strawberries frozen at ?70°C were the highest among the samples. Drip loss of strawberries frozen at ?70°C was the lowest as 14.39%, compared with strawberries frozen at ?20 and ?196°C. In addition, the effects of combined treatment of 50 ppm chlorine dioxide and 1% acetic acid on the microbial growth in frozen strawberries were investigated, and the populations of preexisting microorganisms in the frozen strawberries were not detected by the combined pre-treatment. These results suggest that rapid freezing at ?70°C using a gas nitrogen convection chamber is an appropriate freezing method for preserving quality of strawberries, and as a pre-freezing treatment, the combined treatment of aqueous chlorine dioxide and acetic acid can be effective for improving microbiological safety of frozen strawberries.