Effects of Mild Heat Combined with Dimethyl Dicarbonate on the Quality of Litchi Juice.

The effects of dimethyl dicarbonate (DMDC), mild heat and their combination on the microorganisms and physicochemical indices of litchi juice were compared. The results showed that the sterilization effect of DMDC alone or mild heat alone was poor, whilst the number of residual microorganisms in the litchi juice treated by the combination was the lowest, with the total number of colonies and lactic acid bacteria being 0.41 and 0.36 lg CFU/mL, respectively, and no yeast and mold being detected. Compared to fresh litchi juice, DMDC treatment had no effect on the quality of Litchi juice, and the changes in ascorbic acid content and color of the mild heat alone group and the combined treatment group were insignificant, causing the increases in the total phenolics (total flavonoids) by 40.16% (7.16%) and 38.01% (4.35%), respectively, and increases in the ferric ion reducing antioxidant power (DPPH free radical scavenging ability) by 15.55% (11.85%) and 7.61% (3.71%), respectively. These results indicated that mild heat could promote the release of phenolics and improve the antioxidant activity. Correlation analysis showed that the ΔE of litchi juice was negatively correlated with Vc content, and the antioxidant activity was positively correlated with the contents of total phenolics and total flavonoids. Cluster heat map analysis and sensory evaluation revealed that the combined treatment could promote the release of flavor substances without causing a pronounced cooking flavor. The total number of colonies in the combined treatment group stored at 4 °C for 21 days was less than 100 CFU/mL. In conclusion, the combination of mild heat and DMDC treatment led to a good sterilization effect on the microorganisms in the litchi juice without causing adverse effects, and the shelf life of the juice was up to 21 d. This study provides a scientific basis for the industrialization of high-quality litchi juice. [ABSTRACT FROM AUTHOR]