Effects of Various Inhibitors on the Flavor and Nutritional Quality of Heat-treated Lychee Juice

In order to reduce the cooked off-flavor of lychee juice after thermal processing, six inhibitors were screened, including pyrogallol, gallic acid, rosmarinic acid, catechins, ascorbic acid, and glucose oxidase. These inhibitions were evaluated based on flavor and nutritional properties such as color, pH, flavor profile, electronic nose, volatile components, sulfur-reducing rate, as well as total phenols, flavonoids contents, and antioxidant properties. The results showed that the samples treated with ascorbic acid and gallic acid had the smallest color difference compared to fresh juice. The overall aroma profile indicated glucose oxidase was the most effective inhibitor in reducing cooked off-flavor, followed by rosmarinic acid. The electronic nose results showed that the lychee juice treated with glucose oxidase was closest to fresh juice, followed by catechins and pyrogallol. The principal component analysis of volatile components showed that the sample treated with ascorbic acid was closest to fresh juice, followed by gallic acid, catechins, and rosmarinic acid. The sulfur reduction rate showed that glucose oxidase had the most significant sulfur reduction effect, with inhibition rates of 100% for dimethyl sulfide, dimethyl trisulfide, and methional, and 61.11% for dimethyl disulfide. In terms of nutritional quality, polyphenol and ascorbic acid treatment significantly improved the total phenol, total flavonoid contents as well as antioxidant properties, while the total phenol and total flavonoid contents of glucose oxidase-treated samples were higher than those of fresh juice but the antioxidant activities showed no significant difference compared to fresh juice. Partial least squares discriminant analysis (PLS-DA) of lychee juice quality, integrating factors such as color, pH, aroma profile, nutritional quality, and sulfur reduction effect, revealed that glucose oxidase had the best effect on the overall quality. The findings of this study can provide references for quality improvement in lychee and other subtropical fruits processing industry.