Identification of carotenoids from fruits and vegetables with or without saponification and evaluation of their antioxidant activities

This study investigates the composition and form of carotenoids in typical fruits and vegetables obtained through saponification or non-saponification and evaluates the correlation between carotenoids and antioxidant capacity. The results showed that the content of the total carotenoids in non-saponified broccoli was the highest, reaching 1505.93 ± 71.99 µg/g d.w. The content of the total carotenoids in pumpkin flesh and broccoli after saponification was reduced by 71.82% and 52.02%, respectively. The content of lutein in spinach decreased by 24.4% after saponification, but the content of β-carotene increased compared to non-saponification. After saponification, the total antioxidant activities of apple peel, radish peel, radish flesh, and maize were significantly increased by 30.26%, 91.74%, 425.30%, and 242.88%, respectively. Saponification also improved the antioxidant activities of carotenoids in maize under six different antioxidant assays. The highest correlation was found between the total amount of carotenoids and oxygen radical absorbance capacity (R = 0.945), whereas the correlation coefficients among reducing power, 2,2-diphenyl-1-picrylhydrazyl, 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid), hydroxyl and superoxide radical scavenging activity, and total carotenoids' content were 0.935, 0.851, 0.872, 0.885, and 0.777, respectively, all showing significant correlations. The study demonstrates that saponification can increase the total carotenoid content and antioxidation for apple peel, radish peel, radish flesh, and maize. Moreover, carotenoids were significantly positively correlated with most in vitro antioxidant assays. This study provides a theoretical basis for improving the postharvest added value of fruits and vegetables and rationally utilizing their byproducts.