Antioxidant and lipid peroxidation inhibitory potentials of the unripe and ripe of Citrus mitis Blanco pulps and peels from south Thailand

Abstract

Citrus mitis Blanco fruit contains high levels of vitamin C, phenolics, and flavonoids, which exhibit a wide range of beneficial biological effects. The current research aimed to evaluate the levels of vitamin C, flavonoid, total phenolic contents, and antioxidant properties, as well as the inhibitory effects on lipid peroxidation, in both unripe and ripe fruit tissues (pulps and peels) of C. mitis Blanco. The fruit tissues were obtained from the Hat Som Paen subdistrict in Ranong province, located in the southern region of Thailand. Fruit tissues were extracted using maceration with 80% ethanol and water solvents. Vitamin C quantification was achieved using the 2,6-dichloroindophenol titrimetric method. Total flavonoid content was determined using the aluminium chloride colorimetric method, while total phenolic content was assessed using the Folin-Ciocalteu procedure. Additionally, ABTS and DPPH assays were used to assess the antioxidant properties. The measurement of lipid peroxidation inhibitory activity was carried out using the thiobarbituric acid reactive substances (TBARS) assay. The findings indicated that the water extract exhibited higher levels of vitamin C compared to the 80% ethanolic extract. In contrast, the 80% ethanolic extract revealed greater amounts of total phenolic and flavonoid contents than the water extract. The water extract of unripe pulp exhibited the highest vitamin C content among all the extracts, reaching 36.74 mg/100 g fresh weight (FW). The 80% ethanolic extract of unripe peel demonstrated the highest level of total phenolic content (35.67 mg gallic acid equivalent (GAE)/g extract), while ripe peel exhibited the highest total flavonoid content (16.88 mg catechin equivalent (CE)/g extract). Both unripe and ripe fruit extracts exhibited antioxidant and lipid peroxidation inhibitory activities. The 80% ethanolic extract from unripe peel demonstrated the most significant antioxidant activities against DPPH (6.31 mg trolox equivalent (TE)/g extract) and ABTS (7.69 mg TE/g extract). Moreover, the 80% ethanolic extract of unripe peel showed the highest level of inhibitory activity against lipid peroxidation, with a value of 74.62%. These results underscore the potential bioactivities of unripe and ripe C. mitis Blanco fruit tissues, which can offer nutritional and health benefits. These properties make them particularly valuable in the food industry due to their excellent antioxidant and lipid peroxidation inhibitory characteristics.