Antioxidant and physicochemical properties of <i>Chrysophyllum albidum</i> fruit at different ripening stages

Abstract

Chrysophyllum albidum (African Star Apple) fruit is an indigenous African fruit. The African Star Apple plant popularly referred to as the “alasa” tree grows widely in tropical Africa. Ripening influences biochemical processes and subsequently affects the nutritional and bioactive characteristics of the fruits. This study sampled Chrysophyllum albidum fruit of three maturity stages and determined the colour, proximate, total phenol and antioxidant characteristics of the fruits. Spectrophotometric methods were used in the determination of total antioxidant activity using 1,1-diphenyl- 2-picrylhydrazyl (DPPH) radical scavenging activity, 2,2-azinobis,3- ethylbenzothiazoline-6-sulfonic acid (ABTS) and Ferric reducing ability of plasma (FRAP) assay. Significant differences (p<0.05) were observed in the colour of the fruit across all the ripening stages. The ripe stage of the fruit recorded the highest extent of lightness among all the other ripening stages. Both the ripe and over-ripe fruits appeared reddish in colour with the ripe fruit demonstrating a higher red intensity than the over-ripe fruit. The calculated metric chroma of the Chrysophyllum albidum fruits were in the range of 2.33-21.67 for the three ripening stages. Hue angle values recorded were in the range 46.46-92.00. Browning and colour indices for fruits of all the stages of development were of range 6.40-80.30 and -14.30-16.96, respectively. Proximate analysis of the three fruit categories showed that the unripe fruits had higher carbohydrate (69.27 %), crude protein (8.17 %), and crude fat (7.99 %) content relative to fruits which were ripe and over-ripe. The over-ripe fruit had higher crude fibre (7.36 %) and ash (3.86 %) content. Total phenolic content for the unripe fruit (20μg GAE/mg) was also higher than fruits of the other ripening stages. The antioxidant ability of the Chrysophyllum albidum fruit showed that the unripe stage recorded the highest DPPH (29.24 %) and ABTS (99.09 %) radical scavenging activity. The ferric reducing antioxidant potential of the fruit at different ripening stages was significantly different (p<0.05) with the unripe stage recording the highest potential. The unripe fruits demonstrated higher proximate and antioxidant composition than the ripe and over-ripe fruits. Extracts from the unripe fruit can serve as useful nutraceuticals in functional food formulations.