Total Phenolic Contents and Antioxidant Variations in Raw and Cooked Dried Fruit of Xylopia aethiopica

Abstract

Most plant products undergo one or more different thermal processes before consumption despite the claims that cooking fruits and vegetables could have detrimental effects on the beneficial properties of the plants. This work investigated the changes in antioxidant status occurring in dried fruit of Xylopia aethiopica subjected to cooking at different temperatures. The analyses were performed on both raw and boiled samples to assess the total phenolic contents (TPCs) and the antioxidant potential through reduction of ferric chloride salt and bleaching of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. The data obtained were subjected to analysis of variance and pairwise comparisons by Tukey-Kramer test at p < 0.05. There was a significant heat-trend difference between the phenolic contents of the samples at the selected temperatures with the highest TPC recorded at 70°C. Similarly, the ferric reducing potentials of the cooked samples were significantly different (p <0.05) from the raw. However, uncooked samples had significantly (p <0.05) higher percentage of DPPH radical scavenging activity compared to cooked samples. The overall effect of cooking the dried fruit of X. aethiopica was due to an elevation in total phenolics concentrations and reducing potentials of the aqueous infusions. However, boiling decreases the DPPH radical scavenging ability of the samples. Therefore, this study suggests an optimum cooking temperature of 70°C which could result in the highest retention of phenolic contents and ferric reducing potentials in the fruit of X. aethiopica and lowest appropriate temperature to conserve its intrinsic radical-scavenging activity in order to assure a higher quality food for the maintenance of human health. Moreover, losses in the phenolic contents and antioxidant potential should be considered when the procedural temperature during processing is unalterable.