Effect of Mature Stages on Phenolic Contents, Antioxidant Activities and Mineral Distribution in Different Parts of Kei Apple Fruit

Abstract

This study aimed to evaluate the concentrations of the heavy metals, macro and micro-elements as well as the distribution of phenolic constituents in different parts of half-ripe and full-ripe kei apple fruits. For mineral analysis, fruit samples were digested and analyzed using inductively coupled plasma optical emission spectrometry (ICPOES). The colorimetric determination of total polyphenolic contents (TPs) and the antioxidant capacity using DPPH and total antioxidant capacity (TAC) assays were done using aqueous alcoholic extracts. Also, the phenolic profiles were identified and quantified using high performance liquid chromatography (HPLC). The results showed that the highest antioxidant activity using DPPH and TAC and total phenolic content were detected in the pulp of full-mature fruits and its values were 2.03 mg GAE/g d.w, 22.61 mg AAE/g d.w and 26.24 mg GAE/g d.w, respectively. Average of mineral concentrations in dried samples (in μg/g), were ranged between: 6,164.99 to 18,339.61 (K); 2,538.06 to 3,488.92 (Ca); 749.26 to 2,110.12 (Mg); 82.13 to 733.36 (Fe); 22.74 to 58.02 (Zn); 6.43 to 11.85 (Mn); 10.17 to 20.02 (Cu); 1.86 to 8.73 (Ni) and much lower concentrations of Co, Pb and Cd. The key phenolic constituents of the fruit harvested in different times were 4-hydroxy benzoic acid, chlorogenic acid and catechol. Overall, harvesting of kei apple fruit in the first week of June indicates the full maturity of the fruit with characteristic higher phenolics, antioxidant capacity without any deterioration in most of elemental minerals.