Seasonal variation of the qualitative and quantitative composition of triterpenic compounds and antioxidant activity in vitro in the apple extracts of cultivars grown in Lithuania

Abstract

Apple (Malus domestica Borkh.) fruits are rich in phenolic glycosides, triterpenic acids and other biologically active compounds. The apples are widely used as food products due to their biologically active compounds that have specific biological effects. It is important to use high quality apples or their recycling products, so it is necessary to investigate the qualitative and quantitative composition of the bioactive compounds. The amount of triterpenic acids varies during different phenological stages of apple development and maturation. In order to determine in which phenological stage of apple growth the quantity of triterpenic acids was highest, high-performance liquid chromatography was applied. The highest total amounts of triterpenic compounds were detected at the beginning of the phenological stage of fruit development. The study showed that the highest amounts of triterpenic acids were detected at the beginning of the phenological stage of apple development, while as the apple matured, the amount of triterpenic acids decreased from 2.63 ± 0.26 mg/g to 1.6 ± 0.28 mg/g. In this study, we identified and quantified four triterpenic compounds, which by the quantitative composition of triterpenic acids could be arranged in the following ascending order: betulinic acid < corosolic acid < oleanolic acid < ursolic acid. In order to use herbal extracts for medical practice it is important to perform biological effects study in vitro and in vivo. Antioxidants with different mechanisms of action neutralize harmful reactive oxygen and nitrogen forms and enhance antioxidants protection systems. The antioxidant activity of apple extracts in vitro varied during different phenological stages of the fruit. The strongest antiradical and reductive activities were observed at the beginning of apple development. In order to determine the relationship between the antioxidant activity of the acetone extracts of apples assessed by DPPH, ABTS, CUPRAC and FRAP assays and the total amount of triterpenic acids in these extracts, a correlation analysis was carried out. The strongest positive correlation was observed between the amount of oleanolic acid and the antioxidant activity assessed by DPPH, ABTS and CUPRAC methods (respectively, r = 0.778, r = 0.784 and r = 0.720).