Storage temperature and time changes of phenolic compounds and antioxidant properties of Natal plum (Carissa macrocarpa)

Abstract

Natal plum is a South African indigenous fruit. Natal plum were stored at 2, 4, 10 and 25 °C (control) temperatures up to 12 days, and fruit were evaluated at 4 day intervals for changes in quality and phenolic compounds. The results showed that 2 °C significantly reduced the weight loss and total colour difference while maintaining the quality attributes. Supervised Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) and the ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometer and chemometric approach separated the fruit stored at low temperature from those stored at 25 °C, and a unique marker compound quinic acid was identified with the low temperature fruit. Similarly, cyanidin (aglycone) separated the fruit stored at 2 °C from those stored at other lower temperatures (4, and 10 °C). Thus, it can be proposed that the temperature stress at 2 °C had favoured the cold-induced accumulation of cyanidin derivatives (anthocyanins) to provide chilling tolerance. The bioactive compounds (cyanidin-3-O-pyranoside (10.4 mg kg−1), cyanidin-3-O-glucoside (54 mg kg−1), and quercetin 3-O-rhamnosyl glucoside (57 mg kg−1)] and the antioxidant activity (FRAP assay) were significantly higher in fruit stored at 2 °C for 12 days. Thus, storage of Natal plum at 2 °C for 12 days can be recommended if the fruit are used as a functional ingredient.