Stability of the total antioxidant capacity and total polyphenol content of 23 commercially available vegetable juices before and after in vitro digestion measured by FRAP, DPPH, ABTS and Folin–Ciocalteu methods

Vegetables are known to contain a wide variety of antioxidants which may provide protection against the development of a number of disease states. Recently there has been a large increase in the number of vegetable juices which have become commercially available. The objective of the present study was to analyse the total antioxidant capacity of 23 commercially available vegetable juices [via Ferric Reducing Antioxidant Power (FRAP), 2, 2-diphenyl-1-picrylhydrazyl (DPPH), 2, 2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+) and Folin–Ciocalteu Reagent (FCR) for total polyphenols] and to determine the stability of the antioxidant capacity following an in vitro digestion procedure using the same methods. All 23 juices were significant sources of antioxidants both in terms of total antioxidant capacity and total polyphenols, although results varied considerably between the juices [1369–9500 μmol/L (FRAP), 57.8–100% inhibition of DPPH, 10.9–90.7% inhibition of ABTS+ and 449–3025 μg ferulic acid equivalents/mL for FCR]. Beetroot juice displayed the highest level of total antioxidants and total polyphenols compared to the other juices which were analysed (tomato, carrot, mixed vegetable, mixed fruit and vegetable). The antioxidant capacity of the juices remained high throughout the in vitro digestion.