Changes in anthocyanin and antioxidant contents during maturation of Australian highbush blueberry (Vaccinium corymbosum L.) cultivars

The Australian blueberry industry is worth over $300 million, but there is limited information on factors influencing their chemical composition, particularly their ripeness and harvest stage. This pilot study aimed to investigate changes in the total monomeric anthocyanin content (TMAC) and total antioxidant capacity (TAC) of four common Australian blueberry cultivars at different times and stages of maturity. Four highbush blueberry cultivars (Denise, Blue Rose, Brigitta and Bluecrop) were analysed for TAC (using the cupric reducing antioxidant capacity assay) and TMAC (using the pH-differential method) at four time points and three maturity stages (unripe, moderately ripe and fully ripe). The TAC of most cultivars decreased with increasing ripeness (by 8-18%), although that of the Blue Rose cultivar increased markedly. However, the TAC of ripe fruit from this cultivar also fluctuated markedly throughout the harvest season (between 1168-2171 mg Trolox equivalents 100 g^-1). The TMAC increased sharply between the medium-ripe and fully ripe maturity stages, with the Blue Rose cultivar showing the highest TMAC values (211 mg 100 g^-1, compared to 107-143 mg 100 g^-1 for the remaining varieties). The TMAC of ripe fruit from this cultivar also rose steadily throughout the harvest season, in contrast to most other cultivars where the TMAC fell slightly over time. These results indicate that the levels of health-benefitting compounds in Australian-grown highbush blueberries may depend not only on the cultivar, but also upon the time of harvest.