Fruit Growth and Bioactive Development in Pomegranate Fruit

Recent research has shown that pomegranate juice has many positive health benefits such as reducing blood pressure and low density lipoprotein (LDL) oxidation. These activities are attributed to the high levels of antioxidant activity and the high polyphenol content. Pomegranates are generally harvested when fully ripe but is this the optimum harvest time in terms of the concentrations of polyphenols and antioxidants that are important parameters for some of the new pomegranate juice products? Experiments were carried out in a commercial orchard at Condobolin, the north-west in New South Wales, Australia from November 2007 to April 2009 using already established pomegranate cultivar 'Wonderful'. Fruit development, juice content, phenolic content (gallic acid equivalents) and antioxidant capacity (Ferric Reducing Ability of Plasma: FRAP) was measured 8 times during fruit development from flowering to harvest at 23 weeks after flowering. Total phenolic content of juice from whole pomegranates peaked 10 weeks after fruit set at 6000 mg L-1, and by week 23 had declined by 90% to 588 mg L-1. Total antioxidants followed a similar pattern, peaking at 6 weeks after fruit set at 42 mmol Fe2+ L-1 and declined by 57% to 18 mmol Fe2+ L-1 by week 23. Fruit juice volume increased during fruit development from 21 ml fruit(-1) six weeks after flowering to 274 ml fruit(-1) at week 23. The yield of bioactives per fruit is a function of the increase in juice volume per fruit as fruit matures and is offset by the decline in the concentrations of phenolics and FRAP. The highest yield of phenolics occurs when fruit is harvested at 10 weeks after flowering 310 mg fruit(-1), with a secondary peak of 224 mg fruit-1 20 weeks after flowering. The maximum yield of antioxidants (FRAP) 4.9 mmol Fe2+ fruit(-1) per occurs 23 weeks after flowering, and these results affect optimum harvest time depending on whether the target so to maximize yield of fruit, juice, antioxidant or phenolics.