The antioxidant capacity of fresh fruit and vegetables does not decrease during storage, and the polyphenol content even increases, suggests new research.
According to Belgian researchers from the University of Liege, storing selected fruit and vegetables at room temperature or under refrigeration did not result in any loss of phenolic compounds, ascorbic acid or flavonols - a trio of chemical classes associated with antioxidant content.
The health benefits of consuming a diet rich in fruit and vegetables are backed up by a multitude of studies, with the Five-a-day message now well engrained in the consumer's awareness. However, applying this does not seem to be filtering down into everyday life, with recent studies indicating that the average consumption of people in developed countries is three portions a day.
"The new and interesting result of this study was the relative stability of the antioxidant capacity in most fruits and vegetables during storage," wrote lead author Claire Kevers in the Journal of Agricultural and Food Chemistry.
"In general, fruits and vegetables visually spoil before any significant antioxidant capacity loss occurs. Nevertheless, it could be stressed that, in general, polyphenolic content increased."
Kevers and co-workers obtained various fruit and vegetables from Belgian market and, after measuring its initial antioxidant content, stored the produce at room temperature or refrigerated them (four degrees Celsius). The antioxidant levels of the fruit and vegetables were measured at various times until the produce visually spoiled.
The antioxidant capacities were evaluated using three measure: the total phenolic content; the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay; and the oxygen radical absorbance capacity (ORAC).
According to the researchers, black grapes contained the highest phenolic levels (582 mg of CAE per 100 g), followed by bananas, green grape, lemon, strawberry, and plum. Red and yellow peppers topped the phenolic ranking for vegetables with 296 and 284 mg of CAE per 100 g, respectively.
Similar results were observed in terms of radical scavenging activity, with grapes, bananas, and lemon leading the way with DPPH measures, while the red, yellow and green peppers had DPPH values six times that of the other vegetables.
The ORAC assay ranked strawberry, cherry, plum, and black grape as the top four for the fruit, while peppers again ranked high for the vegetables. These were closely followed by spinach, broccoli, and garlic.
After storage, Kevers and co-workers report that the DPPH values were, in general, relatively stable. However, the phenolic content - particularly the flavonoid content - did increase during storage.
"The preservation of fruit phenolic content has a great impact on the quality of fruits because of the contribution of phenols not only in enzymatic browning reactions but also on nutritional value of the product, as antioxidant capacity," wrote the researchers.
"The results of this study indicated that in most fruits and vegetables the storage did not affect negatively the antioxidant capacity. In some cases an increase of the antioxidant capacity was observed in the days following their purchase," they stated.
"A validation of the antioxidant capacity approach is essential for investigating the role of food antioxidants in human health," they added.
A report from the European Union showed that global fruit and vegetable production was over 1,230 million tonnes in 2001-2002, worth over $50bn (€41,000m). Asia produced 61 per cent, with Europe and North/Central America both producing nine per cent.
Source: Journal of Agricultural and Food Chemistry
Published on-line ahead of print. ASAP Article, doi: 10.1021/jf071736j
"Evolution of Antioxidant Capacity during Storage of Selected Fruits and Vegetables"
Authors: Claire Kevers, M. Falkowski, J. Tabart, J.-O. Defraigne, J. Dommes, J. Pincemail