Processing-induced changes in total phenolics and procyanidins in clingstone peaches

Clingstone peaches contain a wide array of complex secondary plant metabolites and polyphenolics, and increasing evidence indicates that many of these components are important in human health. Oligomeric flavan-3-ol metabolites (procyanidins) are particularly interesting owing to their potent antioxidant activity and protective cardiovascular effects. To date, little information is available on how postharvest and processing conditions impact levels of phenolics and procyanidins in fruit. This research addresses the impact of lye peeling, freezing, storage temperature (4 and 30degreesC) and three different time-temperature sterilisation combinations on levels of total phenolics (TPs) in Ross clingstone peaches. Additionally, we describe the profile of procyanidin oligomers (monomers through heptamers) in clingstone and freestone peaches and demonstrate a dramatic decrease in procyanidins in thermally processed peaches. TP levels ranged between 316 and 397 mg/kg in peeled peaches and between 376 and 609 mg kg(-1) in unpeeled peaches. Cold storage at 4 degreesC for 14 days or freezing and storing at -12 degreesC for 3 months produced no loss in TPs. Peaches stored at 30 degreesC for 24h resulted in a 1.7-fold increase in TPs. Studies of TPs in peaches processed at temperatures of 213 degreesF for 40 min, 220 degreesF for 10 min and 230 degreesF for 2.4 min indicate that processing above 213 degreesF decreases levels of both TPs (up to 21%) and procyanidins (up to 100%). Processing at 213 degreesF for 40 min produced no significant loss in TPs. Furthermore, studies reveal that a 30-43% loss in phenolic levels occurs during the first 3 months in storage after canning. It is clear that both storage and thermal processing conditions profoundly impact the levels of polyphenolics in peaches. More interestingly, these studies indicate that peaches are a rich source of procyanidins, having profiles similar to those found in cocoa, apples, wine and tea.