Secondary phenolic metabolites play an important role in plant defense mechanisms, and increasing evidence indicates that many are important in human health. To date, few studies have investigated the impact of various agricultural practices on levels of secondary plant metabolites. To address this issue, the total phenolic (TP) content of marionberries, strawberries, and corn grown by sustainable, organic, or conventional cultural practices were measured. Additionally, the effects of three common postharvest processing treatments (freezing, freeze-drying, and air-drying) on the TP content of these agricultural products were also investigated. Statistically higher levels of TPs were consistently found in organically and sustainably grown foods as compared to those produced by conventional agricultural practices. In all samples, freeze-drying preserved higher levels of TPs in comparison with air-drying.

Effects of arbuscular mycorrhzal (AM) fungi on plant growth and nutrition are well-known, but their effects on the wider soil biota are less clear. This is in part due to difficulties with establishing appropriate non-mycorrhizal controls in the field. Here we present results of a field experiment using a new approach to overcome this problem. A previously well-characterized mycorrhizal defective tomato mutant (rmc) and its mycorrhizal wildtype progenitor (76R MYC+) were grown at an organic fresh market tomato farm (Yolo County, CA). At the time of planting, root in-growth cores amended with different levels of N and P, were installed between experimental plants to study localized effects of mycorrhizal and non-mycorrhizal tomato roots on soil ecology. Whilst fruit yield and vegetative production of the two genotypes were very similar at harvest, there were large positive effects of colonization of roots by AM fungi on plant nutrient contents, especially P and Zn. The presence of roots colonized by AM fungi also resulted in improved aggregate stability by increasing the fraction of small macroaggregates, but only when N was added. Effects on the wider soil community including nematodes, fungal biomass as indicated by ergosterol, microbial biomass C, and phospholipid fatty acid (PLFA) profiles were less pronounced. Taken together, these data show that AM fungi provide important ecosystem functions in terms of plant nutrition and aggregate stability, but that a change in this one functional group had only a small effect on the wider soil biota. This indicates a high degree of stability in soil communities of this organic farm.

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 30°C) 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 À1 in peeled peaches and between 376 and 609 mg kg À1 in unpeeled peaches. Cold storage at 4°C for 14 days or freezing and storing at À12°C for 3 months produced no loss in TPs. Peaches stored at 30°C for 24 h resulted in a 1.7-fold increase in TPs. Studies of TPs in peaches processed at temperatures of 213°F for 40 min, 220°F for 10 min and 230°F for 2.4 min indicate that processing above 213°F decreases levels of both TPs (up to 21%) and procyanidins (up to 100%). Processing at 213°F 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.