Resveratrol (3,4',5-trihydroxy-trans-stilbene) is a polyphenolic compound accounting to the stilbene class. Most stilbenes in plants act as antifungal phytoalexins, compounds that are usually synthesized only in response to infection or injury. Resveratrol has been detected in trees, in a few flowering plants, in peanuts, and in grapevines. The major dietary sources of resveratrol include grapes, wine, peanuts, and peanut products. Numerous in vitro studies describe different biological effects of resveratrol. The major impacts are the antioxidative, anti-inflammatory, and estrogenic effects as well as anticancer and chemopreventive activities. In order to reveal information on absorption, metabolism, and the consequent bioavailability of resveratrol, different research approaches were performed, including in vitro, ex vivo, and in vivo models, all of which are considered in this review. Summarizing the data, resveratrol is absorbed and metabolized. Around 75% of this polyphenol are excreted via feces and urine. The oral bioavailability of resveratrol is almost zero due to rapid and extensive metabolism and the consequent formation of various metabolites as resveratrol glucuronides and resveratrol sulfates. The potential biologic activity of resveratrol conjugates should be considered in future investigations.

The manuscript reviews beneficial aspects of food processing with main focus on cooking/heat treatment, including other food-processing techniques (e.g. fermentation). Benefits of thermal processing include inactivation of food-borne pathogens, natural toxins or other detrimental constituents, prolongation of shelf-life, improved digestibility and bioavailability of nutrients, improved palatability, taste, texture and flavour and enhanced functional properties, including augmented antioxidants and other defense reactivity or increased antimicrobial effectiveness. Thermal processing can bring some unintentional undesired consequences, such as losses of certain nutrients, formation of toxic compounds (acrylamide, furan or acrolein), or of compounds with negative effects on flavour perception, texture or colour. Heat treatment of foods needs to be optimized in order to promote beneficial effects and to counteract, to the best possible, undesired effects. This may be achieved more effectively/sustainably by consistent fine-tuning of technological processes rather than within ordinary household cooking conditions. The most important identified points for further study are information on processed foods to be considered in epidemiological work, databases should be built to estimate the intake of compounds from processed foods, translation of in-vitro results to in-vivo relevance for human health should be worked on, thermal and non-thermal processes should be optimized by application of kinetic principles.

A diet that is based on high-heat-treated foods increases markers associated with an enhanced risk of type 2 diabetes and cardiovascular diseases in healthy people. Replacing high-heat-treatment techniques by mild cooking techniques may help to positively modulate biomarkers associated with an increased risk of diabetes mellitus and cardiovascular diseases.

The purpose of this study was to investigate the implications of selected chemopreventive parameters and metabolic conversion of resveratrol in vivo. In two 8-week long feeding experiments with rats, a low-resveratrol diet containing 50 mg resveratrol per kg body weight (bw) and day and a high-resveratrol diet with 300 mg per kg bw and day were administered. For chemopreventive evaluation selected phase I and phase II enzymes of the biotransformation system, the total antioxidant activity, and the vitamin E status of the animals were determined. The level of resveratrol and its metabolites in the feces, urine, plasma, liver, and kidneys was identified and quantitated by high-performance liquid chromatography-diode array detection (HPLC-DAD) using synthesized resveratrol conjugate standards. Feeding of different dosages of resveratrol revealed no effect on the different chemopreventive parameters, except for the total antioxidant activity, which was elevated in plasma by 19% after feeding 50 mg resveratrol per kg bw and day. The formation of trans-resveratrol-3-sulfate, trans-resveratrol-4'-sulfate, trans-resveratrol-3,5-disulfate, trans-resveratrol-3,4'-disulfate, trans-resveratrol-3,4',5-trisulfate, trans-resveratrol-3-O-beta-D-glucuronide, and resveratrol aglycone was detected by HPLC analysis, depending on the biological material. Total resveratrol recovery in urine and feces of rats fed on 50 mg resveratrol per kg bw and day was 15% and 13%, respectively. For rats fed the higher dosage of 300 mg resveratrol per kg bw and day recovery was 54% and 17%, respectively. This is the first study performed with synthesized standards of relevant resveratrol conjugates. The lack of effect on the chemopreventive parameters is probably due to the formation of various resveratrol conjugates reducing its bioavailability in the rat.

When the COST Action 919 started to investigate the role of melanoidins in food and health in 1999, the chemical structures of dietary melanoidins were poorly defined and hardly anything was known about structure-specific health effects of this chemical class. In addition, the degradation of melanoidins in the gut and their absorption and function or that of any of their degradation products had not yet been reported. In the past five years, results from in vitro studies demonstrated that at least some of the dietary melanoidins are degraded by intestinal microorganisms, possibly influencing their growth rate. The absorption and excretion rates of individual Maillard reaction compounds and melanoidin structures have been investigated in animal studies. These studies show that at least 30% of the ingested dose of low-molecular-weight compounds are absorbed. Structure-specific health-promoting effects of newly identified compounds have been described by means of their antioxidant and chemopreventive activity in cell culture investigations as well as in animal feeding studies and human trials. Harmful effects of dietary melanoidins have been investigated in the context of their ability to promote glycation reactions in vivo, which are involved in the progression of several diseases, such as diabetes mellitus, cardiovascular complications, and Alzheimer's disease. Toxicological studies were performed showing that melanoidin structures can not be classified as potent dietary mutagens or genotoxins. Thus, substantial knowledge on the health effects of melanoidins has been gained within COST Action 919. But still, further studies are needed to distinguish between chemically identified harmful and health-beneficial melanoidins.