RECOVERY OF PHYTOCHEMICAL RICH FRACTIONS FROM WINEMAKING BYPRODUCTS FOR NOVEL FOOD APPLICATIONS

The food industry is facing the significant challenge of developing new ingredients and foods addressing prevention of the major chronic diseases, while optimizing processing technologies in order to achieve a sustainable use of natural resources. Grape pomace, the byproduct of winemaking, is available on a large scale and is comprised of various compounds associated with potential health benefits. In this context, the overall PhD project aimed at developing an integrated strategy for recovery and reuse of value added fractions of winemaking byproducts in the food system. Grape pomace samples, differing for the varieties and winemaking conditions were collected from winemaking processes and evaluated for valuable components, i.e, dietary fibre, total phenolics, soluble and insoluble proanthocyanidins (n-butanol/HCl assay), individual phenolic compouns (UPLC-DAD-MS), tocopherol and tocotrienol contents (HPLC with fluorimetric detection). This led to the design of a comprehensive recovery plan, bringing about the overall value of winemaking byproducts. The aim of targeting a specific health functionality by grape phenolics was tackled in chapter 1, focused on their protective effects on hyperglyacemia induced damage. In the current scenario, prevention of diabetes complications is of utmost importance due to an upsurge in the prevalence of this disease among the world population (with an estimation of 300 million cases that could be registered by 2030). In vivo study has shown that phenolics can prevent the leading cause of hyperglycemia damage, i.e., non-enzymatic protein glycaton, most likely via radical scavenging, metal chelation and carbonyl trapping. However to target this effect, there is a need for phenolic fractions with high concentration and efficiency. An in vitro model system using fructose as glycating agent and bovine serum albumin as target was set up. The protective ability of grape skin phenolics was evaluated with both a novel methodological approach by 2D-SDS/IEF-PAGE and quantification of the formation of advanced glycation end-products by fluorescence measurements. Structural modifications of BSA upon glycation, as evidenced by changes in pI and Mr were found to be inhibited by the grape skin extracts. The antiglycation activity ranking was: quercetin-3-O-glucoside > malvidin-3-O-glucoside > catechin > procyanidin A2 >> aminoguanidine (reference drug). Despite variability in phenolic content (in the range 4.6-53.6 g gallic acid equivalents (GAE)/kg) and composition among grape skin extracts, upon equalization of the phenolic content, similar antiglycation properties were observed. Grape skins (I50 in the range 9.2-20 µg GAE/mL) were more efficient than the commercial nutraceutical products Leucoselect® (I50 38 µg GAE/mL) and Pycnogenol® (I50 34 µg GAE/mL) and hence could provide cost-effective antiglycation agents, to be used either as food ingredients or as nutraceutical preparations. The task of designing new foods by the incorporation of grape skins, which can deliver both dietary fibers and phenolics, was examined in chapter 2. Grape skins have been proposed as ingredients for “solid” or “gel-like” foods, but knowledge on their possible application in complex food fluids that could represent low caloric vehicle for value added ingredients is lacking. Hence, a tomato puree added with grape skins was studied as a model application and a production process was designed to increase potential health benefit of this product with maximum consumers’ liking. To optimize grape skin ingredient incorporation in tomato puree, six formulations (3% dietary fibre and ~ 0.7% proanthocyanidins) varying in the particle size (assessed by a laser granulometer) were considered in parallel. Stabilization was performed by either an intensive autoclave treatment or an optimized microwave treatment achieving six decimal reductions of the target microorganism (Alicylobacillus acidoterrestris). Upon processing, major changes in the fortified purees were both decrease in proanthocyanidin solubility (by ~ 40%, probably due to interaction with tomato protein) and decrease in flavonol glycosides with parallel increase of their aglycones. However, phenolic contents, reducing capacity and antiglycation activity remained ~ 3 times higher in all the fortified purees than in the controls. These chemical parameters were related to particle size distribution, since with decreasing surface-weighed mean diameter, d(3,2), proanthocyanidin solubility increased. The addition of grape skins played a major role on the color (measured by Hunter colorimeter), storage (G’) and loss (G’’) moduli, complex viscosity (studied by means of dynamic oscillatory measurements) and Bostwick consistency of the formulations. A sensory test based on consumers’ preference disclosed that the formulation having the maximum appreciation was that incorporated with the smallest particle sizes. Liking ratings were found to be inversely correlated to the volume-weighted mean diameter, d(4,3) values. The overall results obtained from this methodological approach represent a basis for the optimization of fibrous byproducts incorporation into complex food fluids. Besides use of grape skins as source of antiglycation and fortifying agents, utilization of grape seeds which forms a major part of the pomace is of importance in the recovery strategy. Chapter 3 focused on assessment of supercritical-CO2 (SC-CO2) extraction for the recovery of oil, as a “green technology” alternative to n-hexane extraction and mechanical extraction. Extraction by SC-CO2 can be a sustainable technology, if the process is carried out at optimum operating conditions ensuring high yield and in a sufficient extractor volume. The breakeven point, which makes the process economically sustainable, is also linked to the quality of the oil obtained. Besides oil, the defatted seeds rich in phenolics were also considered as a relevant co-product of this process. Hence, grape seed phenolics were studied as inhibitors of starch digestion enzymes, which is the first relevant step to control blood glucose level. Extraction by SC-CO2 provided the same oil yield as that of n-hexane extraction (10.1-16.6 g oil/100g seeds). 1H-NMR spectra showed that diacylglycerols and oxidized lipids were present only in trace amounts. The levels of tocols were in the range: 355-559 mg/kg higher than those of the oils obtained by n-hexane extraction and similar to those of oils obtained by mechanical extraction. Tocotrienols, which possess high antioxidant and antiproliferative properties were the prominent compounds present. In the defatted grape seeds, levels of phenolics one order of magnitude higher than those of the grape skins were observed (49-277 g GAE/kg). The anthocyanin rich grape seed extracts showed the highest inhibitory effectiveness towards α-glucosidase (I50 47 µg GAE/mL ~ half than that of the drug acarbose). Inhibitory effectiveness towards α-amylase activity was similar among grape varieties, with I50 values comparable to that of acarbose and correlated to proanthocyanidin contents. The overall results could pave the way for recovery and value-addition of winemaking byproducts for food and nutraceutical uses, including grape skins as a source of antiglycation agents or as dietary antioxidant fibre, grape seeds as a source of tocol rich oil, defatted grape seeds as a source of phenolics.