Effect of dietary polyphenol-rich grape by-products on growth performance, some physiological parameters, meat and meat products quality in chickens

Five studies were designed to investigate the potential use grape pomace (GP), grape seeds (GS) and grape skins (SS), the major residues from wine-making industry and a good sources of polyphenols, as a cheaper but functionally equivalent product, with antioxidant activity, that could partially replace vitamin E in broiler chickens diet and be able to improve poultry performance and welfare, besides to warrant high-quality, safe and functional meat products. The studies were carried out at the Department of Metabolism and Nutrition and Department of Products of the Institute of Food Science, Technology and Nutrition (ICTAN-CSIC) of Madrid. The first studies assessed the effect of dietary GS (15 and 30 g/kg), SS (110 g/kg) and GP (37.5 g/kg) and α-tocopheryl acetate (200 mg/kg) inclusion on performance, ileal and excreta content of total polyphenols and tannins, ileal digestibility of protein and ileal and excreta polyphenols digestibility in one hundred and eighty 21-day-old broiler chickens. In addition, plasma and meat α-tocopherol concentration and meat lipid oxidation during refrigerated storage (at 1d and 7d) were evaluated. SS diet reduced daily weight gain (P<0.01) and feed conversion ratio (P<0.001). α-T diet had no effect on ileal and excreta polyphenols content while significantly higher values were observed in GS, SS and GP groups, compared to the control birds. GS, SS and GP diets increased ileal tannins content, with no effect on excreta content. Protein digestibility significantly decreased in birds fed SS diets. Ileal polyphenols digestibility statistically increased in GS, SS and GP groups, while no differences were observed for excreta digestibility. Plasma α-tocopherol increased significantly in birds fed α-T, SS and GP diets, while γ- tocopherol only in birds fed GP diets. Meat α and γ- tocopherol levels were statistically higher in birds fed α-T diet at 1 and 7 days of storage, compared to the other groups. GP and α-T improved the stability of meat to lipid oxidation by reducing MDA values after 1 day and 7 days of storage. The second study aimed to investigate the effect of dietary fermented (FS) and unfermented (UFS) grape skin at different doses (30 g/Kg, FS30 and UFS30, and 60 g/kg, FS60 and UFS60) and of α-tocopheryl acetate (200 mg/kg) in one hundred and fifty 21-day-old broilers. The same parameters of the previous experiment and intestinal microflora were assessed, except for plasma and meat vitamin E concentrations. FS60 and UFS60 negatively affected growth performance and UFS60 significantly decreased protein digestibility. UFS increased ileal and excreta polyphenols content; whereas ileal and excreta tannins content increased in all experimental groups. UFS30 diet statistically increased ileal polyphenols digestibility, while both FS and UFS diets significantly increased the excreta digestibility with higher values in birds fed UFS in comparison to those fed FS. Intestinal microflora was not affected by dietary treatment. Dietary FS and UFS grape skin were not effective as vitamin E in delaying meat lipid oxidation. The third study investigated the effect of dietary GS (40 g/kg), SS (40 g/kg) and GP (40 g/kg), different combination of GS and SS (20 g/kg GS and 20 g/kg SS; 30 g/kg GS and 10 g/kg SS; 10 g/kg GS and 30 g/kg SS) and α-tocopheryl acetate (200 mg/kg) on the same parameters evaluated in the first experiment, in addition to plasma reactive oxygen metabolites (ROMs). Performance parameters were not affected by dietary treatments. GS, SS and GP diets increased intestinal polyphenols and tannins content. GS and SS combinations decreased ileal proteins digestibility and had no effect on polyphenols digestibility, unlike the other groups. Excreta polyphenols digestibility was statistically higher in all treated groups, compared to the control and vitamin E groups. Plasma α-tocopherol was higher in birds fed α-T, SS and GP, compared to the control ones. GS, SS and GP diets increased plasma ROMs values and meat oxidative stability was improved only in the α-T group. The fourth study was a continuation of the previous one (third study) and investigated the effect of dietary GS (40 g/kg), SS (40 g/kg) GP (40 g/ kg) and α-tocopheryl acetate (200 mg/kg) on lipid peroxidation levels (TBARS), antimicrobial capacity and physico-chemical characteristic of chicken breast meat patties during refrigerate storage (4°C) during 0, 3, 6 and 9 days. In general, the compositions of the raw meat was similar among groups. The lowest levels of polyphenols were observed in the PE (Control+vitamin E), PSS (Control+Grape skin 4%) and PGP (Control+Grape pomace 4%) patties. Polyphenols levels statistically increased during chilled storage in all samples until day 6. Increased polyphenols content was also observed in cooked patties. PE and PSS patties showed the lowest levels of LAB (lactic acid bacteria). Lower significant TBARS values were detected in PE, PSS and PGP patties. No clear effect was observed for the color and textural characteristics and the products were acceptable for the panelists. The last experiment investigated the effect of GS (2%) and SS (2%) direct addition on physico-chemical and sensorial properties of chicken thigh patties during refrigerated storage (4°C). GS and SS addition decreased pH values and reduced lightness, yellowness and redness values, compared with the control sample. Moreover, reduced TBARS levels were observed in relation with the higher total phenolic content also found in cooked patties. The GS and SS patties acceptability was not negatively affected. The use of grape by-products in the development of meat products could have positive effects in the human body and open interesting possibilities in the development of more healthy foods.