Addition of fermented and unfermented grape skin in broilers’ diets: effect on digestion, growth performance, intestinal microbiota and oxidative stability of meat

Abstract

Grape skin is a source of polyphenols with antioxidant and antimicrobial properties. Little information is available regarding its application in animal feeding. The present study investigated the effect of inclusion of fermented (FS) and unfermented (UFS) grape skin at two different doses (30 g/kg, FS30 and UFS30, and 60 g/kg, FS60 and UFS60) and 200 mg/kg vitamin E (α-tocopheryl acetate) in a corn–soybean diet on growth performance, ileal protein digestibility, ileal and excreta total extractable polyphenols content and digestibility, intestinal microbiota and thigh meat oxidation in broiler chickens. Growth performance was depressed in chickens fed UFS and FS diets. A reduction in ileal protein digestibility was also observed in birds fed UFS, being this effect more pronounced in those fed 60 g/kg. The dietary inclusion of grape skin increased both ileal and excreta polyphenols contents, being higher in birds fed UFS than in those fed FS. Excreta moisture content increased in birds fed UFS and FS diets. No effect of dietary inclusion of grape skin was observed on ileal counts of lactic-acid bacteria and Clostridium, but UFS inclusion in the diet reduced ileal count of Escherichia coli as compared with FS dietary inclusion. After 7 days of refrigerated storage, values of thiobarbituric acid reactive substances (TBARS) were lower in chicken meat when grape skin was added in the diet at 60 g/kg instead of 30 g/kg, and meat from birds fed 60 g/kg of grape skin reached TBARS values similar to those of birds supplemented with vitamin E. In conclusion, high doses of grape skin polyphenols depressed growth performance and protein digestibility, and increased excreta moisture content. Unfermented grape skin contained more polyphenols than FS, and its inclusion in the diet led to higher ileal and excreta polyphenols contents and to a lower ileal count of E. coli. Furthermore, the antioxidant potential of the polyphenols present in grape skin was observed after 7 days of meat storage, with the dose of 60 g/kg of grape skin being as effective as vitamin E supplementation in maintaining oxidative stability of meat.

Feeding Broiler Chickens with Grape Seed and Skin Meals to Enhance α- and γ-Tocopherol Content and Meat Oxidative Stability

“…Besides, no significant difference arose between these two dietary treatments for MDA values. These results are consistent with previous findings of our laboratory [ 10 , 23 , 24 ] since dietary doses of grape polyphenols ranging from 1.17 to 2.92 g/kg also reduced MDA concentration in chicken stored meat, with no significant difference with respect to the dietary supplementation with vitamin E. Interestingly, despite in the present study grape byproducts treatments contained a similar concentration of grape polyphenols, the meat lipid oxidation was only mitigated with the dietary combination of GS and GK, designed to meet grape pomace composition, whereas the individual inclusion of GS or GK in the diet did not reduce MDA values. As reported before, the combination of GS and GK resulted in the highest content of γ-tocopherol when compared to the other groups.…”

“…In the excreta, TEP content was also higher for birds fed grape byproducts. These results agree with previous findings also reporting the effect of feeding grape pomace, grape seed extract or grape skin on grape polyphenol digestibility [ 10 , 21 , 23 , 24 , 45 ]. Additionally, in the present study we also observed differences in the digestibility of polyphenols when comparing GS and GK treatments.…”

“…With a dietary concentration of total extractable grape polyphenols (2.34 g/kg) similar to that of the grape byproduct diets of the present study, a previous dietary inclusion of grape pomace at 10% [ 10 ] had not caused any negative effect on chicken performance. Nevertheless, in another study [ 24 ] a higher dietary concentration of grape polyphenols (4.27 g/kg), obtained with an inclusion of unfermented grape skins at 6%, impaired both chicken growth rate and feed conversion ratio. Regarding grape seed extracts, a detrimental effect on growth performance was observed from a dietary grape polyphenol dose of 1.48 g/kg [ 40 , 41 ].…”

“…For instance, several publications [ 43 , 44 ] have highlighted the detrimental effect of a high dietary inclusion of tannin-rich ingredients such as sorghum and faba bean in poultry diets. In previous research works conducted by our team in which the dietary inclusion of GK [ 24 ] or that of other grape byproducts like grape seed extract [ 40 ] or grape pomace [ 21 ] made the diets contain a high concentration of non-extractable polyphenols (from 0.740 to 2.28 g/kg), ileal digestibility of protein of broiler chickens was decreased in a similar extent (from 2.37 to 6.97%) to that observed in the current work (4.75%).…”

“…The effectiveness of grape byproducts depends not only on the total polyphenol content but also on the nature of the polyphenolic compounds incorporated to the diet. In this sense, different antioxidant potential has been observed after feeding broilers with grape skins and grape seeds [ 11 , 24 ]. In general, grape seeds contain higher amounts of phenolic compounds than grape skins.…”