Abstract

Grape pomace represents the main by-product generated during winemaking and is characterised by its richness in polyphenols, dietary fibre, residual sugars, lipids, and triterpenes. These bioactive compounds derived from grapes are known to positively influence oxidative status, metabolic balance, and animal productivity, positioning grape pomace as a promising, environmentally and economically sustainable alternative feed ingredient for conventional feed components. This research evaluated the effects of incorporating different inclusion rates (0, 6, 12, and 18% DM) of ensiled red grape pomace (RGP) into isoenergetic and isoproteic diets on the nutritional and technological characteristics of goat milk. Seventy-two Murciano-Granadina dairy goats were selected and distributed into eight homogeneous groups (n = 9 per group) based on physiological traits. Each diet was randomly assigned to two groups, and the feeding trial extended over eight weeks. After a two-week adaptation to the experimental diets, four biweekly milk samplings were performed to obtain representative bulk tank samples from each treatment group. Milk samples were analysed for gross composition, pH, mineral profile, fatty acid composition, coagulation properties, colourimetric parameters, and antioxidant capacity. The collected data were analysed using a general linear model, considering the effect of the treatment, sampling days, and their interaction (Proc. GLM, SAS v9.4). Dietary RGP inclusion had no significant effect on milk gross composition or on the antioxidant activity of the milk. However, it led to a significant reduction in milk urea content and somatic cell count, alongside improvements in the lipid profile from a human health perspective. The magnitude of the effects observed in the colourimetric parameters (<0.5 units) fell below the threshold of human visual perception and was therefore not considered relevant. RGP-fed milk also showed increased calcium and potassium concentrations, while RGP_12 milk exhibited the highest phosphorus content. In addition, the lowest RGP levels (RGP_6) reduced the rennet coagulation time while increasing milk curd aggregation rate. Despite these targeted effects, the overall milk composition remained stable, which is critical for maintaining its technological functionality.

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