Abstract
Background:
Quebranta grape pomace (Vitis vinifera, Quebranta variety), a by-product of winemaking and pisco production, contains a distinct metabolite profile of phenolic compounds shaped by the arid agroecological conditions of the Ica valley. Its incorporation into ruminant diets may enhance milk quality while contributing to the valorization of agro-industrial waste; however, its effects on dairy goat milk composition have not been evaluated in Peru.

Aim:
To assess the effects of Quebranta grape pomace powder supplementation on the physicochemical properties, lipid profile, phenolic compounds and antioxidant activity of Saanen goat milk.

Methods:
Twenty primiparous Saanen goats were assigned to two dietary treatments (n = 10 each) for seven weeks: a control diet (T0) and a diet supplemented with 8% grape pomace powder (dry matter basis) replacing maize stover (T1). Milk was sampled weekly for physicochemical analysis. Pooled samples from three time points were used for lipid profile, polyphenol, anthocyanin, and antioxidant capacity analyses; these results were therefore considered descriptive given pseudoreplication. Treatment effects were evaluated using linear models including day in milk as a covariate.

Results:
Grape pomace supplementation increased milk fat content by 16.96 % (p < 0.05) without affecting milk yield, protein, lactose, or total solids. Lipid profiling indicated a potential enrichment of polyunsaturated fatty acids, particularly linoleic acid, based on the magnitude of changes observed. Milk phenolic content and antioxidant capacity (>6,000 µmol Trolox/100 g) were not detectably altered, although further validation with increased replication is warranted.

Conclusion:
Quebranta grape pomace improved milk lipid content in Saanen goats, with evidence suggestive of polyunsaturated fatty acid enrichment, while preserving milk yield, physicochemical characteristics, and antioxidant capacity. These findings support grape pomace as a functional and sustainable feed ingredient for dairy goat production.

Key words: Agro-industrial residues; Goat milk; Phytochemicals; PUFA; Tannins.