Abstract
In the Trentino Alto Adige region, disposal of grape stalks (GS) represents a major cost for wineries, despite their content of phenolic and tannin-rich compounds with potential functional value in ruminant nutrition. This study evaluated whether dietary GS supplementation could influence milk microbiota and cheese quality, supporting local circulareconomy strategies. GS from three red cultivars (L-GS, CS-GS, M-GS) were dried, milled, and assessed for safety; their average total polyphenol content was approximately 15 g/kg DM. 3 Holstein cows underwent a 7-week trial consisting of alternating control (CTRL) and GS-supplemented periods (2% DM). Weekly milk samples (n = 21) and corresponding mini-cheeses (n = 21) were analyzed. GS supplementation did not affect milk coliforms (2.3–2.5 log CFU/mL), while total mesophilic counts were significantly lower in M-GS (2.8 ± 0.46 log CFU/mL) than in CTRL (4.5 ± 0.71; p < 0.05). Acinetobacter dominated the milk microbiota but decreased from 34.0% in CTRL to 18.0% in L-GS. Cheese total polyphenols were highest in CS-GS (224 ± 34 mg/kg). 1H-NMR and VOCs profiling indicated cultivardependent shifts in carbohydrate-related metabolites and short-chain fatty acids. Overall, GS supplementation subtly modulated cheese biochemical and aromatic traits without impairing technological performance, supporting the valorization of winery by-products within integrated dairy-viticulture systems.