Optimisation of alkali hydrolysis to enhance the nutritional value of grape stems for ruminant diets

Wine production generates large volumes of grape stems (GS), which are rich in fibre and phenolic compounds but have low digestibility due to their high lignin content. This study optimized alkali hydrolysis conditions to improve GS digestibility for ruminant diets using Response Surface Methodology (RSM) and a Box–Behnken design (BBD). Optimal conditions—90 °C, 2.08 h, and 33% solids—yielded a predicted in vitro organic matter digestibility (IVOMD) of 41.9%, representing an 42% increase compared to the untreated control (CTR) with 30.3%. Hydrolysis also modified fibre fractions and fermentation patterns. However, trade-offs included a reduction in total reducing sugars (TRS) and total phenolic compounds (TPC), which may lower antioxidant capacity (AOC). Despite these compositional changes, structural modifications enhanced fibre degradability, which supports the inclusion of GS as a functional feed ingredient. This approach promotes circular economy principles by upcycling winery by-products into sustainable livestock feed resources. • Grape stems, despite being rich in fibre and polyphenols, are often considered waste in winemaking. • Grape stems in animal feed is explored due to their beneficial fibre and polyphenols content. • High lignin content in grape stems can limit nutrient assimilation in animals • Alkali hydrolysis is a promising method to improve digestibility. • Optimal conditions for alkali hydrolysis to maximize digestibility include a temperature of 90°C, a duration of 2.08 hours, and a solids content of 33.0%.