Effects of drying method on bioactive compounds contents, rumen fermentation parameters and in vitro methane output of waste dried País grape (Vitis vinifera L.) marc

Grape marc (GM) from País winery is an abundant resource with potential use in animal feed in Chile, but information on its chemical composition, bioactive compounds and enteric methane (CH4) emissions is not reported. Drying conditions could change the chemical composition and bioactive compounds of País GM, and affect CH4 output. Thus, the objectives of this study were to assess the effects of drying conditions on the chemical composition and bioactive compounds of País GM, and rumen fermentation parameters and CH4 output. The first experiment evaluated the effects of three drying conditions (freeze-drying, and oven drying at 40 °C/72-h and 60 °C/48-h) on the contents of bioactive compounds, antioxidant capacity and chemical composition of País GM. The second experiment evaluated and compared rumen fermentation parameters and CH4 output of dried País GM. Freeze-dried País GM had the highest concentrations of phenolic compounds (p = 0.001), but oven-dried País GM (60 °C/48-h) showed the highest content of proanthocyanidins (p = 0.043). Ash (p = 0.003), ether extract (p = 0.042) and non-fiber carbohydrate (p = 0.033) contents were higher in oven-dried País GM, as opposed to neutral detergent fiber or acid detergent fiber. Oven drying GM at 60 °C/48-h reduced dry matter disappearance (p < 0.001), and gas production (p = 0.001), but also showed lower CH4 production (p < 0.001) and yield (p = 0.001) as compared to freeze dried GM. Results suggest that oven-drying is useful to conserve GM chemical value, extend its’ shelf-life and allows use of País GM as ruminant feed with potential positive environmental effects on enteric CH4 emissions but further in vitro and in vivo studies with GM as a dietary ingredient are required.