Ensiling Grape Pomace With and Without Addition of a Strain: Effect on Polyphenols and Microbiological Characteristics, Nutrient Apparent Digestibility, and Gas Emission.

The present study investigated the effects of different grape pomace storage techniques on the effectiveness as feed on ruminant digestion efficiency. Grape pomace from an autochthonous red grape variety (cv Nero di Troia) was used as fresh (GP) or ensiled, both without additives (SIL) and with the addition of a bacterial strain, 5BG (SIL+). All the different storage treatments were subject to chemical and microbiological evaluation, as well as digestibility, and gas production. Microbiological data revealed the good quality of grape pomace and silages due to the lactic acid bacteria populations and low presence, or absence, of undesirable microorganisms. The addition of 5BG influenced the chemical characteristics of the silage (SIL+). Ensiling technique deeply changed the polyphenolic composition, reducing anthocyanins, flavonols, and flavanols (condensed tannins precursors), particularly when 5BG was added. Antioxidant capacity was reduced by ensiling, in correlation with the polyphenolic content decrease. The oxygen radical absorbance capacity (ORAC) value of SIL+ was the lowest ( < 0.01) and its total phenol content was lower than SIL ( < 0.01). No statistical differences were observed between GP, SIL, and SIL+ on the antioxidant capacity by TEAC assay ( > 0.05). Ensiling did not affect the grape pomace nutrient profile, except for the reduction in NFC content. Apparent digestibility showed how ensiling increased dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), crude protein (CP), ether extract (EE), and non-fiber carbohydrates (NFC) disappearance ( < 0.01), particularly with the 5BG inoculation. Moreover, SIL+ showed the lowest propionic acid ( < 0.05) and the highest methane ( < 0.01), butyric acid ( < 0.01), and nitrogen ( < 0.05) production. Ensiling GP resulted in a better digestibility, particularly if 5BG strain is added, probably due to the reduction of flavanols and their lower microbial activity inhibition.