Bioconversion of grape pomace waste into suitable alternative feed for ruminants with Pleurotus cornucopiae and Ganoderma resinaceum via solid-state fermentation bioprocess

Grape pomace is a polluted waste that is usually deposited in landfills, disrupting plant growth and polluting water. The present study aimed to convert this abundant biomass into a suitable feed for ruminants using white-rot fungi via a solid-state fermentation bioprocess. For this purpose, two white-rot fungi, Ganoderma resinaceum (medicinal fungus) and Pleurotus cornucopiae (edible fungus), and different durations of solid-state fermentation (0, 4, and 8 weeks) were used to determine the best fungus and the optimal duration of solid-state fermentation. The results showed that fermentation of grape pomace with both white-rot fungi reduced lignin and condensed tannin content and increased crude protein and mineral content. This bioprocess improved rumen fermentation and dry matter and fiber digestibility. This enhanced concentration of volatile fatty acids and ammonia-nitrogen in the rumen which contribute to better microbial crude protein synthesis and metabolizable energy by ruminants. Fermentation of these wastes with P. cornucopiae better reduced lignin content and improved rumen fermentation and metabolizable energy than with G. resinaceum. However, increasing the fermentation periods with both white-rot fungi reduced the gain of metabolizable energy and ruminal microbial crude protein synthesis. In conclusion, fermentation of grape pomace waste inoculated with P. cornucopiae after 4 weeks is the better strategy to bio-convert into suitable ruminant feed. Reduction of feed costs, overcoming of disposal problems of this waste, and provision of a new source of income for the grape juice and wine industry can be achieved through this alternative feed.