Integrated Approach for the Valorization of Red Grape Pomace: Production of Oil, Polyphenols, and Acetone-Butanol-Ethanol

Grape pomace (GP) is a major solid waste resulting from the wine industry. GP is rich in structural carbohydrates, lignin, and other components such as oil and polyphenols, products with potential value. One of the major challenges to GP valorization is the lack of technology to fully utilize GP components and minimize waste generation. To overcome this challenge, we developed a novel, integrated process to fully utilize each component of GP for the production of oil, polyphenols, and biochemicals (acetone, butanol, and ethanol; ABE). GP was first subjected to pressurized liquid extraction to recover grape oil and polyphenols sequentially. The solid residue was pretreated with NaOH to partially dissolve lignin and was then hydrolyzed with enzymes to obtain reducing sugars. Finally, those reducing sugars were fermented to ABE by Clostridium beijerinckii. The key process conditions, including polyphenol extraction and pretreatment conditions, were optimized. Under optimized conditions, approximately 71.9 g of oil, 322.8 g of crude polyphenols, and 20.7 g of total ABE were obtained from 1 kg of dry GP. The developed process paved a new way to convert GP to both value-added food ingredients (grape oil and polyphenols) and bulk biochemicals (ABE), along with minimizing waste generation from GP.