Submitted to: Proceedings of American Society of Agricultural Engineers
Publication Type: Proceedings
Publication Acceptance Date: 5/30/2007
Publication Date: 6/1/2007
Citation: Wilkins, M.R., Widmer, W.W., Grohmann, K. 2007. Enzymatic hydrolysis of grapefruit peel to produce ethanol and other products. Proceedings of American Society of Agricultural Engineers [serial online]. Paper No. 057047. Available: http://asae.frymulti.com/request.asp?search=1&JID=5&AID=19664&CID=tfl2005&v=&i=&T=1 Interpretive Summary: Grapefruit juice processors generated approximately 500,000 tons of grapefruit peel waste in 2003/04. Most of this waste was dried and fed to cattle at a loss for the processors. Grapefruit peel waste can be broken down with pectinase and cellulase enzymes to sugars that can be used to make ethanol, a renewable fuel that can be added to gasoline. This study tested several different enzyme loadings to determine which were best for producing sugars. Loadings of five mg pectinase protein/g peel solids and one mg cellulase protein/g peel solids produced the most sugars. Less ethanol can be potentially produced from grapefruit peel waste than from Valencia orange peel waste because grapefruit peel waste has greater moisture content.
Technical Abstract: Over 1 million tons of grapefruit were processed in 2003/04 resulting in 500,000 tons of peel waste. Grapefruit peel waste is usually dried, pelletized, and sold as a low-value cattle feed. This study tested several different loadings of commercial cellulase and pectinase enzymes to hydrolyze grapefruit peel to produce sugars that can be fermented into ethanol and other products. Pectinase and cellulase loadings of zero, one, two, five, and ten mg protein/g peel dry matter were tested. All hydrolyses were supplemented with 2.1 mg beta-glucosidase protein/g peel dry matter to hydrolyze cellobiose produced by cellulase and pectinase. Five mg pectinase/g peel dry matter and one mg cellulase/g peel dry matter were the lowest loadings to yield the most total sugars. Theoretical ethanol yields for grapefruit peel were lower than previous studies utilizing orange peel, due to less dry matter in grapefruit peel than in orange peel.