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Enzymatic Hydrolysis of Grapefruit Peel to Produce Ethanol and Other Products

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  057047,  2005 ASAE Annual Meeting . (doi: 10.13031/2013.19664) @2005
Authors:   Mark R. Wilkins, Wilbur W. Widmer, Karel Grohmann
Keywords:   citrus, grapefruit, peel, enzymes, ethanol, renewable fuels

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.

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