ARS | Publication request: HYDROLYSIS OF GRAPEFRUIT PEEL WASTE WITH CELLULASE AND PECTINASE ENZYMES

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2006
Publication Date: August 24, 2006
Citation: Wilkins, M.R., Widmer, W.W., Grohmann, K., Cameron, R.G. 2006. Hydrolysis of grapefruit peel waste with cellulase and pectinase enzymes. Bioresource Technology. 98:1596-1601.

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 and pH levels 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. Optimum pH for hydrolysis was pH 4.8. 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: Approximately 1 million Mg of grapefruit were processed in 2003/04 resulting in 500 thousand Mg of peel waste. Grapefruit peel waste is usually dried, pelletized, and sold as a low-value cattle feed. This study tested different loadings of commercial cellulase and pectinase enzymes and pH levels to hydrolyze grapefruit peel waste 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. Temperature was maintained at 45 °C. Hydrolyses were supplemented with 2.1 mg beta-glucosidase protein/g peel dry matter to hydrolyze cellobiose. Five mg pectinase/g peel dry matter and two mg cellulase/g peel dry matter were the lowest loadings to yield the highest levels of glucose. Optimum pH was pH 4.8.