ARS | Publication request: EFFECT OF SEASONAL VARIATION ON ENZYMATIC HYDROLYSIS OF VALENCIA ORANGE PEEL

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2005
Publication Date: February 28, 2006
Repository URL: http://www.ars.usda.gov/sp2UserFiles/Place/66210000/Reprint966.pdf
Citation: Wilkins, M.R., Widmer, W.W., Cameron, R.G., Grohmann, K. 2006. Effect of seasonal variation on enzymatic hydrolysis of Valencia orange peel. Proceedings of Florida State Horticultural Society. 118:419-422.

Interpretive Summary: Approximately 5 million tons of orange peel waste are generated by Florida orange juice processors every year. Peel waste currently has low value, but previous studies have shown that it has potential as a feedstock for ethanol production. A key step in producing ethanol from peel waste is enzymatic hydrolysis to produce fermentable sugars that yeast or other microorganisms can use to make ethanol. This study explored whether fruit maturity during the course of the Valencia orange harvest had an effect on sugar yields from enzymatic hydrolysis. Valencia oranges were picked from the same tree at four times during harvest. Juice was extracted from the oranges, and the peel waste left over was hydrolyzed to sugars using enzymes. Harvest time had an effect on arabinose and galacturonic acid yields. Dry matter content of the peel waste before hydrolysis increased during the course of the harvest, which resulted in increased potential ethanol yields.

Technical Abstract: Approximately 10 million tons of oranges are processed in Florida each year, producing approximately 5 million tons of waste consisting of peel, seeds and segment membranes. Most of this peel is currently dried and pelletized to produce citrus pulp pellets, a low value cattle feed. Several researchers have converted orange peel waste into valuable sugars using enzymatic hydrolysis. After hydrolysis, many of these sugars can be utilized to produce ethanol, a valuable fuel, and other chemicals. This study focuses on the effect of harvest time on sugar yields from enzymatic hydrolyses of Valencia orange peel. Valencia oranges were obtained from the same tree at four times during the 2005 harvest season. A commercial juice extractor was used to extract juice and the processing waste collected for hydrolysis. Peel was comminuted to a size less than 0.7 millimeters in a food processor. Cellulose, hemicellulose and pectin were hydrolyzed using pectinase, cellulase and beta-glucosidase enzymes to produce sugars. Arabinose and galacturonic acid yields were affected by harvest time. Dry matter content of the peel increased over the harvest season. Potential ethanol yields also increased over the harvest season as a result of increased peel dry matter content.