BACKGROUND: Approximately 0.7 − 1 × 10 6 dry tons of citrus processing waste (CPW) are produced annually in the United States. CPW is sold as animal feed but often the financial return does not exceed the production cost. Polysaccharides comprise 40% of the total dry matter of which pectin is the major component. CPW was steam treated to extract pectin fragments (PFs) as a value added co-product prior to fermentation of other sugars for biofuels production.RESULTS: PFs were extracted in high yields, along with polymeric arabinans, galactans and arabinogalactans. The extracted polysaccharides ranged in size from small oligomers to polymers of ∼ 700 000 g mol −1 . Acidified treatments led to greater fragmentation of water soluble polysaccharides, but did not enhance fragmentation of pectins to small oligomers (> 30 mer). Methylesterified PFs, arabinans and galactans were recovered by ethanol precipitation while demethylesterified PFs were recovered and purified by precipitation with dilute HCl. CONCLUSION: Steam treatment of CPW provides for rapid, efficient fragmentation of protopectin into highly methylesterifiedPFs that could be recovered by precipitation. The steaming process for preparation of PFs is environmentally friendly. No toxic chemicals are introduced and the remaining CPW can be used in fermentations to produce ethanol and other compounds.

Executive SummaryFlorida has 103 million citrus trees on 800,000 acres that last season provided 287 million boxes of citrus (80% of U.S. production); 85% went to Florida's 23 citrus processing plants. In juice processing one half of a citrus fruit is waste, yielding 5 million tons of wet waste, equating to 1.25 million tons of dry waste. Traditional use for these residues is as cattle feed which currently does not have sufficient value to cover the production/transportation costs. These materials are rich in pectin and other polysaccharides which can be hydrolyzed into sugars. This equates to a potential production of 120 million gallons of ethanol per year. Renewable Spirits LLC in collaboration with a CRADA partner, USDA/ARS Citrus and Subtropical Products Laboratory, developed an innovative process for the production of ethanol from citrus processing waste (CPW). The novel process based on enzymatic hydrolysis of CPW and fermentation of resulting sugars by yeasts was successively scaled up from laboratory scale to a 10,000 gal fermentor level. Numerous technical obstacles were overcome and continuous pretreatment and hydrolysis/fermentation sections were designed, constructed and successfully tested.