Submitted to: Biotechnology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 13, 1998
Publication Date: N/A
Interpretive Summary: Approximately one half of the weight of citrus fruit processed into juice ends in byproducts, such as peels, cores and fruit membranes. The residues are currently dried and sold at a marginal profit as a cattle feed. The residues are rich in soluble sugars and polymeric carbohydrates, which can be efficiently hydrolysed to sugars by action of enzymes. The resulting stream of mixed sugars can then be fermented to ethanol and other value-added products by genetically improved bacteria or other microorganisms. We have investigated simultaneous hydrolysis and fermentation of orange peel to ethanol and organic acids by genetic constructs of pectinolytic and hemicellulolytic bacteria. Two promising constructs were identified, but additional genetic improvement of these strains is needed for potential commercial application. Utilization of these constructs will eliminate addition of costly hydrolytic enzymes to the processed orange peel.
Technical Abstract: We have conducted preliminary investigations of the conversion of sugars in citrus pectin and orange peel to ethanol by four ethanologenic constructs of bacteria in the genus Erwinia. The investigations identified two constructs which depolymerized pectin and other polysaccharides in citrus peel by exocellular enzymes. These bacteria also converted galacturonic acid and other sugars in orange peel hydrolysates to ethanol, acetate and lesser amounts of other organic acids. Application of these or similar microorganisms decreases or eliminates costly enzyme addition from the overall process.