The Carbohydrates in the Peel of Oranges and Grapefruita

Abstract

SUMMARYThe carbohydrates of the citrus peel were divided according to their solubility in 80% ethanol. The alcohol‐soluble solids were composed of about 80% total sugars. Free xylose was found in trace amounts. Glucose, fructose, and sucrose were the main sugars present. Sucrose content of the peel was in general lower than the total reducing sugars. The alcohol‐insoluble solids were separated into “pectic substance,”“hemicellulose,” and “cellulose” fractions by extracting with different solvents. The “pectic substance” fraction upon hydrolysis yielded arabinose, galactose, and galacturonic acid. “Hemicellulose” fraction contained xylose, arabinose, galactose, glucose, and some uronic acids in its hydrolysate. In the “cellulose” fraction, glucose was dominant with some xylose and arabinose being also present. Traces of galactose and some uronic acids and in some cases mannose were found. On the average only between 53 and 70 per cent of the alcohol‐insoluble solids were recovered as carbohydrates in the peel of various citrus varieties.