Methods of analysis of soluble carbohydrates and pectic substances of citrus fruits

Sinclair, W.B.; Joliiffe, V.A.

Food Res 25(1): 148-156


DOI: 10.1111/j.1365-2621.1960.tb17947.x
Accession: 025009303

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Methods are described for the separation and analysis of the carbohydrate fractions of the peel, pulp, and juice of citrus fruits. The carbohydrates were separated into alcohol-soluble and alcohol-insoluble fractions with 80% ethyl alcohol. A diagram is given for the separation and analysis of the nonvolatile organic acids and the soluble mono- and disaccharides (glucose, fructose, and sucrose) from the other constituents of the alcohol-soluble fraction. The amino acids are in this fraction and they also can be quantitatively determined by column and paper chromatography. A diagram is given for the separation and analysis of the alcohol-insoluble solids, with special reference to the fractionation of the pectic substances of citrus peel. The alcohol-insoluble solids contain the proteins, pectic substances, and other high molecular weight compounds. The water-soluble materials were extracted from the alcohol-insoluble solids, and from this extract the water-soluble pectic substances were subsequently determined on aliquot samples by the carbazole colorimetric method, total uronide CO2 and the calcium pectate methods. The protopectin and pectate or acid-soluble pectic substances are extracted with dilute hydrochloric acid solution from the water-insoluble residue of the alcohol-insoluble solids, and the analyses for pectic substances are made by the methods described for the water-soluble fraction. Experimental data presented show CO2 and methoxyl contents in relation to the anhydrogalacturonic acid of the alcohol-insoluble solids of citrus fruit tissues, and certain analytical data are presented on the alcohol-insoluble and alcohol-soluble fractions of Valencia and Navel orange peels.