Changes in Pectic Constituents of Valencia Oranges During Growth and Development

Abstract

1. The alcohol- and acetone-insoluble solids were recovered periodically from peel and pulp of Valencia oranges. These fractions were analyzed for total pectic substances, using the CO2 method. The results of the two were practically the same. The water-soluble pectins were extracted from the alcohol-insoluble solids and determined colorimetrically by the carbazole method, which analyzes directly for the total anhydrogalacturonic acid units present. A comparison of this method was made with the calcium pectate method, which precipitates the pectic substances down to a limited polymer size and which, because of purity, must be further analyzed by means of CO2 determinations, to determine the uronide content. 2. Seasonal changes in concentrations of pectic substances in peel, pulp, and juice of Valencia oranges were followed by determining the total and the water-soluble pectic substances as anhydrogalacturonic acid during growth and development under normal conditions. After a tremendous initial increase in the total pectic substance in peel and pulp, there is a gradual decrease throughout the remainder of the season. The water-soluble pectins of both peel and pulp also show a gradual decline, but, when observed in relation to the total pectic substances of the corresponding component, the percentage is found to increase in the peel and decline in the pulp before eventually increasing also. The pectic substances found in the juice remain relatively constant throughout.