Chemical Study of the Ripening Process of Bosc Pears

Abstract

1. A study of the ripening process of Bosc pears held at 67⚬ F. has been made by means of chemical analyses of individual sample lots removed from the ripening room on each of 17-20 successive days. Pears of three different lots, picked ten days apart, were studied in this way and determinations made of total solids, alcohol insoluble residue, soluble solids, dextrose, levulose, sucrose, and sorbitol. 2. The losses of weight during the ripening period were recorded. The results of sugar and other determinations were calculated in terms of fresh weight at the time of sampling as well as in percentages of the original fresh weight. The latter method, involving correction for changes in effective size of sample taken, appears to give a more accurate method of studying the changes taking place during ripening. 3. A study of the sugar changes during ripening showed that levulose increased during the entire ripening period. Sucrose increased for the first six to eight days and then decreased throughout the rest of the period studied. Dextrose remained constant during the formation of sucrose, but increased later as sucrose disappeared. The increases in dextrose and levulose accompanying the decrease in sucrose were approximately equal, and their sum was about the same amount as that of the sucrose hydrolyzed. 4. The principal difference in the sugar content of fruit of the three pickings lay in the differences in the amounts of sucrose present. Throughout the ripening period the early picked fruit showed the least sucrose, the fruit of the commercial picking an intermediate amount, and the late picked fruit the highest values of this sugar. 5. Total sugars, calculated as the sum of dextrose, levulose, and sucrose, increased during the ripening process; this increase was considerably greater than could be accounted for by the observed decreases in the alcohol insoluble residue. 6. Sorbitol was identified as a constituent of Bosc pears, and a quantitative method was devised for its measurement. Sorbitol was observed to decrease during the ripening process in fruit of all three pickings, and these decreases were large enough to account for the observed increases in total sugars.