Variation in Fruit Constituent Sugar Concentrations and Their Stability During Processing of Selected Genotypes in Prunus Domestica

Abstract

The Prunus domesticabreeding program at the University of California, Davis has several selections which produce fruit that many processors find difficult to dry, sort, rehydrate, and pit using current processing machinery. Unlike the commercial ‘Improved French’ cultivar, UC Davis breeding program germplasm selections have highly variable ratios of various sugar constituents. The goal of this project was to determine if the different ratios of soluble sugars and sorbitol correlate with difficulties in processing. Thus, the objectives of this research were to select cultivars with distinctly different sugar profiles and then determine what changes in sugar and sorbitol concentrations occur as the fresh fruit is dried and subsequently processed. This research could help determine what sugar ratios in plums are preferential for industrial processing. Based on previously published information, it was anticipated that sucrose would more readily hydrolyze during drying and processing than sorbitol and that higher concentrations of sorbitol would be more stable and potentially act as a preservative, inhibiting degradation of sucrose and reducing sugars. In 2010 and 2011, fruit of 17 and 10 prune genotypes, respectively, were analyzed for glucose, fructose, sucrose, and sorbitol concentrations before and after drying. In 2011, the dried fruit were also rehydrated and pitted using commercial machinery. As anticipated, sucrose concentrations generally decreased during drying and processing while glucose, fructose, and sorbitol concentrations remained relatively stable. There was no apparent concentration-related preservative effect of sorbitol on the other sugars, however the rate of change in fructose and glucose differed among cultivars. The change in sugar profiles from fresh to dried was much greater than the change from dried to processed. Additionally, sugar profiles of the ten genotypes dried in both years were consistent between years.