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Title: CHANGES OF MOISTURE, DRY MATTER, AND SOLUBLE SUGARS IN DRY-ON-THE-VINE GRAPE BERRIES DURING TRANSFORMATION INTO RAISINS WITH SPECIAL REFERENCE TO SORBITOL

Author
item Aung, Louis
item Ramming, David
item Tarailo, Ronald

Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2001
Publication Date: 10/8/2001
Citation: Aung, L.A., Ramming, D.W., Tarailo, R. Changes in moisture, dry matter and soluble sugars of dry-on-the-vine raisins with special reference to sorbitol. Journal of Horticultural Science and Biotechnology. 2002. v. 77(1). p. 100-105.

Interpretive Summary: California raisins are an important export commodity valued at over $200 million annually. But in order to compete profitably in the global market, California production of quality raisins must be efficient and cost-effective. Introduction of dry-on-the-vine (DOV) raisins and the analysis of their sugar composition showed predictable patterns in both the berries and cluster during raisin formation which have use in evaluating quality and harvest maturity. The information will be useful to facilitate DOV mechanical harvesting and reducing cost of production of quality raisins for export and consumption.

Technical Abstract: The moisture, dry matter and soluble sugar composition of several advanced selections of dry-on-the-vine (DOV) raisins were determined. During the transformation of the mature grape berries into raisins: 1) moisture loss from the mature detached (harvested) or attached (on peduncle growing naturally on the vines) berries occurred in a graduated stepwise manner, with an initial rapid decline followed by a slower loss and then a final accelerated loss; 2) the pattern of dry matter accumulation in large, medium, or small berries was similar except that the amount of dry matter was higher in the large than medium or small raisins; 3) an incipient browning occurred at the distal berry region and a sugar gradient was established with a higher sugar content in the distal than in the proximal (pedicel) region; 4) the sucrose content in the raisins exhibited two maxima and each maximum occurring before the rise in glucose, fructose, and dsorbitol and decreasing as these sugars increased; and 5) sorbitol which was undetected initially in the mature berries increased significantly in raisins. Based upon the results, it was proposed that sorbitol content or its biosynthetic enzyme may be of potential use for estimating harvest maturity of DOV raisins. Furthermore, it is noteworthy that the raffinose and sucrose content of the peduncle was consistently higher than the raisins and may be indicative of the importance of these sugars in the metabolic function of the peduncle.