Postharvest dehydration of wine white grapes to increase genistein, daidzein and the main carotenoids

Wine white grape bunches of the Grechetto variety were dehydrated at 10, 20 and 30 C, RH 45% and forced air ventilation of 1.5 m/s. Chemical and metabolic changes due to the effect of dehydration were studied at various stages of weight loss: 10%, 20%, 30% and 40%. Berry colour at 10 and 20 C tended to become greener with dehydration but at 30 C, at the final sampling, the colour darkened. Acidity decreased in all samples, while sugars increased. Total phenol content increased at 10 C until 30% weight loss was reached and then declined, while at 20 and 30 C the concentration decreased immediately. The contents of lutein and b-carotene (respectively 68 and 58 mg/kg d.w.), representing the 80% of total carotenoids, did not change significantly until the 30% of weight loss, when at 30 C the value increased above all for lutein while at 10 and 20 C, the contents decreased significantly. Daidzein, at 10 C, rose significantly from about 150 lg/kg d.w. to 1434 lg/kg d.w. at 20% weight loss and then declined; at the same weight loss percentage, the genistein concentration began to increase. At 20 C both isoflavones rose until the end of the experiment, reaching values similar to the sample at 10 C. A temperature of 30 C was deleterious to grape isoflavones. A discussion on the changes in isoflavones related to temperature and time is report