STUDIES ON PHENOLASB AND PHENOLICS IN GRAPES

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Date
1988
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Mahatma Phule Krishi Vidyapeeth, Rahuri.
Abstract
The present investigation was undertaken to study the biochemical differences in three cultivars of grapes viz; Thompson Seedless, Cheema Sahebi and Anab-e-Shahi during development and storage. The developing berries of these cultivars were collected at 30, 45, 60 and 75 days after flowering and at 4, 8, 12 and 16 days after harvest. Grape berries at different stages of development and storage were analysed for physico-chemical and bio chemical parameters viz; colour, taste, size, moisture, titratable acidity, pH, total soluble solids, reducing sugars, soluble proteins, total phenols, anthocyanins and polyphenoloxidase (or phenolase) activity. During development, the colour of berries changed from green to yellow or golden yellow and the taste changed from sour to sweet. The weight and volume of berries' increased during development. Moisture content, titratable acidity and total phenols of the berries decreased, while pH, total soluble solids, reducing sugars, soluble proteins, anthocyanins and phenolase activity increased during development. The effects of enzyme concentration, substrate concentration, pH and temperature on the activity of crude preparation of poly phenoloxidase were studied. Among the three cultivars studied, the levels of total soluble solids, TSS/acidity ratio, reducing sugars, anthocyanins and phenolase activity were found to be relatively higher and those of berry size, moisture, titratable acidity, pH, soluble proteins and total phenols were found to be lower in the developing berries of Thompson Seedless than the other two varieties. Corre lation studies revealed that sugars and anthocyanins, polyphenoioxidase and anthocyanins were positively correlated while, sugars and total phenols, total phenols and anthocyanins, total phenols and polyphenoioxidase activity were negatively correlated during development of grape berries. During storage, the colour of berries changed to dark yellow and taste changed to sour. The weight, volume, moisture content, total soluble solids, TSS/ acidity ratio, pH, reducing sugars, soluble proteins, anthocyanins and total phenols in grape berries decreased while titratable acidity and polyphenoloxidase activity increased during storage. Among the three cultivars studied, the levels of TSS, TSS/acidity ratio, reducing sugars, anthocyanins and phenolase activity were found to be relatively higher and those of berry size, moisture, titratable acidity, pH, soluble proteins and total phenols were relatively lower in Thompson Seedless variety than the other two varieties during the storage of grapes.
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