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Changes in free sugar content of Campbell Early grapes grown in plastic house with and without heating, rainshelter, and in the field were analyzed by HPLC during ripening period. The objectives were to obtain informations For the improvement of cultural environment, production of high quality fruits, and breeding of cultivars for protected culture. The sugar of grape juice was composed mostly of fructose and glucose with small amount of maltose, but sucrose was not detected. The contents of fructose at the ripening stage were 5.46-6.09%, 5.22-5.61%, and 5.82-5.88% under cultivation without heating, rainproof cultivation and field culture, respectively, while the content under cultivation with heating was significantly low as 4.27%. The contents of glucose at the ripening stage were 6.14-6.96%, 5.27-5.95%, 5.71-5.83%, under cultivation without heating, rainproof cultivation and field culture, respectively, whereas the value under cultivation with heating was 4.40%. The concentration of maltose ranged from 0.52 to 0.62% throughout the ripening stage. The fructose and glucose increased rapidly 50 days after anthesis under cultivation without heating, rainproof cultivation, and field culture. These sugars under cultivation with heating slightly increased up to 70 days. The maltose content was found to be low under all cropping systems and remained constant throughout the ripening stage. Glucose content at the ripening stage was similar or slightly higher than fructose under controlled cultivation, but the value was lower under cultivation without heating. Fructose, however, was similar or somewhat higher than glucose under field culture. The rapid increase in soluble solids content was observed 50 days after anthesis, resulting in a slight increase with cultivation with heating. The titratable acidity decreased inversely to the increase of soluble solids content.
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