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In tomatoes, polygalacturonase(PG) activity increased rapidly at 7 to 10 days after harvest, and the amount of water-soluble pectin (WSP) also increased. However, cellulase activity remained constant at the lower level. Therefore, it is conceivable that PG has a more influence on the softening of tomato fruit than cellulase. As ripening progressed, weight of tomato decreased, total soluble solids increased, and acidity decreased slightly. In colors of tomato fruit, red color became deeper at the later stage of ripening than at the initial days. It was suggested from these results that tomato fruits were most favorable in quality, particularly in flavor and color at 12 days after harvest Ca-treated tomatoes were greater in firmness arid less in PG activity than non-treated ones. Thus, softening of Ca-treated tomatoes progressed less rapidly. Inhibitor studies showed that PG activity of ripening tomato was inhibited most significantly by tannic acid.
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