Role of Pectic Constituents and Polyvalent Ions in Firmness of Canned Tomatoes

SUMMARY Twelve sets of canned tomatoes, each set composed of three fruits harvested from the same plant and subjected to different ripening conditions, were analyzed for pectic constituents. Firmness was highly significantly correlated with total pectic constituents and with the ratio of the carhonyl and pectic content. Correlation between firmness and mineral content was also significant. These results indicate that a high content, large molecular size, and a low methoxyl content of the pectic constituents result in firmer tomatoes. From the results it appears that firmness is related to retention of the original pectic content and controlled demethylation. This induced demethylation increases the extent of ionic bonding and results in firm fruits.