Firmness- There have been studies on the peptic substances found in tomatoes. Most of the studies agree that these materials have an important influence on the firmness of the fruit.  It is evident insoluble protopectin is laid down in the primary cell walls during the development  of the fruit, but with the onset of ripening the protopectin is gradually converted to soluble.  There for as ripening , the pectins decrease in concentration, and the fruit become softer. (Locular Comparison Commercial to Heirloom)