EFFECT OF PREHEATING ON POTATO TEXTURE

Preheating potatoes at 50 to 80-degrees-C has a firming effect on the cooked potato tissue. This effect is particularly pronounced at a preh eating temperature of 60 to 70-degrees-C followed by cooling. Several theories have been presented in the literature to explain this firming effect: retrogradation of starch, leaching of amylose, stabilization of the middle lamellae and cell walls by the activation of the pectin methylesterase (PME) enzyme, and by the release of calcium from gelati nized starch and the formation of calcium bridges between pectin molec ules. Most probably, none of these theories alone can explain the phen omenon and more than one mechanism seems to be involved. Some of these mechanisms seem to be interdependent. As an example, calcium could be considered as a link all the way through release after starch gelatin ization to cross-linking pectin substances in the cell wall and the mi ddle lamellae, which has been demethylated by the PME enzyme. More res earch and ''clear cut'' experiments re needed in order to elucidate th e role of each mechanism, especially which of them is the main contrib utor to the process of firming. Most probably, the calcium-pectin-PME mechanism plays a secondary role, that is, it only retards the collaps e of the tissue structure that would otherwise occur during the final heating without preheating, and it is not the main factor of firmness.