Firming of cooked sweet potatoes as affected by alum treatment

Abstract

Sweet potato slices were cooked for 5 min in distilled water, alum (aluminum potassium sulfate), AlCl3 and several pH level buffer solutions. Slices preheated (60°C) in these solutions were boiled in water. The slices cooked at about pH 4 were firmest among those in the range pH 2-pH 12. Firmness was (greatest to least); preheated in alum > preheated in water > cooked in buffer (pH 3.5) >AlCl3 (pH 3.5) > alum (pH 3.5) > water. Preheating, Al3+ and acid prevented softening of slices. Acid-treated slices were firmer than Al3+ treated slices. Alum contains K+ and SO4-2, which accelerate solubilization of pectin, thus slices cooked in alum were softer than those in AlCl3. Scanning electron microscopy showed the middle lamella separated when cooked in water but not when cooked in other solutions.