Induction of Textural Changes in Sweet Potato Roots by Chilling1

Hardcore was apparent in cooked sweet potatoes ( Ipomoea batatas Lam.) which had been chilled and transferred to nonchilling temperatures prior to cooking. The severity increased with duration of chilling at 2°C. Hardcore was not observed in roots boiled immediately after chilling, although these roots were firmer than those not chilled. Enhanced levels of pectic substances, soluble in sodium hexametaphosphate, were associated with hardcore tissue, while starch, protopectin, and hemicellulose were related to enhanced firmness of continuously chilled roots. No differences in pectinmethylesterase activity were observed between storage treatments. Reduced levels of alpha amylase activity in continuously chilled roots probably accounted for the enhanced levels of starch after the roots were processed. From data on U.V. absorption, phenolic levels, and electrolyte leakage, we believe that hardcore develops when phenolics or related substances, and possibly cations, bind with cell wall materials.