MECHANISM OF HARDCORE FORMATION IN CHILL-INJURED SWEET POTATO (IPOMOEA BATATAS) ROOTS

Hardcore in sweet potatoes is caused by chilling followed by non-chilling temperatures and appears as hard tissue after cooking. Changes in pectic substances and the involvement of tissue softening by beta-elimination of pectic substances were studied in relation to hardcore development. Pectic substances from cell wall, middle lamella extracts of hardcore tissue resisted degradation by betaelimination. This resistance was associated with reduced esterification and increased levels of bound cations. The mechanism of hardcore formation appears to involve activation of demethoxylation during chilling and rapid demethoxylation of pectic substances when subsequently exposed to nonchilling temperature. Demethoxylated pectic substances and pectate salts may then restrict degradation by beta-elimination and concomitant softening during cooking.