POTATO EXTRACTIVES: EFFECT ON FIRMNESS OF PECTIN JELLIES AND VISCOSITY QF POTATO STARCH PASTES

SUMMARY— Pectin jellies and potato starch pastes were prepared with aqueous extracts of potato tissue. All jellies containing potato extractives were weaker than distilled water control jellies. Jellies containing extractives from bud tissue were weaker than those containing extractives from stem tissue. Extractives from tubers stored continuously at 38°F weakened the jellies to a greater extent than those from tubers stored at 38°F and conditioned for 1 wk. Jellies containing extractives from boiled tissue were weaker than those prepared with extractives from blanched or steamed tissue. The most viscous pastes were those made with distilled water. In every case, viscosity of pastes containing extractives from raw tissue was less than half that of distilled water pastes. When extractives from blanched, steamed or boiled tissue were used, the viscosity decreased still further. The rigidity of jellies and the viscosity of pastes prepared with deionized extracts were similar to those of jellies and pastes prepared with distilled water. The data suggest that extractives leached from potato tissue increase sloughing of potato tissue during cooking by weakening the pectic materials in the intercellular cement rather than by enhancing the swelling of starch in the cells.