CARBOHYDRATE TRANSFORMATIONS, COLOR AND FIRMNESS OF CANNED SWEET POTATOES AS INFLUENCED BY VARIETY, STORAGE, pH and TREATMENT

SUMMARY– Two varieties of sweet potatoes were canned at three storage intervals, six buffered pH levels, and two holding times to determine the influence on color, firmness, carbohydrates and other constituents. Color and firmness were improved when the pH was decreased from 8 to 3. There was an increase in brightness of color and firmness by holding peeled sweet potatoes 24 hr in buffers before canning. The sugars and phenolic substances were leached out during holding. Total polyphenols decreased with an increase in pH although tannic and chlorogenic acids were not changed appreciably. There was a decrease in starch and hemicellulose as a result of storage; whereas, water‐ and Calgon‐soluble pectin were not affected. Starch decreased with an increase in pH regardless of other variables. Water‐soluble pectin increased when pH was altered up or down from the normal pH of canned sweet potatoes of approximately 6.0. In comparison, Calgon‐soluble pectin and hemicellulose reacted inversely to pH. It appeared that pH had a far greater effect on color and firmness than length of post‐harvest storage of raw product after curing and other variables because of the direct effect on carbohydrate transformations and discoloration.