Enzymatic hydrolysis of baked sweet potato puree

The objective of this study was to produce fructose enzymatically from starch and starch degradative products in baked sweet potato puree. This would have the effect of sweetening the puree without having to add sugar(s). It was hypothesized that the puree would compare favorably in sweetness with puree sweetened with sucrose to the desired level.

Three enzymes (alpha-amylase, amyloglucosidase, and glucose isomerase) and the appropriate cofactors were added to the puree which was hydrolyzed at combinations of five pH levels (pH 4.0, 4.8, 5.4, 6.2, and 6.8) and four temperatures (55, 62, 69, and 76°C) for 21 hours. The hydrolysate was analyzed for fructose, glucose, sucrose, and maltose content. Hunter L, a, and b values for color were measured also. The optimum condition for fructose production within the range studied was pH 6.8 at 64°C. As temperature and pH were increased the puree became darker, less yellow, and less red. Due to considerations of color, flavor, and odor, pH 6.8 at 55°C was chosen as the most ideal condition.

A panel of 20 university staff, employees, and students scored sweet potato puree sweetened with five levels of sucrose and sweet potato puree sweetened with five levels of hydrolysate for preference of sweetness. The panel preferred puree with 14.86% added sucrose. The puree sweetened with hydrolysate was strongly disliked and a true evaluation of its sweetness could not be obtained. The poor flavor and odor of the hydrolysate masked the perception of sweetness in the samples.

The caloric value of the puree samples sweetened with the five levels of sucrose was determined. The increase in Calories due to added sucrose was statistically highly significant.

This study shows that the enzymatic production of fructose in baked sweet potato puree, under the conditions evaluated, produces an unpalatable product containing only a small percentage of the fructose needed to compare favorably in sweetness with puree sweetened to the desired level with sucrose.