Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


School of Nutrition and Food Sciences

First Advisor

Paul W. Wilson


A critical problem associated with the production of sweetpotato puree is the inconsistency of final product. Two possible factors, amylase activity and carbohydrate content in sweetpotatoes during storage, were investigated. It was found that $\alpha$- and $\beta$-amylase activities do not significantly change during storage, and have no significant effects on viscosity of sweetpotato puree. The inconsistent products in sweetpotato puree processing are mostly due to the change of alcohol insoluble solids (AIS) in sweetpotatoes during storage. The decrease of AIS is partially due to respiration that converts starch into CO$\sb2$ and H$\sb2$O. A new bio-processing method was proposed to improve the consistency in sweetpotato puree products based on the results obtained in this study. In addition, two methods for specific determination of $\alpha$- and $\beta$-amylase (using blocked p-nitrophenyl maltoheptaoside and p-nitrophenyl maltopentaoside as substrates respectively) were adapted for amylase assays in sweetpotatoes. Both methods have major advantages of simplicity, speed, high sensitivity, and specificity. The thermal stability of native $\alpha$- and $\beta$-amylase in sweetpotatoes, and the interaction between $\alpha$- and $\beta$-amylase on starch hydrolysis were also studied. The $\alpha$-amylase was very heat labile, and lost most activity in just 30 seconds of heating at 75$\sp\circ$C. $\beta$-Amylase had a higher thermal stability. The synergistic hydrolysis of starch could occur when $\alpha$-amylase is combined with $\beta$-amylases, but it is not always true, depending on the concentrations of amylases.