OIL CONTENT IN FRIED PROCESSED SWEETPOTATO PRODUCTS

Ninety-four different sweetpotato cultivars with various dry matter contents were used to process crisps and the end product was analyzed to determine the oil content. A linear relationship between dry matter content in raw sweetpotato storage roots and the level of oil uptake in crisps was determined. Sweetpotato storage roots with 23–25% (fwb) dry matter content gave crisps containing between 21% and 32% of oil, while the fat contents of crisps from potatoes having a similar dry matter content were 36% and more. Consequently, storage roots from Kemb 10 sweetpotato cultivar having a high dry matter content of 32.9% (fwb), either in boiled and mashed, raw and grated, or flour form, were used to partially substitute wheat flour in processing fried products. It has been found that boiled and mashed sweetpotato lessens oil uptake in mixtures of fried products such as "mandazis" (doughnuts).     

Sweetpotato α- and β-Amylases: Characterization and Kinetic Studies with Endogenous Inhibitors

Sweetpotato α- and β-amylases were characterized to assist optimization of direct hydrolysis of starch by endogenous amylases. In kinetic studies purified starch was substrate, and ascorbate, oxalate, phenolics, phytate and sweetpotato extracts were assayed for inhibitory activity. α-Amylase had optimum pH between 5.8 and 6.4 and was stable from pH 5.0 to 9.0. Optimum activity occurred at 71.5°, but it was inactivated by heat in the absence of Ca²⁺ at > 63°. The Km for soluble starch was 2.08 mg/mL. The molecular weight was 45000 daltons. α-Amylase activity was reduced up to 70% by 0.2 mM K-ascorbate and moderately by Na-oxalate and Na-phytate. β-Amylase had optimum pH between 5.3 and 5.8, and was stable from pH 4.0 to 8.0. Its maximum activity was at 53° and it was inactivated at 60°. Km for soluble starch was 3.71 mg/mL. At 0.08 mM, K-ascorbate strongly inhibited β-amylase activity.