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The potential to use orange-fleshed (β-carotene-rich)

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In western Kenya, where vitamin A deficiency is common and the white sweet potato is an important secondary staple, orange-fleshed sweet potatoes were introduced and their consumption was promoted, along with other vitamin A-rich foods. Ten women's groups grew a number of varieties of sweet potato on group plots in on-farm trials. Five of the groups also received an intervention consisting of nutritional education, individual counseling, and participatory rapid appraisal techniques to promote vitamin A consumption, while the other five formed the control group that received no additional promotion. Changes in consumption of children under five years of age were assessed before and after a one-year intervention period using the Helen Keller International food-frequency method. Varieties were tested for yield, agronomic performance, taste and appearance, and dry matter content. They were also assessed for β-carotene content in the forms of boiled and mashed puree, sweet potato flour, and processed products. Children in the intervention group consumed vitamin A-rich foods almost twice as frequently as control children (93% more), especially orange-fleshed sweet potatoes, mangoes, dark-green leafy vegetables, butter, and eggs. The yields of orange-fleshed sweet potatoes were at least twice those of white sweet potatoes, as were the taste and appearance ratings. The dry matter content of the varieties exceeded 25%, except for one that was preferred as a weaning food. β-Carotene values were high enough that one cup of boiled and mashed sweet potato fed daily to children of weaning age would alone meet their requirement of vitamin A, even using the higher 12:1 β-carotene:retinol conversion. Orange-fleshed sweet potatoes produced and prepared by women farmers can serve as a key foodbased entry point for reducing vitamin A deficiency.

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Sweetpotato cy-and 8-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. a-Amylase had optimum pH between 5.8 and 6.4 and was stable from pH 5.0 to 9.0. Optimum activity occurred at 71S"C, but it was inactivated by heat in the absence of Ca*+ at > 63°C. The Km for soluble starch was 2.08 mg/mL. The molecular weight was 45000 daltons. cx-Amylase activity was reduced up to 70% by 0.2 mM K-ascorbate and moderately by Na-oxalate and Na-phytate. 8-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°C and it was inactivated at 60°C. Km for soluble starch was 3.71 mg/mL. At 0.08 mM, Kascorbate strongly inhibited 8-amylase activity.

In vitro activity measurements indicate that storage sweetpotato roots contain high amounts of extractable amylolytic enzymes. These storage roots also have a very high starch content, a characteristic indicating that the in vitro measurements estimate potential amylolytic activity rather than actual physiological activity. We are interested in optimizing the use of endogenous amylases when processing sweetpotato roots and have undertaken a study to identify physiological parameters that control in vivo starch breakdown. Sweetpotato roots were allowed to germinate for 35 days in controlled conditions. Using a combination of in vitro activity measurements and immunochemical detection, the spatial distribution and changes in activity levels for the three major amylolytic enzymes in storage sweetpotato roots—α-amylase, β-amylase, and starch phosphorylase—have been followed. After 6 days, α-amylase protein increased in the outer starchy parenchymatous tissues surrounding the cambium layers, a result suggesting a de novo synthesis of the enzyme in cambium or laticifers layers. β-Amylase was abundant throughout the root at all times, and its high levels did not directly affect starch degradation rates. Starch phosphorylase protein level remained constant, while its extractable activity increased. Starch content decreased during sweetpotato seed root germination. However, the amount of starch that disappeared during germination was low compared with the calculated starch hydrolysis potential estimated by amylolytic activity measurements.

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).