Nutritional quality sweet potatoes

Feeding studies. Although sweet potatoes are a significant source of calories in many parts of the world, very little information is available concerning the nutritional quality of sweet potato protein as determined by controlled feeding studies in humans. 

A report by Bressani et al. (3J7), which evaluated the nutritional value of diets based on starchy foods and beans, indicated that for the rat, sweet potato protein was of poor nutritional quality. When methionine was added to all diets to raise sulfur amino acids, sweet potato still required the largest amount of supplementation with bean flour to maintain animal weight (Table II). 

Sweet potato flour contained 3.8% protein, the second highest amount of protein among starchy foods, and yet the protein appeared to be the poorest in nutritional quality. However, it should be noted that the sweet potatoes used in this study were dried at 60 C but were not cooked. Uncooked sweet potato starch is not completely digestable by rodents. As a consequence, maintenance requirements would increase. This is the most likely explanation for the increased requirement for bean flour, but there also may have been interference with digestion from protease inhibitors present in uncooked sweet potatoes. 

In recent years, a number of workers have published amino acid analyses of the sweet potato (38, 43, 35, 22, 18). The overall picture is that the sweet potato amino acid pattern is of good nutritional quality but that the variability of individual amino acids both within the same cultivar and across cultivars is very high. For example, Walter et al. (44) reported that with the exception of aromatic amino acids, every essential amino acid has a score of less than 100 in one or more cultivars. The amino acid score is defined as the g of amino acid in 100 g of test protein divided by the number of g of that amino acid in the FAO/WHO reference pattern times 100. Bradbury et al. (22) showed that, for the same cultivar, environmental effects on the amino acid patterns is significant. For three cultivars, they found a mean percent standard deviation for all amino acids of 24.2,... 

The literature on concentrated sweet potato protein is sparse. Amino acid patterns for sweet potato protein isolates have been reported by three groups (16, 45, 46). One report showed that when compared to the FAO standard (47), no amino acids were limiting. The other reports showed total sulfur amino acids and lysine to be limiting (Table III). The patterns indicate a nutritionally well balanced protein. The improvement in nutritional quality, when compared to amino acid patterns from whole sweet potato, is due to the fact that whole sweet potatoes contain substantial amounts of NPN, which consists mainly of nonessential amino acids. This effectively dilutes the EAA and lowers the amino acid score. 

Feeding studies with the rat as the test animal verified the high nutritional quality indicated by the amino acid pattern (45). Using isolates and concentrates prepared from Jewel and Centennial cultivars, PER values were equal to that of casein (milk protein) (Table IV). Examination of the amino acid patterns of sweet potato protein and casein revealed that both contained... 

Bashasha and Scott (2001) conducted a study in northeastern Uganda to assess the status and market potential of processed sweet potato, namely, inginyo and amukeke. Their results indicated that sweet potato was processed primarily for household food security. Respondents reported lack of time, high labor cost, and lack of market as the main bottlenecks, while peeling and slicing were the most labor-intensive activities. Owori and Hagenimana (2000) conducted research to improve the quality (odor, color, sensory, nutritional, and... 

Over the last decade or more, sweet potato production has increased in Uganda while the decline in cassava production has allowed the crop to play a role in food security. However, the sweet potato has the potential to play a much more substantial role in the Ugandan food system. Further fundamental research is needed to upgrade the quality of sweet potato production, processing and product development, and identify ways to effectively educate Ugandans regarding exploitation of the nutritional benefits of the sweet potato, and how it can play a role in eradicating VAD and food insecurity. 

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