Abstract
Nutritional attributes of flours obtained from five different cultivars of sweet potato roots commonly available in Sri Lanka showed significant differences in the tested parameters. The starch level ranged between 33% and 64% on the dry basis and the extractability from fresh tubers was governed by the quantity of starch. The crude fiber level ranged between 2.1% and 13.6% on dry basis and the highest level was observed in swp7 (CARI 273) and resistant starch ranged from 14.2% to 17.2%. Higher percentage of resistant starch from total starch was found in Wariyapola red (swp1) cultivar resulting in lower digestion level while higher levels of digestion was evident in cultivars with lower levels of resistant starch with high level of total starch. Low levels of calcium and significant levels of iron were found in the five cultivars studied. Crude protein level was in the range of 1.2–3.3% on dry basis and trypsin inhibitor activity level (TIA) was significantly different (P > 0.05) in the cultivars studied while heating resulted in a significantly high reduction in the TIA level than in unheated condition. Polygonal or round shaped starch granules were in the range of 16.8–23.5 μm and low level of starch digestion was shown in cultivars containing larger granules. Total amylose content lies in the range 15.4–19.6% and cultivars having higher percentage of amylose showed higher level of in vitro pancreatic digestion (Pallepola [swp4] and swp7). The starch digestibility of sweet potato flour was in the range of 36–55% and the highest digestion was observed in swp7. Orange fleshed cultivars (swp4 and swp7) were comparatively rich in nutrients and digestibility than the other three studied cultivars.
Highlights
The sweet potato (Ipomea batatas (L) Lam) is a tuberousrooted perennial plant belonging to the Convolvulaceae or morning glory family
The highest amount of starch was observed in swp7, while the lowest was seen in swp1 cultivar
The difference between the extracted starch and the total starch may be due to the presence of high level of soluble sugars and resistant starch (RS) present in the swp1 cultivar
Summary
The sweet potato (Ipomea batatas (L) Lam) is a tuberousrooted perennial plant belonging to the Convolvulaceae or morning glory family This family includes about 45 genera and 1000 species, but only Ipomea batatas is of economic importance as food (Onwueme 1978). In Sri Lanka, sweet potato is a traditional crop grown mainly in the wet and intermediate zones and nearly about 50,000 tones are produced annually (UN – FAO stats, 2009). All of this production is used for human consumption as high consumer preference for roots prevents the utilization of it as an animal feed because the production is insufficient.
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