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.

A study was done to analyse the change in swelling power (SP) and the water soluble index (WSI) of native starches obtained from five different cultivars of sweet potatoes (swp 1 (Wariyapola red), swp 3 (Wariyapola white), swp 4 (Pallepola variety), swp 5 (Malaysian variety), and swp 7 (CARI 273)) commonly consumed in Sri Lanka. Extracted starch from fresh roots, two to three days after harvesting has been modified using 20%, 25%, and 30% moisture levels and heated at 85 ∘ C and 120 ∘ C for 6 hours and determined the SP and WSI. Results were subjected to general linear model, and analysis of variance (ANOVA) was carried out by using MINITAB version 14. Overall results showed a significantly high level ( < 0.05) of SP and WSI in all the cultivars of moisture-temperature treated starches than their native starch. Correlation analysis showed an effect on SP with the variation in the cultivar, temperature, and moisture; temperature combination and moisture alone had no significant effect. Significantly high levels of swelling power ( > 0.05) were observed in 20%-85 ∘ C, and 30%-120 ∘ C and the highest amount of swelling in the modified starch than its native form was observed in swp 7 cultivar. Results revealed a nonlinear relationship in the WSI with the cultivar type, moisture level, and the lower moisture-temperature combinations but higher temperature-moisture combinations had a significant effect. SP and WSI had a slight positive linear relationship according to analysis. Based on the results, a significantly high level of swelling and water solubility of native starches of different cultivars of sweet potatoes can be achieved by changing the moisture content to 30% and heating at 120 ∘ C for 6 hours.

A study was carried out to determine the levels of starch, protein, crude fat, crude fibre, ash and a few phytochemical constituents (saponins, flavanoids and alkaloids) and mineral elements (Calcium, Magnesium, Iron, Potassium and Zinc) in four cultivars of yams and tubers cultivated under similar agro-climatic conditions in Sri Lanka. Tubers of Dioscorea alata (Rajala and Hingurala), Dioscorea esculenta (Kukulala) and Xanthosoma sagittifolium (Kiriala) were subjected to the above analyses. The total starch percentage in crude flours ranged between 74.66 ± 0.66 to 80.46 ± 0.62% on dry weight basis and no significant difference found in total starch (P <0.05) between the studied varieties. The protein level ranged from 2.66 ± 0.21 to 10.16 ± 0.64% whereas D. alata was found to contain a higher protein level. The crude fat levels in tubers varied ranging from 1.5 ± 0.2 to 2.3 ± 0.1% and the highest level was observed in Xanthosoma sp. The crude fibre content in tubers was found to range from 1.

Potential application of modified sweet potato starch as a substitute thickener for corn starch was studied, by using native starches extracted from five different cultivars of sweet potatoes commonly available in Sri Lanka. Physicochemical properties (swelling power, water solubility index, pasting, and gelatinization) and digestibility of native and modified (heat-moisture treated, 20% moisture, 85°C for 6 hrs) starches were analysed. Modified Swp3 (Wariyapola white), Swp4 (Pallepola), and Swp5 (Malaysian) starches were selected based on the favourable conditions shown in the required physical and chemical properties and applied in a vegetable soup formula as a thickening aid. Corn starch added samples were kept as controls and the viscosity difference and sensory attributes were tested. Viscosity of the reconstituted soup powder and sensory analysis showed that Swp4 and Swp5 had significantly high level (P<0.05) of sensory quality and the average rank for mouth feel (taste), texture and overall acceptability was significantly high (P<0.05) in Swp5 added samples. Shelf life studies ensured 6 months of stability with negligible level of moisture increase and total plate count in air tight polypropylene packages at ambient temperatures (28–31°C). Results of this study revealed a possibility of applying physically modified Swp4 and Swp5 starches as a substituent food ingredient for commercially available corn starch to improve the thickness of food products.

No abstract