Composition and pasting properties of starch from two cocoyam cultivars

The composition and pasting properties of starches from two cocoyam cultivars were evaluated and compared with cassava starch. The starch, amylose and amylopectin contents of Xanthosoma and Colocasia cultivars ranged from 79.2 to 79.8%, 23.3-23.6%, 56.1-56.2% and 77.6-77.8%, 25.4-25.7%, 52.1-52.2%, respectively. The Xanthosoma and Colocasia starches had significantly low levels (0.12-0.24%) of lipid, with trace concentrations of crude fiber. Manihot utilissima had significantly (P [less-than or equal to] 0.05) higher starch and amylopectin but lower amylose contents than Colocasia and Xanthosoma starches. Average granule sizes of Xanthosoma and Colocasia starches ranged from 4.3 to 5.6 μm and 2.5-3.4 μm, respectively. Xanthosoma and Colocasia starches showed restricted swelling and solubility patterns with high initial gelatinization temperatures ranging from 78.3 to 78.5C and 74.6-74.8C, respectively. Between 19.0-19.2% and 16.8-17.1% soluble carbohydrates were obtained from Xanthosoma and Colocasia starches, respectively, at 95C. The Xanthosoma starches had higher peak, hot paste and cooked paste viscosities and stability than Colocasia starches. This study shows that the application of cocoyam starches in food would depend largely on the knowledge of their physicochemical properties which differed with the cultivars. The properties of importance include composition, granular characteristics, swelling, solubility and pasting characteristics. The low lipid content of Xanthosoma and Colocasia starches was important to their functionality because lipid complexes with carbohydrates and reduce swelling and solubility of starches by restricting gelatinization. Xanthosoma starches had significantly higher amylopectin but lower amylose contents than Colocasia starches. The relatively high amylose contents and smaller granular characteristics were associated with the low swelling and solubility patterns of starches from both cultivars. Xanthosoma starch had higher solubilities than Colocasia starch at higher temperatures (80-95C). Xanthosoma brasillience and Xanthosoma sagittifolium starches had superior viscosity stabilities than Colocasia antiquorum and Colocasia esculenta starches, and would be useful in baked products like biscuits, cakes and breads. C. esculenta and C. antiquorum starches would be desirable in sauces, soups and as thickeners in products requiring continuous heating and stirring where viscosity is not desired.