Some properties of starches from cocoyam (Colocasia esculenta) and cassava (Manihot esculenta Crantz.) grown in Malawi

Abstract

The physicochemical and functional properties of starch from cocoyam and ten varieties of cassava grown in Malawi were studied to unravel their potential in industrial application. The properties of starch varied significantly with crop and among varieties. Cocoyam starch granules exhibited polygonal truncated shapes and small sizes (average of 7µm) while the cassava starch granules were rounded, irregular with oval and truncated ellipsoidal-granules with average size of 10.14µm. The cocoyam starch gave lower values of amylose content and paste clarity but higher phosphorus content, maximum wavelength of iodine complex absorption and blue value than cassava starches. Cassava starches gels were more stable to freeze thawing releasing 28.40 – 46.92% of the water than cocoyam which released 54.06% of its water. Swelling and solubility of both cocoyam and cassava starches increased with temperature (60-90°C). Cocoyam starch exhibited lowered swelling power and solubility than cassava starches. Gelatinization and retrogradation studies gave similar enthalpy values of gelatinization of cocoyam and cassava starch; cocoyam starch displayed higher retrogradation tendencies than cassava starches.   Key words: Cocoyam, cassava, amylose, blue value, swelling, solubility, paste, freeze-thaw, gelatinization, retrogradation.