PASTING, FUNCTIONAL AND MORPHOLOGICAL CHARACTERISTICS OF NATIVE AND MODIFIED TIGERNUT AND PEARL MILLET STARCHES

Abstract

Starch is a mixture of branched polysaccharides called amylopectin and a linear polysaccharide called amylose. However, functional restriction is experienced in the food applications of native starches because of their structural weakness. Therefore, this study aimed to evaluate the functional, pasting characteristics of native and modified tigernut and millet starches. Starches of Millet and Tigernut were modified using annealing (physical) and acetylation (chemical) modification and were coded as native millet starch (NM), native tigernut starch (NT), acetylated millet starch (AM), acetylated tigernut starch (AT), annealed millet starch (PM) and annealed tigernut (PT). The moisture contents ranged from 6.50 g/100g in native starches to 8.72 g/100g in modified starches. The protein content of starch samples ranged from 2.25 g/100g in NM to 3.25 g/100g in NT. Total ash content was in the range of 1.00%-1.39%. Bulk density of the native starches range from 0.75g/mL in tigernut to 0.73g/mL in millet, and was significantly lower when compared to the annealed starches 0.96g/mL in PTand 0.98 g/mL in PM and also significantly lower when compare to acetylated starches 0.90 g/mL in AT and 0.87 g/ML in AM. The water absorption capacity of the acetylated starch samples ranged from 1.6 mg/g in AT to 1.2 mg/g in PT and was significantly higher (p<.0.05) than the native starch samples (0.60 mg/g in NT and 1.0 mg/g in NM). The peak viscosity was in the range of 2070.66 – 2782.00 RVU. Amylose content was in the range between 10.34 % – 20.38 % while amylopectin was in the range of 79.50% - 89.61%. Morphological results of the starch show that the majority of the granules occurred singly with oval or round shapes in the native structure. Both annealing and acetylation affected the smooth structure of the starch. In conclusion modified starch samples exhibit better functional, pasting and morphological characteristics. Hence, application in food industries will promote the value addition and economic importance of these underutilised crops