Gelatinisation and Rheological Characteristics of Minor Millet Flours

Abstract

Gelatinisation characteristics and rheological behaviour of minor millet flours of foxtail millet (Sestaria italia), little millet (Panicum miliare), poroso millet (Panicum miliaceum), kodo millet (Paspalum sorobiculatum), finger millet (Eleusine coracana) and barnyard millet (Echinochola colona) were studied using differential scanning calorimetry and dynamic shear studies. In the differential scanning calorimetry study, samples were heated at the rate of 10 °C min−1 from 10 to 140 °C and cooled back to 20 °C at the same rate. Onset, peak and conclusion temperatures in °C and gelatinisation enthalpies in kJ kg−1 were obtained. Storage and loss modulii G′ and G″, phase angle δ and viscosity were measured for the flours at 5% (by weight) concentration. The results from thermograms indicate that foxtail millet yielded a higher gelatinisation range of 28·4 °C (101·8–73·4 °C) followed by 17 °C for finger millet and little millet, a lower range of 12 °C. Other flours yielded a range around 13 °C. The data obtained from rheogram indicated that viscosity of all millet flours studied increased during heating, started decreasing just before holding, again increased during the start of the cooling cycle. The viscosity values observed ranged from 0·058 to 0·288, 0·249 to 0·419, 0·333 to 0·705, 0·209 to 0·953, 0·001 to 0·493 and 0·055 to 0·220 Pa s, for the little, barnyard, finger, kodo, poroso and foxtail millets, respectively. The storage modulus was higher than the loss modulus at all stages during heating, holding and cooling of the sample, showing that the paste has a tendency to behave like weak gel. The storage modulus ranged from 3·97 to 15·5, 10·6 to 112, 16·3 to 56·8, 5·90 to 39·2, 14·9 to 68·1 and 2·55 to 20·8 Pa and the loss modulus ranged from 0·365 to 1·81, 1·56 to 2·63, 1·93 to 4·43, 1·31 to 6 and 0·06 to 2·9 Pa, for the flours of little, barnyard, finger, kodo, poroso and foxtail millets, respectively. The phase angle values which give information about the phase shift during heating/cooling cycle showed a very broad range. The values of phase angle ranged from 2·7 to 14, 1·1 to 9, 3·7 to 9·9, 6·7 to 19·3, 0·3 to 8·4 and 1·1 to 12·8 degrees for the flours of little, barnyard, finger, kodo, poroso and foxtail millets, respectively.