GELATINIZATION PROPERTIES OF NAVY BEAN STARCH

Gelatinization properties of navy bean (Phaseolus vulgaris) starch und er different combinations of concentration (6, 8, 10 and 12%) and cook ing temperature (75, 85 and 95 degrees C) were studied using a rotatio nal viscometer. The torque response due to swelling and/or breakdown o f starch granules approached equilibrium after either a gradual increa se or a relatively rapid increase to a peak followed by a decline duri ng cooking. For every condition, the difference between the final torq ue values obtained for the rapid and the slow heating processes was no t significant. In general, the viscosity of the paste increased as the starch concentration and/or cooking temperature increased. However, c ooking temperature of 75 degrees C did not cause a significant ge gela tinization or swelling of starch granules in pastes of 6 or 8% concent ration. Maximum final viscosity values were obtained at 85 degrees C f or all starch concentrations except for a maximum at 95 degrees C for 6%. Thixotropic breakdown was observed at 10 and 12% concentrations du ring initial shearing at 85 and 95 degrees C. The threshold concentrat ion for significant viscosity effects in this study was in the range o f about 8 to 10% or 95 degrees C. The calculated activation energy (14 .5 Kcal.g(-1)mole(-1)) of navy bean starch gelatinization was similar to values reported for rough rice and rice starches.