Effect of processing of sword beans (Canavalia gladiata) on physicochemical properties of starch
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The effect of various processing methods on physico-chemical properties of sword bean starch was studied. Seed grits and flour were cooked with and without soaking, wet-autoclaved, and roasted. The changes in starch associated with these processing methods were studied by observing changes in granular structure, water solubility index, water absorption index, molecular size distribution and the degree of gelatinization estimated by differential scanning calorimetry. Intact, ungelatinized starch granules of raw and dry-heat treated samples were observed under the light microscope. The starch granules were elliptical in shape and had an average length and breadth of 37-40 mu m and 27 mu m, respectively. Wet-processed samples had the lowest water solubility, higher water absorption and lower gelatinization enthalpies than the raw bean flour, whereas the dry heat-treated samples showed higher water solubility and higher gelatinization enthalpies. The starch molecular size distribution pattern showed a higher amount of high molecular size carbohydrates in dry heat-treated samples and a large fraction of intermediate molecular size carbohydrates in the wet-processed samples. The low molecular size carbohydrate content was low in wet-processed samples where processing was done with excess water.