Determination of starch in plant material

Starch has been determined in the pasture legume Stylosanthes humilis (Stylo) by hydrolysis with amylo-glucosidase and subsequent analysis for glucose with glucose oxidase. Prior gelatinisation of starch granules within the plant sample by water at 130°c gave low values and it was concluded that the complete solubilisation of starch by alkali was necessary, with subsequent neutralisation of the extract with acetic acid. It was shown that the alkali also extracted material which inhibited one or more of the enzymes involved in the subsequent glucose analysis, but this inhibition was removed by treatment of the extract with charcoal. Under the above conditions the high acetate concentration decreased the efficiency of the final glucose analysis, but this effect was readily corrected by use of appropriate blank solutions. The proposed method of starch analysis is relatively economical in time compared with previous methods and is believed to give more meaningful values for plants with low starch content.