Cereal Chem 54:429 - 435.  |  VIEW ARTICLE
Measurement of Total and Gelatinized Starch by Glucoamylase and o-Toluidine Reagent.

B.-Y. Chiang and J. A. Johnson. Copyright 1977 by the American Association of Cereal Chemists, Inc. 

A method to quantitatively determine gelatinized starch in flour- or starch-containing foods was developed. It is based on the principle that gelatinized starch is easily digested by glucoamylase to form glucose, which condenses with omicron-toluidine to give a green chromogen in glacial acetic acid. A sample of flour was dispersed in water and subjected to glucoamylase digestion under controlled conditions for 30 min; then the glucoamylase was precipitated with 25% trichloroacetic acid (TCA) solution. The reaction mixture was centrifuged, the supernatant was reacted with omicron-toluidine, and the color was measured with a spectrophotometer at 630 nm. Total starch was determined by a similar procedure, except that the intact starch in the sample was gelatinized in NaOH solution. From these two readings, the percentage of starch gelatinization could be calculated. The recovery test was satisfactory. Total starch content was calculated by multiplying glucose produced by 0.90. The correlation coefficient between this method for total starch and the official AACC polarimetric method was 0.98. The newly developed method has the advantage of rapidity and precision.