Detection of Waxy Maize Starch Adulteration in Waxy Rice Cake by Use of Stable Carbon Isotope Ratio Analysis

Abstract

Waxy rice cake, a popular New Year food in Japan, is occasionally adulterated with waxy maize starch. The stable carbon isotope ratios (¹³C/¹²C) of 132 samples of 71 waxy rice cultivars grown in Japan and 54 samples of maize starch have been determined by isotope ratio mass spectrometry. The ¹³C/¹²C values of fully-milled waxy rice and maize starch ranged from -24.4 to -27.3 parts per thousand (per mil) and from -9.6 to -11.1 per mil, respectively. Rice cakes with δ¹³C values higher than -24.2 per mil, 3 standard deviations from the mean of fully-milled rice, should be considered adulterated.