Identifying the origin plant of starches by numerical description of the coloration of iodine-starch reaction solutions

Abstract

Microscopy is the primary technique for identifying the origin plant of a starch sample but requires operators with highly proficient skills and experience, and is unsuitable for discriminating modified starches such as pregelatinized starches. The plant species from which the starch is isolated is reflected in the characteristic color of the iodine-starch reaction solution. However, visual observation is subjective and vague because color perception is organoleptic and color is expressed by ambiguous names such as “orange-red” and “deep blue”. Quality management using the color of samples is gaining wider acceptance in the field of natural products as well as industrial products because simple, easy to use, high-performance spectrophotometers are now widely used. In this study, the color of iodine-starch reaction solution of 31 kinds of starches and pregelatinized starches from maize, wheat, potato and rice were measured spectrophotometrically and the color was numerically described using the L^*a^*b^* color system. The characteristic (a^*, b^*) values grouped together on the color system according to the origin plant for each starch, suggesting that numerical information on the color reaction is useful for estimating the origins of starches.