Physicochemical properties of normal and waxy job's tears (Coix lachryma-jobi L.) starch

Abstract

Physicochemical properties of starches from eight coix (Coix lachryma- jobi L.) accessions were investigated. There was considerable variation in most measured traits, generally corresponding to the separation into waxy and normal amylose types. The amylose contents of five normal coix ranged from 15.9 to 25.8%, and those of three waxy coix were 0.7-1.1%. Swelling power of waxy coix starches varied between 28.6 and 41.0 g/g, generally higher than waxy maize. Normal coix starches had significantly higher gelatinization peak temperature (T(p)) than the normal maize, 71.9 75.5°C. The T(p) of waxy coix starches was 71.1-71.4°C, similar to waxy maize. Rapid Visco-Analyzer (RVA) pasting profiles of normal coix showed little variation and closely matched the normal maize starch profile. Pasting profiles of waxy coix showed more variation and had lower peak viscosities than waxy maize starch. Waxy coix starches formed very weak gels, while the gel hardness of normal coix starches was 11.4-31.1 g. Amylose content was the main factor controlling differences in starch properties of the coix starches.