STRUCTURE AND CHEMICAL AND PHYSICOCHEMICAL PROPERTIES OF JOB'S TEAR (COIX LACRYMA-JOBI L.) KERNELS AND FLOURS

Abstract

In Job’s tear, the germ is enfolded inside the kernel and comprises ca. one third of the whole grain. To assess the effect of germ on flour properties, degermed flour was manually prepared from grains of white and black husk cultivars. The protein of whole grain and degermed flours was not significantly different (p > 0.05). The antioxidant properties, which were total phenolic content, DPPH radical scavenging and reducing power, and coixenolide of whole grain and degermed flours of both cultivars were in the ranges of 7.33-8.18 mgGAE/g, 5.40-7.53%, 2.56-2.88 and 0.02-0.53 µg/g, respectively. The Job’s tear starch granules showed a round and polyglonal shape and their average size was 11.68-12.29 µm. The gelatinization temperature range of white and black Job’s tear starch was 67-81 o C and the retrogradation behavior of Job’s tear starch occurred after storage at 4 o C for 39 days as monitored by differential scanning calorimetry. The peak viscosity of the white Job’s tear flours was greater than those of the black cultivar flours but the setback and pasting temperature was lower. The swelling power of the white Job’s tear flours was higher than that of the black cultivar flours, but their solubility was lower and the opposite result was found in the starch.