Physicochemical and morphological properties of starch from fresh waxy corn kernels.

The characteristics on physicochemical and morphological properties of starches were investigated in fresh waxy corn kernels. Starches were isolated from eight waxy corn genotypes at the immature kernel stage growing in Thailand. The starch content showed variation with genotypes and ranged from 77.76 to 90.97 %. Granule size distribution showed a two population of starch granules with peak values ranged from 0.8 to 1.1 µm (small) and 9.0 to 12.2 µm (large). Genotypes were also significantly different for average chain length (CL), unit chain length distribution and pasting properties. The small granule (<5 µm) was negatively correlated with CL and degree of polymerization (DP) 25-36 of amylopectin (-0.82 and -0.67, respectively, P < 0.01). And a strong relationship between trough and final viscosity was consistent with the contribution of pasting properties.

Changes in physicochemical properties of waxy corn starches after harvest, and in mechanical properties of fresh cooked kernels during storage.

Changes in the physicochemical properties of waxy corn starches after harvest and in the mechanical properties of cooked fresh kernels during storage were investigated. Immature waxy corn ears from four genotypes were stored at ambient temperature, and starches were isolated from kernels removed at 0, 2, 4 and 6 days after harvest. Starch content in the kernels generally increased with storage time, and also significantly differed depending on the genotype. For all the days after harvest, medium granules had the highest contribution to the total starch volume, followed by small and large granules. The average chain length distribution of amylopectin increased in relation to storage time. Starches at harvesting state exhibited the lowest peak viscosity in all four genotypes, which increased relative to postharvest periods. Moreover, the average force behaviours of cooked kernels were greatly affected by storage times after cooking.

Changes in physicochemical properties of waxy corn starches at different stages of harvesting.

Starches were isolated from immature waxy corn kernels harvested at 0, 2, 4 and 6 days after optimum stage (DAO) and from mature kernels at 16 DAO. The starch contents showed varied according to genotypes and harvesting stages. The accumulation of starches showed an increasing trend in relation to delayed harvesting time, from the optimum stage until the physiological maturity stage. Among all harvesting stages, medium granules had the highest contribution to the total starch volume (60.8-81.5%), followed by large (5.7-30.1%), and small granules (9.1-15.3%). Average chain length distribution of amylopectin ranged from DP 14.7 to 16.9 for KKU-UB, DP 16.9 to 17.4 for KKU-JD, and DP 5.7 to 30.1 for Violet white. The pasting behaviors of starches were greatly affected by harvesting times. The peak viscosity of starches increased with delayed harvesting until physiological maturity and then decreased until dried kernels at 35 days after pollination.