2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

A barley branching enzyme IIa was introduced into Hi II and OH43 maize by using a biolistic gun, the maize was then crossed to OH43 or OH43aeae inbred lines to produce cornstarch with altered structures. Kernels were collected at 20 day-after-pollination (DAP) for the analysis of branching enzyme activity, monitored by the phosphorylase A stimulation assay. Thermal properties of starches isolated from mature kernels were determined by differential scanning calorimetry. Some mature kernels displaying different phenotypes from normal maize kernel indicated 1:1 segregation of normal and transgenic maize kernels. Branching enzyme activities of 20 DAP kernels varied form 5 to 200%. Onset and peak gelatinization temperatures of transgenic cornstarch were in range of 64.0-70.1°C and 74.3-103.0°C, respectively. Onset retrogradation temperature ranged from 37.9-78.8°C. Retrogradation rate varied from 13.9 to 100%. Starches from corn kernels with mildly shrunken appearance showed wide gelatinization temperature ranges and high percentages of retrogradation. Results suggested that some transgenic corns might have suffered silencing of maize branching enzyme gene, producing starch with high retrogradation rate, whereas others expressed barley branching enzyme and displayed lower gelatinization temperature and retrogradation rate.