VARIATION FOR THERMAL-PROPERTIES OF STARCH IN TROPICAL MAIZE GERM PLASM

The thermal properties of starches during gelatinization are important to the food industry, primarily because of the rapid market growth of convenience foods. Few studies have been conducted on the amount of t hermal variation of maize starch in normal maize genotypes. Inter- and intrapopulation variability for thermal properties of laboratory-isol ated starch from 35 tropical and semitropical maize populations, repre senting a range of sources and maturity groups, was evaluated by using differential scanning calorimetry. Starch was isolated from a bulk of 10 kernels from each of 16 plants in each population; two subsamples from each plant were analyzed independently. Endotherms were analyzed to determine enthalpy (DELTAH), peak onset (T(o)), peak maximum (T(p)) , and peak conclusion (T(c)) temperature. The temperature range of gel atinization was calculated as (T(c) - T(o)). Among 35 populations, hig hly significant differences (P less-than-or-equal-to 0.01) for all mea sured thermal properties were observed. Means of T(o), T(p), and T(c) were 63.0, 71.0, and 77.8-degrees-C, respectively; ranges were 64.3-69 .6-degrees-C, 70.1-73.9-degrees-C, and 76.8-79.6-degrees-C, respective ly. Temperature ranges of gelatinization varied between 9.8 and 13.O-d egrees-C. Average enthalpy (DELTAH) was 10.5 joules per gram with a ra nge of 8.2-12.3 J/g. Within each population, highly significant differ ences were noted in the T(o) values of endotherms in all populations; highly significant differences were also noted in the T(p), T(c), and temperature range in most populations. Within each population, there w ere few significant differences in the DELTAH. There was little relati onship between starch thermal properties and population origin, kernel color, kernel weight, kernel starch content, or plant maturity group. The results demonstrate that genetic variability for thermal properti es of maize starches exists in tropical and semitropical maize germ pl asm. Compared to the range of starch thermal properties found in maize endosperm mutants, the range of variability in this germ plasm was li mited.