ESTIMATION OF CONTRIBUTIONS OF HYDRATION AND GLASS-TRANSITION TO HEAT-CAPACITY CHANGES CURING MELTING OF NATIVE STARCHES IN EXCESS WATER

Contributions of the heat capacity changes by hydration (Delta(m)C(p)( hydr)) and by glass transition (Delta(m)C(p)(glr)) to the hear capacit y changes (Delta(m)C(p)(exp)) measured during melting of various nativ e starches in excess water were estimated. Whereas Delta(m)C(p)(grt) w as independent of the origin and polymorphous structure of the starche s, Delta(m)C(p)(hydr) depended on the origin of starch. It is shown th at Delta(m)C(p)(exp) of native starches can be calculated as the sum o f Delta(m)C(p)(gtr) and Delta(m)C(p)(hydr). Calculated values of Delta (m)C(p)(gtr) (12.5 +/- 2.8 Jmol(-1) K-1) were similar to those of synt hetic polymers. The values of Delta(m)C(p)(hydr) of all investigated s tarches varied from 10.7 to 18.5 Jmol(-1) K-1 except for maize starch (56.1 Jmol(-1) K-1). It is suggested that this difference is due to sp ecial structural features of maize starch.