THERMAL-BEHAVIOR OF POTATO AMYLOSE AND ENZYME-RESISTANT STARCH FROM MAIZE

The thermal properties of potato amylose (degree of polymerization 5,5 00) and of enzyme-resistant starch (RS) (degree of polymerization 65) from autoclaved maize starch in a concentrated aqueous system (22%, w/ w) were studied by differential scanning calorimetry (DSC). Heating of amylose and RS in the DSC instrument to 180-degrees-C (heating rate 5 -degrees-C/min) gave melting transitions at 153.6 and 139.8-degrees-C, respectively, indicating disordering of fairly thermostable regions. This heating to high temperatures was accompanied by a partial thermal degradation of the linear amylose and RS chains. Reappearance of endo therms during repeated heating and the appearance of exotherms during each cooling phase suggested (re)association of chains from the polyme r melts of both amylose and RS. Association of amylose and RS chains a ppeared to start between 80-75-degrees-C and 60-55-degrees-C, respecti vely. Whereas interactions between the long amylose chains were reduce d at cooling rates of >10-degrees-C/min, interchain contacts between t he shorter RS chains seemed not to be affected by the rate of cooling. In the presence of the complexing agent L-alpha-lysophosphatidylcholi ne (LPC), the process of association of linear chains was competitivel y affected by the formation of inclusion complexes of the linear chain s with LPC. At an LPC concentration of 10% (w/w), complex formation do minated, and no association of amylose or RS chains was observed.