Influence of heating rate and annealing on the melting thermodynamic parameters of some cereal starches in excess water

Some normal (maize, wheat, barley, rye) and high amylose (barley) starches were studied using the method of differential scanning microcalorimetry (DSC). It was shown that a decrease of heating rate from 3 K/min to 0.25 K/min for 1% aqueous dispersions of starch does not lead to changes of the thermodynamic melting parameters of crystalline lamellae irrespective of the origin of starches. With the exception of the results for maize starch, the same behavior is observed for melting of amylose-lipid complexes. For maize starch, a decrease of heating rate and an annealing of crystalline lamellae lead to an increase of melting enthalpy of amylose-lipid complexes but does not change their melting temperature. The melting cooperative units for crystalline lamellae of the cereal starches were calculated. Using the average value of the melting cooperative unit, the lamellar thickness was determined. It is practically equal to the thickness of crystalline lamellae in the amylopectin model proposed by Robin. It was shown that the temperature dependence of the heat capacity for starch maize lipids has a negative increment. Some concepts concerning melting mechanisms of crystalline lamellae and amylose-lipid complexes are discussed.