Effects on Maize Starch Properties of Heat-treatment with Water–ethanol Mixtures

Maize starch (1 part) was heated at 120 °C for 20 min in water–ethanol mixtures (5 volumes), in which the water content varied over the range 0–70%, and the product solvent-exchanged with acetone. On treatment with mixtures containing 40–60% water, the swelling power and solubility at 97 °C decreased and the differences between these values measured at 25 and 97 °C narrowed. The properties of starch treated with a mixture containing 30% water resembled those of heat–moisture treated starch. The values of ΔH and ΔS for swelling were greatly decreased by treatment in mixtures with a water content greater than 20–40% (0·39–0·63 mole fraction). Furthermore, the digestibility ratio ofalpha-amylase (endo-type) to glucoamylase (exo-type) was at a maximum after treatment with a mixture containing 30% water. These findings suggest that rearrangements between the amylose and amylopectin in starch granules are occurring after treatment with mixtures containing more than 30% water. These changes in the starch granule are enhanced when the treatment temperature is increased to 100–130 °C.