The effect of heat-moisture treatment on the structure and physicochemical properties of normal maize, waxy maize, dull waxy maize and amylomaize V starches

Normal maize, waxy maize, dull waxy maize and amylomaize V starches were heat treated at 100 degrees C for 16 h at a moisture content of 30%. The results showed that the X-ray intensities of the major d-spacings of all starches increased on heat-moisture treatment (waxy maize > normal maize > dull waxy maize > amylomaize V). This treatment decreased the apparent amylose content (amylomaize V > normal maize), swelling factor (amylomaize V > waxy maize > dull waxy maize > normal maize), amylose leaching (amylomaize V > normal maize), pasting viscosities (amylomaize V > normal maize), acid hydrolysis (amylomaize V > normal maize > waxy maize > dull waxy maize), enzyme hydrolysis (amylomaize V > normal maize > dull waxy maize > waxy maize) and syneresis (amylomaize V > normal maize > waxy maize approximate to dull waxy maize). The gelatinization transition temperatures of all starches increased on heat-moisture treatment (amylomaize V > normal maize > waxy maize > dull waxy maize). However, the gelatinization temperature range increased only in normal maize and amylomaize V starches (amylomaize V > normal maize), while it remained unchanged in both the waxy starches. The enthalpy of gelatinization remained unchanged on heat-moisture treatment in all starches and the pasting viscosities of the two waxy starches were also unaffected. The foregoing data showed that starch chains within the amorphous and crystalline regions of the granule associate during heat-moisture treatment. However, the extent of this association was of a greater order of magnitude within the amorphous regions. DSC studies have indicated associations involving amylose chains (amylose-amylose and amylose-native starch lipids) resulted in the formation of new crystallites of different stabilities. In contrast, associations involving amylopectin chains (amylopectin-amylopectin) did not lead to crystallite formation. (C) 1996 Academic Press Limited