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 we re 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-spacing s of all starches increased on heat-moisture treatment (waxy maize > n ormal maize > dull waxy maize > amylomaize V). This treatment decrease d 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 (a mylomaize V > normal maize), acid hydrolysis (amylomaize V > normal ma ize > waxy maize > dull waxy maize), enzyme hydrolysis (amylomaize V > normal maize > dull waxy maize > waxy maize) and syneresis (amylomaiz e V > normal maize > waxy maize approximate to dull waxy maize). The g elatinization transition temperatures of all starches increased on hea t-moisture treatment (amylomaize V > normal maize > waxy maize > dull waxy maize). However, the gelatinization temperature range increased o nly in normal maize and amylomaize V starches (amylomaize V > normal m aize), while it remained unchanged in both the waxy starches. The enth alpy of gelatinization remained unchanged on heat-moisture treatment i n all starches and the pasting viscosities of the two waxy starches we re also unaffected. The foregoing data showed that starch chains withi n the amorphous and crystalline regions of the granule associate durin g heat-moisture treatment. However, the extent of this association was of a greater order of magnitude within the amorphous regions. DSC stu dies have indicated associations involving amylose chains (amylose-amy lose and amylose-native starch lipids) resulted in the formation of ne w crystallites of different stabilities. In contrast, associations inv olving amylopectin chains (amylopectin-amylopectin) did not lead to cr ystallite formation. (C) 1996 Academic Press Limited