Relevance of amylose-lipid complexes to the behaviour of thermally processed starches

Maize grits of 50% moisture content (db) were thermally converted at 140 de greesC without shear. Analysis of the samples using X-ray diffraction, diff erential scanning calorimetry, optical and scanning electron microscopy and by measurement of hot water absorption and solubility indices indicated th at maize grits heated for 15 min or longer had undergone virtually complete melting of crystalline structure without loss of granular integrity and am ylose-lipid complexes were formed. Rapid visco analysis (RVA) profiles of t hese samples were characterised by decreasing gelatinisation peak and final viscosities with longer heating times, but no cold swelling peak was obser ved for any heat treatment. Similar RVA patterns were also obtained for cer eal starches (maize, wheat, rice) as well as for cassava starch in the pres ence of glycerol monostearate (GMS), whereas cassava, potato, waxy maize st arch and waxy maize starch in the presence of GMS, all characterised by low lipid or amylose contents, showed cold swelling behaviour. It was conclude d that the presence of amylose-lipid complexes in the granular starch parti cles played a key role in restriction of water penetration into the particl es as well as starch granule swelling and solubilisation in cold water.