Relevance of Amylose-Lipid Complexes to the Behaviour of Thermally Processed Starches

Abstract

Maize grits of 50% moisture content (db) were thermally converted at 140 °C without shear. Analysis of the samples using X-ray diffraction, differential scanning calorimetry, optical and scanning electron microscopy and by measurement of hot water absorption and solubility indices indicated that maize grits heated for 15 min or longer had undergone virtually complete melting of crystalline structure without loss of granular integrity and amylose-lipid complexes were formed. Rapid visco analysis (RVA) profiles of these samples were characterised by decreasing gelatinisation peak and final viscosities with longer heating times, but no cold swelling peak was observed for any heat treatment. Similar RVA patterns were also obtained for cereal starches (maize, wheat, rice) as well as for cassava starch in the presence of glycerol monostearate (GMS), whereas cassava, potato, waxy maize starch and waxy maize starch in the presence of GMS, all characterised by low lipid or amylose contents, showed cold swelling behaviour. It was concluded that the presence of amylose-lipid complexes in the granular starch particles played a key role in restriction of water penetration into the particles as well as starch granule swelling and solubilisation in cold water.