Characterization of starches from wild and long grain brown rice

Starch from wild rice (Zizania palustris L) was isolated and yielded only 38.3% on a whole seed basis, compared with 64.4% starch yield from long grain brown rice (Oryza sativa indica). The granules were angular to polygonal in shape with a diameter of 2-8 mu m, similar to starch granules from long grain brown rice. Scanning electron micrographs revealed the presence of smooth granular surfaces. Lipids were extracted by acid hydrolysis and by selective solvent extraction with chloroform-methanol 2:1 v/v at ambient temperature, followed by n-propanol-water 3:1 v/v at 90-100 degrees C. The acid-hydrolyzed extracts which represented the total starch lipids averaged 0.29%. The free lipid in the chloroform-methanol extract was 0.04%, whereas the free and bound lipids in the n-propanol-water extracts totalled 0.24%. The amylose content of wild rice starch was 29.4%, of which 28.6% was complexed by native lipids. The gelatinization temperature range was 51-64 degrees C and the enthalpy of gelatinization was 7.5 J/g. The visco-amylographic examination on starch pastes (6% w/v) showed high thermal stability during the holding cycle (at 95 degrees C), and the absence of a set-back on cooling. Native starch was readily hydrolyzed by alpha-amylase (92.3% in 72 h) and 2.2 N HCl (99.0% in 20 days). Differential scanning calorimetry and acid hydrolysis studies on stored gels showed that wild rice starch was resistant to retrogradation. Copyright (C) 1996 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology