Preparation And Properties Of Rice Resistant Starch By Extrusion

Resistant starch (RS) refers to starch that is indigestible in small intestine and is fermented in colon by microbial. The rice resistant starch is either natural occurrence or artificial made with rice grain. Extrusion, due to its production capasity, is a prospective approach to manufacture rice resistant starch (RRS) in the industrial scale.The objectives of this study were to investigate the influence factors of extrusion on RRS, screen the optimum parameter for the RRS production, explore the formation mechanism of RRS, and analyse the character of RRS.Moisture content at 40 %( dry bases), barrel temperature of 170℃, screw frequency of 35 Hz, feeding rate of 20 Hz and then stored for 7 d at 4℃were the optimal conditions for RRS producture with the yield of 8.77%.Moisture content of the material, rotating speed of the screw, temperature of the barrel, storage temperature and feeding rate have significant effects on the preparation of the RRS, especially the moisture content and the storage temperature.Among the material components, amylose, protein, lipids and reduced sugar, the content of the amylose was the key factor in the yielding rate. Protein had the embedding effects on the starch granule with significant effects on the yielding rate. Lipids, reacted with the amylose, due to its specific structure, also showed effect on the yield rate. Reducing sugar acted as the role of plasticizer under the condition of high pressure, high temperature and strong shear force, promoted the yielding rate of RRS.Extruded-cooled processing cycle increased the yield of RRS. However, no significant effect was observed when stored with persistent variable temperature.Compared with the normal rice starch, the water absorption value of the RRS was lower. The maximum absorption spectra wavelength of the rice resistant starch was 578 run, in agreement with reference. The viscosity peak of the RRS is significantly lower than that of the rice starch. RRS granule had irregular structure. The characteristic crystalline peaks of RRS and rice starch were concentrated within 30°, and the advanced microcrystal area of the RRS was less than that of the rice starch. Compared to the original rice starch, RRS showed higher thermal-stability and the more stable crystallize region.This study showed that extrusion in preparation of RRS was an effective method, with broad prospects. However, improvement of the RRS yield by extrusion was worth futher studying.