Preparation And Qualities Of Whole Grain Rice Produced By Improved Extrusion Cooking Technology

In this thesis, whole grain rice (WGR) was prepared of brown rice (BR) as raw material, by a novel physical processing means, improved extrusion cooking technology (IECT). The optimal extrusion process parameters for preparing WGR was studied by using textural properties, hardness and stickiness, as indicators, and the WGR product was obtained. What’s more, the effect of drying temperature on qualities of WGR and the differences between WGR and BR in eating qualities, nutrition properties and storage performance were also studied in this thesis. The results are as follows.Orthogonal test was used to investigated the influence on hardness and stickiness by material moisture content from24%to36%, screw speed from22.5rpm to28.5rpm and four-zone temperature in the screw extrusion machine from90℃to110℃using polished rice as a reference. The optimal extrusion conditions were as follows:when material moisture content was33%, screw speed was25.5rpm, four-zone temperature in the screw extrusion machine was100℃, the WGR product was with a hardness was763.01N and stickiness was-70.85N, which were similar to the textural properties of polished rice, of which the hardness was769.68N and stickiness was-76.12N.Effect on the nutrition, eating quality and thermal properties qualities of whole grain texturized rice prepared by improved extrusion cooking technology by drying temperature in range of40℃to80℃was studied. The results show that the content of crude fat and free fatty acid decreased with the increasing temperature and then there’s no significant difference in other nutrients when the drying temperature changed from40℃to80℃; However, the whole grain texturized rice shows an easier digestion, softer and more sticky eating quality when the drying temperature is below50℃; Meanwhile, whole grain texturized rice with the thermal properties of lower pasting temperature, shorter pasting time and smaller gelatinization enthalpy was prepared when drying temperature was under50℃.The difference of physical chemical indicators, textural properties, thermal properties and pasting properties were compared between WGR and BR using polished rice as a reference. The results showed:WGR had higher amylose content, gel consistency, WAI and WSI, and the WAI and WSI of WGR improved nearly2.71times and1.64times to BR. A significant increase was observed in stickiness and springiness, while a decrease observed in hardness. In DSC tests, BR exhibited a peak in the62-82℃interval, with an enthalpy value of7.23J/g while WGR prepared by IECT exhibited a small peak (from67℃to78℃) with an enthalpy value of only2.39J/g. After treated by improved extrusion cooking technology, WGR flour presented a higher gelatinization temperature, in comparison with BR flour and Polished rice flour, whereas enthalpy significant decreased. The data obtained by DSC suggests that sample WGR requires higher temperature values for melting, and lower energy required during cooking, which leads the WGR more stable and more desirable cooking qualities. Lower PV, FV, BD, SB were observed from the RVA curves, which may be caused by the paste degree improved after IECT.The influence on the nutritional behavior and storage performance of WGR by IECT were studied the changes of dietary fiber, phytic acid, γ-oryzanol, fat and free fatty acids, combined with SEM and X-ray diffraction and other means. The results showed:phytic acid, γ-oryzanol and crude fat decreased after treated by IECT separately from1.03%to0.68%,66.85mg/100g to43.91mg/100g and2.10%to0.69%, and the amount of γ-oryzanol reduced was much lower than the tradition extrusion method. What’s more, the free fat acid content reduced after treated by IECT from18.26mL KOH/g to15.89mL KOH/g but increased after storage in common condition for two months. However, the amount of free fat acid increased of BR was2.8times to that of WGR. A smoother, tighter, smaller granule was observed with WGR than with BR, In addition, BR was with a loose structure when many small particles, maybe lipid or protein, were on the surface, whereas WGR was with a tightness structure with few small particles. We speculated that the residual lipid and protein were packed in the strong starch structure that formed in the gelatinization during IECT. From the results of X-ray, a characteristic diffraction peak at2θ=17°existed, which indicted the crystal type changed to type B and weakened after IECT treatment. and a characteristic diffraction peak at2θ=20.03°was observed in WGR which inferred amylose-lipid complex existed, which may be one of the reasons that lead the fat decreased after IECT. The relative degree of crystallinity reduced from21.96%to12.94%inferred that Starch molecules than raw brown rice tends to be less orderly state, lower gelatinization enthalpy.