| The Improved Extrusion Cooking Technology (IECT) which was different from traditional gelatinization method and extrusion cooking was a new physical processing approach. Based on the present situation, IECT was chosen to prepare resistant starch-fortified rice and investigate the physiochemical, properties and RS content. Effect of process parameter (moisture content, screw speed, barrel temperature) on product properties were studied based on IECT. It was studied that resistant starch-fortified rice was prepared by IECT and its properties were characterized. The cooking quality and in vitro digestion of RS rice were also studied. Preparation process parameters of RS rice Were designed and optimized based on IECT to manufacture the products which show the similar taste with natural long rice and can be used as staple food to meet people with diabetes.Using long-grain starch as the raw material, IECT conditions, including feed moisture content (25-50%), screw speed (22.5-45rpm), shearing compression metering zone temperature (SCMT,90-140℃) on the physicochemical and content of RS rice, were investigated by response surface methodology using Central Composite Design. The results showed that the expansion of starch extrudate changed from126%to166%. Increased feed moisture content significantly decreased the expansion, WSI (P<0.05) whereas increased the WAI. The trend was increased first, then decreased as feed moisture increased. Increased the SCMT significantly increased first then decreased expansion, WAI, RS content whereas increased WSI. Increased screw speed significantly increased first then decreased WSI whereas increased RS content. As for expansion, the trend was increased first, and then kept stable. The RS content would be reached to4.6%when the feed moisture content, screw speed and SCMT were38%,34.5rpm and115℃respectively.Using rice flour and RS as raw material, the RS rice was prepared by IECT based on previous results of rice starch. By comparing the properties of RS rice with natural rice and control rice, the results indicated that the granule size of RS rice was smaller than that of control rice whereas it was bigger than natural rice. Furthermore, the RS rice showed the shape of continuous paste. The DSC thermograms showed that two peak of enthalpy were observed for the RS rice sample which could be the ungelatinized residue granule and retrograded starch. The RS rice showed the V-type pattern and15.69%of relative crystallinity. Furthermore, the RS rice showed the similar texturized properties with natural rice.By comparing the cooking qualities of RS rice with those of natural rice, the results showed that the RS rice belonged to the good quality of level two. At the same time, the amylose content (24.88±0.11%) was higher than the natural rice (23.66±0.24%). Gel consistency and alkali spreading value were similar between RS rice (65±2,5.2±0.1) and natural rice (66±1,5.8±0.1). Bibulous rate (102.3±3.1%) and inflation rate (103.5±3.4%) of RS rice was less than natural rice (150.6±3.7%,120.1±2.2%). Iodine blue value (0.22±0.01) of RS rice was less than natural rice (0.43±0.02) whereas light transmittance (78.4±0.24%) of RS rice is higher than the natural rice (62.6±0.45%). The experiments of in vitro digestion results showed that comparing to natural rice (RDS41.22±0.84%, SDS54.94±0.69%, RS3.84±0.23%), the digestive properties were greatly improved for the natural rice (RDS62.92±0.91%, SDS34.75±0.34%, RS2.32±0.11%). However, the RS rice showed slow digest starch (46.04±0.29%) and resistant starch content (9.99±0.47%) greatly were increased, and at the same time the digestive rate (0.66min-1) and postprandial blood sugar index (78.02) were both reduced.In all, all the results showed that the resistant starch-fortified Rice with the low digestive rate and postprandial blood sugar index would be prepared by IECT. Furthermore, the resistant starch-fortified rice would be showed the similar texturized properties with natural rice and would be used as staple food to meet people with diabetes. |
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