| Rice is a staple food for most of the world’s population,which could be processed into foods such as rice and porridge,and often ground into flour and then processed into rice products such as rice flour,rice crackers,rice cakes and rice cereal.Resistant starch has a series of functional characteristics,but people don’t get the resistant starch they expect from eating food that is significantly reduced during processing.Therefore,it is improtant to increase the content of resistant starch after cooking.This project mainly used early indica rice as raw material,removed lipids to different degrees and different types of proteins,and explored the changes of resistant starch content before and after cooking by pullulanase complex moist-heat treatment,and studies are carried out from the aspects of composition,structural characteristics and thermal stability,The main research contents and conclusions are as follows:(1)Using early indica rice flour as raw materials,determined the conditions of defatting,deproteinization,the gelatinization time of rice flour and the amount of water added during cooking.The results showed that the preparation conditions of weakly degreasing,medium degreasing and strong degreasing rice flour were 30℃-1 min,50℃-30 min and 50 ℃-24 h,respectively,and the removal time of albumin,globulin,prolamin and gluten in rice flour were 6 h,4-h,4 h and 24 h,respectively.The gelatinization time of rice flour was 15 min,the improvement effect of resistant starch content after cooking reached 223.5%,,there was no significant change in the content of resistant starch,when the gelatinization time exceeded 30 min,and the powder-water ratio was 2:1 during cooking,the content of resistant starch increased after cooking.(2)The effect of endogenous components on the increase of resistant starch content of rice flour before and after cooking by pullulanase complex moist-heat treatment was studied.The results showed that the lower the endogenous lipid content,the better the enzymatic hydrolysis and moist-heat treatment that the increase rates of resistant starch content before and after cooking were 24.63%,36.14%and 35.54%,respectively,and the decrease of starch lipid content was not conducive to the formation of resistant starch after cooking.The removal of endogenous proteins promoted the formation of resistant starch in rice flour treated with pullulanase complex moist-heat.Albumin and globulin had inhibiting effect on the formation of resistant starch after treatment,and prolamin and gluten had promoting effect.In a word,the removal of different types of proteins at different strengths had different effect on the formation of resistant starch before and after cooking.(3)The effect of endogenous components on the structure of rice flour before and after cooking was improved by pullulanase complex moist-heat treatment.The results showed that the crystal structure of rice flour with endogenous lipids removed was C-type before and after cooking,and the crystal structure of rice flour with endogenous protein removed by pullulanase complex moist-heat treatment changed from C+V type to A+V type.With the deepening of defatting and the removal of different types of protein,the total starch and amylose content increased significantly.The content of amylose in rice flour with different degrees of defatting and different types of proteins was significantly increased by pullulanase complex moist-heat treatment,and the content of amylose decreased significantly after cooking,while the content of amylose in rice flour with four proteins removed under different strength defatting was significantly reduced by pullulanase complex moist-heat treatment.The endogenous components had significant effect on the secondary structure of protein,the short-range ordered structure and double helix structure of starch after cooking,and inhibited the formation of resistant starch before and after cooking of rice flour treated by pullulanase complex moist-heat treatment(4)The effect of endogenous components on the improvement of thermodynamic properties of rice flour before and after cooking by pullulanase complex moist-heat treatment was studied.The results showed that the gelatinization temperature of rice flour and different types of proteins with different degrees of defatting increased significantly before and after cooking by pullulanase complex moist-heat treatment,the gelatinization temperature under different intensity degreasing with the removal of albumin,medium and high strength degreasing with the removal of globulin and medium intensity degreasing with the removal of prolamin were significantly increased,Tp under high strength degreasing was significantly reduced.The treated rice flour has an increased gelatinization temperature after cooking and is thermally stable. |
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