| Resistant starch refers to starch or starch degradation products that cannot be digested and absorbed by small intestine of healthy human which has a series of physiological benefits,including reducing postpranpranal blood glucose,preventing cardiovascular diseases,preventing obesity,and promoting intestinal health,etc.Using it as food raw material can improve the health care value of products,but its content in food often decreases greatly because of heat treatment,which makes it difficult to play its due health care role.In order to promote the application of resistant starch in hotprocessed food,this project takes early indica rice flour as raw material,adopts physical,enzyme and compound treatment methods to prepare rice flour which can increase the content of resistant starch after reheating,and studies the formation mechanism of resistant starch in this rice flour.The main research contents and results are as follows:(1)The method of increasing resistant starch content in rice flour was studied.With pearl NO.3 rice flour as raw material,through studying different physical/enzyme treatment method for resistant starch content in rice flour,the influence of four kinds of method of annealing treatment(ANN),pullulanase(PR),annealing combined pullulanase(ANP)and and heat-moisture combined pullulanase treatment(HMP)was used to improve the resistant starch in rice flour.And the processing conditions of these four methods were optimized.The results showed that annealing treatment could improve the resistant starch content of rice flour before reheating,and the resistant starch content of rice flour before reheating was 26.27%when the treatment conditions were 80%water content,50℃ and 12 h.Pullulanase,annealing combined pullulanase and heat-moisture combined pullulanase treatment could improved the resistant starch content of rice flour after reheating.When the pullulanase treatment conditions were enzyme addition 40 U/g and enzymatic hydrolysis 10 h,the resistant starch content of rice flour before and after reheating was 10.52%and 13.98%,respectively.When the annealing combined pullulanase conditions were enzyme addition 40 U/g,enzymatic hydrolysis 10 h,water content 80%and annealing treatment at 50℃ for 24 h,the resistant starch content of rice flour before and after reheating was 17.73%and 22.05%,respectively.When the heat-moisture combined pullulanase conditions were enzyme addition 40 U/g,enzymatic hydrolysis for 12 h,water content adjusted to 30%and heatmoisture treatment at 120℃ for 4 h,the resistant starch content of rice flour before and after reheating was 12.50%and 30.60%,respectively.(2)The effect of improving the preparation method of resistant starch of rice flour after reheating on the properties of rice flour was studied by RF and ANN as pairs.The results showed that the resistant starch of untreated rice flour and four samples by different treatment had irregular shape and a wide range of granule size distribution.Among them,the granule shape of rice flour after annealing treatment was similar to that of untreated rice flour,but its surface was relatively uneven and has holes.And ANN had increased polarization cross strength,amylopectin content,double helix structure and crystallinity,and had increased V-type crystal structure.Compared with RF and ANN,PR,ANP and HMP had increased particle size.PR and HMP had dense particle shape,while ANP had partial coarser surface and porous structure.The crystal structure of PR and ANP were C-type,and that of HMP was A-type like RF and ANN.A large number of amylose-lipid complexes were formed in PR,ANP and HMP,and their relative crystallinity increased to 30.86%,32.52%and 31.27%,respectively.The hydrogen bond strength of the PR,ANP and HMP decreased significantly,and the short-range order of starch was higher.The amylose content,amylopectin and amylose size increased,and the amylose content of PR was 36.12%,ANP was 30.81%,HMP was 36.18%.(3)The effect of improving the preparation method of resistant starch of rice flour after reheating on the properties of rice flour was studied.The results showed that the thermal stability of rice flour after annealing treatment decreased significantly,and appeared as solid after gelatinization,its solubility and freeze-thaw stability increased compared with untreated rice flour,while its apparent viscosity,swelling power decreased and it appears as shear thinning under the action of shear force.After pullulanase,and its combined annealing or heat-moisture treatment,To,Tp and Tc,while enthalpy of rice flour decreased,the weight loss rate in the second weight loss stage of thermogravimetric analysis ranked as HMP(56.44%)<PR(58.81%)<ANP(59.89%)<RF(64.49%)<ANN(65.00%).Theresidual mass of PR,ANP and HMP were larger than RF and ANN at 700℃,and the thermal stability was increased.The solubility of PR,ANP and HMP were always greater than RF and ANN,and when the temperature was greater than 60℃,the overall trend of swelling power was RF>ANN>PR>HMP>ANP.Rapid viscosity analyzer(RVA)analysis showed that the RVA curves of PR,ANP and HMP were relatively flat,and the viscosity of the sample system was always lower than RF and ANN.Under the action of shear force,G’ of the PR,ANP and HMP were always greater than G",indicating that the system had outstanding elasticity and appears as a solid state.The apparent viscosity was always lower than RF and ANN,and the variation range was small.After freeze-thaw treatment,the water extraction rate increased significantly and the freeze-thaw stability decreased.(4)Correlation analysis was conducted to explore the relationship between the structure and properties of rice flour with higher resistant starch content after reheating,and the formation mechanism of resistant starch was analyzed.The results showed that the thermal stability of rice flour samples was mainly related to particle size,shortrange order,amylose content,chain length and amylopectin size,and the change of thermal stability also led to the change of swelling degree and apparent viscosity.The formation mechanism of resistant starch of rice flour with higher resistant starch-content after reheating was mainly as follows,rice flour were gelatinized and enzymolized to form a large number of linear starch chains,recrystallization formed a new stable crystal structure in the cooling process,which significantly improved the thermal stability,and increased the interaction between protein,lipid and starch and the content of amyloselipid complex.The PR,ANP and HMP only expanded slightly in the reheat cooking process,which reduced the contact area between amylase and starch particles,and significantly increased the resistant starch content of rice flour samples after reheating.The resistant starch content and thermal stability of rice flour with higher resistant starch after reheating cooking was significantly increased by using pullulanase,annealing combined pullulanase and heat-moisture combined pullulanase treated rice flour.The application of this kind ofrice flour in hot-processed food industry can reduce the loss of resistant starch caused by heat treatment,improve the resistant starch of products,and ensure the health care value of high resistant starch products. |
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