| The pre-cooked treatment of coix seed,oats,white sorghum and black rice was carried out by thermostatic soaking and microwave technology to achieve a certain degree of gelatinization and the same maturity with rice after cooking together.First of all,the response surface and orthogonal test methods were used to optimize the process of same maturity when cooked with rice.The effects of various factors on the degree of gelatinization and sensory properties of four kinds of coarse rices were studied,respectively.Then the effects of precooked treatment on the main nutrient composition,chroma,rehydration,texture and digestion characteristics of coix seed,oats,white sorghum and black rice were studied.Starch was isolated from natural and pre-cooked coarse rices respectively,there was a comparative study of their differences in physicochemical properties,morphology,crystal structure,thermal properties and layered structure through using scanning electron microscopy,polarization cross,differential scanning calorimetry,fourier transform infrared spectroscopy,X-ray diffraction,small angle X-ray scattering means.Experimental research conclusions are as follows:? Through constant temperature soaking and microwave processing of coarse rices to achieve the same maturity after cooking with rice.The optimal process parameters of pre-cooked coix seed were: the soaking temperature 46.4 ? for 0.9 h,microwave power 600 W,intermittent microwave 85 s;pre-cooked oats with the optimal process parameters of the soaking temperature 40 ?,microwave power 1200 W,intermittent microwave 40 s;pre-cooked white sorghum with the optimal process parameters of the soaking temperature 55 ?,microwave power 800 W,intermittent microwave 80 s;and pre-cooked black rice with the optimal process parameters of the soaking temperature 50 ?,microwave power is 600 W,intermittent microwave 60 s.?After precook,the total starch and protein of four coarse rices were increased compared with natural coarse rices and the protein content of coix seed was not significantly decreased.After precook treatment,the crude fat of coix seed,oats and black rice was significantly increased and the crude fat of white sorghum decreased.The resistant starch content of the pre-cooked four coarse rices decreased.After precook,coix seed was changed transparent white and lose luster,oats became shiny and bright yellow,white sorghum became slightly dark yellow,black rice lose some luster and black and purple.After precook,the hardness,adhesion and chewiness of the four coarse rices were significantly reduced when cooking with rice,and the adherence,cohesion,adhesion and restoring force were closer to rice.Rehydration of fourcoarse rices were significantly improved.After precook treatment,the content of fast digested starch in four coarse rice was increased.The content of slow digestive starch in coix seed and black rice increased.The SDS content of oats and white sorghum decreased.The resistant starch content of the four coarse rices was significantly decreased after pre-treatment.? The natural coix seed starch was mostly ovoid and elliptic.The natural oat starch was mostly irregular polygon,a small part of the ellipse.The natural white sorghum starch was mostly recognizable quasi-circular object.The natural black rice starch was polygonal,more uniform size.After precook,the surface of the four coarse rices was cracked and broken,some umbilical points of the starches appeared pits,and the surface of the coix seed starch granules became rough.After precook,the birefringence of coix seed,oat and white sorghum starches blurred and disappeared and the birefringence of oat starch disappeared,the particles swelled totally.The enzymatic hydrolysis rate of four coarse rices was significantly improved after pretreatment.Amylose of pre-cooked coix seed and black rice decreased.Amylose of precook oat and white sorghum rose.? After precook,the maximum absorption peak wavelengths of the four coarse rices were shifted to the right and red shift occurred.The maximum absorption peak wavelength of coix seed starch was close to the amylopectin,and the waveform of the scanning spectrum was similar to the amylopectin,which were symmetrical distribution.After precook,the maximum absorbance of four coarse rices was not changed greatly.The gelatinization peak temperature of four coarse rices starch was between 62 ? and 76 ?,and the ?T and ?H values of four coarse rices were decreased after pretreatment.With the decrease of the resistance starch in the four coarse rices,the gelatinization enthalpy of DSC also decreased.The crystal structure of four coarse rices starch were all type-A crystals,while the starch crystal structure did not change after precook,still type-A starch.The crystallinity of the natural coix seed,oats,white sorghum and black rice starch was 24.74%,18.74%,25.88% and 25.85% respectively.The relative crystallinity of pre-cooked coix seed,oats,white sorghum and black rice starch decreased to18.89%,14.98%,18.08% and 24.43% respectively,and the decrease in gelatinization enthalpy was also echoed.The relative crystallinity of black rice increased from 24.86% to 27.37% after pretreatment.Compared with the FT-IR spectra of the starch,the coarse rices in the whole spectrum of 400 ~ 4000 cm-1 had the same structural characteristics before and after the treatment.The absorption peak position was basically one-to-one.Precook treatment did not change the chemical composition of starch molecules,nor did it produce new chemicals.The results showed that there were obvious broad scattering peaks in the range from 0.6 to 0.8 nm-1,and the DB of the four pre-cooked coarse rices were smaller and the peak value decreased.Afterpre-cooked treatment,the difference(?L)of DB value and LP value of oats was not significant,and ?L value of coix seed,white sorghum and black rice changed significantly.After precook,the LP values of coix seed,oats and white sorghum decreased and the LP value of black rice increased.Then this was consistent with the result of the above X-ray diffraction relative crystallinity. |
PDF Full Text Request