Preparation Of Starch Saccharides From Broken Rice By Extrusion And Enzyme

The consumption of corn is increased continuously with the yield of the starch saccharidesand corn alcohol, etc increasing sharply, which had resulted the demand of corn exceeded itssupply. It has been restraining the rapid growth of the starch industries. Moreover, the broken riceis by-products in the rice milling. It is utilized to produce the starch syrup, which will decrease theconsumption of the corn and solve the shortage of corn output, meanwhile, improve the additionalvalue of rice. The extrusion and enzymolysis technologies were combined in order to increase theefficiency of starch saccharides production. The optimal parameters and physicochemicalproperties of broken rice syrup were determined. The results are as follows:1. The impact of extrusion pretreatment on the structures and properties of broken rice wasresearched. It was found that the α-amylase hydrolysis of broken rice was remarkably increased bymore than25%after the broken rice had been extruded at17%moisture and115℃, as well as140rpm, which caused the significant changes of the structural performance of broken rice.The contain of amylopectin was decreased from68.92%to59.17%, and that of amylose wasincreased from18.32%to26.75%. The ratio of amylopectin to amylose was reduced from original3.8﹕1to2.2﹕1. Moreover, there was a certain degree of decline for the contain of protein andfat etc. The morphology features and crystal structure of the broken rice starch granules wereobserved and determined using scanning electron microscopy and X-ray diffraction analysis beforeand after the extrusion processing. It has been demonstrated that the complete granules of theextruded broken rice has hardly existed, which were distributed more closely and gathered togetherwith the irregular surface. The characteristic peaks of crystalline structure of extruded broken ricegranules were obviously destroyed at15°,17°,18°and23°diffraction angles, but two unknownpeaks appeared at13°and20°diffraction angles with lower heigh of peak and smaller area. Thecrystallinity degree of the broken rice was reduced from23.19%to6.35%. The rheologicalproperty of the broken rice paste has displayed that the sheer stress of the extruded broken ricepaste was obvious less than that of the untreated at the identical sheer rate, even its shear thinningphenomenon appeared faster and presented more remarkable. It is the gelatinization property of theextruded broken rice has been changed significantly that final, setback and breakdown viscosities,peak temperature as well as peak time decreased from2343cP,1209cP,446cP,78.8℃and5.82minto114cP,49cP,94cP,55.0℃and1.85min, respectively. The swelling force of extruded broken rice was significantly less than the untreated, on the contrary, which solubility obviously exceeded thelatter.2. The broken rice syrup was produced by enzymolysis with mesophilic α-amylase andglucoamylase from extruded powder (called extruded rice flour). Firstly, the optimal parametersobtained by the single factor experiments was that20%extruded broken rice flour at65℃and pH6.5~6.6for15min with1mM CaCl2per gram of α-amylase. In addition, the saccharification wasbrought at pH4.5~4.7.Then the orthogonal experiments of central composite rotatable design results indicated theeffect order of four factors on the DE value of starch syrup was that glucoamylase amount,saccharification time, saccharification temperature and α-amylase amount. The results showed theoptimal condition was10.30U/g α-amylase and80.02U/g glucoamylase at58.8℃for55.6min.The predicted DE value of saccharification was42%under this condition. Moreover, the practicalresult reached44.09%which had no significantly difference compared with the predicted resultwith0.47%(p≤0.5) relative error between them.3. The broken rice syrup was purified using ion exchange resin. The transmissivity of thepurified syrup was98.7%that was improved by21%compared with the unpurified; Desaltingeffect reached80%, and pH was increased from4.6to6.3.4. The components in purified syrup from broken rice were determined using HPCL. Thesyrup from extruded broken rice compared with that of the untreated broken rice with approximateDE value. Both of them included glucose, maltose, maltotriose, maltohexaose and otheroligosaccharides. The contain of these saccharides was16.53%,25.81%,17.42%and34.75%inthe syrup from extruded broken rice, respectively. Glucose, maltohexaose and otheroligosaccharides were reduced by5.51%and5.19%, while maltose and maltotriose were increasedby8.94%and3.36%. The physicochemical properties of the syrup were determined using TextureAnalyzer, differential scanning calorimeter and absorption spectrophotometer, etc.. The resultsshowed that the syrup from the extruded broken rice had a favorable moisture holding andhygroscopicity. Moreover, its consistency and cohesiveness were less than that of the untreatedunder the same condition, and its viscosity was greatly influenced by temperature. Itsthermostability and browning degree with sodium glutamate were lower compared with the controlgroup of syrup.