Processing Of Instant Millet Gruel And Mechanism Of Its Gelatinization And Retrogradation

Insant millet gruel (IMG) is one kind of new convenient food.Nowadays,few studies about ithave been reported.In this experiment, preheatingtreatment,methods of gelatinization and methodsof drying for IMG were studied systematically with high-quality raw millet based on degree ofgelatinization,rehydration time,degree of dispersion,hardness and sensory evaluation,then,itsoptimal process route was established. Mechanism of starch gelatinization and retrogradation andmicrostructure of IMG were studied respectively by differential scanning calorimeter (DSC)andscanning electron microscopy (SEM).Two kinds of process route of IMG were optimized on the basis of degree of gelatinization,rehydration time, dispersion, hardness and sensory evaluation and processing cost,the results are asfollows:①raw high-quality millet→removing impurity→cooking with boiling water→draining→steaming with normal pressure→dispersing with cooling water→draining→freezing→drying byhot air→packaging→product②raw high-quality millet→removing impurity→cooking withboiling water→draining→steaming with normal pressure→dispersing with coolingwater→vacuum freeze-drying→drying by hot air→packaging→product, Parameters in theprocess steps are as follows: boiling time:1min, steaming time:10min,freezeing time andtemperature:1h/(-20℃), time and temperature for hot air drying:30min/150,conditions for vacuumfreeze-drying:temperature:50℃, time:5h,vacuum degree:10Pa,time and temperature for hot airdrying(the second process route):10min/80℃..IMG produced by these two process routes hasobvious shortcomings such as: low viscosity of millet water, Therefore, a kind of flavor rpowderwas developed,the powder comprise the same ingredients for these two process routes,it has fouringredients:1.00%konjak gum,3.75%gelatinized millet powder,3.50%polydextrose,5.00%sucrose.Quality of IMG was analysed by determination of protein content,fat content,carbohydratecontent and energy.Thermodynamic property of IMG produced by different drying methods was studied by DSC,The result shows that IMG produced by different drying methods do not exist starch retrogradationphenomenon at low moisture content（below10%）. Microstructure of IMG produced by differentdrying methods was studied by SEM.The result shows that there are numerous pores of uniformsize in IMG produced by vacuum freeze-drying, so its rehydration time is short.The number ofpores of IMG produced by hot air drying is less, therefore its rehydration time is longer.