Preparation Of Instant Multigrain Porridge By Extrusion And Its Digestibility

Porridge is one of the traditional staple foods in China.It has a soft and sweet taste,but has a high digestibility.Because it is rich in protein,dietary fiber and a variety of antioxidant substances,multigrain porridge has a low glycemic index(GI)and glycemic load(GL),which helps the human body maintain blood glucose stability.However,the cooking of multigrain porridge is time-consuming and laborious,which is difficult to meet the needs of the current fast-paced life,limiting its development.Therefore,the goal of this project is to use twin-screw extrusion processing technology to prepare slow-digestible instant multigrain porridge with good edible quality.Based on the objectives described above,this paper carried out three parts of research.Firstly,the effects of raw materials and raw material ratio on starch digestibility and edible quality of instant multigrain porridge were studied.Secondly,the effect of extrusion parameters on the edible quality of instant multigrain porridge was studied.Finally,the storage stability of slow digestibility instant multigrain porridge prepared under the optimum raw material ratio and extrusion parameters was studied.The main results of the above three parts are as follows:(1)With starch digestibility as the main index and appearance(formability and expansibility)as the auxiliary index,the main raw materials of slow digestibility multigrain porridge were screened.The results showed that the low GI(≤55)grains included kidney bean,chickpea and black bean;medium GI(55-70)grains included black rice,barley rice,red bean and mung bean;high GI(>70)grains included purple rice,red rice,quinoa,buckwheat,oat,millet,sorghum,barley,highland barley and corn.In terms of appearance,black rice,corn,millet,red rice and highland barley had better extrusion formability and expansibility,while other grains and beans had poor extrusion formability and expansibility,and even cannot be formed.Based on starch digestibility and appearance,kidney bean,black bean,red bean,black rice,barley rice,corn,highland barley and oat were selected as the raw materials of multigrain porridge.The selected eight kinds of raw materials were extruded according to different mass ratios,and the formula of instant multigrain porridge was screened with edible quality and starch digestibility as indexes.The results showed that the multigrain porridge prepared with 50% black rice,10% corn,10% barley rice,15% highland barley,5% oat,5% red bean,3% kidney bean and 2% black bean had better edible quality.The sensory score and transverse expansion degree were the highest,which were 83.25 and 1.63,respectively.The rehydration time was 23 min.(2)Taking rehydration time and sensory score as indicators,the range of extrusion parameters was determined by single factor test: extrusion temperature130-170 °C,feeding moisture 28%-32%,screw speed 250-350 rpm.On the basis of single factor text,the orthogonal text of three factors and three levers was further carried out with the indexes of transverse expansion degree,rehydration time and sensory score.The results showed that the order of influence of extrusion parameters was screw speed>extrusion temperature>feed moisture.The optimal extrusion process parameters were extrusion temperature 150 °C,feed moisture 30%,screw speed 300 rpm.The edible quality of multigrain porridge prepared under this extrusion condition was the best.The transverse expansion degree was 3.41,the rehydration time was 5 min,and the sensory score was 83.(3)The storage stability of instant multigrain porridge was investigated by fatty acid value,peroxide value and malondialdehyde value.After accelerated storage at37 ℃ and 50 ℃ for one month,the fatty acid value,peroxide value and malondialdehyde value of multigrain porridge increased slightly,indicating that its storage stability was good.For example,after one month of storage at 37 ℃,the fatty acid value,peroxide value and malondialdehyde value of multigrain porridge increased from 21.67 mg KOH/100 g,0.41 meq/kg,and 0.48 ug/g to 22.50 mg KOH/100 g,0.59 meq/kg,and 0.54 ug/g,respectively.Through the above raw material screening,formula screening and extrusion parameter optimization,the prepared instant multigrain porridge had a short brewing time(5 min)and good edible quality.Its fat,dietary fiber and protein contents were1.15,8.01,11.25 g/100 g,respectively,belonging to low-fat,high-fiber,protein-rich food;The content of slowly digestible starch and resistant starch accounted for69.07%,and the GI and GL values were 69.65 and 15.80/25 g dry basis,respectively,which belonged to medium GI and medium GL foods.