Effect Of Physical And Chemical Properties Of Raw Materials On The In Vitro Digestion Characteristics Of Extruded Coarse Grain Powder

Rich in dietary fiber,polyphenols,mineral elements and a variety of functional factors,coarse grains occupy an important position in the diet culture in China.Compared with refined rice and noodles,coarse grains have lower Glycemic Index(GI),which is beneficial to control the blood sugar level in human body.As a new food processing technology,extrusion has many advantages,such as short processing time,wide adaptability of raw materials and less damage to nutrients.In this study,Tartary buckwheat,millet,highland barley,quinoa,mung bean and oat were selected as the research objects.The changes of basic components and antioxidant active substances of cereals from different producing areas before and after extrusion,as well as the in vitro digestion characteristics of extrusion powder were analyzed.The relationship between the properties of raw materials and the in vitro digestion characteristics of extrusion powder was also analyzed.The low GI cereal materials were selected,and the content of fast digested starch,slow digested starch,resistant starch and Estimated Glycemic Index(EGI)were used as the indexes to investigate the effect of grain co-extrusion on the in vitro digestion characteristics of extrusion powder.The influence mechanism on the in vitro digestion characteristics of millet and Tartary buckwheat co-extrusion powder was investigated and the main research conclusions are as follows:(1)The contents of basic components,antioxidant active substances and in vitro digestion characteristics of cereals were significantly different(P<0.05).The average contents of total phenols and flavonoids in Tartary buckwheat were significantly higher than those in other cereals.Millet is rich in starch but low in dietary fiber.starch and protein are the main components of mung bean.Quinoa and oats have slightly higher average fat content than other grains.After extrusion processing,the contents of total starch,fat,total phenols and total flavonoids decreased obviously,the contents of amylose and dietary fiber increased,and the protein content had no significant change.The average EGI of millet and oat extrusion powder was higher,while that of quinoa extrusion powder was lower.Correlation analysis of grain composition and in vitro digestion characteristics of extrusion powder showed that the in vitro digestion characteristics of extrusion grain powders have different correlations with different fractions.For example,the in vitro digestion characteristics of Tartary buckwheat powder was significantly correlated with the contents of total starch,protein and total flavonoids(P<0.05),and the in vitro digestion characteristics of millet extrusion powder was significantly correlated with total phenol content(P<0.05).(2)The extrusion powders of Tartary buckwheat,highland barley,quinoa,mung bean and oat were prepared by co-extrusion with millet,and their in vitro digestion characteristics were obviously different.With the increase of different cereal supplemental amount in co-extrusion powder,the EGI value of millet Tartary buckwheat co-extrusion powder decreased first and then increased;The EGI value of millet highland barley and millet oat co-extrusion powder decreased gradually;The EGI value of millet mung bean co-extrusion powder increased gradually;The EGI value of millet quinoa co-extrusion powder was significantly lower than that of single grain extrusion powder when the dry base mass ratio of millet to quinoa starch was 5:5(P<0.05).In general,multi-grain co-extrusion reduced the content of fast digested starch and slow digested starch,and increased the content of resistant starch.Compared with single grain extrusion,multi-grain co-extrusion was more conducive to the preparation of low GI food.(3)According to the analysis of the factors affecting the digestibility of the extrusion powder,it was found that the physical and chemical properties of the co-extrusion powder prepared by different proportions of millet Tartary buckwheat starch with dry base mass ratio were obviously different.With the increase of the content of Tartary buckwheat in the system,the irregular particles on the surface of co-extrusion powder gradually disappeared.The gelatinization characteristics of the whole showed a fluctuating change without obvious rule.When the dry base mass ratio of millet Tartary buckwheat starch was 3:7,the diffraction peak of starch lipid complex in X-ray diffraction pattern was significantly higher than that of other co-extrusion powder.Infrared spectrum analysis showed that the low EGI extrusion powder had higher short-range order and crystallinity,which indicates that the digestibility of starch depend on its crystal properties.The results of this study have guiding significance for the selection of low GI grain raw materials and the development of low GI food in actual production.