| At present,chronic diseases such as obesity and diabetes have become a health problem attracting worldwide attention,and the diet of low Glycemic Index(GI)is beneficial to the prevention of chronic diseases.However,there is little study on foods with low glycemic index in domestic researches now.Seven kinds of whole grains including highland barley,quinoa,oats,coix,millet,mung beans and peas were selected as subject in this study.The proximate components,polyphenol contents and anti-oxidant properties of 7 whole grains,and the in vitro digestion after extrusion were measured.Whole grains with relatively low eGI and strong antioxidant activity were screened out.The selected whole grains(highland barley,quinoa,oat,millet and mung bean)were studied to analyze the influence of grain ratio on in vitro digestion and physical characteristics,and the formula was designed according to eGI and sensory score.The effects of different extrusion parameters on the eGI of multi-grain co-extruded were studied,and the processing parameters were optimized by the numerical optimization method.Particle size,water temperature and water content were the selected as influencing factors,solubility index,agglomeration rate,dispersibility and wettability were selected as objective indexes to study the dispersal of multi-grain instant nutrition powder.The research conclusions are as follows.(1)The total phenols contents of selected grains were 19.09~128.85 mg/100 g,among which the content of mung bean was the highest.The flavonoids content of the seven grains was 169.58~ 390.11 mg/100 g,among which the content of highland barley,quinoa,oats and mung beans was significantly higher than other cereals(P<0.05).There were significant differences in antioxidant activities among the 7 cereals(P<0.05),among which the highland barley had the strongest ability to scavenge DPPH· and ABTS+· and the total antioxidant capacity,followed by oat and mung bean.There was no significant correlation between antioxidant capacity and total phenol content of seven cereals(P>0.05),but high correlation with flavonoid content.The results of in vitro digestion test showed that millet was high GI food(82.49),whereas the other grains were medium GI food(61.96~73.24).(2)The effects of different grain ratios on expected Glycemic Index(eGI)of extruded grains were researched by D-Optimal mixture design experiments.It was found that the eGI value increased and then decreased with the increase of the addition amount of millet,highland barley,quinoa and oat,while decreased and then increased with the increase of the addition amount of mung bean.According to the determination of the nutritional composition of the extruded products with different ratios of grains,the contents of starch,amylose and protein generally decreased,and the contents of dietary fiber increased.And a significant negative correlation between eGI and protein,dietary fiber,amylose,and resistant starch were observed.The optimized formula of the multi-grain co-extrusion powder was quinoa 15.00%,oatmeal 5.30%,highland barley 29.70%,mung bean 10.00% and millet 40.00%.Under optimal conditions,the multi-grain powder was light yellow and brown with a grain flavor,and the eGI value of 64.85,which belonged to the middleGI food.(3)The effects of extrusion process parameters on in vitro digestion characteristics of multi-grain co-extruded powders were studied.It was found that eGI value decreased and then increased with the increase of screw speed,extrusion temperature and material moisture.The gelatinization characteristics of the extruded samples under different conditions were determined,and significant differences between peak viscosity,minimum viscosity and recovery value were found in the extrusion temperature and moisture content(P<0.05).Microstructure observation showed that the higher the screw speeds caused the greater irregular the particle structure and the rougher the surface than those with lower the screw speeds.Optimized the process parameters were obtained as the screw rotation speed of 250 r/min,extrusion temperature of 170?,and material moisture of 17%.Under optimal condition,eGI value of multi-grain powders was 64.32,and the product was identified as medium GI food.(4)It was found that the grain size of multi-grain instant nutrition powder was poor when the grain size exceded 100 mesh,and the optimum grain size of multi-grain instant nutrition powder was 80~100 mesh.When mixing water of the ratio of 1:6 g/m L,the water temperature is 70?,multi-grain co-extrusion instant nutrition powder had fine taste.The multi-grain co-extrusion instant nutrition powder obtained in this study has proper consistency,uniform color and low eGI value,which is helpful to prevent chronic diseases such as obesity and diabetes.The results of this study can provide theoretical guidance for the development of products with low glycemic index. |
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