Extrusion Of Brewer’s Spent Grain And Its Effect On Wheat Doughs And Steamed Breads

Brewer’s spent grain,with low fat and sugar,high protein and dietary fiber,is the solid residue after mashing during the brewery process.Brewer’s spent grain obtained from wheat beer（WBSG）is the major by-product of wheat beer,which presented greater advantages in nutritional composition and functional properties.Brewer’s spent grain with high moisture makes it difficult to store due to its perishable property,therefore,it is important to choose the optimal choice of brewer’s spent grain pretreatment in order to achieve value-added utilization on WBSG-based foods.In this research,the fresh WBSG was dried and extruded,respectively.The effect of extrusion and different WBSG levels on processing properties of wheat doughs and steamed breads by multiple measurements such as farinograph,rapid visco analyzer,texture tests and rheology was investigated.The results obtained will be beneficial for the improvement of diet structure,quality and efficiency development of food industry,with a significant effect on social,economic and ecological benefits.The main research results are as follows:（1）The moisture,dehydration rate,total acid and sensory quality of WBSG with different temperature by hot-air drying and drying time were compared.The optimal hot-air drying process was 60℃for 20 h.The solubility,water absorption and emulsification of WBSG remarkably increased with the material moisture of 25%,extrusion temperature at 80℃and screw speed of 100 r/min.Additionally,the content of soluble dietary fiber increased 2.8%and the amount of undersized WBSG nearly doubled.（2）Doughs of mixed WBSG and wheat flour at different ratios were prepared.With the increase of WBSG addition,the water absorption,mixing tolerance index,development time,stability time and softening degree of doughs gradually increased.The upper limit addition of WBSG in wheat doughs was 15%.The gelatinization viscosity and pasting time of wheat flour gradually decreased with the increase of WBSG addition,while the pasting temperature increased.The rheological results showed that the increase of WBSG substitution level led to the increase of elastic modulus（G’）and viscosity modulus（G’’）,and G’was always greater than G’’.WBSG showed significant impact on the adsorbed water in the dough.The greater addition,the higher proportion of adsorbed water,and the looser gluten network structure inside the dough.Steamed breads with WBSG were elaborated.The specific volume,spread ratio and springiness of steamed breads were negatively correlated with the amount of WBSG,while hardness showed an opposite result.The addition of WBSG decreased the L*and b*values of steamed breads and increased a*andΔE values.As for the sensory evaluation,the highest score of steamed bread was when the amount of WBSG at 2.5%.（3）WBSG was selected as the control,extruded brewer’s spent grain obtained from wheat beer（EWBSG）with different moisture content at same addition of 10%were prepared to make doughs and steamed breads.The addition of EWBSG reduced the water absorption of wheat flour,the stability time and viscoelasticity（i.e.G′and G′′）of wheat dough.Compared with WBSG,EWBSG addition significantly reduced the proportion of adsorbed water in wheat dough.With the increase of EWBSG addition,the water absorption,dough development time and stability time of wheat flour significantly increased.In addition,the gelatinization viscosity decreased,while the pasting temperature increased.The rheological result showed that G′and G′′increased,and G′was always greater than G′′.The content of adsorbed water(A₂₂)gradually increased with the increase of EWBSG addition,and the transverse relaxation time(T₂₂)moved toward negative direction,which indicated that EWBSG reduced the freedom degree of adsorbed water.The effects of EWBSG addition on color,specific volume,spread ratio and hardness of steamed breads were consistent with those of WBSG.However,when the addition of EWBSG exceeded 20%,the surface of steamed bread appeared to be cracked.The sensory evaluation results showed that the addition of EWBSG in steamed bread formula should be less than 10%.