Effect And Mechanism Of Oat ?-glucan Incorporation On The Quality Of Flour, Dough And Steamed Bread

According to the Dietary Guidelines for Chinese Residents,the recommendation for dietary fiber(DF)intake is 30 g/day.Nevertheless,the count shows that the average dietary fiber intake of Chinese adults is only 10.8 g/d and a level of up to 95% people whose DF intake is lower than that in Chinese DRIs.Numerous studies have revealed that the high incidence of metabolic disease can be partially ascribed to inadequate intake of DF,and increased intake of DF is currently recommended for good health.Mantou,so-called Chinese steamed bread,is a traditionally eastern staple food and often selected as carriers of DF.Water-soluble oat ?-glucan(O?G),an indigestible polysaccharide,has been demonstrated to have diverse bioactivities.As a functional food ingredient,O?G has been incorporated into a variety of food products.However,to the best of our knowledge,no information on incorporating O?G into steamed bread is available.Based on the above considerations,the effects and working mechanism of O?G addition on the powder properties,dough properties and steamed bread quality are investigated in this study.The major research results are as follows:(1)The blends with O?G incorporation beyond 3 g/100 g were darker than wheat flour,which caused by the darker color of O?G versus wheat flour.Compared to wheat flour,O?G and wheat flour were quite similar in average particle size,but the particle size distribution of O?G powder was relatively wider.The flocculent particles in O?G powder were aggregates of fine particulates less than 1 ?m.O?G particles were frangible and broken during the mixing.The addition of O?G(1 g/100 g to 5 g/100g)had negligible effects on the average particle size and particle size distribution of blended flour.The compressibility of wheat flour was comparable to that of O?G and did not substantially change with O?G addition.O?G powder presented better flowability than wheat flour and the blends with O?G addition of 3 or 5 g/100 g were more flowable than wheat flour.The water absorption capacity of O?G was far greater than wheat flour,so the water absorption of blend flours was linearly and positively correlated with the addition of O?G.Wheat flour with oat ?-glucan were more resistant to gelatinization and retrogradation.For the blend with 5 g/100 g O?G,a higher pasting temperature while lower values in peak viscosity,breakdown and setback were concluded in contrast to wheat flour.Oat ?-glucan addition did not change water vapor adsorption of wheat flour at 20 °C.The Oswin was the best model to describe the sorption isotherms of wheat flour and O?G.To guarantee the product safety during storage at 20 °C,the moisture content of wheat flour,O?G and the blends must be<12.6 g/100 g.(2)The dilution effect of O?G,competing for water and interaction between O?G and gluten proteins,impeded the formation of gluten network.As a result,the continuity,homogeneity and strength of the gluten network in wheat dough deteriorated with the addition of O?G.The strength of the gluten network and the stability of dough deteriorated accordingly,and this led to the increases in dough develop time and dough softening degree,while decreases in dough stability time,energy,draw ratios,the resistance to maximum extension and up to 50 mm at constant deformation.Rheological evaluation revealed that O?G affects the ratio of the viscous to the elastic portion and an increasing tendency to solid-like behavior with increasing addition of O?G.The presence of O?G resulted in increased relaxation times and a degree of water migration occurred from bound water to mobile water.This is related to the excellent water absorption of O?G,which can cause migration of water from gluten.The sample with 5 g/100 g O?G had fewer free sulfhydryl content,total sulfhydryl content and disulfide bonds than the control or samples with 1~3 g/100 g O?G.Besides,the content of disordered secondary structure increased and those of ordered structure decreased.Regarding dough fermentation properties,O?G had no effect on yeast activity but reduced the gas retention capacity of dough.(3)In terms of specific volume,texture properties and moisture content,compared to the control,the addition of 1 g/100 g O?G presented an insignificant effect,while those with 3 g/100 g and 5 g/100 g had more moisture content.The increased moisture content in the dough made from blended flours favored the yield and counteracted the cracking,staling and shrinkage of steamed bread in steaming and subsequent cooling.O?G addition of 5 g/100 g substantially lowered the specific volume,deteriorated the texture properties and the crumb structure of steamed bread.In terms of overall consumer acceptance,the addition of less than 3 g/100 g of O?G had negligible effects,while a significant deterioration of up to 12% was observed for the addition of 5 g/100 g.Glutens cloud improve the quality of O?G-enriched steamed bread.Additionally,O?G-enriched steamed bread had a centain hypoglycemic effect in vivo and in vitro.In contrast to the control,O?G addition of 5 g/100 g brought about decreases in the incremental area under the curve of up to 19.5% and 24.7% within 90 min and 120 min,respectively.(4)Steamed bread staling was a time-dependent process during storage.The major causes of steamed bread staling could be concluded as: starch retrogradation,water loss and gluten plasticizing.O?G addition of 3~5 g/100 g could retarded the staling of steamed bread.This effect could be partly attributed to the inhibition of starch retrogradation and partly due to the higher water holding capacity caused by the presence of O?G.