Research On The Effect Of Modified Soy Protein Isolate On The Chinese Steamed Bread Quality

Steamed bread,as one of the most important staple food in north China,is lack of Lys,which makes its nutrition poor.Soybean protein,rich in Lysine,occupies a wondeful balance properties of amino acid to complement for wheat flour.In this paper,Enzyme hydrolysis and extrusion were used to deal with soybean protein to get two modify soybean protein,then the influence law of modified soybean protein on the dough rheology characters and the quality of steamed bread was exploredFirstly,Hydrolysis degree(HD)acted as an index reflecting the enzyme hydrolysis extent of soybean protein isolate(EHSPIs).Then six different EHSPIs which HD were 0.8%,2.5%,3.6%,4.4%,5.7%and 7.6%respectively were obtained.Five different extruded soy protein isolate(ESPIs)were obtained by extrusion and their in vitro digestibility(IVD)were 84.3%,85.9%,88.3%,91.1%and 92.4%respectively.After enzymatic treatment,the 7S and A subunit of 11S disappeared quickly,while B subunit in 11S was slowly hydrolyzed to three new peptide chains and their molecular weight were 31.9 kDa,27.3 kDa and 24.0 kDa respectively.Moreover,results of ESPIs showed that the subunits of SPI decreased after extrusion,especially the subunits of 90.8 kDa,32.8 kDa and 31.3 kDa were disappeared,whereas no isopeptide bond was formed.Secondly,1.5%of EHSPs and 3%of ESPIs were added to flour respectively,and their influences on dough rheology and the quality of steamed bread were studied.The results showed that dough stability time,tensile resistance and other parameters are increased and the degree of softening was reduced when the hydrolysis degree was lower than 3.6%;stability time,energy and other parameters reduced stretching and dough strength began to decline when the HD was more than 5.7%.ESPIs could improve the dough rheological properties.And the result of scanning electron microscope(SEM)was basically consistent with the rheological properties of dough.Thirdly,the hardness and chewiness of steamed bread increased when the degree was 0.8%,then it decreased along with the HD increase;the hardness and chewiness of steamed bread increased and then decreased with 3%of ESPIs addition.Adding two kinds of modifiedsoy protein,chromatism ?E and L*of steamed bread decreased and the a*and b*value increased.While add EHSPIs and the digestibility of 84.3%ESPIs,the a*was increased slowly.Complementing HD of 7.6%EHSP,steamed bread sensory has the highest score 85.4 points;with IVD of 84.3%ESPIs,steamed bread sensory has the highest score 87.8 points.Finally,on the basis of the previous results,the influence law of different amounts of DH 7.6%of EHSPIs and IVD 84.3%of ESPIs on steamed bread quality were studied.After addition 1.5%of DH 7.6%of EHSPIs,steamed bread sensory had the highest score(85.6 points),and after adding 2%of IVD 84.3%ESPIs steamed bread sensory had the highest score(87.2 points).Lysine of two kinds of steamed bread were all increased from 0.3%percent to 0.4%and 0.6%,respectively.