Study On The Relationship Between The Structure Of Soy Gel And The Diffusion Behavior Of Non-network Proteins Or Properties Of Network Proteins

The ability to form a gel is one of the most important functional attributes of soy protein,thus,soy protein are widely used in the food industry to improve the storage modulus,hardness,water holding capacity and retaining flavour components properties of the products.Gel-type soy protein isolate are widely used in meat sausage,chiba tofu and surimi products.Gelation of globulin protein occurs at certain conditions,analyzing the reasons of changes of soy protein gel network at different conditions and understanding the relationship between these changes and the characteristics of soy gel would be helpful to obtain appropriate relevant products.In this research,the protein compositions of non-network proteins and network proteins were firstly analyzed,then the soy gel network was characterized by investigating the diffusing behavior of non-network elements and rheological and microstructural properties.The reasons inducing the changes of soy gel network had been uncovered by determinating the protein composition of the proteins and the protein content and interactions among network proteins.The non-network proteins and network proteins were separated by a diffusion method,and the protein composition and existing form of these two kinds of protiens were analyzed by different electroresis methods.Non-network proteins(in soy gel formed at 18%(w/v),0.1 M NaCl,95 ? heating 30 min)contained higher amounts of A polypeptides,B polypeptides and BBI,and lower amounts of ?',? and A3.A polypeptides were released from gel network as forms of monomer,dimer,trimer and polymer,and B polypeptides were in the forms of AB and A5B3,moreover,BBI was released as monomers.In the network proteins(in soy gels formed by different protein compositions),7S-? and ?' subunits were existed as polymers or aggregates,while 7S-? subunit was existed as aggreagates only.11 S A and A3 polypeptides took part in gel netwrok in the form of polypers,and B polypeptides concributed to gel network as nonomer,dimer,polymer and aggregates.The changes of soy gel network as effects of protein concentration and heating time were characterized by the diffusion behavior of non-network proteins.The protein composition of non-network proteins and protein content of network proteins were also analyzed.SEC-HPLC analysis of non-network proteins revealed three major protein peaks,with molecular weights of approximately 253.9,44.8,and 9.7 kDa.The experimental data showed that the timedependent release of the three fractions from soy protein gels fit Fick's second law.An increasing protein concentration or heating time resulted in a decrease in diffusion coefficients of non-network proteins.A power law expression was used to describe the relationship between non-network protein diffusion coefficient and molecular weight,for which the exponent(?)shifted to higher value with an increase in protein concentration or heating time,indicating that a more compact gel structure was formed.The increase of denaturation ratio of 11 S proteins and network protein were two main reasons of forming more compacter gel networks.In this section ectogenic PEG were used as probes to investigate the effect of different 7S/11 S ratio and ionic strength on the stucture of soy gels,and SEM was applied to confirm the results in the diffusion procedure.In a same gel network,the diffusion coefficients of the probes decreased with increasing molecular weight.In different gel networks,the deffusion of larger probes were more sensitve to the changes of gel network.The diffusion coefficents of PEG increased with increasing ionic strength or 11 S ratio.The changes of PEG diffusion coefficients in soy protein gel were consistent with the variations of gel structure characterized by scanning electron microscopy(SEM),where networks with larger pores were found at higher NaCl concentration or 11 S ratio.Non-network components were the topic of the above two sections,and the correlation between the diffusion behavior of non-network components and the change of gel structure was discussed.However,in this section we focused on the study of network proteins.The forces involved in gel network were characterized by the dissolution rate constant which was measured by dissolving soy gel in two different solutions,and the relationship between the protein interaction and the breaking force of gel network was analyzed.Results revealed that hydrophobic interaction,hydrogen bond and disulfide bond were involved in gel network,and the stronger the forces,the higher the breaking force values.The intensities of these three interactions increased with increasing 11 S ratio or heating temperature,which was in agreement with the increase of breaking force of soy gel.When the heating time was prolonged,the breaking force first increased and then decreased,the same trend was also observed in the changes of the forces involved in gel network.The change of heating temperature had the greatest impact on the breaking force of gel comparing to the changes of 11 S ratio or heating time.Finally,the effects of non-network proteins,network proteins ratio and protein aggregates size on the storage modulus of soy gel were investigated.The removal non-network proteins from gel network had been performed through a release process and no effect of removal of non-network proteins on the storage modulus of gel was observed.An exponential relationship between the storage modulus and network protein ratio was found at different heating temperature,which was due to different denaturation ratio of glycinin was observed at different temperature.A positive correlation between the gel storage modulus and protein aggregates size was obtained in gels as effects of different 11 S ratio and ionic strength.