Effect Of Ultra High Pressure Treatment Combined With Sodium Chloride/Sodium Tripolyphosphate On The Properties And Forming Process Of Heating Gel Of Rabbit Myosin

Sodium chloride(NaCl)and sodium tripolyphosphate(STPP)are important ingredients as well as quality modifiers for the production of meat products.However,excessive intake of NaCl and STPP could cause various diseases such as cardiovascular disease and metabolic osteopathy,which is harmful to human health.Thus,it has become an urgent issue to reduce the dosage of Nacl and STPP while maintaining the qualities of the products.Ultra high pressure(UHP)processing technology is an emerging non-thermal processing technology which could enhance the functional properties of muscle protein through pressure-induced denaturation.Hence,the dosage of Nacl and STPP could be reduced.However,the mechanism of salt-reducing were still unclear.This study investigated the effect of different UHP treatment and additive amount of NaCl and STPP on the changes of molecular conformation of rabbit myosin during heat-induced gelling process and the properties of formed gel.Meanwhile,the interactions between UHP and Nacl as well as UHP and STPP were studied as well.This study could provide theoretic support to the production of low salt meat products through UHP processing.The research includes following contents:1 Effects of UHP processing and NaCl content on the gel properties of rabbit myosinThis research studied the effects of UHP levels(100,200,300 MPa)and NaCl contents(1.0,1.5,2.0%)on the solubility of myosin as well as water-holding capacity(WHC),T2 relaxation time,penetration force and microstructure of gel.The results indicated that pressure treatment of 100 MPa could enhance the solubilization of myosin,improve the microstructure of formed gel and reduce the T2 relaxation time of myowater inside the gel.The WHC and penetration force of gel were improved consequently.As pressure level increased to 200 MPa,the solubility of myosin and the penetration force were decreased.Pressure treatment up to 300 MPa could led to significant decrease in protein solubility.Therefore,disordered and coarse gel structure with low WHC and penetration force were formed.Increase in NaCl content could bring limited effect to protein solubility as well as gel properties.Myosin containing 1%NaCl and pressurized under 100 MPa formed gel with highest WHC and penetration force.Although the increase in NaCl content could improve the solubility of myosin as well as its gel properties under 300 MPa,there are still extreme variation between them and the control group.2 Effects of UHP processing and NaCl content on the molecular conformation of rabbit myosin during heat-induced gellingThis research studied the effects of UHP levels and NaCl contents on the surface hydrophobicity,reactive sulfhydryl group contents,secondary structures as well as storage modulus(G')of myosin during subsequent heating.The results showed that pressure treatment could change the secondary structures as well as spatial conformation of myosin,and led to increase in surface hydrophobicity and reactive sulfhydryl group contents.Myosin containing 1%NaCl and pressurized under 100 MPa exhibited sufficient unfolding of molecule conformation as well as rapid exposure of buried residues during heating,the aggregation and cross-linking abilities of protein were enhanced,which led to highest G'eventually.Nevertheless,the increase in pressure level as well as NaCl content could intensify the conformational changes before heating.Thus,conformational changes and exposure of buried residues during heating were restrained,and the aggregation as well as cross-linking abilities of the protein were weakened.G' was decreased consequently.Pressure treatment of 300 MPa led to serious changes in protein conformation,massive amount of sulfhydryl and hydrophobic groups were exposed before heating.However,no significant changes in secondary structures as well as spatial conformation of myosin were observed during heating.Increase in NaCl content could promote the gelling process whereas its final G' were still significantly lower than the control group.3 Effects of UHP processing and STPP content on the gel properties of rabbit myosin Rabbit myosin containing 1%Nacl was used as raw material in this experiment to study the effects of UHP levels(100,200 and 300 MPa)and STPP contents(0,0.15,0.3 and 0.45%)on protein solubility,WHC,T2 relaxation time,penetration force and microstructures.Results indicated that interactions between UHP processing and STPP changes with pressure levels and STPP contents.Pressure treatment of 100 and 200 MPa could promote the solubization of protein,decrease T2 relaxation time of water groups in gel and improve the microstructure of formed gel.However,the addition of 0.15%STPP could counteract the effect of pressure treatment and decrease the WHC and penetration force significantly,the counteract effect diminished as the content of STPP increased to 0.3%and the WHC and penetration force reached to its highest.Although the increase in STPP content could improve the protein solubility and gel properties under 300 MPa,there are still significant differences of WHC and penetration force between them and the control group.4 Effects of UHP processing and STPP content on the molecular conformation of rabbit myosin during heat-induced gellingThe study aimed to investigate the effect of UHP and STPP contents on the ATPase activity,hydrolysis of STPP and the secondary structural changes,surface hydrophobicity,reactive sulfhydryl group contents as well as rheological properties of protein during heating.Results showed that 0.15%STPP exhibited counteract effect against pressure treatment of 100 and 200 MPa,which hindered the decrease in ATPase activity and conformational changes of myosin.Also,the unfolding of protein structures and exposure of buried residues during subsequent heating were suppressed as well.With the increase in STPP contents,the content of Pi increased and the counteract effect was diminished.The speed of heat-induced denaturation was increased and the agglomeration of myosin heads and cross-linking of its tails were promoted.Ordered gel network with high elasticity was formed finally.The ATPase of myosin was basically inactivated under 300 MPa.Massive exposure of buried residues and rapid conformational changes of myosin after pressurization led to low extent of protein denaturation and weakened cross-linking during subsequent heating.No significant effect of STPP contents on its gelling process were detected under this pressure level.