Thermal Aggregation Behaviors,Interfacial And Emulsifying Properties Of Myosin

Meat is an important animal-sourced protein.Meat protein contains all essential amino acids,which has a very high nutritional value for human.However,so far,meat protein has not been widely used in the food industry like vegetable protein and milk protein,especially in the beverage industry.This is due in large part to the heat sensitivity of meat proteins.Heat treatment is an essential operating unit in the food industry.Although meat protein has good emulsifying properties,it is easy to aggregate due to heating,making emulsion flocculation.In recent years,with the development of research on food protein emulsions,the stability of protein based emulsions has not only been limited to simply modified proteins.Various protein aggregates,copolymers and insoluble particles can be used as good emulsion stabilizer,which encouraged us to develop and study meat protein based emulsions.In this paper,myosin was selected as the research object,and pH and heat-induced myosin modification were taken as the core.The thermal aggregation behavior of myosin under different pH conditions was studied.The emulsification and interface properties of myosin induced by different pH were explored.These results will help us understand and reveal the mechanism of heat treatment and pH on the stability of myosin emulsions,and may provide a theoretical reference for the development of new meat protein emulsion products.1.Alkaline pH-dependent thermal aggregation of chicken breast myosinSoluble aggregates,were formed on heat-treated chicken breast myosin through alkaline pH-induced electrostatic regulation.Heat treatment of myosin at pH 9.0 significantly increased solubility,decreased turbidity,and resulted in the highest content at 260 nm particle size compared with those at pH 7.0 and 8.0.Results indicated that soluble myosin aggregates were produced at pH 9.0.The surface hydrophobicity and reactive sulfhydryl(R-SH)of unheated sample revealed gradual increases with increased pH.This increase was related to the decreased a-helical,thereby suggesting myosin unfolding.After heating,treatment at pH 9.0 showed the lowest surface hydrophobicity and R-SH,which may contribute to the highest dispersibility.Moreover,heated myosin(pH 9.0)after reshifting pH still exhibited excellent stability.2.Interfacial behavior and Emulsifying properties of alkali-heat induced myosin aggregatesThe interfacial and emulsifying properties of native myosin and alkali-heat induced myosin aggregates were investigated.After proteins subjected to the thermal treatment(75℃,30min)under controlled pH conditions(pH 7.0,8.0 and 9.0)and the pH adjustment(adjust the pH back to 7.0),the myosin aggregates were formed.The turbidity and the partcile size distribution results indicated that the alkali pH effectively decreased the degree of aggregation.Smaller aggregates had the higher interfacial pressure and diffused to the vicinity of the o/W interface more rapidly.They took more time to reach the interfacial pressure equilibrium,which indicates the longer structural rearrangement of the absorbed proteins for more proteins loading.And the emulsions stabilized by the smallest myosin aggregates S3(9→7)presented the smallest droplet size and highest protein concentration in the heated groups.Moreover,almost no phase separation was observed in the S3 emulsion after two week storage.The CLSM analysis demostrated that the bridging flocculation was the main reason for poor emulsifying properties in aggregates based emulsions.The emulsifying properties of the heat induced myosin aggregates were improved a lot.3.Effect of alkaline pH-shifting on the stability of myosin emulsionIn this study,an alkline pH-shifting driven conformation of interfacial proteins was established to improve the heat stability that especially against flocculation of myosin emulsions.We used the unfolded myosin at pH 12 to emulsify soy oil and then readjusted the pH of the emulsion to neutral.The corresponding myosin emulsion EM3(0.5%w/v protein,10%v/v soy oil,and 0.6 M NaCl)almost not flocculated when heated at 75℃ for 30 min.Moreover,the EM3 emulsion after heated can even have the smilar particle size as the emulsion before heating and do not exhibit a creaming phenomenon after a week.According to our CD and FTIR analysis,the superiority of the emulsion is closely related to the alkaline pH-shifting-driven conformational arrest of myosin at the interface.And according to the data of Cryo-SEM,the steric stabilization might be the main factor for the improved heat stability of EM3.Overall,a unique approach involving conformational arrest was shown and may contribute considerably to improving the heat stability of protein-based O/W emulsions.