Effects Of Heating Under Pressure On The Gelation Of Chicken Batters And Its Mechanism

Gel-type meat products are very popular in the world and are also the main products of the Chinese meat industry.The gel properties of meat products are related to the visual appearance,water holding capacity and texure of the products.In order to improve the gel-forming ability,some ingredients or additives,such as salt,phosphates,TG(Transglutaminase),starch,protein,are added into the meat products.However,these ingredients may potentially bring hazards to human health or reduce the nutritional quality of the product.With the upgrading of consumption,the demands for high quality foods are increasing.Therefore,it is important to employ new technologies to improve product quality.Since the commercial application of high-pressure processing for the first time in the 1990s,this technology has been widely used.High pressure processing(HPP)not only has proven to have the special advantage of sterilization at low temperatures,but also has a positive effect on the gel quality of meat products.In recent years,attempts have been made to find a way that could combine and optimize the effect of sterilization and texture modification at the same time.Research have shown that hot isostatic pressing was superior to cold isostatic pressuring in sterilizing.However,there is still controversy about the texture adjustment effect of hot isostatic pressing.The main purpose of this study is to investigate the effect and mechanism of hot isostatic pressuring on the gelation of meat products.In this study,we first compared the effect of different combinations of high pressure and heating on the gel-forming of chicken batters,and found out that high pressure processing with simultaneously combined heating(heating under pressure)had the same,if not better,gelation properties as pressurizing before heating.The effect of heating under high pressure on the gelation of low salt chicken batters was further investigated,and found that there were synergistic and antagonistic effect between high pressure and heating,and the high pressure induced disruption of myofibrils did not necessarily lead to an increase in gel quality.In order to further understand the role and mechanism of high pressure and heating during the gelling process,the gel qualities and protein denaturation property during heating under pressure were determined.It was found that the thermal denaturation of protein was affected by high pressure,and the gel properties were also affected.To further analyze the effects of high pressure on proteins,the myofibrillar proteins and myosin were extracted,treated with heating under high pressure individually,the physical,chemical and structural changes were determined,and the antagonistic effect on gelling and gelation properties were evaluated.This study provides a strong theoretical support for the application of pressure assisted heating in the processing of gel-type meat products.The main research contents and results are as follows:1 Effect of high pressure/thermal combinations on gel properties of chicken battersThe effect of different combinations of high pressure and heating on the gelation ofchicken meat was investigated.There are three combinations of high pressure and heating applied:pressurizing followed by heating,heating under pressure,heating followed by pressurizing.The parameters used were:pressure 0.1/200 MPa,temperature 20/75? time 5/30 min.The effect of different treatments on visural appearance,water holding capacity,texture,water distribution,and microstructure was studied.The result showed that the effect of heating followed by pressurizing was basically the same as that of heating-only.In other words,the pressurizing in the former treatment had limited effect on improving the gel qualities for the heated meat products with porteins denaturated.Both pressurizing followed by heating and heating under pressure treatments had greatly improved the qualities of the product,and the latter was superior to the former on improving the gel properties of the chicken batters.The chicken sausages induced by heating before pressurizing or heating-only showed a rough and uneven sectional surface,high cooking loss and low gel strength.However,the pressurizing before heating-induced chicken sausage had smooth and flat cut surface,low cooking loss,and the highest gel strength.The heating under pressure-induced chicken sausage showed smooth and rigid cut surface,low cooking loss,but a relatively weaker gel texture than that of pressurizing before heating-induced chicken sausage.A large amount of myofibrillar fragments was observed in heating-only and heating before pressurizing induced sausages,while was not visible in sausages induced by the other treatments.It indicated that the myofibrils were disrupted under high pressure,thus,promoted the forming of a gel network and reducing water loss with enhanced proportion of immobilized water.In general,it was obvious that heating under pressure was superior to pressurizing before heating in improving protein gelling.2 Effect of heating under pressure on the gel properties of low-salt chicken battersThis chapter further studied the gel properties of chicken batters that were induced by heating under pressure,with a focus on the effect of pressure levels on gelation.The pressure levels used were 0.1/200/400 MPa.The samples studied were chicken batters with different addition amount of salt.The results showed that pressure level imposed a dominating effect on gel property,while the influence of salt is very limited.The chicken sausages induced by heating under 200 MPa had smooth visual appearance,high water holding capacity,and rigid texture,while 400 MPa-induced sausages had loose sectional surface,low water holding capacity,and soft texture.The quality properties could be impaired by reducing salt,but not fundamentally.For products induced by heating-only,the quality properties,such as visual appearance,water holding capacity,and texture,were markedly impaired with the reducing amount of salt.By comparing the quality properties,it was rational to conclude that the quality of low salt gel-type meat product could be improved by high pressure,which was a decisive factor for the gel-quality of chicken sausage.The reducing of salt significantly negatively affected the quality of chicken sausage,but its effect was very limited under high pressure.The pressure treated sausages,regardness the pressure was 200 MPa or 400 MPa,showed a low cooking loss and a three-dimensional gel network.Obviously,the breakdown of myofibrils did not necessarily improve the quality of meat gel,the gel quality was likely to be influenced by the denaturation of protein as well.3 Effect of high pressure and heating on the gelation process of chicken battersThis chapter studied the effect of heating under pressure in the formation of chicken batter gels,with a focus on the roles of high pressure and high temperature.The central temperature of chicken sausage was recorded during being heated under high or atmospheric pressure,and found that the higher pressure the quicker of temperature rising.According to the temperature curve,the heating time of 0,3,6,9,12,18,24,and 30 min was selected,and gel properties were determined.The study found that the gel structure formed gradually from the outside to the inside of chicken sausage,accomply with increasing gel strength,decreasing centrifugal loss,and forming gel network.The trend of these indices was basically consistent with that of temperature,indicating the mian factor in the formation of a gel was temperature,while high pressure was not a decisive factor.However,high pressure significantly affected the qel qualities.The gelation was improved by high pressure treating at 200 MPa,but impared at at a pressure of 400 MPa.The decrease in the gel forming ability under high pressure(400 MPa)can not ascribed to the less denaturation,but probably due to a less interaction or less stable connection betweem proteins.It found that actin was the most susceptible to high pressure,followed by myosin,and collagen was the most stable.Both promotion and inhibition effects of high pressure on protein denaturation were observed.The higher the pressure,the remarkable the denaturation.However,a certain mount of protein remained native after being treated by heating under pressure.In general,the gel qualities were affected by both high pressure and high temperature significantly.4 Effect of heating under pressure on the denaturation and gelation of myofibrillar proteinsThis chapter investigated the effect of heating under pressure(HUP)on the denaturation and gelation of myofibrillar proteins.Pressurizing before heating(PBH)and heat-only(HT)were taken as controls,the treatment parameters were:pressure 0.1/200/400 MPa,temperature 20/75? ant time 30 min.The results showed that heating promoted a transformation of the main chemical force from mainly ionic bonds into mainly hydrophobic interactions.It also found that more covalent bonding introduced by PBH treatment,while more weak bonding retained by HUP treatment.HUP-induced gels had higher solubility of myosin heavy chain,light chain,and actin,lower surface hydrophobicity,and secondary structure transformation,these alterations may be caused by the less denaturation of myofibrillar proteins.The gel network of myofibrillar proteins induced by heating under pressure was more uniform and even,while the gel network was more prone to form aggregates by the other two treatments.Heating under pressure enhanced the water holding capacity of protein gel,but impaired its gel strength.In general,the structural transformation and denaturation of myofibr illar proteins were retained by high pressure in heating under pressure treatment.5 High pressure induced protein denaturation and inhibited the effect of heatingThis chapter investigated the gelling properties of myosin at different temperatures and pressures,and the interaction effects on gelling between pressure and temperature.The treatment parameters were:0.1/200/400 MPa,20/35/50/65?,30 min.Within the denaturation temperature(<40?),myosin was partially denatured,the surface hydrophobicity increased,and the percentage of ?-helix reduced;the solubility and turbidity of myosin remained stable,and gelling was not occured.Above the denaturation temperature(>40?)?myosin denaturation first occurred in the heating-only treatment,the solubility,turbidty,surface hydrophobicity,and secondary structure were significantly changed.Myosin was completely denatured and formed a gel network.While,such obvious change only occurred at 65? in heating under pressure treatment.It was obvious that the denaturation temperature for myosin increased when heating was combined with high pressure,indicating that high pressure inhibited the denaturation of myosin.In general,high pressure hindered the heat-induced denaturation of myosin,and resulted a modified conformational structure of denatured myosin.This disturbance deteriorated the formation of gel network at 400 MPa,while was not obvious at 200 MPaIn summary,heating was the main driving force for gel formation,and high pressure had a decisive influence on the gel quality.Heating under pressure showed the effect of disruption of myofibrils(below the denaturation temperature)and an inhibition effect on the thermal-induced transition of protein structure(above the denaturation temperature).The influence of latter effect on gel properties varied according to the pressure level exerted.Heating under 200 MPa promoted gel formation,while heating under 400 MPa impaired gel formation.