Study On Formation And Mechanism Of Heat-induced Gel From Food Hydrocolloids-fish Protein Mixture

Gel properties is one of the most important features of fish protein products. The heat-induced gel of food hydrocolloids-fish protein mixture was prepared, and the food grade carrageenan, algin, xanthan gum and the tilapia muscle was used in this study. Effect of heating rate, protein concentration, ionic strength, colloid addition on the rheological and gel properties of food hydrocolloids-fish protein mixture was determined. And then the actomyosin and myosin was extracted from tilapia muscle, the dynamic viscoelasticity, the microscopic structure and chemical interactions of heat-induced gel from food hydrocolloids and actomyosin(myosin) mixture was studied. Main purpose was to enhance the basic theory of fish muscle protein gelation and reveal the mechanism of thermal induced gelation for food hydrocolloids-fish protein mixture. The main results were as follows:(1) Tilapia muscle protein system was a typical pseudoplastic fluid, and shear thinning phenomenon was observed. Study on heat-induced gel formation process showed that, the dynamic elastic modulus(G’) of all tilapia muscle protein system was greater significantly than the viscous modulus(G"), which indicated the formation of viscoelastic gel system with priority to elasticity. The obvious influence of heating rate(1~5 ℃ /min) on the rheological properties was obtained for the heat-induced fish protein system, and the larger G’ value was obtained at small heating rate of 1 ℃/min and 2 ℃/min. The tilapia muscle protein system could form a better protein gel network structure by processing at heating rate of 2 ℃/min, and the heat-induced gel processing of fish protein system was mainly divided into three stages, namely the gel setting, gel weakening and gel strengthening.Effect of protein concentration(4%~10%) and NaCl concentration(1%~5%) on the elastic modulus of protein system was obvious, and the dynamic viscoelastic modulus increased with the increasing of protein concentration. At 1% of NaCl concentration, the G’ value of heat-induced protein system was significantly lower, and no stable gel system was observed. At 3% of NaCl concentration and 8% of protein concentration, the system of G’value increases rapidly and gel system gradually formed by a programmed temperature(20~ 90℃, 2℃/min) and cooling produce(90~20℃, 2 ℃/min), and the G’ value increasedwith the increase of frequency in the range of frequency from 0.01 to 100 Hz. All results indicated that the heat-induced gel of tilapia muscle protein was weak gel.(2) The heat-induced gel of food hydrocolloids-fish protein mixture was prepared by the second period heating method at 40 ℃ for 1 h and 90 ℃ for 30 min, and the protein concentration was 10%, the carrageenan, algin, or xanthan gum addition was from 0.2% to1.0%. The formation and mechanism of heat-induced gel from food hydrocolloids-fish protein mixture. The results showed that the three kinds of hydrocolloids could improve the texture of thermal induced gel. Comparatively, the addition of carrageenan could improve the texture properties of gel, the addition of xanthan gum could obviously increase the gel elasticity and whiteness, and the addition of alginate on the gel strength of system has certain improvement. Dynamic rheology research showed that food gum addition can significantly increase the dynamic viscoelasticity of tilapia muscle protein dispersion.Dynamic G’ value of heat-induced carrageenan-fish protein mixture increased with the increasing concentration of carrageenan. The addition of xanthan gum was not favorable for the formation of fish protein gel system. The chemical interactions analysis for heat-induced gel showed the hydrophobic interaction, disulfide bond and non-disulfide crosslinking was main chemical reaction for maintaining the heat-induced gel structure of carrageenan-fish protein mixture. Comparison, when 0.8% of carrageenan was added, the non-disulfide crosslinking of heat-induced gel from carrageenan-fish protein mixture accounted for 40.8%. Microstructure analysis showed that the surface of fish protein gel was uneven, and the surface of gel from carrageenan-fish protein mixture was smooth and uniform. Therefore, the addition of carrageenan was helpful to form homogeneous solid thermal induced gel three-dimensional network structure.(3) The actomyosin was extracted from tilapia muscle, and 20 mg/mL of actomyosin was mixed with 0.2% ~ 1.0% carrageenan, algin, or xanthan gum, and then the heat induced rheological properties, microstructure and chemical interaction of gel from food hydrocolloids-actomyosin mixture was determined. Results showed that shear thinning phenomenon was observed for food hydrocolloids-actomyosin mixture, and xanthan gum could significantly increase the viscosity of mixture. The dynamic viscoelastic modulus decreased with the increasing heating rate in the range of 1 to 5 ℃/min. The addition of carrageenan could obviously increase the elastic modulus of heat-induced actomyosin gel,but 0.8% ~ 1.0% of carrageenan showed inhibitory effect on the gel properties of system.The heat-induced gel of xanthan gum and actomyosin mixture has better holding water capacity. The microstructure of heat-induced gel from carrageenan and actomyosin mixture was uniform and compact, and the surface was smooth. Disulfide bond was the main chemical reaction for maintaining the heat-induced gel structure of carrageenanactomyosin mixture. Therefore, the interaction of carrageenan and actomyosin have a reinforcing effect on gel network structure.(4) The myosin was extracted from tilapia muscle, further research was done for effect of the heating rate, the protein concentration of 5~14 mg/mL, pH value(2.0~12.0),the NaCl concentration of 0.2~0.2 mol/L on the dynamic rheological properties of myosin.The rheological properties and gel formation mechanism of carrageenan-myosin mixture was determined. Results showed that effect of protein concentration and NaCl concentration on the elastic modulus of heat-induced myosin dispersion was obvious, and the G’ value increased with the increasing of protein concentration and NaCl concentration.At the heating rate of 1 ℃ /min and ionic strength of 0.6 mol/L, the tilapia myosin dispersion could form a good heat-induced gel. The effect of pH on gel properties was that the neutral pH condition was suitable for gel formation, the alkaline environment was second, and the acidic environment was the last one. Carrageenan could obviously increase the elasticity modulus of heat-induced myosin dispersion. When the addition amount of carrageenan was 0.4%, and the greatest G’ value and the best gel characteristics of heat-induced carrageenan-myosin mixture was obtained.