| Fish noodles,eaten in the area of Hubei Yunmeng,Fuzhou and Chongqing Changshou Lake,are traditional regional surimi products in China,which are well known for its delicious taste and rich nutritional value.Traditional fish noodles are mostly produced in small family workshops,which the production standardization is low and the product quality is uneven,due to lack of key equipment,the large-scale industrial continuous production cannot be achieved.In order to solve the problems in traditional fish noodle production,the preparation process of small-scale fish noodles based on catering supplies and the twin-screw extruded fish noodles process that can be used for continuous production were explored in the study.And the flow field changes were simulated during the extrusion process of fish noodles in the fluent,and the changes of fish protein molecules were explored during the extrusion process,which elaborate the formation mechanism of fish during the twin screw extrusion process,and provide a theory for uncovering the "black box" effect in the extrusion process reference.The specific conclusions are as follows:(1)The preparation process of small-scale fish noodles based on catering supply was investigated.It was found that the addition of 5 % starch to surimi can significantly improve the adhesion problem of fish noodles after high-pressure steam sterilization.The best combination of additions were clarified through single factor and orthogonal experiments,the results show that the addition of 2 % table salt,0.02 % complex phosphate,6 % egg white and 0.5 % transglutaminase(TG enzyme),the value of elasticity of fish noodles can reach 0.8055.And a portable fish noodle extruder was designed and developed which is convenient for manual extrusion to realize the small-scale standardized production of fish noodles.The equipment is light and flexible,which the filling is convenient,and the fish noodles prepared are well flexible.the focus was on the length of the die hole for the improvement of the problem of rough surface of fish surface and heavier graininess.The results showed that when the length of the die hole was 10 mm,the appearance of the fish surface is more delicate and smooth,and the organization state of production is the best.(2)The twin-screw extruded fish noodle process was studied,the result showed that water activity is the key to surimi extrusion,and the addition of a certain amount of sodium alginate and xanthan gum can significantly reduce the water activity of surimi.When the water activity was 0.872 ~ 0.784,it could be formed by extrusion.The effects of extrusion parameters(second zone temperature,third zone temperature,screw speed and raw material water activity)on the physical and chemical properties of fish noodles were studied through single factor experiments and orthogonal center rotation experiments.The results showed that when the second zone temperature was 123 ℃,the third The zone temperature was 97 ℃,the screw speed was 41 r / min,the water activity was 0.81(2 % sodium alginate,1.5 % xanthan gum),and the elasticity of the fish noodle was better,up to 0.8032.And the fish preservation program was studied,and 0.04 % sodium dehydroacetate,0.1% potassium sorbate,and 0.2 % sodium D-isoascorbate were used to preserve the freshness of the fish noodles.The shelf life of fish noodles can reach 45 ~ 60 days under 40 ℃ storage conditions.(3)Based on the calculation of fluid mechanics(CFD),the flow field change model of the fluid during the extrusion process is constructed,and the changes of the velocity field,temperature field,pressure field and fluid trace are expressed.It can be seen from the model that the fluid passes through the transfer zone,cooking zone,mixing zone and forming zone from the inlet to the outlet.In the transmission area,the temperature and pressure of fluid were both low,and the fluid moved in a parallel flow;in the cooking area,the pressure and temperature were both increased in a gradient,and the flow pattern remains the same.At this time,the fluid was being cooked in the screw;in the mixing area,the value of pressure is increased to the highest,and then slightly lowered in the die head between the screw and the die-the head joints,and a negative pressure zone appeared,which aggravated the mixing of the materials,the temperature decreased slightly,the fluid trace began to be turbulent,at this time the fluid was strongly mixed and shearing effect;the final fluid is ejected linearly at the die or molding area.(4)The forming mechanism of twin-screw extruded fish noodles was explored by measuring the changes of protein molecules during extrusion through the shutdown sampling method.The results show that in the transport zone,the hydrogen bond was decreased,the hydrophobic interaction was enhanced,the α-helix was unfolded,and the irregular curl was increased;in the cooking zone,the hydrophobic effect predominated,the α-helical content continued to decrease,and the irregular curl was increased;from the cooking zone to the mixing zone,the thermal effect leaded to the destruction of noncovalent bonds,and large amounts of disulfide bonds were formed,it was found a further reduction in spiral content,and an increase in random curling in the protein;during the formation of the fish surface,the cooling process leaded to the reformation of hydrogen bonds,and disulfide bond and hydrogen bond maintained the newly formed structure as the main chemical force,it was found the content of α-helix was increased,and the irregular curl was decreased. |
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