Process Creation Of Enzymatic Extruded Noodles Based On The Mechanism Of High Molecular Orientation And Rehydration

Noodles are generally an edible and nutrient-rich food product.It is usually consumed as a staple food or could be included as a fast-preparing food.Therefore,it is preferred and acceptable by consumers all over the world.Nowadays,noodle consumption markets have become huge,with expected sales of noodle products likely to reach 180 billion yuan in 2020.However,after years of accelerated development in noodles production,regardless of the type of product,there have been no major changes or developments in the field of long-term noodles processing,as only technical innovations can bring significant technological progress in this vital industry.Screw extrusion technology integrates mixing,stirring,crushing,heating,cooking,sterilizing,and shaping in one process.It is efficient,energy-saving,economical,and practical,with broad application prospects for noodle processing.In this study,concepts and principles related to polymer physics have been successfully introduced to the noodle production field.Based on the laser transmission method,the extruded noodles?EN?orientation measurement method was established,a higher-order response optimization model for orientation degree was constructed,and the formation mechanism of mucedin-starch network composite structure extrusion orientation was explored.The preparation of EN by Ca²⁺-controlled?-amylase extrusion technology considered both the texture characteristics and the rehydration properties and analyzed the mechanism of quality improvement of EN from multiple angles,so as to create a technical route for the industrial processing,understand the technical principle,establish related research methods,and explore the key mechanisms of EN.The main contents and conclusions of each chapter are as follows:?1?Based on the principle of laser transmission,a quantitative non-destructive measurement method for orientation degree was constructed.In this method,the laser scattering image was collected by a laser transmission system that was designed and built by authors.MATLAB software was employed for images analysis to obtain the degree of orientation?B value?.The final optimal parameters for image acquisition were as follows:the exposure time of the digital camera was at 1/1600 s,with the laser incident angle at 45°and the transmission direction was parallel to the sample orientation direction.The orientation degree B values of the plain flour extruded noodles?PF-EN?,cake flour extruded noodles?CF-EN?,and purchased noodles?PN?were 1.525,1.435,and 1.127,respectively,with significant differences among them.This method can measure the degree of orientation consistently,reliably and non-destructively,as well as,quantitatively determine the internal tissue direction of various noodles that are invisible to the naked eye.This novel method can also be applied to determine the tissue orientation of various foods.?2?With a higher degree of orientation,the noodle texture possesses better“Jindao”tastes.Thus,the EN extrusion process was optimized based on the measurement method of orientation degree.A wide adjustment of various extrusion operation parameters-barrel temperature 90–130°C,screw speed 80–120 r/min,water addition 47–56%,feed speed 7–11kg/h-to obtain the rule of orientation variation.Based on these results,a highly optimized orientation response model was successfully constructed.The F value was extremely significant,while the misfit was insignificant.The Signal-to-noise ratio was high,and the model fit was largely valid.These findings indicated that the model could be used to explain94.51%of the response value changes.The predicted optimal conditions of barrel temperature,screw speed,water addition,and feeding speed were 121.47°C,102.20 r/min,50.42%,and8.26 kg/h,respectively.The average orientation degree of the noodle samples under this condition was 1.531,as only 0.39%less than the model predicted value.?3?Based on the aboved-mentioned study,polymer physical principles such as polymer mechanical state and flow behavior were applied to study the protein and starch orientation changes in noodles.The orientation mechanism of the mucedin-starch network composite structure is as follows:glassy protein and starch components in the flour were mixed with water and rabidly absorbed water with increase in the ambient temperature,pressure,and shear force rate.During that,the processof“low water gelatinization”occurred.At this stage,gliadin and glutenin crosslinked and polymerized with each other and part of the non-covalent bond has broken.The content of free thiol,cysteine,?-helix,random coil,and?-sheet was decreased.The initial elastic gluten protein segments were formatted.At the same time,the layered crystal structure of the starch granules was destroyed.Double helix segments opened up.Then,crosslinked with mucedin segments to form a highly elastic mucedin-starch mixture.When this mixture reached the melting zone at the end of the barrel,the flexibility of the mucedin segment has improved with increased content of disulfide bonds and?-turn angles,and the main chemical cross-link bond form changes to the interaction of disulfide bonds and non-covalent bonds.The degree of structural order between the double helices of the starch molecule was reduced.The chain length distribution shifted to a low degree of polymerization?DP?,and the mechanical state of the material changes from a highly elastic state to a viscous flow state,showing viscous flow characteristics.Due to the screw shear stress,mucedin wrapped around starch and undergoes the Weissenburg effect and then continuously oriented.The polymer that has been preliminarily oriented enters the die with a constricted flow channel and was further oriented along the flow direction by shearing and stretching force of the die wall.When the polymer reached the die setting section,the temperature started to drop,the pressure in the extrusion die suddenly fallen,the shear force disappeared,the moisture evaporated sharply,and the temperature of the material decreased rapidly.Therefore,the oriented gluten-starch network composite structure was instantly frozen.The experiments on protein structure and starch chemistry supported the above mechanism speculation.?4?To balance and improve the texture quality and rehydration quality of EN,enzymatic extrusion with amylase addition was employed.The effect of thermostable and medium temperature?-amylase?TS-?A and MS-?A?on key quality of EN and the analysis of action mechanism results showed that a small portion of starch molecules was degraded into water-soluble oligosaccharide and dextrin during the enzymatic extrusion.The rapid dissolution of water-soluble ingredients in the rehydration process bring noodles a good honeycomb porous structure,greatly speeded up the heat and mass transfer rate during rehydration,and significantly improved the quality of EN.To a certain extent,the effect of the orientation of the starch polymer chain was weakened due to the length and strength of the starch molecular chain modified by?-amylase are reduced.However,the modified starch plays the role of lateral adjustment and modification of the overall texture quality of the noodles.A small amount of TS-?A or MS-?A promoted starch gelatinization.In contrast,an excessive amount of?-amylase might cover or adhere to the granule surface and to inhibit starch gelatinization.The overall quality characteristics of EN modified with 0.8‰TS-?A,and 1.6‰MS-?A were significantly better than those noodles without enzymes.Among these treatments,EN added with 1.6‰MS-?A showed short rehydration time?5.40 min?,less cooking loss?6.14%?,as well as high-quality retention rate?3.67 g/g?,which has the best overall quality acceptance.?5?Combining the above research methods,we took both the texture quality and rehydration quality into account,the multi-objective optimization model of Ca²⁺-controlled enzymatic EN process was constructed to obtain key technical parameters.With a small additional amount of Ca²⁺,the relative enzyme activity of MS-?A significantly increased,and the rehydration time of EN was significantly affected by the changes in enzymatic reaction efficiency.Therefore,0.08%Ca²⁺was used in conjunction with 0.12‰MS-?A to prepare Ca²⁺-controlled enzymatic EN,and the degree of orientation B value,rehydration time,and extrusion operating parameters?barrel temperature,screw speed,and water addition?were used to construct target response model.When the objective function weight coefficients set at 0.5 to 0.5,the optimal extrusion conditions were as follows:barrel temperature 105.78°C,screw speed 102.48 r/min,water addition 51.89%.The average orientation degree of the obtained EN was at 1.506,with the rehydration time at 5.30 min.The texture quality of EN prepared by the optimized process was close to hand-scratched noodles,and the quality of rehydration was similar but better than traditional Chinese instant noodles.The feasibility of the EN process proposed in this paper has laid a method and theoretical basis for the industrial development of EN.?6?Furthermore,molecular dynamics?MD?simulation technique was employed to study the mechanism of metal ions regulating?-amylase relative enzyme activity,in order to provide a theoretical basis for explaining why CA(Ca²⁺)could reduce the amount of MS-?A added in EN.The results indicated that the bonded CA is the key reason for the stable secondary structure and conformation of?-amylase,which further increased the relative enzyme activity.Especially the CA or NA bonded near the CA-NA-CA metal triad played a vital role in stabilizing the conformation of the?-amylase structure.Those ligands near the metal binding site are mainly negatively charged Asp,Glu followed by His,and less steric hindrance Ala.The main binding force was attributed to the electrostatic attraction between metal ions and energetic polar atoms,such as carboxyl oxygen atoms,carbonyl oxygen atoms,an amide oxygen atom,and methylamine,etc.Additionally,the high-temperature ambinet and excess bonded metal ions lead to the changes in the unstable side-chain movement mode,relative position of key residues,and the internal dynamics of?-amylase molecules.Consequently,the addition of excess CA leads to the decrease of relative enzyme activity of?-amylase as shown in the previous chapter.