Modification Mechanism Of Industry-scale Microfluidizer On Pea-based Food Macromolecules

Natural food macromolecules have some defects,such as poor hydration properties of plant protein,insufficient inherent properties of starch and rough taste of fiber.Modifying food macromolecules to overcome their defects or endowing them with more superior properties has become the focus of food basic research.Based on previous researches,our team realized that the dynamic high-pressure microfluidization technology had limitations in modifying macromolecules.For example,it was easily blocked when processing food macromolecules with large particles or insoluble characteristics,and the treatment capacity was small.Additionally,there was a lack of research about the impact of dynamic high-pressure microfluidization on macromolecules in complex food systems.In recent years,an industry-scale microfluidizer（ISM）has been created in our research group,which possessed a reaction chamber with a large size and unique impact mode,and it could effectively process multiphase fluids containing large solid particles.It made it possible for truly modifying food macromolecules and processing complex food systems on a large and industrial scale.Therefore,this paper took the second largest edible bean in the world“pea”as the processing objects.Firstly,the modification effect and mechanism of industry-scale microfluidizer on food macromolecules based on pea was explored.Subsequently,the influence of industry-scale microfluidizer on the main components in whole component pea was investigated,and the differences between the effect of ISM treatment on the main components in whole component pea and the effect of modifying single pea macromolecule by ISM were compared.The results would provide reference for the industrial application of high-pressure microfluidization technology in the modification of food macromolecules and the preparation of whole component foods.The main conclusions are as follows:（1）Modification of pea starch by industry-scale microfluidizer and its effect:Taking pea starch as the modification object,larger particle size of potato starch and smaller particle size of rice starch were selected to compare the modification effect.Starches were treated by ISM at different pressures（30,60,90 and 120 MPa）.SEM observation found that the surface of pea starch became rough,and granules of potato starch were swelled and subsequently collapsed into pieces.In a differential manner,granules of rice starch were deformed and aggregated.With the increasing of ISM treatment pressure,particle size of pea starch and rice starch was increased,and that of potato starch was first increased and then decreased.ISM treatment caused starch damage to different degrees,and the damage degrees of pea starch,potato starch and rice starch were increased from 0.89%to 3.39%,0.52%to 21.87%and 4.52%to 17.99%respectively.Meanwhile,XRD and FITR analysis results showed that ISM treatment reduced the relative crystallinity and 1047/1022 cm^-1values of starches,indicating disrupting their long-range crystalline structure and short-range order structure.DSC analysis showed that ISM treatment reduced gelatinization enthalpy of starches,giving rise to gelatinization of starches.Gelatinization of pea starch induced by ISM was the main reason for the changes of morphological structure,crystal structure and internal ordered structure of pea starch.Gelatinization and disruption of internal structure of starches caused an increase in starch pasting viscosity.The results of RVA test showed that the pasting viscosity of pea starch gradually increased,while the pasting viscosity of potato starch and rice starch first increased and then decreased with the increasing of ISM treatment pressure.Dynamic rheological properties analysis showed an increase in elastic modulus of pea starch and potato starch,as well as a decrease in loss factor,while rice starch presented a decrease in elastic modulus and an increase in loss factor.It was indicated that ISM technology would effectively adjust the strength of gel network and the stability of mechanical processing of starches.The research results provided a theoretical basis for the application of ISM in the processing of whole grain products.（2）Modification of pea fiber by industry-scale microfluidization technology and its effect.Taking pea fiber as the modification object,dense corn bran were selected to compare the modification effect.Pea fiber and corn bran were treated by ISM technology at different pressures（60,90 and 120 MPa）for one pass and at 120MPa for two passes.Particle size analysis showed that ISM treatment reduced particle size of pea fiber and corn bran.CLSM and SEM observations founded that large and dense thick pea fiber was broken into fluffy curly flakes.ISM also loosened the thick and dense corn bran,and the distribution of carotenoids,flavonoids and other active components in corn bran was changed.XRD analysis showed that ISM treatment destroyed the crystalline structure and reduced the crystallinity of pea fiber and corn bran,but the higher crystalline structure of corn bran weakened the effect of ISM modification.Meanwhile,bulk density,WRC and OHC of pea fiber were increased by 3.7,2.1 and 2.6 folds,respectively.The disruption of dense structure,exposure of larger surface area,and disruption of crystalline structure might expose more water binding and oil adsorption sites,allowing ISM treatment to improve hydration properties and OHC of pea fiber.Compared with pea fiber,the degree of increasing WRC and OHC of corn bran was lower,which may be related to the dense morphology and crystal structure of corn bran.The research results would provide ideas for improving the utilization of food waste resources rich in fiber by ISM technology.（3）Modification of pea protein by ISM technology and its mechanism.Pea protein was treated by ISM at different pressures（30,60,90 and 120 MPa）.The results showed that ISM treatment increased the solubility of pea protein form16.99%to 64.28%.After ISM treatment,a decrease in particle size,an increase in specific surface area and the alteration of morphology from thick block to thin sheet of pea protein were conducive to its interaction with water,leading to the increase of solubility of pea protein.Fluorescence spectroscopy analysis showed that ISM treatment increased the intrinsic fluorescence intensity and surface hydrophobicity of pea protein,indicating that ISM induced the unfolding and denaturation of pea protein.Meanwhile,ISM treatment reduced the content of disulfide bonds in pea protein.SDS-PAGE analysis showed that ISM treatment changed the fraction patterns of pea protein and faded the bands of legumin,implying that ISM treatment interrupted the disulfide bond of pea protein and changed its primary structure.These results suggested that ISM promote the transformation of large insoluble protein molecules or aggregates into soluble particles by inducing protein denaturation,breaking disulfide bonds and changing primary structure,so as to improve solubility of pea protein.Research results would provide some theoretical basis for industry-scale microfluidizer to develop plant protein-based foods.（4）The effect of industry-scale microfluidizer on main components in whole component pea.ISM technology was used to treat whole component pea at different pressures（60,90 and 120 MPa）for one pass and at 120 MPa for two passes.As the pressure increased,particle size of the whole component pea was gradually decreased.D_[4,3],D₅₀and D₉₀were decreased from 123.7μm,119.0μm and 269.0μm to 33.9μm,27.7μm and 70.7μm,respectively.It was implied that ISM treatment could refine the whole component pea.After ISM treatment,the content of damaged starch in whole component pea was increased from 0.63%to 22.89%.SEM morphology showed that ISM treatment destroyed the starch granules in whole component pea.The observation of microstructure by CLSM found that ISM treatment induced the changes of fiber structure in whole component pea from dense blocks to loose structure.After centrifugal separation,protein content in the precipitate of whole component pea was decreased,and X-ray energy spectroscopy（EDS）analysis found that the content of N element in the precipitate was reduced,indicating that ISM treatment resulted in more dissolution of pea protein in the whole component pea.Analyzing the differences between the effect of ISM treatment on the main components of pea and the effect of modifying pea macromolecules by ISM,it was found that the changes of components in whole component pea caused by ISM treatment were similar to those of single pea macromolecule caused by ISM modifying,including damage of starch,disruption of fiber and solubility of protein.Nevertheless,degree of component change in the whole component pea was different from that caused by modifying single macromolecule,which may be related to the strengthening or weakening of the mechanical force on a component owing to the coexistence of multiple components in the whole component pea.