Response Of Different Foodstuff System To Varying Magnetic Flux At Open And Closed States

It is can be dated to 1938 for the study of the effect of magnetic field on microorganisms.Whereas,it was the first time for the magnetic flied to be reported as a non-thermal technology for food processing in 1985.This delay was caused by the stagnant exploration of magnetic devices,shortage of food and agricultural resources,and the complex food components.With the development of industrial technologies and human life,people focus more on the food diversity,natural characteristics and healthy quality,rather than just intake food for the basic survival necessity.Therefore,magnetic field was introduced into the food filed,as an assisted non-thermal technique.Researches on how the magnetic field impacts the food materials also gradually increased.Existing reports mainly concentrate on food examination,analysis,and processing,that is,1)application of nuclear magnetic resonance technology to analyze and test food qualities?mostly related to inner water?;2)application of pulsed magnetic field in the sterilization and enzyme deactivation for the preservation of food materials.As far,permanent magnets and excitation coils are the two main types to generate magnetic field.In order to broaden the research on the processing of food by using magnetic field and promote the development of magnetic field technique in food industry,we design two different magnetic field systems based on the electromagnetic induction principle and the Hall effect,respectively.One is an open circuit system,which is applied for the determination and assessment of food quality.The other one is closed circuit system,which is for the process and treatment of food materials or relative byproducts.Main contents and conclusions are concluded as follows:Firstly,a transformer structural system was designed and built for the measurement of electrical parameters of food materials according to electromagnetic induction theory.Instead of metals,food liquids?salty cucumber juice and whole egg mixture?with different inductive properties were chosen to act as the secondary coil.When the metal primary coil was applied with alternative voltage?at different frequencies and amplitudes?,the electrical parameters of secondary coils were detected and recorded.Results indicated that the liquid food materials did response the alternative magnetic flux by presenting different terminal voltages?Us?in the secondary circuit.Meanwhile,we calculated the corresponding ratio?? value?of excitation voltage on the primary coil to the terminal voltage in the secondary coil.Terminal voltage Us and ? value depended on the amplitude of excitation voltage and the natural physicochemical properties of food materials.However,the frequency of excitation voltage had slightly influence on the terminal voltage Us and ? value.As details,the more inductive of the food liquids,larger terminal voltage Us and smaller ? value they presented.But these electrical parameters of secondary liquid food materials almost kept in the same level in the whole testing frequency range of 120 to 400 Hz when same excitation voltage was applied.The mathematic relationships between electric parameters and physiochemical parameters were calculated.For salted cucumber juice,its terminal voltage Us was positively linear correlated with salt content and soluble solid content;while ? value was negatively correlated with these physicochemical index.Oppositely,for whole egg liquid,the terminal voltage Us was negatively linear correlated with total solid content and lipid content;while ? value was positively correlated with these physicochemical index.The correlation coefficient R2 is larger than 0.8 in both situations.Therefore,electric parameters obtained by using alternating flux to excite liquid food as the secondary coil can be used as a potential technique for efficient measurement of the physiochemical indexes.Secondly,we deigned a magnetic field system with electrolyte solution circuiting in a closed loop for brining or ion intensification of vegetables and fruits.According to Hall effect theory,when the electrolyte solution flows through a non-parallel magnetic field,the interior charged ions will experience a force in the direction perpendicular to both the velocity and the magnetic field.The positive ions and the negative ions will be enforced to depart and move towards in opposite direction since they undergo the forces in opposite direction.Results showed that the negative exponential model Y?t??28?a?10?b[1-exp?-kt?] could be used to describe the diffusion of ions during the brining of the garlic and calcium ion intensification of the apple.Through the comparison of k and b values under different treatments,it was demonstrated that the combination of magnetic field and the flowing of impregnation solution accelerated the ions diffusion progress.Furthermore,the impregnation rate increased monotonically with the increasing magnetic flux density?0⁰.13 T?and impregnation temperature?5³0oC?;while it increased and then decreased as the frequency of magnetic field?0¹0 Hz?and the Reynolds number Re?0⁴134?of rose.The impregnation conditions were optimized to be of the magnetic flux intensity of 0.13 T,frequency of 7.5 Hz,Reynolds number Re of 1197.At these conditions and temperature of 30oC,the impregnation rate was improved by 89.87% for the brining of garlic and by 202.55% for the calcium intensification of apple,compard with the traditional static impregnation.The parameters of magnetic field just impacted the dynamics of impregnation,while the temperature could influenced both the impreganting rate and the final equilibrium of impregnation.Meanwhile,the closed-looped system was applied to assist the hydrolysis of food raw material and byproduct?pumpkin powder and corn straw?.Different from the results of impregnation of vegetables and fruits,the increment of Reynolds number Re monotonously enhanced the hydrolysis of the pumpkin powder and the corn straw.That is,the negative effect of high velocity of the reaction solution was not discovered in the examined range.The high rotating frequency of magnetic field initially promoted and then inhibited the hydrolysis process.For the polysaccharides extraction from pumpkin powder,it was obviously that concentrated acid and high temperature could boost the hydrolysis.The optimized conditions were the rotating frequency of 7.5 Hz,Reynolds number Re of 2500,pH 2 and the temperature of 50°C.Under those conditions,the pumpkin polysaccharides yield was 16.88%,increasing by 51.37% as compared to the traditional acidic extraction method.The pumpkin polysaccharides obtained under the optimized conditions were determined to be in the average molecular weight of 1.435 × 105 Da;its scavenging activity of DPPH·,O₂^-·,OH· were 52.8%,22.42% and 92.13%,respectively,under the concentration of 5mg/m L,which indicated that the polysaccharides extracted by the closed-looped system under the magnetic field had desirable scavenging activity of free radicals.For the pretreatment of corn straw with alkaline solution,its saccharification was promoted by the moderate increment in the rotating frequency of magnetic field and the concentration of alkaline solution.However,the excessive increment in the above two parameters negatively affected the saccharification of corn straw.When the velocity of the alkaline solution rose,the sugar?C5+C6?yield was improved.With response surface methodology,the best treatment conditions were determined to be 6.75 Hz of rotating frequency for the magnetic field,and 0.5 L/min of velocity as well as 1.02% of concentration for the NaOH solution.A total of 429.24 mg sugar was yielded from 1 g of dry corn straw at these conditions,which is 8.34% higher than the traditional agitation treatment.No matter whichever the food material systems are in open circuit or closed-looped circuit,the electrical conductive system will respond the applied variable magnetic flux.On one hand,this response depends on the natural physicochemical properties of food material.On the other hand,the response are influencmed by the devices operating parameters,including the magnetic flux density and rotating frequency of magnetic field,the velocity of reactive solution,and the treatment temperature.The open-circuit magnetic system is designed for the examination of the physicochemical characteristics of food materials;the closed-looped magnetic system is for the processing of food raw material and byproducts.Results in current research provide some references for enhancing the application of magnetic field in the food industry.