Effects Of Superfine Grinding On Structure And Functional Properties Of Flaxseed Protein

Flaxseed is the dominant characteristic resource in Inner Mongolia.It is mainly used in pressing oil.Flaxseed meal,a by-product of oil extraction,is rich in protein,with a content of 32%～49%.The results show that flaxseed meal protein has reasonable composition and proportion of necessary amino acids and is a high quality plant protein resource.But at present,linseed meal protein has not been fully processed and utilized,resulting in a waste of resources.Studies have shown that plant protein has different functional properties,which have a significant impact on the sensory,texture and flavor of food.Therefore,as food ingredients and additives,plant protein is one of the ways to further processing and utilization.The functional properties of flaxseed meal protein extracted by conventional alkali-soluble acid precipitation method are poor,which limits its application.How to further improve the functional properties of flaxseed meal protein is the core of protein modification technology.In recent years,ultrafine grinding,as a kind of physical processing technology that is easy to realize industrialization,can significantly improve the functional properties of proteins and is a better protein modification technology.Therefore,in this study,low temperature degreased flaxseed meal was used as raw material to extract protein,and different sizes of flaxseed meal protein were prepared by superfine grinding technology.The influence of superfine grinding on the structure and functional properties of flaxseed meal protein was studied,and the correlation between functional properties and structural properties was analyzed.Foamability and foamability stability are one of the important functional characteristics of plant protein.Plant protein with good foamability and foamability stability can replace traditional foamability and widely used in bread,cake,beverage and other food industry fields.In this thesis,the effect of ultrafine grinding on the frothing property and frothing stability of flaxseed protein was studied.The main research results are as follows:1.Flaxseed meal protein was prepared with low temperature degreased flaxseed meal as raw material by alkali soluble acid precipitation method.Flaxseed meal protein of different particle sizes was obtained by ultrafine grinding with high-energy nano impact mill.The average particle size of L1 of non-ultrafine flaxseed protein was41533.33 nm.The average particle sizes of L2,L3,L4 and L5 were 3700.67,3105.00,2668.00 and 2108.67 nm,respectively.Compared with L1,the average particle sizes of L2,L3,L4 and L5 decreased significantly.The effect of superfine grinding on the protein structure of flaxseed protein was further studied.SDS-PAGE gel electrophoresis showed that the molecular weights of protein L1,L2,L3,L4 and L5 of ultrafine flaxseed protein had no significant changes.Fourier infrared spectroscopy and secondary structure content analysis showed that theα-helix content of L2,L3,L4 and L5 increased,while theβ-fold andβ-angle content decreased compared with L1.Compared with L1,surface sulfhydryl contents of protein L2,L3,L4 and L5 in ultrafine pulverized flaxseed protein decreased.The Zeta potential analysis results showed that the absolute value of Zeta potential of L2,L3,L4 and L5 increased compared with L1,and the absolute value of Zeta potential of L2 was the highest.The results of endogenous fluorescence spectra showed that the fluorescence intensity of L1,L2,L3,L4 and L5 increased first and then decreased.Compared with L1,the surface hydrophobic values of L2,L3,L4 and L5 were increased.The results of scanning electron microscopy showed that the protein powder of flaxseed protein changed from compact and smooth to loose and porous granules.2.The effect of superfine grinding on functional properties of flaxseed protein was studied.The results showed that the solubility,water holding capacity,emulsification capacity and emulsification stability of flaxseed protein were significantly improved after ultra-fine grinding.The solubility of L5 was the highest 53.17%,which was 57.35%higher than that of untreated linseed protein L1,and the water holding capacity of L2 was the highest 2.81 g/g.Compared with untreated flaxseed protein L1,the emulsification ability of ultrafine pulverized flaxseed protein L3 was up to 5.54 m~2/g,compared with untreated flaxseed protein L1 was up to 16.88%,the emulsification stability of L4 was up to 60.76%.Compared with untreated flaxseed protein L1,it increased by 79.92%.The oil retention of ultrafine flaxseed protein decreased continuously.The gel properties of superfine grinding flaxseed protein increased first and then decreased,and L2 had the best gel properties.3.The results showed that the frothing ability of flaxseed protein increased significantly with the decrease of particle size.The frothing ability of L5 was up to 181%,which was 34.07%higher than that of untreated flaxseed protein L1.The frothing stability of L5 first increased and then decreased with the decrease of particle size,and L2 had the highest frothing stability.Compared with untreated flaxseed protein L1,foaming stability was improved by 77.04%.The relationships among the bubble microstructure,gas/liquid interface behavior and macroscopic foam properties were evaluated by inverted metallography microscope,surface tensimeter and interfacial rheometer.The macroscopic foam volume diagram showed that the foam volume formed by L1,L2,L3,L4 and L5 gradually increased.It was confirmed that the foaming property of flaxseed protein gradually increased with the decrease of particle size,and the volume decay rate of the stable foam system formed by flaxseed protein L2 was significantly slower than that of L1,L3,L4 and L5 after standing for 30 min.Flaxseed protein L2 was found to have the best foaming stability.The surface tension results showed that the maximum surface tension of L1,L2,L3,L4 and L5 showed a gradually decreasing trend,which confirmed that with the decrease of flaxseed protein particle size,the foaming property showed a gradually increasing trend.After the ultrafine pulverized flaxseed protein foam system stood for 30 min,the bubbles formed by L2 showed smaller sizes than L1,L3,L4 and L5,and the bubbles were more densely distributed,which confirmed that L2 had the best foaming stability.The surface viscosity trend diagram shows that the apparent viscosity of L2 is always the highest,which further confirms that L2 has high foaming stability.