| Highland barley?-glucan,as an important active ingredient in highland barley,has great research value.Highland barley?-glucan has five major physiological effects of"clearing the intestine,regulating blood sugar,reducing cholesterol,improving immunity,and anti-tumor".However,?-glucan coexisted with starch,protein and lipid in the form of complex in the endosperm and aleurone cell wall of barley,which hindered the extraction of?-glucan to a certain extent.There are currently various extraction methods for barley?-glucan,but it is unclear how different extraction and preparation methods affect the molecular weight and physicochemical properties of barley?-glucan.Comparative studies on the content and its physical and chemical properties have not been reported.Based on the above problems,this paper comparatively studied the physical and chemical properties of barley?-glucan distributed by different extraction methods and different parts of barley,with a view to providing a theoretical basis for the extraction and comprehensive utilization of barley?-glucan.First,the?-glucan yield is the test index,and the highland barley?-glucan was extracted by ultrasonic-microwave synergy.The extraction process was optimized by single factor and orthogonal experiments,and compared with the extraction effect of water extraction method,ultrasonic method and microwave method.Scanning electron microscope was used to observe the surface structure changes of highland barley bran powder,and the mechanism of ultrasonic-microwave synergetic extraction was preliminarily analyzed.Secondly,the effects of different extraction methods(ultrasonic-microwave synergistic method,water extraction method,ultrasonic method and microwave method)on the physical and chemical properties of?-glucan such as molecular weight,solubility,rheology,emulsifying and foaming properties were compared and analyzed.Finally,the law of nutrition composition,?-glucan content,molecular weight and physicochemical properties of different parts of barley was explored.The main conclusions are as follows:(1)The experimental results of ultrasonic-microwave synergetic extraction of highland barley?-glucan showed that:the optimal extraction conditions of ultrasonic power at 250 W,ultrasonic time 20 min,microwave power 800 W,microwave time 3min and material-to-liquid ratio 1:25(g/m L)produced?-glucan yield about 2.29%.Compared with water extraction,ultrasonic and microwave extraction,the yields were increased by 120.19%,57.93%and 18.65%,respectively.Scanning electron microscopy showed that water extraction method caused the bran powder to swell and the structure becomes loose from firmness;Ultrasonic extraction makes the bran powder flakes finer;The thermal effect of microwave causes the bran powder to be puffed and enlarged due to rapid heating.The ultrasonic-microwave synergy method makes the structure of the bran powder bulky,loose and porous.This indicates that the ultrasonic-microwave synergistic method can better extract barley?-glucan,and the yield of?-glucan is related to the degree of destruction of bran structure.(2)Molecular weights of highland barley?-glucan prepared by different extraction methods(ultrasonic-microwave synergistic method,water extraction method,ultrasonic method and microwave method)through analysis methods such as ultraviolet spectrum,infrared spectrum,gel permeation chromatography,and rheological analysis,and other analytical methods.The relevant results show:The purity of highland barley?-glucan prepared by different methods is between 84.91%and 88.17%,and there is no significant difference in purity and infrared structure(p<0.05).The average molecular weight of?-glucan(UMG)extracted by ultrasound-microwave synergy is 3.376×105 Da,which is about 1.33 times that of traditional water extraction.UMG has a molecular weight dispersion width value of1.453,the smallest of 4 samples.UMG has the lowest solubility and the highest apparent viscosity.UMG has the smallest flow index n and the largest consistency coefficient K,which are 0.713 and 0.104,respectively.Under the same conditions,the emulsification size of the highland barley?-glucan extracted by these four methods is:UMG>WG>MG>UG,and the foaming size is:UG>MG>WG>UMG.The differences are significant(p<0.05).This shows that the extraction and preparation method of barley?-glucan will affect its molecular weight,molecular weight distribution,and cross-linking between molecules,and then affect its physicochemical properties such as solubility,rheology,foamability and emulsification.(3)The experimental results of the effect of site distribution on the physicochemical properties of highland barley?-glucan showed that:After the highland barley was milled and layered,the fat content gradually decreased with the increase of the number of milled passes.The content of?-glucan increased with the increase of the number of milling passes.The contents of starch and protein in the first and second bran are relatively small.The weight-average molecular weight of?-glucan(BG-1?BG-5)increased from bran to highland barley core(from outside to inside),and?-glucan extracted from highland barley core powder Sugar BG-5 has the largest number average molecular weight and weight average molecular weight,and its molecular weight distribution width index is 1.639,the smallest among 5 samples.The flow index n of highland barley?-glucan solution is less than 1,and the shear thinning characteristics of non-Newtonian pseudoplastic fluids are reflected in the range of shear rate from 0 to 100 s-1.The viscoelasticity of highland barley?-glucan solution will increase as the molecular weight increases.At the same shear rate,as the molecular weight of highland barley?-glucan increases,the flow index n of the solution decreases and the consistency coefficient K increases.Among them,the apparent viscosity of BG-5 is the largest,and the flow index n is the smallest.The consistency coefficient K is the largest,0.617 and 0.221 respectively.The solubility of highland barley?-glucan is affected by site distribution and temperature changes.High molecular weight?-glucan easily aggregates at low temperature,which increases the viscosity of the solution and decreases the solubility.As the temperature increases,the viscosity of the?-glucan solution decreases and the solubility increases.At the same concentration,temperature and pH,the emulsification size of highland barley?-glucan is:BG-5>BG-4>BG-3>BG-1>BG-2,and the foaming size is:BG-2>BG-1>BG-3>BG-4>BG-5,the difference was significant(p<0.05).This indicates that the barley mash can obtain?-glucan with different molecular weight and different physical and chemical properties by layer milling.The viscosity and solubility of barley?-glucan are related to the molecular weight distribution of ?-glucan and its solution temperature. |
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