| Rhamnogalacturonan Ⅰ(RG-Ⅰ)is a kind of natural pectic polysaccharides that widelydistributed in the cell wall of higher plants.Its content is only inferior to that of Homogalactumoan(HG),and it can form sugar free gel and has intestinal prebiotics.However,the traditional HG type pectin production adopts thermal acid method to improve product stability and gel properties.RG-Ⅰ is removed and has not been utilized.The molecular structure of RG-Ⅰ pectic polysaccharide is complex,and there is no recognized extraction and separation method.Previous studies found that the components extracted by alkali solvent were rich in RG-Ⅰ,but the yield of solvent extraction was low and the amount of reagent was large;ultrasonic extraction is green and efficient,but the polysaccharide system is viscous,which affects the process;furthermore,the technology of combining ultrasound and pressure,that is,manosonication,has the advantage of enhanced ultrasound effects.However,there are relatively few studies on the extraction of cell wall polysaccharides,and the specific release mechanism of RG-Ⅰ domain is not clear.Therefore,this work aimed the manosonication-assisted method(MSE)for RG-Ⅰ enriched pectic polysaccharides extraction from citrus peel.Phychemical analysis characterization,extraction kinetic model,Raman imaging and immunofluorescence labeling,as well as the extraction mechanism with different effects were symmetrically studied.The main results were summarized as follows:(1)Release law and kinetics of MSE on RG-Ⅰ enriched pectic polysaccharidesThe effects of different MSE parameters on the yield and monosaccharides characterization were studied and compared.The results revealed that pressure,amplitude,sonic time and temperature significantly affected the yield.Na OH concentration significantly affected the yield and RG-Ⅰ domins.Meanwhile,in the developed quadratic polynomial model,the maximum extraction yield of 25.51±0.81%was obtained at 42℃,40%amplitude,250 k Pa for 20 min sonication with 50mmol/L Na OH solutions.Moreover,P_E represents the theoretical value of pectic polysaccharides that can be extracted from raw materials.The extraction kinetic models of the manosonication-assisted extraction,ultrasound-assisted extraction,high-temperature alkaline extraction,and low-temperature alkaline extraction methods revealed that the extraction process was accompanied with the degradation of the dissolved pectic polysaccharides,and MSE facilitated the extractability,dissolution,and degradation of pectic polysaccharides,leading to a higher extractability(P_E=27.83%).(2)Effect of MSE on the structural and properties of RG-Ⅰ enriched pectic polysaccharidesMSp was a typical RG-Ⅰ enriched pectic polysaccharide(RG-Ⅰ=60.05 mol%)with low galacturonic acids contents(41.02 mol%)and high arabinoses contents(37.06mol%).Compared with the production method of commercial pectin,the extraction time of MSE was reduced by 62.97%,the reaction temperature was reduced by 47.50%,the yield of product was increased by 39.09%,and the RG-Ⅰ domain was increased by57.32%.The molecular structure of the product was characterized by IR,NMR and atomic force microscope.The results showed that MSp had low degree of methylation and acetylation,and contained highly branched polysaccharide chains.MSp revealed higher degradation temperature and enthalpy,indicationg the better thermal stability.MSp were non-Newtonian behaviour and could be defined as thick liquids at 1%(w/v).MSp showed better emulsifying activity and stability due to its high solution viscosity and the branching structure.(3)Mechanism of MSE on RG-Ⅰ enriched pectic polysaccharidesThe pressure can increase the ultrasonic power,and damage the cell wall.Ultrasonicmechanical effect is the dominant factor in the MSE system.Sufficient mechanical effect can promote the dissolution of pectin polysaccharide and resulting an RG-Ⅰ enriched products.The in-situ distribution of cell wall polysaccharide components was realized by Raman imaging and monoclonal antibody immunofluorescence technology.Ultrasound can destroy the cellulose network structure of cell wall and MSE increased the damage.Comparing the fluorescence intensity of different treatment groups,it was found that arabinan antibody LM6 and xyloglucan antibody LM25 in the cell wall of untreated citrus peel were weak,and the fluorescence increased significantly after MSE as manosonication treatment destroyed the cellulose network structure and helped the explosion of the immune sites of neutral sugar and hemicellulose.Accordingly,the alkaline solution based synergistic mechanism model of manosonication assisted extraction of RG-Ⅰ pectic polysaccharide from citrus peel was constructed:in the dissolution stage of pectic polysaccharide,pressure combined with ultrasonic mechanical effect destroyed the cell wall polysaccharide network structure,promoting the RG-Ⅰ structure dissolution,increased the yield and resulting a yield synergistic effect.Pressure enchanced the ultrasonic mechanical effect and helped the degradation effecte on HG domins,increasing the RG-Ⅰ structure ratio within pectic polysaccharides.(4)Application and characterization of MSE on RG-Ⅰ enriched pectic polysaccharides from different citrus peel wastesThe quality of MSE extractions from four citrus cultivars including Eureka lemon,Guanxi pomelo,navel orange and grapefruit peels were systematically reviewed and compared with commercial citrus peel pectin(CCPp).It was found that MSE was suitable for the extraction of RG-Ⅰ pectic polysaccharides from different citrus sources(RG-Ⅰ=40.50 mol%-68.48 mol%),and the molecular weight decreased(5.58-7.94×10~4 g/mol).In terms of functional properties,RG-Ⅰ pectic polysaccharides from lemon peel and grapefruit peel showed better thermal stability with larger degradation enthalpy values,RG-Ⅰ pectic polysaccharide solution of grapefruit peel had higher viscosity and can be used as thickener,and RG-Ⅰ pectic polysaccharides from lemon peel and navel orange peel had good emulsifying stability,and implied the application of emulsifying stabilizers. |
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