| Majia pomelo(Citrus Grandis L.Osbeck)is a characteristic grapefruit in Jiangxi province.In recent years,the industry has developed rapidly,with extensive planting and rich production.Pomelo peel accounts for 30～50% of the weight of the whole fruit,which is rich in pectin.Deep processing of pomelo peel can produce pectin with high added value.The application of pomelo peel and heavy metal removal can not only realize the resource utilization of pomelo peel,but also obtain good economic benefits.In this paper,the effects of storage time and extraction methods on the physicochemical properties,structural characteristics and functional characteristics of pomelo peel pectin in Majia pomelo fruit were studied.Focusing on the adsorption of heavy metal ions by pomelo peel pectin.This paper provides a reference for the comprehensive development and utilization of Majia pomelo peel and heavy metal removal.The main research results are as follows:(1)Majia pomelo fruit was stored at room temperature for different time(0-150d),and the pomelo peel pectin was extracted by citric acid method to obtain MPP-0,MPP-60 and MPP-150.The results showed that the extraction yield and neutral sugar content of pectin decreased gradually with the extension of storage time.The content of galacturonic acid,esterification degree and zeta potential increased gradually,while the Molecular weight of pectin decreased first and then increased slightly.Under different storage time,the pectin of pomelo peel has the same monosaccharide composition,but the content is different,and the degree of branched chain of pectin decreases gradually.In addition,pectin showed similar functional groups,microstructure and thermal stability during storage.The apparent viscosity of pectin increased gradually at different storage times,showing a pseudoplastic fluid,and the viscoelasticity of pectin was different.MPP-0 mainly showed elastic properties,while with the extension of storage time,the viscosity characteristics of MPP-60 and MPP-150 were more dominant.The antioxidant activities of MP-0,MP-60 and MP-150 decreased with the increase of storage time.In addition,pectin has adsorption effect on a variety of heavy metal ions,among which pectin has the best adsorption effect on Pb(Ⅱ).(2)The pectin of pomelo peel was extracted with water,hydrochloric acid and citric acid,and was named WEP,HEP and CEP,respectively.The chemical composition,molecular weight,apparent morphology,FTIR,rheological properties and emulsification properties were determined to study the effects of extraction methods on the physicochemical properties and functional properties of pectin.The results show that: The extraction methods had great influence on the physicochemical properties of pectin.CEP had higher extraction yield(28.62%)and galacturonic acid content(77.02%),WEP had higher neutral sugar content(15.81%)and esterification degree(91.93%),HEP had the highest ash content(3.80%)and molecular weight(728 kDa).The minimum esterification degree(58.20%)and zeta potential value of CEP made the pectin solution more stable.WEP,HEP and CEP have similar characteristic absorption peak,flake structure,emulsifying activity and emulsifying stability.All the three pectins are pseudoplastic fluids,and CEP has higher apparent viscosity.(3)WEP,HEP and CEP were used as adsorbents to remove Pb(Ⅱ)from aqueous solutions.The effects of initial p H value,initial Pb(Ⅱ)concentration and adsorption time on the adsorption performance of Pb(Ⅱ)were investigated,and the adsorption isotherm model and kinetic model of pectin were analyzed.It was found that the three pectins had higher binding activity and better adsorption capacity for Pb(Ⅱ),among which CEP showed stronger adsorption capacity for Pb(Ⅱ)due to its smaller molecular weight and lower esterification degree,and the maximum adsorption rate could reach 87.26 mg/g.Langmuir model is the best adsorption isothermal model,and the adsorption processes of Pb(Ⅱ)by the three pectins all conform to the pseudo-first-order kinetic model. |
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