Modification Of Sweet Potato Pectin Under High Hydrostatic Pressure Assisted Pectinase And Its Effect On The Pb²⁺ Adsorption Capacity

Sweet potato?Ipomoea batatas.L?is the sixth most important food crop in the world,and China is the world largest producer.Large amount of sweet potato residues were generated during the starch extraction process,causing huge environmental pollution and resources waste.These residues can be used as viable source for pectin extraction.In addition to use as a gelling and thickening agent in food industry,pectin has gained its attraction as novel and high-efficient biosorbant for various heavy metal contaminants,especially for Pb²⁺in recent years.However,as a natural biopolymer with high molecular weight and complex structure,the usefulness of pectin has been limited,which need to be modified in order to improve its physicochemical properties,and to enhance its heavy metal adsorption capacity.Therefore,high hydrostatic pressure?HHP?and/or pectinase treatment was used to modify the natural sweet potato pectin in this study,and investigate the effect of modification on structural,physicochemical,functional properties,Pb²⁺adsorption capacity and adsorption mechanism of natural and modified sweet potato pectin.Thus providing theoretical support for the utilization of sweet potato pectin.HHP and pectinase were used to modify the sweet potato pectin,and the structural,physicochemical and emulsifying properties was investigated.The results showed that the optimum conditions which gave the lowest molecular weight and degree of esterification?DE?value was found at200 MPa,15min with enzyme concentration of 72 U/g.Compared to HHP-and pectinase-treated samples,pectin treated with HHP-pectinase exhibited the lowest molecular weight?0.05×10⁵ g/mol?and DE?18.16%?.Moreover,it displayed the highest rhamnose?16.73%?and galacturonic acid content?757.38 mg/g?as well as the highest emulsifying activity and stability?52.24%,71.28%?.In addition,the pectin exhibited cracked,more porous surface,and contained shorter chains within higher proportion of exposed protein after HHP and pectinase treatment.The effects of HHP and pectinase modification on the Pb²⁺adsorption capacity were investigated.The maximum adsorption capacity(Q_max)of modified sweet potato pectin was 263.15 mg/g at pH 7 and60oC in 60min with the pectin concentration of 0.5g/L.Crucially the modified sweet potato pectin showed better Pb²⁺adsorption capacity than commercial citrus pectin.After adsorption of Pb²⁺,all the pectin samples exhibited irregular,wrinkled,more fragile and porous surface and polysaccharide chains tended to form entangled networks.Overall findings from batch experiments and characterization analysis demonstrated that chemical absorption process involving O containing functional groups?O-H,COO-?,and cation exchange controls the whole Pb²⁺absorption process by pectin subordinate with electrostatic interactions.The effects of HHP and pectinase modification on the Pb²⁺adsorption capacity in the gastrointestinal tract?in vitro?were analyzed.All pectin samples exhibited highest Pb²⁺adsorption capacity under simulated in vitro intestinal conditions and the adsorption capacity was increased with the pectin amount under both in vitro gastric and intestinal digestion conditions.HHP assisted pectinasemodified sweet potato pectin exhibited the highest total?81.32%?and net?53.21%?Pb²⁺adsorption capacity under in vitro intestinal digestion conditions compared to the citrus and sweet potato pectin.Characterization analysis through XPS,FTIR and H¹ NMR demonstrated that chemical absorption process involving O containing functional groups?O-H,COO-?.The results of this study confirmed that HHP-assisted pectinase treatment is a novel,high efficiency,and environmental friendly technique for modification of pectin with great potential for application in the food industry.Moreover,modified sweet potato pectin showed better Pb²⁺adsorption capacity than commercial citrus pectin,thus it could be used as novel,ecofriendly adsorbent for the purification of heavy metal from contaminated wastewater.