Effect Of Dynamic High-pressure Microfluidization (DHPM) On The Adsorption Capacity Of Heavy Metals By Dietary Fiber From Okara

With the development of the industry, the heavy metal pollution has been widelyattention.Through drinking water polluted by heavy metals, eating crops irrigated bywastewater and fish and shrimp grown in heavy metal polluted water or sea,breathing polluted gas exhausted by buys and cars, using cosmetics containing heavymetals, occasionally consumed agricultural products processed with excessiveamounts of heavy metals by undesirable businessman (such as, toxic pidan events),people are troubled by heavy metals. Long-term accumulation of heavy metal in thebody will damage the body’s nervous and blood systems, and cause organs like heart,lung, kidney, bone disease and even cancer. Dietary fiber because of its structurecontains a large number of hydroxyl, carboxyl group, phenolic hydroxyl groups, hasstrong adsorption ability for heavy metal.In this paper, the adsorption ability and clear effect of heavy metals (lead, copper,cadmium and mercury) within body by dietary fiber from soybean residue weredetermined using an in vitro model simulated gastrointestinal tract. The aims are toevaluate the effect of DHPM on the adsorption capacity of heave metals (Pb, Cu, Cdand Hg) by dietary fiber from soybean residue, to discuss the relationship betweenthe bind ability and physicochemical properties, such as particle size, density,specific surface area, SDF content, SDF:TDF, uronic acid content, water holdingcapacity, cation exchange capacity, total negative charges, and to analysis themechanism of heavy metal binding ability to dietary fiber via determining themicrostructures of fibers before and after binding heavy metals. The results are asfollows:1) The heavy metal adsorption behavior by dietary fiber mainly occurred insimulated small intestine rather than stomach. The adsorption ability of four heavymetal ions by dietary fiber from soybean residue ranked as follows: Cu2+> Cd2+>Hg2+> Pb2+;2) The effect of DHPM on binding capacity for the four heavy metal ionsPb2+、Cu2+、 Cd2+and Hg2+were different.. For Pb2+and Hg2+, the adsorptionability increased with the increasing of pressure. The BCmaxvalue reached highest at 160MPa for429.7±4.2μmol/g and444.4±8.8μmol/g, respectively increasing by15%and16%than the untreated dietary fiber sample. For Cu2+, with the increasingof pressure, the binding capacity increased first and decreased when the pressure wasabove120MPa. The maximum value765.3±5.8μmol/g at120MPa was1.12fold ofthe sample at0MPa. For Cd2+, the adsorption ability increased within80MPa anddecreased when the pressure was above80MPa, the maximum value increased by16%than untreated dietary fiber sample.3) The physical-chemical properties such as particle size, density, specificsurface area, SDF content, SDF:TDF, uronic acid content, water holding capacity,cation exchange capacity, total negative charges, of dietary fibers modified byDHPM had different variation tendency with DHPM pressure: with the increasingof DHPM pressure, the particle size decreased first and then increased, theminimum value was250.4nm at120MPa; the surface area increased before120MPa and then decreased; the largest density was at40MPa; the content of SDF, theratio of SDF to TDF, and the content of uronic acid increased with the increasing oftreatment pressure between0to160MPa; water holding capacity increased with theincreasing pressure between40to160MPa; cation exchange capacity increased first,then decreased and then increased, the maximum value reached at160MPa; totalnegative charges increased before80MPa and decreased when the pressure wasabove80MPa.4) The mechanism of binding heavy metal ions for Pb2+, Cu2+, Cd2+, and Hg2+ofdietary fiber from soybean residue was different. The adsorbing type for Cu2+wasphysical adsorption while for Pb2+, Cd2+, and Hg2+was chemical adsorption. Theadsorbing capacity for Pb2+and Hg2+was directly influenced by water holdingcapacity of dietary fiber. Samples with larger specific surface area owned strongerbinding capacity for Cu2+, meanwhile dietary fibers with more total negative chargesadsorbed more Cd2+.5) For the SEM image of dietary fibers before and after adsorbing heavy metals,it was also different. Silk-like material appeared on the surface of samples adsorbedwith Pb2+and Hg2+; A great number of alveolate-like fragments were emerged on thesurface of samples adsorbed with Cu2+; Particles with Cd2+adsorption became thin and internal porous, whose holes were filled by great balls of oakum. It showed thatthe Cd mainly attacked fiber surface structure, damaged on chemical bond and wasadsorbed (physically or chemically) into the holds, making its network structurereorganization and forming the porous and hole-crossed sheet structure.6) The mechanism of binding heavy metal ions was also discussed by FT-IRanalysis. The result indicated that the adsorption of Pb2+and Hg2+by dietary fiberfrom soybean residue was mainly through oxygenous negative charges; For theadsorption of Cu2+, none chemical bonds participated; For the adsorption of Cd2+,the groups of C=C and C–O were involved. Parts of C=O and C=C wasdamaged and intramolecular O—H bond was easily formed.