Lycium Barbarum L. Leaves Polysaccharides Degradation Improves Bioaccessibility And Gastrointestinal Absorption Of Endogenous Minerals

Lycium barbarum L.leaves(LL)have very high content of minerals and polysaccharides Nevertheless,the absorption rate of these minerals is low due to its high molecular weight(Mw)and conformation nature.To overcome this issue a degradation method was used to modify the chemical structure and the conformational nature of Lycium barbarum L.leaves polysaccharide(LP)For this purpose,the mineral extract containing crude Lycium barbarum L.leaves polysaccharide(LPC)was first extracted,then chemically modified with vitamin C and hydrogen peroxide to produce degraded Lycium barbarum L.leaves polysaccharide(LPD).To explore the degradation effect on LP,both LPs were further characterized using Gas Chromatography-Mass Spectrometry(GC-MS),Fourier Transform Infrared Spectroscopy(FTIR),Nuclear Magnetic Resonance(NMR)and Inductively Coupled Plasma(ICP-MS).To comprehend the uptake efficiency of minerals,in vitro studies were performed using the digestion/Caco-2 cell model to evaluate the bioaccessibility and digestive absorption of the essential minerals:Ca,Fe,Zn and Mg from both LPC and LPD extracted from LL.The main results were as follows1.LPC Proximate Composition and CharacteristicsLPC is the LL mineral rich polysaccharide extract.Results show that:a)LPC was highly purified with protein content of 2.5%and abundant amount of sugar and uronic acid of 79%and 13%,respectively.b)LPC was highly rich in minerals.Minerals contents were of 10.8,2.29,0.41 and 3.96 mg/g for Ca,Fe,Zn and Mg,respectively.c)LPC was consisted of six monosaccharaides:arabinose,rhamnose,ribose,xylose,galactose and glucose.d)FTIR results showed a typical absorption peak of polysaccharide with stretching vibrations of carboxyl group,suggesting the presence of uronic acid.While NMR results confirmed that LPC was consisted of six monosaccharaides and the spectrum has a strong signal at ? 174.36 ppm,indicating the presence of uronic acids.e)LPC has a high Mw of 162 kDa and the curve slope of the radius of gyration(Rg)vs.Mw was 0.32,suggested a generally globular compact spherical conformation,which allows minerals to be wrapped inside the polysaccharides,thus being not conducive to the dissociation and release of mineral elements.2.Degradation Effect on LP Composition and CharacteristicsLPD was obtained after degradation using vitamin C and hydrogen peroxide.Main results were:a)GC analysis shown that LPC composed of six monosaccharaides:arabinose,rhamnose,ribose,xylose,galactose and glucose.This indicates that degradation had no major effect on LP monosaccharaides composition.b)LPD was rich in soluble sugar and that degradation had no significant effect on total sugar content.The total sugar decreased to 77.2%while uronic acid content slightly increased to 19.2%.c)Mineral content of Ca and Zn increased significantly after degradation to 11.5 and 0.72 mg/g,respectively.While Fe and Mg content decreased to 1.56 and 3.63 mg/g,respectively.d)FTIR of LPD showed a typical absorption pattern of sugar,which further proved that both LPs contained abundant amount of polysaccharide.The main peaks of LPD were almost the same as those of LPC,suggesting that no major functional group transformations caused by degradation.e)NMR results confirmed that both LPD were consisted of six monosaccharaides and that degradation had no major transformations effect on LPC.Signals of 13C NMR at ? 90-110 ppm confirmed the presence of both a-and(3-configurations in both LPs,and both spectrums share a strong signal at ?174.36 ppm,indicating the presence of uronic acids.f)The Mw was significantly decreased by degradation to 94 kDa,while the Rg vs.Mw slope increased to 0.52,indicating significant changes in LP molecular structure after degradation.3.LP Structure and ConformationLPC has a generally globular compact spherical conformation.This conformation allows the mineral elements to be wrapped inside the polysaccharides,which is not conducive to the dissociation and release of mineral elements.Degradation using H2O2 and vitamin Chad significant effect on LP molecular structure.This could be caused by the hydroxyl radicals originating from the reaction system of H2O2 and Vc which react with hydrogen atoms of polysaccharides to break glycosidic links.This reaction transforms LPC molecular structure from a compact spherical to a loose bar conformation,freeing and allowing more elements to be dissociated and released.4.Digestion and Gastrointestinal BioaccessibilityIn vitro digestion results showed that:a)FTIR spectrums of the gastric and intestinal mixtures share almost the same main peaks as those of LPC and LPD before and after the gastrointestinal phases,suggesting that no major functional group transformations occurred during digestion.b)The bioaccessibility increased by degradation,and LPD gastric and intestinal fractions were higher for all minerals comparing to those in LPC.The highest bioaccessible mineral was Mg in LPD intestinal mixture(68.18±3.32%),while the lowest was Fe in LPC gastric(10.52 ± 1.73%).c)No significant changes were found between LPC and LPD in the gastric bioaccessibility.However,the results of the intestinal mixtures showed clearly the effect of the degradation on the LP mineral bioaccessibility.5.Absorption in Caco-2 CellDegradation enhanced LP minerals absorption and the absorption rates of LPD in Caco-2 cells were higher than that of LPC.Degradation increased LP Ca,Fe,Zn,and Mg uptake by 6.1,1.9,7.1 and 10.8%respectively.The highest absorption was for Mg in the intestinal LPD(71.3 ± 3.1%),while the lowest was for Fe in the gastric LPC(8.2±0.82%).In conclusion,this study demonstrated that the physical configuration of the polysaccharides from LL strongly affects endogenous minerals digestive bioaccessibility and thus in vitro bioavailability.LP is the LL extract containing substantial amount of mineral elements,especially calcium,iron,magnesium and zinc.The absorption of mineral elements is greatly affected by the Mw and structure conformation of LP.