Speciation Analysis And Distribution Characteristics Of Iron,Copper And Manganese In Wine

Oxidation browning seriously affects the sensory quality and nutritional value of wine.Iron(Fe),copper(Cu)and manganese(Mn)played a key catalytic role in wine oxidation reaction.However,there are many studies on the total amount of Fe,Cu and Mn,but few involved their speciation analysis and distribution in wine.Therefore,developing a method for speciation analysis of Fe,Cu and Mn in wine,especially red wine,clarifying their speciation in domestic bottled wines,as well as the relationship between speciation distribution and the chemical composition,is of great theoretical value and practical significance to further study the aging chemistry of wine,so as to effectively improve Chinese wine quality.The main results achieved are as follows:1.Development of a tandem solid phase extraction and an atomic absorption spectrometry technique for the speciation analysis of Fe,Cu and Mn in wineA rapid and accurate method for determining the fractionation of Fe,Cu and Mn in wine was developed using a tandem column solid phase extraction and an atomic absorption spectrometry.The optimization of SPE conditions,and the effects of p H values(3.00-4.00)and organic acids(single or blend)on recovery rates of metal fraction were investigated in wine-like solutions.Under the optimized activation conditions(20 m L methanol,30 m L water,10 m L 1 mol/L HCl,30 m L water,20 m L model wine)and flow rate(1 m L/min)of Polyclean X-HLB column,linking the column of Superclean SCX at a flow rate of 2m L/min with the eluent was 2 mol/L nitric acid,these metals were efficiently fractionated into hydrophobic,cationic and residual forms,with a subsequent direct determination of metal ions by Graphite Furnace AAS.The limit of detection for Fe,Cu and Mn was from0.39 to 1.56?g/L,obtaining the recoveries from 90.53%to 112.18%,with the relative standard deviation between 0.89%and 7.12%,suggesting the assay is sensitive with good reproducibility.In aqueous alcoholic solutions,significant effects of p H and organic acids on the distribution of ferric and cupric ions were observed,while few effects were found for manganous(II)ion.Compared with single organic acids,the solubility of metal ions was improved to a great extent when mixed organic acids existed because of they competitively bind Fe.2.Preliminary identification of speciation distribution of Fe,Cu and Mn in domestic wines and revealing relationship between color over-aging of red wine and oxidationThe results of total metal content of 30 wines showed that the average Fe and Cu content(2.35 and 0.15 mg/L,respectively)in red wine were higher than that in white wine(1.27 and 0.075 mg/L,respectively),while Mn was slightly lower(1.73 and 2.21 mg/L,respectively).The results of metal speciation analysis showed that there were significant differences among three forms of the same metal in wine samples.The fraction distribution of Fe or Mn in the same type of wine was relatively stable(the variation between samples was small),while Cu varied greatly(between samples).In wine samples,Fe and Mn mainly existed in the residual fraction(accounting for 80.56%and 52.65%of the total metals,respectively),while Cu was different in the white wine(dominated by the residual fraction,44.91%on average)and red wine(dominated by the hydrophobic fraction,61.46%on average).Fe cationic,Mn cationic and Cu hydrophobic fractions ranked next in white wines,while Fe hydrophobic,Cu residual and Mn cationic fraction ranked second in red wines.The results of physicochemical analysis of 24 Cabernet Sauvignon red wines showed that after being bottled for nearly 3 to 5 years,typical color characteristics of aging wines appeared:brick red or tile red;polymerized anthocyanins were dominant and the ratio of monomeric and cocpigmented anthocyanins was very low.Wine color parameters were significantly correlated with SO₂ content,metal speciation,phenolic compounds and antioxidant activity,indicating that color aging is closely related to oxidation.Excessive oxidation may be the potential reason for color over-aging occurred in domestic red wines.