Risk Assessment,Deterioration Mechanism And Control Technology Of Phvtosterol Oxidation Products In Edible Oils

Consumption of phytosterol(PS)may have beneficial effects on reducing plasma cholesterol levels and low density lipoprotein,inhibiting cancer cell activity and other physiological functions.In recent years,PS was widely used as nutritious supplementary for food,medicine and functional foods.However,given its inherent molecular structure,PS was sensitive to light,heat,and oxygen during the food production,storage and transportation process,easily degrading to produce a series of phytosterol oxidation products(POPs).POPs may bring potential hazard to the human body.However,due to lack of accurate detection methods,simulation system and other factors,the studies aim to investigate the risk assessment,formation mechanism and control technology of POPs are just beginning and need further studied.In this paper,PS and POPs were chosen as the study objects.The risk assessment,formation mechanism and control technology of POPs were investigated systematically,by using gas chromatography-mass spectrometry combination of mathematical modeling and chemometrics methods.The objects were to provide a risk assessment of POPs,and investigated the mechanism of PS deterioration and control methods.The main contents and results were summarized as follows:(1)An efficient gas chromatography-mass spectrometry method was developed and validated for determination of thirty-four POPs in edible oils.The calibration curves for each compound showed correlation coefficients(R2)better than 0.98.The detection limits were all below 36.30 ng/g.The intra-and inter-day determination precisions for diversiform POPs were<10%in relative standard deviations;the recoveries ranged within 89.72%and 117.42%.The developed method was successfully applied to study the presence of different POPs present at low levels in edible oils and other food.(2)The dietary exposure and the hazard index values(HI)associated with POPs from baked food consumption in China were estimated by using Monte Carlo simulation.The median dietary exposure of POP contents in baked food for four age groups in China,were 10.91(children),6.20(adolescents),3.63(adults)and 3.40(seniors)mg/(kgxday).Risk assessment of HI with respect to POPs indicated no risk(HI<1)for people in adolescents,adults and seniors in the country area of China,while a risk(1<HI<10)would occur refer to the baked food consumption of people in urban area and children in country area of China.Sensitivity and uncertainty analysis showed that this risk was increasing in the last decade.(3)The effects of light,heating,metal ions and lipid matrix on PS deterioration in oils were investigated.The results showed that light intensity and heating were positively correlated with PS deterioration.The sites of oxidative deterioration occurred mainly on C5,C6 and C7,and the formation of 5a,6a/5β,6β-epoxysterol,7-ketosterol,7α/β-hydroxysterol,6p-hydroxysterol and triols.Metal ions,especially the transition metal ions,significantly induced PS autoxidation at C5,C6 and C7 on Ring B of steroid nucleus at even a low concentration,and also induced dehydration on the C3 hydroxyl to form dienes and trienes at high concentration.The undersaturated lipid matrixs have an inhibitory effect of PS thermal degaration and the lipid with higher unsaturated degree exerted the stronger the inhibitory effect.(4)The structure-activity relationships between sterols and their thermal stability were studied.All sterols were found to be consistent with first order kinetic model,with all R2>0.9444.Result showed that PS with more double bonds is the more unstable and the double bond on C7 site is more sensitive than on C5;the longer the branch length is,the more hardly PS deterioration occurs;the effect of steroid nucleus was between double bonds and branch length.The QSAR model of sterol structure and its thermal stability were constructed by combining genetic algorithm(GA)with Partial least squares(PLS)and principal component regression(PCR).The results showed that topological structures of sterols had the closest relatives to their thermal stability.(5)Four common antioxidants including butylated hydroxyanisole(BHA),epigallocatechin gallate(EGCG),VE(a-tocopherol)and butylated hydroxytoluene(BHT)were selected to investigate their inhibitory effects on deterioration of PS in model oil.The results showed that the four antioxidants all had inhibitory effects on thermal deterioration of PS,among which BHA had the best effect,followed by VE,EGCG and BHT,and their inhibition rate were 22.8%,5.3%,3.5%and 22.8%,respectively.In the inhibition effects on formation of POPs,BHA,BHT and EGCG had inhibition rate of 7.80%,6.67%and 6.53%,respectively,while VE promote 9.51%formation of POPs.The inhibit mechanism and site of different antioxidants on PS deterioration was studied by combining deterioration pathway and kinetics model.BHA,the most effective antioxidant in this study mainly inhibited C5,C6 site to form epoxy compound and inhibited C7 site to form 7-ketosterol.In conclusion,the results showed that expose to POPs from current consumption of baked food will bring a risk to adults in urban area of China;the effects of heating,lighting and metal ion in the process of food may accelerate PS deterioration,while antioxidants,unsaturation of lipid matrix,branch length and saturation of PS have inhibitory effects.Therefore,in order to prevent loss of PS nutrition and reducing the health hazard of POPs,more studies will be needed in the inhibition of PS deterioration in food process,by avoiding deterioration factors,adding novel antioxidants or structural modification.