99E-7 |
|
H. S. LAM1, A. Proctor2, M. D. Morris3, and G. W. Smith3. (1) Food Science, University of Arkansas, 2650 N. Young Ave., Fayetteville, AR 72704, (2) Food Science, Univ. of Arkansas, 2650 Young Ave., Fayetteville, 72704, (3) Biochemistry and Molecular Biology, University of Arkansas for medical Sciences, Little Rock, AR 72205 Structural modification of low-density lipoproteins (LDL) by oxidation is a primary event in atherosclerosis. We have developed a simple, non-destructive technique to rapidly measure LDL oxidation as a first step to study the protective effects of food phytochemicals against LDL oxidation by using Fourier transform attenuated total reflection infrared spectroscopy (FTIR/ATR) and chemometrics. The objective was to develop an FTIR/ATR technique to measure, in vitro, chemical and structural changes in LDL during oxidatiion. LDL were isolated from fresh human plasma by sequential ultracentrifugation and then dialyzed at 4oC against EDTA solution. LDL suspensions were desalted and 4 mL were incubated at 37oC with 0.5mM CuCl2. LDL oxidation was followed by measuring conjugated diene and total carbonyls formation. LDL samples were also scanned to obtain FTIR spectra (4000 – 650 cm-1). Each LDL spectra were mean centered and standardized before chemometric analysis. Using the spectral region between 4000 and 650 cm-1 and PLS1 chemometric methods, a good calibration model (R=0.96; RMSE=0.009) was produced for measuring LDL conjugated dienes. The model predicted well the conjugated diene content of other LDL samples. Factor loadings of wave numbers on factor 1 from LDL spectra show a close relationship between the C-O vibrations of the peptide in the amide I band and hydroperoxides. Factor analysis also showed that carbonyls were produced in oxidized LDL through a multi-step reaction process which is an indication of the autoxidation process. This method enabled the critical examination of LDL chemical changes during oxidation. Factor analysis gave structural information related to LDL oxidation and simplified LDL spectral data interpretation. This approach is rapid, non-destructive and could be used to continuously monitor the effect of phytochemicals on LDL oxidation.
Session 99E, Nutrition: General II
|