Characterization of saponified vegetable oils, bacterial and synthetic poly(beta-hydroxyalkanoate) and derivatives using matrix -assisted laser desorption /ionization mass spectrometry.

摘要

A new and relatively rapid method for the determination of the fatty acid composition of vegetable oils using MALDI-TOFMS is described and illustrated with the analysis of olive oil, soybean oil, "spent" frying oil, vernonia oil, and castor oil. Solutions of the saponified oils, mixed with the matrix, meso-tetrakis(pentafluorophenyl)porphyrin, provided reproducible MALDI-TOF spectra in which the ions were dominated by sodiated sodium carboxylates [RCOONa + Na]+. Olive oil soap contained 70% oleic, 16% linoleic, 11% palmitic, 1% palmitoleic and 0.5% linolenic. Soybean oil contained 50% linoleic, 26% oleic, 15% linolenic, 6% palmitic, 2% stearic and 0.5% palmitoleic. "spent" oil contained 58% oleic, 19% palmitic, 14% linoleic and 8% palmitoleic.;The saponified vegetable oils were subsequently used as carbon sources for the biosynthesis of poly(beta-hydroxyalkanoate)s (PHAs) by Ralstonia eutropha (formerly known as Alcaligenes eutrophus ). These PHAs were isolated and fully characterized using different analytical techniques. The weight-average molecular mass of the PHAs was in the order of 400 kDa and the melting point (Tm) range was 163--174°C. MALDI-TOFMS analysis performed on partially transesterified PHAs showed intact oligomers weighing less than 10 kDa. These oligomers were detected in their cationized [M + Na]+ and [M + K]+ forms. MALDI data also revealed that the oligomers from base-catalyzed transesterification had an olefinic end-group and those obtained by acid-catalysis had an intact hydroxyl end-group. These end-groups were further confirmed by derivatization leading to the formation of acetates, methacrylates and urethanes. Moreover MALDI data showed that the PHAs from vernonia and soybean oils were copolymers of hydroxybutyrate and hydroxyvalerate. This new finding was confirmed by gas chromatography-mass spectrometry (GC-MS), proton nuclear magnetic resonance (1H NMR) and two-dimensional homonuclear (1H- 1H) correlation spectroscopy (COSY). Both GC-MS and 1H NMR independently confirmed that soybean and vernonia oil PHA contained ∼4% and 1% of hydroxyvalerate units respectively.