Analysis of fatty acid epoxidation by high performance liquid chromatography coupled with evaporative light scattering detection and mass spectrometry

Conventionally, epoxidation of unsaturated fatty acids has been studied either with titrimetric methods or in a lengthy procedure involving derivatization followed by gas chromatography (GC). We have developed a more rapid and descriptive analysis procedure for the substances using high performance liquid chromatography (HPLC) with evaporative light scattering detection (ELSD). Chemo-enzymatic epoxidation of unsaturated fatty acids (oleic, linoleic and linolenic acid, respectively) has been performed using hydrogen peroxide and immobilized lipase from Candida antarctica (Novozym 435). The fatty acids and their epoxidation products were separated by HPLC on a C-18 reversed-phase column using methanol-water containing 0.05% acetic acid as mobile phase. The method facilitated the simultaneous determination of fatty acids and epoxides differing from each other in the number of epoxide rings, the degree of unsaturation and the position of the epoxide rings and double bonds. An important aspect of the method development was the use of electrospray ionization and tandem mass spectrometry to confirm the structure of the epoxide products. It is suggested that the HPLC method, providing more information about the kind and concentration of fatty acids and their epoxides, represents a powerful complement to the existing methods for monitoring epoxidation processes on fatty acids.

Purification and characterisation of acidocin D20079, a bacteriocin produced by Lactobacillus acidophilus DSM 20079

Bacteriocins are natural antimicrobial agents produced by food fermentative bacteria. Lactobacillus acidophilus DSM 20079 produces a small bacteriocin, with a molecular mass of 6.6 kDa, designated acidocin D20079. This antimicrobial peptide was extremely heat-stable (30 min at 121 degrees C) and was active over a wide pH range. It was found to be sensitive to proteolytic enzymes (trypsin, ficin, pepsin, papain, and proteinase K). Acidocin D20079 has a narrow inhibitory spectrum restricted to the genus Lactobacillus which includes L. sakei NCDO 2714, an organism known to cause anaerobic spoilage of vacuum-packaged meat. Maximum production of acidocin D20079 in MRS broth was detected at pH 6.0, and the peptide was purified by ammonium sulphate precipitation followed by sequential cation exchange and hydrophobic interaction chromatography. Purified acidocin D20079 spontaneously formed spherulite crystals during dialysis. As the N-terminus was found to be blocked for sequencing, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used to determine a partial sequence, and the molecular mass of the bacteriocin in the formed crystals (6.6 kDa). Estimates of the molecular weight of the partially purified peptide, using tricine-SDS-PAGE, in which bacteriocin activity was confirmed by overlayer techniques were in accordance with this value.

The role of poly(ethyleneimine) in stabilization against metal-catalyzed oxidation of proteins: a case study with lactate dehydrogenase

The protection provided by poly(ethyleneimine) (PEI) to muscle lactate dehydrogenase (LDH) in metal-catalyzed oxidation (MCO) systems (CuSO(4) or FeCl(2) combined with H(2)O(2)) was studied, and comparisons were made with the chelators EDTA and desferal, respectively. The analytical chelating capacity of PEI was estimated to be around 1 mol Cu(2+)/10 mol ethyleneimine for all molecular weights of the polymer. The effect of [PEI monomer]/[metal ion] molar ratio on the oxidatively induced aggregation of LDH exhibited a similar trend as that of the other chelators; aggregation was enhanced at lower ratios and subsequently decreased until it was undetectable with increasing ratio. In contrast, the LDH activity showed a monotonic increase with increasing concentrations of the chelator. Total protection to the enzyme by PEI was provided at concentrations lower than that needed for full chelation of the copper ions, i.e. at [PEI monomer]/[Cu(2+)] ratio above 9 in case of PEI 2000, and above 7 for PEI 25000 and 2.6 x 10(6), respectively. The polymer also provided protection against oxidation in an iron-based MCO system. Hydroxyl radical formation during the MCO reaction was inhibited in the presence of PEI. The polymer of higher molecular weights also exhibited a stronger free radical scavenging effect.

Stabilizing effect of chemical additives against oxidation of lactate dehydrogenase

Oxidation is one of the major pathways for denaturation of proteins during storage, and also a potential problem in protein production, isolation and purification processes. In this study, a number of additives have been tested for their protective effects against oxidation in the presence of metal ions and hydrogen peroxide. Porcine muscle lactate dehydrogenase (LDH) was used as a model protein. Oxidation and denaturation of the enzyme were followed as activity loss, modification of certain amino acids, altered secondary structure and aggregation. Loss of activity during metal-catalysed oxidation was accompanied by structural damage of the enzyme, which was not the case during oxidation with peroxide. The best protectant during both modes of oxidation was found to be the polycation, poly(ethyleneimine) (PEI), followed by EDTA. Both chemicals also increased the enzyme's half-life during oxidation with a mixture of copper ions and hydrogen peroxide. Ammonium sulphate was an effective stabilizer during metal-catalysed oxidation, while sorbitol, sucrose and hydroxyectoine provided moderate stabilization. The ectoine was also stabilizing against oxidation with hydrogen peroxide, as was poly(ethylene glycol), whereas sorbitol enhanced the rate of enzyme inactivation. The stability of LDH towards denaturation by both oxidation and temperature was increased by addition of both PEI and sorbitol, as indicated by the melting-temperature profiles of the enzyme.