Thu Thao Nguyen

Though liquid chromatography electrospray tandem mass spectrometry (LC–ESI-MS2) has been widely used in the structural elucidation of triacylglycerols (TAG) in vegetable oils, its potentiality for the identification of TAG molecules in omega-3 rich oils remains unexplored till date. Hence, this article investigates the applicability of LC–ESI-MS2 for the structural characterization of naturally occurring TAG in cod liver oil without the TAG fractionation during the sample preparation. A computational algorithm was developed to automatically interpret the mass spectra and elucidate the TAG structures respectively. The results were compared against the lipase benchmark method. A principal component analysis study revealed that it is possible to discriminate genuine from adulterated cod liver oil.

The article presents a comprehensive account of the application of chemometric approaches to determine the factors that influence the tri-α-linolenoylglycerol (TALG) ammoniated adduct signal m/z 890.6 in an ion-trap mass spectrometer coupled to a liquid chromatograph and the estimation of different sources of errors involved in TALG calibration experiments. It was found that by using experimental design, the influence of the nebulizer pressure on the analytical signal is less pronounced than the influence of the drying gas flow and the chromatographic flow rate. The results revealed that without using tandem mass or atmospheric pressure chemical ionization, it is possible to fragment the TALG backbone and obtain the free α-linolenic acid by varying the drying gas flow and using an electrospray interface. The error decomposition approach revealed that the preparation error was 26 times higher than the instrumental error.

A simplified method for quantitative analysis of fatty acids in various matrices by gas chromatography is proposed as an alternative to the conventional method and the variables of the protocol examined to optimize the processing conditions. The modified method involves direct methylation of fatty acids in homogenized samples with boron trihalide (BF3 or BCl3 in methanol) followed by extraction with hexane. The addition of hexane to the reaction mixture after the methylation process can enhance the efficiency of fatty acid methylation and is critical for those samples that contain high levels of triglycerides. A mechanism underlying this effect is proposed.

Exploring the capabilities of instrumental techniques for discriminating n-3 rich oils derived from animals is a very important though much neglected area that was emphasized more than 100 years ago. In this study the potential of gas chromatography (GC) for discriminating full fatty acid methyl ester (FAME) profiles from fish (cod liver and salmon) and marine mammal (seal and whale) oils is evaluated by means of principal component analysis (PCA). The FAME profiles from plant oils such as rapeseed, linseed and soy oils and seven different brands of n-3 supplements are also used in the discrimination process. The results from the PCA plots can reliably distinguish between plant, n-3 supplements, fish and marine mammal oils. By removing the contribution of the n-3 supplements and plant oils it is possible to discriminate between types of fish and marine animal oils. GC offers a rapid, simple and convenient means of discriminating oils from different species, brands and grades.

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important swine pathogens because it is highly infectious and causes economic losses due to decreased pig productivity. In this study, the 603 bp complete major envelope protein encoding gene (ORF5) of 32 field PRRSV isolates from Vietnam collected during 2008-2012 were sequenced and analyzed. Multiple nucleotide (nt) and deduced amino acid (aa) alignments of ORF5 were performed on the 32 isolates: the representative strains (European and North American genotypes), Chinese strains available in GenBank and vaccine strains licensed for use in Vietnam. The results showed 94.8-100.0% nt identity and 94.0-100% aa similarity among the 32 isolates. These isolates shared similarities with the prototype of the North American PRRSV strain (VR-2332; nt 87.8-89.3%, aa 87.5-90.0%), and Lelystat virus, the prototype of the European PRRSV strain (LV; nt 61.1-61.9%, aa 55.1-57.0%). There was greater similarity with QN07 (nt 96.5-98.5%, aa 96.0-99.0%) from the 2007 PRRS outbreak in QuangNam Province, CH-1a (nt 93.2-95.1%, 91.5-93.5%) isolated in China in 1995 and JXA1 (nt 96.5-98.6%, aa 95.0-98.0%), the highly pathogenic strain from China isolated in 2006. The Vietnamese isolates were more similar to JXA1-R (nt 96.5-98.6%, aa 95.0-98.0%), the strain used in Chinese vaccines, than to Ingelvac MLV/BSL-PS (nt 87.2-89.0%, aa 86.0-89.0%). Phylogenetic analysis showed that the 32 isolates were of the North American genotype and classified into sub-lineage 8.7. This sub-lineage contains highly pathogenic Chinese PRRSV strains. This study documents genetic variation in circulating PRRSV strains and could assist more effective use of PRRS vaccines in Vietnam.