Determination of trans double bonds in polyunsaturated fatty acid methyl esters from their electron impact mass spectraThe geometrical isomers of unsaturated fatty acid methyl esters were analysed by gas chromatography -electron impact mass spectrometry. Distinct differences in the electron impact mass spectra of methylene-interrupted tri-and tetra-unsaturated fatty acid methyl esters were observed. The differences were particularly related to the geometry of the central double bond in trienes or the two central double bonds in tetraenes. Trans geometry in these positions led to a significant decrease of m/z 79 [C 6 H 7 ] + , which is the base peak in the all-cis isomers. Disappearance or significant reductions of ions that are used for the determination of double bond positions in the corresponding cis isomers were also observed in the same spectra. The observed differences may be of help in the identification of double bond geometry in fatty acid isomers.

An analytical method that can detect low levels of oxidation in food earlier than a sensory panel would be a valuable tool for food manufacturers as well as research institutes. Two model matrixes, pork back fat and mechanically recovered poultry meat (MRPM), were freeze-stored in air at -20 degrees C for 26 weeks. Peroxide value, thiobarbituric acid reactive substances, volatiles analyzed with dynamic headspace gas chromatography-mass spectrometry (GC-MS) and a gas-sensor array technique (electronic nose), chemiluminescence, and front-face fluorescence were evaluated against sensory analysis with regard to detection of early oxidation and correlation with sensory data. Fluorescence and GC-MS could detect oxidative changes in pork back fat earlier than the sensory panel and the electronic nose at the same time. The three methods were highly correlated with sensory attributes (r = 0.8-0.9). GC-MS gave the best results with regard to detection of small oxidative changes in MRPM.

Triacylglycerols from Atlantic herring (Clupea harengus), sandeel (Ammodytes sp.) and Baltic herring (Clupea harengus membras) have been fractionated by silver ion high‐performance liquid chromatography. An ion exchange column loaded with silver ions was the stationary phase, and a gradient in the mobile phase from 1,2‐dichloroethane/dichloromethane (1∶1, v/v) to acetone and then to acetone/acetonitrile (2∶1, v/v) was used to effect the separation with light‐scattering (i.e., mass) detection. Fractions were collected via a streamsplitter, and fatty acid methyl esters were prepared by transesterification in the presence of an internal standard for identification and quantification by gas liquid chromatography. Triacylglycerols were separated according to the number of double bonds in the fatty acyl residues. Resolution was excellent at first, when the least unsaturated molecules eluted (trisaturated to dimonoene‐monodiene fractions). Base‐line resolution could no longer be achieved when molecules containing trienoic or more highly‐unsaturated fatty acids began to elute because of overlapping components. Nonetheless, some valuable separations of species containing two saturated and/or monoenoic fatty acids and one polyenoic fatty acid were achieved. Double bond indices (average number of double bonds in each triacylglycerol molecule) were calculated to estimate the separations possible. Fractions containing at least 11–14 double bonds per molecule were obtained.

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Fishmeal made from lantern fish (family: Myctophidae; genus: Benthosemapterotum) had proximate, mineral, amino acid and fatty acid composition within the range reported for fishmeal made from conventional fish. Similarly, the pressed-out oil had a fatty acid composition and content of unsaponifiables as reported for conventional fish oil. The content of unsaponifiables in the body fat of the fish indicated that wax esters contributed a minor part of the lipids of this species of lantern fish. Determined in chicks, the true digestibility of the amino acids varied from 92 % (arginine) to 73 % (hydroxyproline) which for most of the amino acids was 1-3 % units lower than that found for a high-quality capelin fishmeal. No differences in rate of mortality, growth rate and feed consumption and utilisation were found between lantern and capelin fishmeal when they replaced increasing amounts (0 to 100 %) of soya bean meal as protein supplements (72% of total protein) to cereal diets, both fishmeals reducing feed consumption and causing a significant improvement in feed utilisation compared with soya bean meal. The data indicate that lantern fish may be used for the production of fishmeal.