High-field (600 MHz) nuclear magnetic resonance (NMR) spectroscopy was applied to the direct analysis of virgin olive oil. Minor components were studied to assess oil quality and genuineness. Unsaturated and saturated aldehyde resonances, as well as those related to other volatile compounds, were identified in the low-field region of the spectrum by two-dimensional techniques. Unsaturated aldehydes can be related to the sensory quality of oils. Other unidentified peaks are due to volatile components, because they disappear after nitrogen fluxing. The statistical analysis performed on the intensity of these peaks in several oil samples, obtained from different olive varieties, allows clustering and identification of oils arising from the same olive variety. Diacylglycerols, linolenic acid, other volatile components, water, acetic acid, phenols, and sterols can be detected simultaneously, suggesting a useful application of high-field NMR in the authentication and quality assessment of virgin olive oil.
SummaryThe isolation and identification of low molecular mass peptides formed during the ripening of Parmigiano-Reggiano cheese is described. A strategy was used based on the fractionation of nitrogenous material using chemical methods followed by HPLC to isolate peptides and fast atom bombardment-mass spectrometry to identify them. It was found that the majority of cheese oligopeptides arose from the proteolysis of β-casein. Several phosphopeptides and oligopeptides known in vivo to be biologically active have also been identified during the ripening of cheese.
Based on proton nuclear magnetic resonance (1H-NMR) spectroscopy, a rapid and structure-specific method for the determination of ¢o-3 polyunsaturated fatty acids (PUFAs) in fish lipids is presented. The different chemical shift observed for the methyl resonance of o~-3 PUFAs (d = 0.95 ppm) with respect to the methyl resonance of all other fatty acids (d --0.86 ppm) has provided the possibility of prc~ posing a new and rapid method for the determination of ¢o-3 PUFA content. Twenty-four fish lipid samples (raw, cooked and canned albacore tuna) produced results that showed good agreement between 1H-NMR analysis and gas chromatographic determination. Raw and cooked samples showed significantly higher levels of ¢o-3 PUFA than canned tuna.
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