Headspace oxygen analysis

There are many other methods for measuring lipid oxidation and quality by chemical means. Among the best-known procedures are the thiobarbituric acid (TEA) test, carbonyl value, and headspace oxygen analysis. These methods have been reviewed and discussed elsewhere (287, 307). 

Assessment of the quality attributes of cod caviar paste (fluorescent behaviour of cod caviar paste, stored under different conditions, in terms of light exposure and concentration of oxygen in the headspace) Sensory analysis and HS-fluorescence spectroscopy MCR-ALS [61]... 

R. B. Gaines, E. B. Ledford-Jr and J. D. Stuait, Analysis of water samples for ti ace levels of oxygenated and aromatic compounds using headspace solid-phase microexti action and comprehensive two-dimensional gas clnomatography , ]. Microcolumn Sep. 10 597-604(1998). 

Rancidity measurements are taken by determining the concentration of either the intermediate compounds, or the more stable end products. Peroxide values (PV), thiobarbituric acid (TBA) test, fatty acid analysis, GC volatile analysis, active oxygen method (AOM), and sensory analysis are just some of the methods currently used for this purpose. Peroxide values and TBA tests are two very common rancidity tests however, the actual point of rancidity is discretionary. Determinations based on intermediate compounds (PV) are limited because the same value can represent two different points on the rancidity curve, thus making interpretations difficult. For example, a low PV can represent a sample just starting to become rancid, as well as a sample that has developed an extreme rancid characteristic. The TBA test has similar limitations, in that TBA values are typically quadratic with increasing oxidation. Due to the stability of some of the end-products, headspace GC is a fast and reliable method for oxidation measurement. Headspace techniques include static, dynamic and solid-phase microextraction (SPME) methods. Hexanal, which is the end-product formed from the oxidation of Q-6 unsaturated fatty acids (linoleate), is often found to be a major compound in the volatile profile of food products, and is often chosen as an indicator of oxidation in meals, especially during the early oxidative changes (Shahidi, 1994). 

Fyhr et al. [201] reviewed several commercially available oxygen analyzers intended for the analysis of oxygen in the headspace of vials. However, preliminary validation revealed insufficient reproducibility and linearity. The authors developed headspace analysis systems. Sample volumes down to about 2.5 ml could be used without significant errors. Sample recovery was in the range 100-102%. It was necessary to measure the head-space pressure and volume in order to be able to present the assay in partial oxygen pressure or in millimoles of oxygen. Up to 40 vials per hour could be analyzed using this technique. 

Table 3. Effect of headspace gas composition on artemisinin and growth of cultures in gas fed systems. Data represent averages and standard deviations of 5-7 replicate flasks, each supplied with the given oxygen and carbon dioxide composition and various ethylene concentrations. Because regression analysis did not indicate ethylene to have significance in determination of these parameters at the 90% confidence level, all ethylene concentrations were lumped in the given oxygen and carbon dioxide concentrations...

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