Authenticity factor

El-Fizga (108) developed a simple, rapid method for the detection of oils high in linoleic acid in olive oil by RP-HPLC and a simple authenticity factor and a derived equation to determine the extent of adulteration with a one short chromatographic step, completed in less than 15 min. They used two 150 X 4.5-mm ID stainless steel columns packed with an octyl-bonded silica stationary phase (Supelcosil-LC 8) (Supelco. Bellefonte, PA, USA) and a differential reffactometric detector. The isocratic mobile phase was acetone-acetonitrile (70 30, v/v) (Table 5). 

The presence of vegetable oils of high linoleic acid content in olive oil can be detected by measuring its authenticity factor (Au) as follows ... 

Anhydrotetracycline oxygenase from Streptomjces aureofaciens which cataly2es the conversion of anhydrotetracycline to dehydrotetracycline, has been isolated and characterized as a flavin-dependent oxygenase (83). It consists of two subunits of mol wt = 57, 500 based on SDS/polyacrylamide—gel electrophoresis. The cosynthetic factor 1 of Streptomjces aureofaciens involved in the reduction of 5a,lla-dehydrochlortetracycline to chlortetracycline, has been identified as 7,8-didemethyl-8-hydroxy-5-deazariboflavin. This work was aided by comparison of spectral data with that of an authentic sample obtained from the hydrolysis of coenzyme F-420 (84). 

Estimating the amount of a metabolite when an authentic reference standard is not available is still a challenge. Yu et al.191 described a procedure that uses the results of an in vitro metabolite identification based on a test compound that produces 14C-labelled metabolites essentially the 14C-labelled metabolites are used to provide a correction factor for the MS response when assaying samples that contain the same metabolite in a study that did not use the 14C-labelled test compound. Flop192 described another novel approach for metabolite quantitation based on the observation that the MS responses for most compounds are very similar to responses from nanospray ESI. Valaskovic et al.193 also reported equimolar MS responses for multiple compounds when the flow rate to the nanospray ESI source was set to about 10 nl/min. It is too soon to know whether these intriguing findings can be readily applied to discovery metabolite identification studies. 

Several objective methods are available to determine the freshness of shrimp however, many require a) raw products for analysis, b) complex chemistry and equipment for testing, or c) highly trained technicians. Additionally, some of these methods require extensive analysis time making results meaningless if product has already spoiled or has been released to consumers. Results for the impedance method discussed in the present paper demonstrate that spoilage of raw or thermally processed shrimp can be detect in 30 min with easy sample preparation. The limitations of this method revolve around the requirement for authentic fresh frozen standards as a basis for comparison. Further research is necessary to define the effect of seasonal and geographical variations, and species and size difference. The sum of these factors will likely affect the reproducibility of this method. 

Chemical Analysis of Extracts. The extracts were analyzed by capillary column GC-MS for OCs, TAAPs, and PAHs (see the list on page 313). The GC-MS parameters used at the two laboratories are shown in Table II. The identification and quantitation were all done by using automatic routines based on a mass spectra library created from authentic standards of the selected compounds. Compounds were located by searching the reconstructed ion chromatogram for each library entry within a narrow retention time window relative to the internal standard (anthracene-dio or phenanthrene-dio). Quantitation was achieved by comparison of characteristic ion areas in the field samples with ion areas of the internal standard. These ion areas were normalized by response factors established by comparison of ion ratios of a standard mixture of all 66 analytes at a concentration of 2.5 ng//zL. 

Enantioselective gas chromatography can provide three quite different kinds of information (1) the amount of each enantiomer present in a food, determined as the enantiomeric purity or the enantiomer excess, and the separation factor a for each pair of enantiomers (2) enantiospecific sensory evaluation using gas chromatography-olfactometry (GC-O) and (3) data used as part of an authenticity determination. 

In the early history of gas chromatogra-phy/olfactometry (GC/O vn/tgu), the goal of GC/O analysis was to determine when an odor elutes from a GC in order to identify it. The analysis yielded a list of times and, with appropriate standards, retention indices. When combined with other chemical analysis methods, such as mass spectrometry (MS), a name for a particular odorant could be proposed. Comparing both the chemical and sensory properties of the odorant with those of authentic standards allowed researchers to identify the odorant with considerable certainty. The number of odorants that are detected, however, is determined by a number of factors, including the design of the olfactometer, the fraction of the extract injected, and, as we now suspect, the genetics of the sniffer. 

If an aDNA extract frails to PCR amplify it should be tested for the presence of PCR inhibitors. This test requires the availability of an authenticated aDNA sample to be used as a positive control.8 Set up side-by-side PCR reactions containing 1) the template suspected to contain inhibitors, to which is added a volume of the ancient positive control equivalent to that of the template, 2) only the template suspected to contain inhibitors and 3) only the positive ancient control. This side-by-side comparison will allow for the preclusion of PCR failure due to factors other than inhibition (e.g. the stochastic nature of PCR amplification). If the template spiked with the positive ancient control (reaction 1) permits its amplification, while the template suspected of containing inhibitors (reaction 2) fails to amplify, the template is likely free of inhibitors and, therefore, does not contain a sufficient amount of DNA for analysis. Alternatively, if the first PCR reaction fails to amplify, whereas the third reaction does amplify, the template is concluded to contain inhibitors. In this case, the silica extraction should be repeated, as described above, and PCR reattempted. Our studies have shown that as may as four repeat silica extractions may be required to sufficiently remove PCR inhibitor from DNA extracts, despite the inherent loss of DNA yield associated with each repetition of the silica extraction (5). 

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