Meat Samples

In the original work, triplicate determinations of the fat content of each sample were performed and the standard deviations (SD) were calculated. The empirical values obtained by MAP proved to be statistically equivalent to values obtained by the official agency that provided the meat standards. The method used to certify the samples were AOAC methods 24.005 and 7.056 (13th edition, 1980) which are based upon a four-hour extraction of the dried sample with petroleum ether using a Goldfisch or a Soxhlet extractor. 

---

Silverlight and Jackman developed an immunoassay for levamisole in meat and milk. The LOD in both milk and meat samples was 1 xg kg The assay was applied to milk directly, and muscle samples required only homogenization in the presence of 10-fold of buffer prior to analysis. The linear range of the assay was between 5 and 50 pg kg for meat and between 0.2 and 25 qg kg for milk. The linear range of the assay was below the MRL for milk (10 qg kg ) and meat (50 qg kg ). 

One can readily see that the conclusions of the authors are based on numerous assumptions rather than on factual data. Unfortunately, this is the nature of retrospective epidemiological studies. One cannot really fault the authors for their sequence of theories leading them to a possible source of the infections. Such efforts are necessary for sorting out the potential source of infections and. through follow-up studies and designed experiments, we can determine sources of infections and methods for prevention. They evidently did omit some observations on the meat samples they did check and observations on the adjacent dairy herd and. they did not take samples from the cattle s environment on the beef farm. If the beef farm was thought to be the source, there should have been more effort to find the organism on that farm. 

The decrease in the concentration of IMP preceded a simultaneous increase in the concentrations of both inosine and hypoxanthine in meat samples. (From Tikk et ah, 2006)... 

Another contributor of MFD is the presence of molecular oxygen. An initial study determined the optimum level of free radical scavenger and chelator required to prevent MFD when added to a meat sample under vacuum 38), Based on those results, subsequent experiments were designed to investigate the synergistic effects of the two compounds, propyl gallate and EDTA (tetrasodium salt), on MFD both in the presence or absence of oxygen. 

Polybrominated Diphenyl Ethers. Information about the concentrations of PBDEs in food stuffs is very limited. Recently, Ohta et al. (2002) determined the concentration of total PBDEs in vegetables and meat samples from Japan. The concentrations of PBDEs in spinach, potato, and carrot were 134, 47.6, and... 

Immunoaffinity cleanup was first applied in drug residue analysis for the determination of chloramphenicol in swine muscle tissue by LC (113). The lAC column was prepared using monoclonal antibodies originally developed for an enzyme-linked immunosorbent assay (ELISA) method (171) specific for chloramphenicol. Meat samples were extracted with water, and a concentrated phosphate buffer was added to the filtered extracts before immunoaffinity cleanup. A phosphate buffer was used in the washing process, whereas chloramphenicol was eluted from the column with a glycine/sodium chloride solution of pH 2.8. For subsequent LC analysis, this eluate was extracted with ethyl acetate, evaporated, and reconstimted in the mobile phase. The same analytical scheme was later successfully applied for the determination of chloramphenicol in eggs and milk as well (170, 172). 

In Belgium, 0.1% of the slaughtered cattle and swine are screened for antibiotic residues each year. In the analytical strategy applied, meat samples are screened with a modified four-plate test followed by screening with a group-specific ELISA for the identification of the antibiotics and confirmation by specific LC methods. 

Common immunochemical assay formats to select from include the 96-well microtiter plates, dipsticks, coated test tubes, and membrane-based flow through devices. If the end-user is a trained technician working in a well-equipped laboratory and needs to detect and tentatively identify, for example, antimicrobial residues in hundreds of meat samples per day, a multiwell or other high-through-put format should be chosen. If, on the other hand, the end user is a quality control inspector at a milk factory who has limited time to find out whether the penicillin residues in the milk waiting to be unloaded exceed a certain level, the same reagents used in the first instance may require a more user-friendly format such as dipstick or membrane-based flow through device. 

Fig. 29.2.1 Chromatograms of a blank meat sample containing 10 ppb nitrofurantoin (A) and a spiked meat sample (B) containing 5 ppb chloramphenicol, furaltadone, furazolidone, and nitrofurazone internal standard nitrofurantoin. Detection at 280 ( ) and 360 nm (----). (From Ref. 38.)...

Fig. 29.3.1 Chromatograms of a blank meat sample (C) and a meat sample (D) spiked with penicillin G (PG), penicillin V (PV), cloxacillin (CL), and dicloxacil-lin (DCL) at 100 ppb level. (From Ref. 119.).

Fig. 29.10.2 Chromatograms of ivermectin. A, Absolute detection limit (250 pg) B, standard solution (3.6 ng) C, blank meat sample D, spiked meat sample (22.5 ppb). (From Ref. 351.).

S. Cancela-Perez and M. C. Yebra-Biurrun, Flow injection determination of Cd in meat samples using a continuous lixiviation/pre-concentration system coupled to a flame AAS, At. Spectrosc., 26(3), 2005, 110-116. 

M. C. Yebra-Biurrun, A. Moreno-Cid and S. Cancela-Perez, Fast on-line ultrasound-assisted extraction coupled to a flow injection-atomic absorption spectrometric system for zinc determination in meat samples, Talanta, 66(3), 2005, 691-695. 

The actual solution chosen depends on the needs of the experiment. For meat samples, it is recommended that the solution contain a buffer so that samples can be measured at a consistent pH. In some practical situations, however, no buffer should be present since the impact of natural pH differences in the samples is part of the desired result. 

As an alternative, centrifugation can be used. The major issue in this approach is how to collect the expressed moisture. One way, as presented in this unit, is to collect the moisture on filter paper and measure either the weight gain of the filter paper or the weight loss of the sample. The material can be put into a few pieces of filter paper and centrifuged. As a practical matter, the author has found that a piece of nylon mesh placed between the meat sample and the filter paper make it easier to remove the meat sample after centrifugation... 

As the levels of tocopherols and tocotrienols in meat samples are usually lower than in oil and fat samples, a larger sample size is needed in the sample preparation. The meat sample is homogenized to weaken the sample matrix. As in Basic Protocol 2, saponification, heating, and liquid/liquid extraction are used to increase the recovery and remove interference compounds. Satisfactory results can be achieved using a reversed-phase HPLC method. 

Meat sample to be analyzed Ascorbic acid (ACS grade)... 

Weigh 0.5 g (exact to 0.001 g) meat sample and 0.05 g ascorbic acid into a 16 x 125-mm test tube. 

Place the tube in an ice bath and homogenize the meat sample with a mechanical tissue homogenizer for 30 sec. 

Static headspace GC involves heating the sample in an air-tight environment until the volatile lipids in the food reach an equilibrium with those in the surrounding air. The air above the sample (headspace) is then sampled and analyzed. Flame ionization detection (GC-FID) can be used for quantification and mass-selective detection (GC-MS) can be used for compound identification. This protocol also outlines semiquantitative and quantitative approaches for determination of volatile lipid concentration, and is particularly designed for analysis of a meat sample. 

Dynamic headspace GC utilizes a constant purge of the sample with an ultra-high purity gas (i.e., helium). The purged volatiles are then adsorbed onto a trap, followed by heat desorption onto the GC for analysis. Either a flame ionization detector or mass selective detector can be used. The protocol presented here is designed to analyze a meat sample. 

Adapted from Wang el at. (1997) with permission from Food and Nutrition Press. Distillation methods were described by Tarladgis el al. (I960). Rhee (1978), and Moerck and Ball (1974). Extraction methods were described by Sinnhuber and Yu (1977) and Witte et al. (1970). Results are expressed as mg malonaldehyde eq/kg meat sample. 

The measurement of cured meat pigment concentration is based on the A540 of the nitrosyliron(II)protoporphyrin group (also known as nitrosylheme or NO-heme mol. wt. 646) in an extraction solution of 80% (final) acetone in water, taking into consideration the 70% water content of the meat sample. Hornsey (1956) established that only the pink NO-heme was extracted in 80% acetone. Heme groups from fresh meat pigments (Table F3.2.1) are not extractable in 80% acetone. However, upon acidification with hydrochloric acid, NO-heme in 80% acetone was completely oxidized to hemin. Thus, NO-heme concentrations could be expressed in equivalent ppm hemin. 

Meat sample to be tested Aqueous acetone (see recipe)... 

Trim oxidized (faded brown or gray) surfaces of a meat sample and dice a lean portion into 2- to 3-mm cubes. 

---