Food/tissue samples

What effect does freezing food have on reaction rates Why is freezing used for preservation of food, tissue samples, and biological samples ... 

Pharmaceutical preparations containing riboflavin have been analyzed by TLC using concentrated ethanolic extracts on silica gel plates developed in butanol-benzene-acetic acid-water (8 7 S 3) or butanol-acetic acid-water (9 4 5) (7). Foods, tissue samples and urine each require particular methods of sample preparation and these, together with a number of solvent systems have been reviewed (8). A darkroom is required for sample preparation and chromatography of flavins to prevent photolytic degradation. The fluorescent property of flavins provides a convenient means of detection and spots have been located under radiation at 254 and 366nm (4). HPTLC followed by fiberoptic fluorimetry has been used to quantitate riboflavin in vitamin mixtures and can detect 48-320 ng (6). Recently, a method has been described using mixed-layer plates of GDX-102 and silica gel G (1 1) precoated with hexadecyl-trimethylammonium bromide developed in 60-70% ethanol (9). 

Table 7.1 Common dietary sources of carotenoids in regular vegetable foods, xg/100 fresh weight. Data are means derived from literature sources. The normal range of values is the mean at least 85%, and depends upon variety, agronomic conditions, tissue sampled and maturity... 

Reliable methods are available for determination of nitrosamines, especially volatile nitrosamines, in a variety of foods, environmental samples, commercial products, blood and animal tissues. Reviews of these methods are available (1, 2) and descriptions of some state-of-the-art procedures are included in papers on nitrosamine occurrence in this volume. This paper is not intended to be a comprehensive review of historical developments or of the many variations of procedures... 

In addition, the difficulty associated with their analysis in complex matrices, such as biota, food and human fluids and tissues samples, should be mentioned. 

When analyzing quinolone residues in semisolid food samples such as muscle, kidney, and liver, a pretreatment step for tissue break-up may be required. This can be accomplished by means of a mincing and/or a homogenizing apparatus. To achieve better recovery of the analytes, drying of the tissue sample with anhydrous sodium sulfate prior to its extraction has been recommended (182-188). 

Before an extraction procedure may commerce, Ure sample must be prepared so that it is in a condition for extraction of the analyte( s). This is particularly relevant for complex matrices such as animal-derived foods, the nature of which determines the kind of pretreatment step required. When analyzing semi-solid food samples, such as muscle, liver, and skin, a pretreatment step may be required. The analyte(s) must be exposed to extracting solvents to ensure maximum extraction. This may be accomplished by mechanical dispersion using a mincer/homog-enizer. The most popular approach for tissue break-up is the homogenization of samples in water or an aqueous buffer. Addition of anhydrous sodium sulfate to the tissue samples, to combine with the water present, has been carried out for facilitating the extraction of dimetridazole (379, 380). 

Liquid samples such as milk do not normally require application of any pretreatment procedure. Semisolid samples such as muscle, liver, and fat tissues usually require more intensive sample pretreatment for tissue break-up. The most popular approach is grinding the sample in a food chopper or homogenization in a Waring blender to expose residues to the extraction solvent. Fatty tissue samples are usually warmed at 35 C until fat melts (491-493), or sometimes blended with immersion blender (494). A fat sample that has been blended with immersion blender melts to produce yellow oil, whereas oil does not separate... 

In general it has to be stated that molecular species analysis of phospholipids is not frequently applied in food analysis most of the studies involving molecular species are instead found in the fields of biochemistry and nutrition. Thus, in the recent reviews by Bell and by Olsson and Salem, special emphasis has been given to the characterization of biological tissue samples (83,84). However, the molecular species composition has been shown to affect the accuracy of the quantification of phospholipid classes and hence is important in food analysis too (47,52). In the vast majority of published methods, isocratic elution has been used. In our opinion, this should be ascribed mainly to the fact that the traditional UV detector remains. Keeping account of the inherent problems associated with UV detection of underivatized phospholipids, it is astonishing that ELSD has hardly been exploited in this subdomain. As far as the stationary phase is concerned, nearly all methods prefer octadecyl-coated stationary phases. 

Enzyme hydrolysis, with papain, diastase, clarase, takadiastase, intestinal phosphatase, or combinations thereof is most commonly used to release pantothenate from food proteins (186). A cold perchloric acid extraction was used to release pantothenic acid from tissue samples (187). Food spoilage prior to analysis may lead to inflated pantothenic acid levels (19). 

Maintenance of bottom fish and marine mollusk communities. Bioaccumulation in the marine food chain will not result in unacceptable tissue COPC concentrations. Measure COPC concentrations in tissue samples and compare to literature-based toxicity reference values. 

Sonication with a waterD methanol solution is the most popular method for the extraction of As species from rice powder [24, 25], algae, chicken meat [26], oyster tissue [27, 28], and baby foods [29]. Sample treatment with triBuoroacetic acid at 100°C was reported to be an efficient method for the extraction of As species present in different food matrices when compared with alternative methods that included sonication and accelerated solvent extraction. Extraction recoveries from 94 to 128 percent were obtained [29]. Low-molecular-weight Se compounds were extracted from nuts with HCIO4 to produce a fraction containing 3 to 15 percent of the total Se in different types of nuts [30]. 

Reinert KH, Hunter JV, Sabatino T. 1983. Dynamic heated headspace analyses of volatile organic compounds present in fish tissue samples. J Agric Food Chem 31 1057-1060. 

A freeze-dryer for food production of tons-per-day capacity (e.g. one for coffee) operates on essentially the same principles as a laboratory freeze-dryer used to prepare grams-per-day amounts of tissue samples for microscopic analysis. 

Several reports have described the use of HPLC in the analyses of ascorbic acid in foods and vitamin products (71, 72,73,74) and in tissue samples (75). Procedures vary in the type of column, mobile-phase, detection systems and means of stabilization of extracts. Reversed-phased,... 

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