Sample preparation wheat extracts

Figure 1. A typical sequence of sample preparation manipulations for a procedure of Soxhlet extraction followed by preparative column chromatography for a solid sample - e.g., glycolipids out of wheat flour. Note that equivalently complex processes are encountered with "simple liquid-solid or liquid-liquid extractions followed by a series of back extractions - e.g., pesticides from fish tissue. (Reproduced with permission by Hewlett-Packard, HP Publication (43)5091-2102E, (1991), in preparation.)...

In one word, a possibly low in vitro extraction efficiency does not necessarily go together with low Se bioavailability. The powdered basic samples of Se speciation (Se-enriched yeast, Allium ssp., wheat flour, etc.) - albeit they are food materials or food supplements - are far less complex than real foodstuffs. At the same time, they facilitate sample preparation and the assessment of Se supply from prepared food materials through the analysis of some raw food materials. 

Sample preparation scheme is presented at Figure 24.4. Grain (wheat, oats, barley, 100 g) should be ground in a laboratory mill for 3 min 25-g portion of the milled grain should be transferred into a 250-mL Erlenmayer flask with a glass stopper and extracted with 100 mL of the extraction solution acetonitrile-methanol mixture (84 16 v/v).This mixture is the most frequently used for the trichothecenes extraction from plant material prior to GC and also LC analyses and provide satisfactory recoveries of target compounds [40,44]. 

Recent reviews on sample preparation include that of Christie (70a) on obtaining lipid extracts from tissues and that of Fried (70b) on obtaining and handling biological materials and prefractionating extracts for lipid analyses. Chapter 2 in Hammond (la) also provides detailed descriptions on lipid extraction of photosynthetic tissue, oilseeds, tiger prawns (crustaceans), coffee whitener, wheat flour, spores, and volatile fatty acids from cells grown in culture media. 

We successfully applied an AChE inhibition assay to the detection of dichlorvos in durum wheat samples using a simplified extraction procedure. The total assay time, including the extraction step, was 30 min. Considering that several extractions and assay steps can be run simultaneously, the throughput for one operator is 12 determinations per hour. It is also important to stress that the choline oxidase biosensor used in this work showed an excellent functioning stability after 20 days from preparation, the blank measurement lost only 10% of the signal intensity. The method allowed the accurate analysis of dichlorvos in wheat samples at the MRL, 2 mg/kg, and below that value. The mean recovery was 75%, and neither false nor positive samples were detected. Finally, the portable electrochemical instrumentation combined with the simple extraction procedure was quite well suited for in situ analysis of dichlorvos in durum wheat. 

The first comprehensive investigation of the volatiles of wheat bread was carried out by Mulders et al. (11. 16-18). After a qualitative analysis (16-18) which led to the identification of 90 compounds, the authors attempted to get an insight into the sensory relevance of the major components which were found in the headspace extract of white bread. A mixture of the main compounds identified was prepared in water to match the gas chromatogram obtained from the bread sample (11,). The odor of the synthetic mixture resembled that of the fermented dough but not that of wheat bread. 

Fig. 3. Process flowsheet for cellulase production in wheat bran culture [25]. A Submerged seed culture of T. viride, B oil-free compressed air C air filter D inoculum E exhaust air F sample collection G centrifugal pump H automatic wheat bran culture of T. viride I water spray I ammonium sulfate, alcohol and water J conveyor belt J screw conveyor K hopper L extraction column M storage tank centrifuge 0 precipitation P mixing tank Q ion-exchange column R membrane concentrator S spray dryer T filter press U rotary dryer V mixer W cellulase preparation and salt stabilizer... 

The same preparation was performed with wheat. At least eight portions of each of the corn and wheat samples were extracted, diluted, derivatized, and analyzed by mass spectrometry. Quantitation of the DON in the sample matrices was accomplished by measurement of the peak area of the molecular ion of the DON-HFB in the sample and comparing this to the peak area of the same ion as the standard. 

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