Fruits sample preparation

The two examples of sample preparation of solids containing low concentrations of the substances of interest will be the analysis of aflatoxins in corn meal (7) and the determination of the fungicide thiabendazole in citrus fruits. It should be pointed out that the applications chosen in this section attempt to reflect a range of analyses that the analyst is likely to meet in both research and industrial laboratories. 

The sample preparation was very simple the sample was centrifuged to remove plant cell residues and 10 pi of the clear juice was placed on the column. This type of separation is common with fruits, vegetables and juices and samples can be obtained by preliminary homogenizing the total tissues and then centrifuging. If it is suspected that the residue still contains significant quantities of the substances of interest, then it can be washed with water or if necessary with solvents and the washings combined with the separated supernatant liquor. The results obtained are shown in figure 15. 

SFE of fruits and vegetables and meat products has been reported, but the sample preparation techniques necessary to obtain reproducible results are extremely time consuming. Solid absorbents such as Hydromatrix, Extrelut " anhydrous magnesium sulfate or absorbent polymers are required to control the level of water in the sample for the extraction of the nonpolar pesticides. Without the addition of Hydromatrix, nonpolar pesticides cannot penetrate the water barrier between the sample particles and the supercritical CO2. The sample is normally frozen and the addition of dry-ice may be required to reduce losses due to degradation and/or evaporation. Thorough reviews of the advantages and limitations of SFE in pesticide residues... 

Because of their polymeric forms, alkylenebis(dithiocarbamates) are insoluble in water and most organic solvents. Additionally, they form strong complexes with different metal ions No extraction and chromatographic procedure has been reported for the parent compound of this chemical class. These compounds decompose readily under acidic conditions, for example by contact with the fruit or plant juice generated during sample preparation. 

Alkylenebis(dithiocarbamates) are not stable and decompose on contact with acidic fruit and vegetable juice generated during the sample preparation. The sample preparation is a critical step in their determination. The homogenization should be made with frozen samples as rapidly as possible followed immediately by the analysis. 

No specific sample preparation or processing is needed for this method. In general, fruits and vegetables were macerated with dry-ice and placed into freezer storage prior to extraction. 

Samples, with no selenium on or in the fruit, were prepared for analysis and known quantities of selenium were added. These were analyzed by the above noted methods. The quantity of selenium recovered and the percentage recovery are presented in Table I. 

The sample preparations and quantitative estimations of residues were completed as soon after the fruits were sampled as proved practicable 14). 

Pome Fruit Types. As with citrus fruit types, the method of sample preparation was modified for the parathion studies. In the earlier studies the DDT-treated apples and pears were scrubbed in a warm 10% solution of trisodium phosphate, and all the peel was removed from the water-rinsed fruit with a household-type potato peeler. The pooled samples of peel and pulp were then processed independently to recover the contained toxicant for subsequent estimation. 

Plants including fruits and vegetables are a vast reservoir of different phytochemicals. As stated previously, flavonoids are a diverse group of polyphenolic compounds, some of which are relatively stable, whereas others such as anthocyanins are labile under ambient conditions. Sample preparation is of paramount importance in studying flavonoids because a good method prevents compounds of interest from being degraded... 

This chapter reviews recent findings about the health benefits of phytochemicals present in fruits, vegetables, nuts, seeds, and herbs, including phenolics, carotenoids, sterols, and alkaloids. These phytochemicals are extracted using emerging technologies such as supercritical carbon dioxide (SC-CO2) extraction, PEF, MWE, HPP, UE, and OH. The impact of important parameters related to sample preparation (particle size and moisture content) and extraction process (temperature, pressure, solvent flow rate, extraction time, and the use of a cosolvent) on the efficiency of extraction and on the characteristics of the extracted products is evaluated based on an extensive review of recent literature. The future of extraction of phytochemicals is certainly bright with the... 

The study of obsidian by NAA has proved to be particularly fruitful because of the relatively limited number of sources and the extent to which it was traded (Beardsley et al. 1996, Cook 1995, Darling and Hayashida 1995, Kuzmin et al. 2002, Leach 1996). Studies have also extended to include other volcanic materials such as pumice (Bichler et al. 1997, Peltz et al. 1999). NAA has also been used for the analysis of flint as OES is insensitive and not reproducible due to the effect of the high silica content, and AAS requires significant sample preparation (Aspinall and Feather 1972). The wide range of appropriate materials extends to organic materials such as human bone (Farnum et al. 1995), and its exceptional sensitivity to trace elements has led to its wide use in geochemistry (for example in determining trace [ppb] contaminants in waters) and more recently in forensic chemistry. 

Fort he determination of preservatives and sweeteners in soft drinks or fruit juices LC analysis with UV detection is widely used. The sample pretreatment, prior to LC analysis, often consists only of degassing, filtration and dilution of the Uqirid [2]. Sometimes a Uqirid-Uqitid extraction, suitable not only for soft drinks but also for more complex matrices, is appUed [3]. Chemometric methods appUed to overlapped spectra offer the advantage of minimizing or eliminating sample preparation by allowing to simirltaneoirsly determining one or more analytes in relatively complex matrices. 

GC/ECD is the method used to detect heptachlor and heptachlor epoxide in foods (butterfat, fruits, vegetables, milk, and animal feed) (Di Muccio et al. 1988 Hopper and Griffitt 1987 Korfmacher et al. 1987 Ober et al. 1987 Santa Maria et al. 1986). Preparation methods vary for the different types of foods. The sample preparation method for butterfat involves GPC. GPC is a rapid clean-up... 

Antolovich, M., Prenzler, P., Robards, K., and Ryan, D., Sample preparation in the determination of phenolic compounds in fruit. Analyst, 125, 989, 2000. 

For most applications, this is all the sample preparation that is necessary. Appropriate dilution is deceptive as it will vary from one commodity to another dependent on the number of anthocyanins in the matrix. The visual appearance and absorptivity of a sample is often not a sufficient indicator for HPLC peak height/area, as samples that have many anthocyanin peaks will need to be more concentrated than a sample that has the same total anthocyanin content but only a single major peak. Most anthocyanin-containing fruit juices will give a suitable response between single strength juice and a dilution of 1 5. 

Vegetables and fruits are prepared as appropriate for typical in home preparation methods (e.g., by removal of outside leaves, peeling, coring). Larger items such as cabbages, may be quartered, and then one quarter from each of the individual samples cut and mixed. Smaller items are cut and mixed. Further subsamples of the individual samples (e.g., 100 g depending on the number of individual samples collected initially) of the cut mixed materials are taken and these subsamples bulked and thoroughly mixed. 

Once the constant-temperature water bath has reached 30°C, measuring the viscosities of pure solutions like standard oils requires 15 min per sample. The most time-consuming part of the measurement is cleaning and drying the viscometer between samples. Preparing fruit pastes and juices for viscosity determination will take 1 hr for two to four different samples and then an additional -15 min/sample for the viscosity measurements. 

The ultrasound-assisted extraction of freeze-dried plant-based materials normally takes 2 hr. If the extract is evaporated to dryness, a total of 3 hr is necessary. As an additional sample preparation step, 2 to 4 days should be allotted for freeze-drying fresh plant materials, depending on the quantity of the material. Homogenizer-assisted extraction of fresh fruit takes <4 hr. 

Samples to be analyzed can be of very complex nature (dairy products, fruit juice, etc.). Therefore, and provided that the preliminary steps—namely, sampling and moisture determination— have been properly attended to, the first important stage is sample preparation, which comprises extraction and cleanup. Once a sufficiently clean extract has been obtained, the carbohydrates therein may be separated prior to their detection and quantitation. 

Many different sample preparation procedures have been employed, ranging from simple filtration of juice products to solvent extraction, and extraction by SPE using C, 8, Sephadex LH-20 (49,50,52), and Amberlite XAD-2 (51,54,57). The Amberlite XAD-2 cleaning step has been used for many phenolic extracts, especially for fruit purees, to remove the sugars and other polar compounds. However, due to the low recovery rate with Amberlite XAD-2 for certain phenol glycosides, a modified sample preparation technique is needed, especially for quantification of ar-butin in pear juice and blends (54). Figure 6 describes the fractionation procedure for phenolics using a Sephadex LH-20 column (58). 

Fig. 7 Sample preparation procedure for phenolics in fruit juices. (From Refs. 22, 49, and 50.)...

As with all methods, this approach has some limitations it uses acetonitrile, which is toxic, and the separation of glucose from fructose can sometimes be problematic after extended use of the column. However, sample preparation is easy since it requires only dilution to the required level (often 1 10) and filtration prior to analysis to remove particulate materials, which protects and extends the useful life of the column. The degradation of the resolution between glucose and fructose is caused by the partial inactivation of the column by materials in the matrix, but this resolution can be recovered by reducing the acetonitrile concentration in the solvent. The same column can also be used to assay the level of ascorbic acid (vitamin C) in a soft drink or fruit juice, although different detection and solvent systems are used. 

The spontaneous development of the macroscopic topographic features in spin-coated samples, or in samples prepared by a gradient combinatorial approach [52,53], has been fruitfully used for the analysis of thickness-dependent morphological behavior by constructing phase diagrams of surface structures [43,49, 53, 54],... 

Dienones 12A-12D were also detected as trace components in quince fruit volatiles after SDE sample preparation. However, as shown in Figure 3, except for the low amount of hydrocarbon 5, the distribution of thermal degradation products from 8 did not correspond to the composition of the major norisoprenoids 5-7 obtained after SDE of quince fruit juice. Consequently, diol 8 had to be excluded as their precursor. 

Tin levels in fruits, vegetables, and juices were found to be higher when unlaquered cans were used [273]. Ethanol affects ICP-MS sensitivity for many elements. Sample preparation can affect the extent of the change in sensitivity. Internal standardization can be used to improve Pb concentration measurement accuracy in wine [274]. Isotope dilution analysis can be used for accurate concentration measurements in wine [275]. 

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