Analysis methods food extraction

Several standard methods for the quantitative analysis of food samples are based on measuring the sample s mass following a selective solvent extraction. For example, the crude fat content in chocolate can be determined by extracting with ether for 16 h in a Soxhlet extractor. After the extraction is complete, the ether is allowed to evaporate, and the residue is weighed after drying at 100 °C. This analysis has also been accomplished indirectly by weighing a sample before and after extracting with supercritical GO2. 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

Analytical Techniques. Sorbic acid and potassium sorbate are assayed titrimetricaHy (51). The quantitative analysis of sorbic acid in food or beverages, which may require solvent extraction or steam distillation (52,53), employs various techniques. The two classical methods are both spectrophotometric (54—56). In the ultraviolet method, the prepared sample is acidified and the sorbic acid is measured at 250 260 nm. In the colorimetric method, the sorbic acid in the prepared sample is oxidized and then reacts with thiobarbituric acid the complex is measured at - 530 nm. Chromatographic techniques are also used for the analysis of sorbic acid. High pressure Hquid chromatography with ultraviolet detection is used to separate and quantify sorbic acid from other ultraviolet-absorbing species (57—59). Sorbic acid in food extracts is deterrnined by gas chromatography with flame ionization detection (60—62). 

Supercritical fluid extraction (SFE) and Solid Phase Extraction (SPE) are excellent alternatives to traditional extraction methods, with both being used independently for clean-up and/or analyte concentration prior to chromatographic analysis. While SFE has been demonstrated to be an excellent method for extracting organic compounds from solid matrices such as soil and food (36, 37), SPE has been mainly used for diluted liquid samples such as water, biological fluids and samples obtained after-liquid-liquid extraction on solid matrices (38, 39). The coupling of these two techniques (SPE-SFE) turns out to be an interesting method for the quantitative transfer... 

In the preceding section, we presented principles of spectroscopy over the entire electromagnetic spectrum. The most important spectroscopic methods are those in the visible spectral region where food colorants can be perceived by the human eye. Human perception and the physical analysis of food colorants operate differently. The human perception with which we shall deal in Section 1.5 is difficult to normalize. However, the intention to standardize human color perception based on the abilities of most individuals led to a variety of protocols that regulate in detail how, with physical methods, human color perception can be simulated. In any case, a sophisticated instrumental set up is required. We present certain details related to optical spectroscopy here. For practical purposes, one must discriminate between measurements in the absorbance mode and those in the reflection mode. The latter mode is more important for direct measurement of colorants in food samples. To characterize pure or extracted food colorants the absorption mode should be used. 

A sequential analysis protocol includes three steps (1) extraction in water or other appropriate solvent for the colorant, (2) purification or concentration of the colorant, and (3) separation coupled with detection of the target molecule. Different methods of extracting synthetic colorants from foods have been developed using organic solvents followed by SPE protocols using as adsorption support RP-C18, amino materials, or Amberlite XAD-2. Eor qualitative evaluations, the easiest option for separating colorant molecules from unwanted ingredients found in an extract is SPE on polyamide or wool. 

Carmen Socaciu was bom in Cluj-Napoca, Romania and earned a BSc in chemistry in 1976, an MSc in 1977, and a PhD in 1986 from the University Babes-Bolyai in Cluj-Napoca, an important academic centre located in the Transylvania region. Dr. Socaciu worked as a researcher in medical and cellular biochemistry for more than 10 years, and became a lecturer in 1990 and full professor in 1998 in the Department of Chemistry and Biochemistry of the University of Agricultural Sciences and Veterinary Medicine (USAMV) in Cluj-Napoca. She extended her academic background in pure chemistry (synthesis and instrumental analysis) to the life sciences (agrifood chemistry and cellular biochemistry). Her fields of competence are directed especially toward natural bioactive phytochemicals (carotenoids, phenolics, flavonoids), looking to advanced methods of extraction and analysis and to their in vitro actions on cellular metabolism, their effects as functional food ingredients, and their impacts on health. 

Various important LC methods for amino acid, peptide and protein analysis were reviewed and evaluated126,127. A review of HPLC methods for the analysis of selected biogenic amines in foods appeared, including methods for extraction and for elimination of interfering compounds128. 

Sample collection and preparation for the analysis of 1,2-dibromoethane in foods includes the purge-and-trap method, headspace gas analysis, liquid-liquid extraction, and steam distillation (Alleman et al. 1986 Anderson et al. 1985 Bielorai and Alumot 1965, 1966 Cairns et al. 1984 Clower et al. 1985 Pranoto-Soetardhi et al. 1986 Scudamore 1985). GC equipped with either ECD or HECD is the technique used for measuring 1,2-dibromoethane in foodstuffs at ppt levels (Clower et al. 1985 Entz and Hollifield 1982 Heikes and Hopper 1986 Page et al. 1987 Van Rillaer and Beernaert 1985). 

Recent trends in pesticide analysis in food aims for reduced sample pretreatments or simplified methodologies (as QuEChERS approaches), the use of online purification processes, the use of new adsorbents (such as molecular imprinted polymers (MIPs) and nanomaterials) for the extraction and clean-up processes, and focused on the development of large multiresidue methods, most of them based on LC-MS/ MS. In spite of the relevant role of LC-MS/MS, GC-MS-based methods still play an important role in pesticide analysis in food. Despite the development achieved in the immunochemical approaches, the need for multi-residue methods has supported the development and use of instrumental techniques. 

The main problem in the vitamin E analysis is that it is easily oxidized, thereby an antioxidant, such as butyl hydroxy toluene (BHT) or ascorbic acid, is added to prevent degradation during the extraction step. The traditional method for extraction of tocopherols and tocotrienols in foods is solvent extraction (like soxhlet) and saponification with KOH [457,458]. Some authors have recently proved that saponification is not necessary [459-462], nevertheless, it has been widely applied until the present day. 

The methods of extraction and analysis can markedly affect the determination of flavonoids in foods.Rigorous application of the selection criteria (Table 4.6) may minimize this confounding effect. Overall, sample preparation and extraction techniques along the lines described by Merken and Beecher were considered acceptable. These included freezedrying, extraction either with aqueous methanol containing an antioxidant such as BHT or... 

In soil analysis, the sample pretreatment varies depending on whether a total elemental analysis or an exchangeable cation analysis is required. In the former, a silicate analysis method (see below) is appropriate. In the latter, the soil is shaken with an extractant solution, e.g. 1 M ammonium acetate, ammonium chloride or disodium EDTA. After filtration, the extractant solution is analysed. Fertilizers and crops can be treated as chemical and food samples, respectively. 

However, a single GC-O run only is usually insufficient to distinguish between the potent odorants that most likely contribute strongly to an aroma and those odorants that are only components of the background aroma. Therefore, to improve the results, two methods, combined hedonic aroma response measurements (CHARM) analysis [4] and aroma extract dilution analysis (AEDA) [5, 6] have been developed. As discussed in Sect. 16.4 in both methods serial dilutions of food extract are analysed by GC-O. 

The determination of diazinon in foods is important because this chemical is used as a pesticide on plant crops and, at least in some cases, in pesticide dips for the control of parasitic infestations in animals (Brown et al. 1987 Miyahara et al. 1992). Because animals are exposed to this compound, both via pesticide dips and by ingestion of crops to which diazinon has been applied, some methods have been reported for animal products. The majority of methods, however, deal with the determination of residues in plant products. Most of the analytical methods found that describe the extraction from, and determination of, diazinon residues in various crops (plant materials) were developed as part of multiresidue methods. They are based on homogenization of the sample with an organic solvent (polar or non-polar) the isolation of the residues from this initial extract and, usually, some additional cleanup prior to the analysis of the extract by GC. The most common non-MS modes of detection exploit the... 

In contrast to liquid-liquid partitioning cleanup, which is particularly suitable for individual drugs or groups of drugs with similar chemical properties, solid-phase extraction is more appropriate for multiresidue analysis. On that account, solid-phase extraction in combination with liquid-liquid partitioning has become the method of choice in many laboratories for the purification of residues of sedatives and -blockers that may occur in biological matrices. Purification is usually accomplished on reversed-phase solid-phase extraction columns. Optimum retention of seven sedatives and carazolol on a reversed-phase solid-phase extraction column was reported when 10% sodium chloride solution was added to the acetonitrile hssue extract prior to its solid-phase extrachon cleanup (523, 524). A silica-based diol solid-phase extraction column was further suggested for efficient isolation of sedative and -blocker residues from food extracts (526). 

A methanol/hexane mixture is used in the best food (BF) method to extract the toxin from the substrate 100 g of sample is added to 500 ml of a methanol-water (55 45) mixture and 200 ml of hexane. After 1 min of vigorous shaking, the resulting solution is centrifuged for 5 min at 2000 rpm. Twenty-five ml of the methanol phase is used for the TLC assay. The method has been adopted by the AOAC Official Methods of Analysis in peanut and peanut products (17). 

Sample preparation for saccharin analysis by HPLC can be performed as indicated in Section I.C. Methods for extraction have also been described for desserts and sweets containing food thickeners (38) soy sauce, orange juice, and yogurt (60) chewing gum (17,39), and different food samples (42). Aminobenzoic acid, theophyllin, sodium fumarate, and adenine sulfate have been used as internal standards (17,31,39,44). 

Knize et al. (200) reported some preliminary results for a new SPE technique for the analysis of aromatic mutagen amines in foods for which no method was still developed, together with results obtained by the SPE-PRS method developed by Gross. The underdevelopment method should also be able to extract trimethyilimidazopyridine (TMIP) and DMIP (2-amino- 1,6-di-methylazo[4,5-fc]pyridine) by using an acid/ion-exchange scheme (SCX method). The extracts were analyzed by HPLC with UV or fluorescence detection. The content of resultant HAAs depended on the kind of meat and on the cooking conditions. 

In Pearson s Analysis of Foods two methods are quoted for the analysis of caffeine. The fust is a simple solvent extraction followed by quantification by ultraviolet absorbance at 273 nm (Egan et al., 1990d) and the other is a GLC method. 

Gas chromatography/olfactometry (GCO) methods have been developed as screening procedures to detect potent odorants in food extracts. The FD-factors or CHARM values determined in food extracts are not consequently an exact measure for the contribution of a single odorant to the overall food flavor for the following reasons. During GCO the complete amount of every odorant present in the extract is volatilized. However, the amount of an odorant present in the headspace above the food depends on its volatility from the food matrix. Furthermore, by AEDA or CHARM analysis the odorants are ranked according to their odor thresholds in air, whereas in a food the relative contribution of an odorant is strongly affected by its odor threshold in the food matrix. The importance of odor thresholds in aroma research has been recently emphazised by Teranishi et al. [58],... 

Dr. Hwang (Frito-Lay, Inc.). Snack food samples, Soxhlet extraction method, Soxhlet extractions, and analysis of Soxhlet extracts. 

Lues, J. F. R., Botha, W. C., and Smith, E. J. (1998). Ion-exchange HPLC analysis of a broad spectrum of organic acids from matured Cheddar cheese and assessment of extraction methods. Food Res. Int. 31, 441-447. 

Extraction can be used as an efficient and selective sample preparation method before analysis by chromatographic, spectroscopic, electroanalytical, or electrophoretic methods (see for example [5-10]). International norms from the International Standards Organization, US Food and Drug Administration, and US Environmental Protection Agency recommend application of extraction methods in analysis of food products and environmental and pharmaceutical samples. Novel ideas and new views concerning extraction have led to many controversies about terminology and to reallocation and softening of the boundaries between extraction and other analytical sample treatment techniques. 

The most obvious shortcoming of these methods is that very few have been applied to residue analyses in crops or foods. A major problem in the application of these methods to residue analysis is sample extraction and cleanup. It is well known (8, 49, 51) that constituents of certain... 

---