Food analysis lipids

SCHWARZ K, BERTELSEN L H, NISSEN L R, GORDNER P T, HEINONEN M I, HOPIA A, HUYNH-BA T, LOMBELET p, MCPHAIL D, SKIBSTED L H and TIJBURG L (2001) Investigation of plant extracts for the protection of processed foods against lipid oxidation. Comparison of antioxidant assays based on radical scavenging, lipid oxidation and analysis of the principal antioxidant components, Eur Food Res Technol, 212, 319-28. 

A number of criteria could be apphed to organize this chapter, depending on the point of view by which foods are considered. In this chapter, application of HPLC to food analysis will be described considering homogeneous classes of food components lipids, carbohydrates and related substances, proteins, peptides, amino acids, biogenic amines, phenolics, vitamins, and some selected contaminants. 

Retinoids The challenge in fat-soluble vitamins analysis is to separate them from the lipid fraction that contains interferents. Alkaline hydrolysis, followed by LLE, is widely applied to remove triglycerides. This technique converts the vitamin A ester to all-trani-retinol. A milder process, which does not hydrolyze vitamin A ester, is alcoholysis carried out with metha-nolic KOH solution under specific conditions that favor alcoholysis rather than saponification. A more accurate explanation of this technique is reported in the book Food Analysis by FIPLC [409]. For some kind of matrices a simple liquid extraction can be sufficient with [421-423] or without [424,425] the purification... 

Accurate determination of lipids in foods is required for nutritional labeling, certification, or for evaluation of standard of identity and uniformity, as well as examination of their effects on functional and nutritional properties of foods. Following lipid extraction and precise quantitative analysis, lipids so obtained may be used for analysis of other lipid characteristics and properties provided that nondestructive and mild extraction procedures are employed that retain the integrity of lipids. Thus, determination of lipid classes, fatty acid composition (unit du), and oxidative state of lipids (Chapter D2), amongst others, may be pursued following the extraction process. 

Pomeranz, Y. and Meloan, C.E. 1994. Lipids. In Food Analysis Theory and Practice, 3rd ed. pp. 678-732. Chapman Hall, New York. 

Caboni, M.F. and Rodriguez-Estrada, M.T. 1997. High-performance liquid chromatography coupled to evaporative light scattering detection in lipid analysis Some application. Seminars in Food Analysis 2 159-169. 

Some basic food analytical methods such as determination of °brix, pH, titratable acidity, total proteins and total lipids are basic to food analysis and grounded in procedures which have had wide-spread acceptance for a long time. Others such as analysis of cell-wall polysaccharides, analysis of aroma volatiles, and compressive measurement of solids and semi-solids, require use of advanced chemical and physical methods and sophisticated instrumentation. In organizing the Handbook of Food Analytical Chemistry we chose to categorize on a disciplinary rather than a commodity basis. Included are chapters on water, proteins, enzymes, lipids, carbohydrates, colors, flavors texture/ rheology and bioactive food components. We have made an effort to select methods that are applicable to all commodities. However, it is impossible to address the unique and special criteria required for analysis of all commodities and all processed forms. There are several professional and trade organizations which focus on their specific commodities, e.g., cereals, wines, lipids, fisheries, and meats. Their methods manuals and professional journals should be consulted, particularly for specialized, commodity-specific analyses. 

Extraction of fat by supercritical carbon dioxide was investigated as an important option for minimizing the expanded use of frequently flammable and carcinogenic solvents in food analysis. Unfortunately, the presence of moisture in foods has an adverse effect on the quantitative extraction of fat by supercritical fluid extraction (SEE). Hence, samples have to be lyophilized first. The total fat content of freeze-dried meat and oilseed samples was found to be comparable to values derived from Soxhlet-extracted samples (26). Besides, only small amounts of residual lipids could be recovered by an additional extraction of the SFE-extracted matrix by the Bligh and Dyer solvent extraction procedure. As far as the minor constituents are concerned, it was found that the extraction recovery ranged from 99% for PC to 88% for PA. Hence, Snyder et al. concluded that SFE can be used as a rapid, automated method to obtain total fat, including total phospholipids, from foods (26). 

The first edition of Food Analysis by HPLC fulfilled a need because no other book was available on all major topics of food compounds for the food analyst or engineer. In this second edition, completely revised chapters on amino acids, peptides, proteins, lipids, carbohydrates, vitamins, organic acids, organic bases, toxins, additives, antibacterials, pesticide residues, brewery products, nitrosamines, and anions and cations contain the most recent information on sample cleanup, derivatization, separation, and detection. New chapters have been added on alcohols, phenolic compounds, pigments, and residues of growth promoters. 

Louter, A.J.H., Bauer-Plank, C.G., Duchateau, S.M.J.E. 2002. Analysis of plant sterol esters as functional food ingredients. Lipid Technol. 14, 87-90. 

Daft (1988) employed a photoionization detector and an electrolytic conductivity detector connected in series to a capillary GC to detect 1,1-dichloroethane at ng /g levels in fumigants and industrial chemical residues of various foods (e.g., diary products, meat, vegetables, and soda). Typically, foods were extracted with isooctane and injected in GC column for analysis. However, foods containing lipid and fat were subjected to further clean-up on micro-florisil column prior to GC analysis. 

A number of very good reviews on food analysis can be found in the literature [7-12]. Table 3 presents a very limited representation of the kind of work involved in a food laboratory. All basic constituents of foodstuffs - proteins, lipids, carbohydrates and vitamins - are amenable to liquid chromatography. Various types of columns and detectors used for those analysis demonstrate the versatility of the technique. Almost any type of food matrix can be extracted in order to identify and quantitate trace amounts of analytes. 

Dr. Kotakowska is a professor at the Faculty of Food Sciences and Fisheries and head of the Food Quality Department in the University of Agriculture in Szczecin. She has published about 120 scientific papers and seven book chapters, mainly in marine food science and food analysis. She holds five patents. Her research deals with food quality and analysis, predominantly with food lipids. 

Liescheski, P.B. 1996. Supercritical fluid extraction coupled directly to infrared spectroscopy for the analysis of lipids in food. Seminars in Food Analysis, 1, 85. 

One of the most interesting fields of application of MAE in food analysis is the extraction of lipids. This step, traditionally performed with conventional Soxhlet extraction, has been performed with the focused microwave-assisted Soxhlet extractor prototype of Figure 2B. Extraction of oil from olives, srm-flower seeds, and soyabeans extraction of the lipid fraction of dairy products (milk and cheese) and extraction of fatty acids from precooked and sausage foods have significant advantages over conventional methods, including dramatically reduced extraction times, lower degradation of thermolabile analytes, and acceleration of other analytical steps such as hydrolysis in milk samples, in addition to completeness of analyte extraction, which is not always achieved with conventional methods. 

See also Activation Anaiysis Neutron Activation. Atomic Emission Spectrometry Principies and Instrumentation. Bleaches and Sterilants. Chiroptical Analysis. Chromatography Principles. Conductimetry and Oscillometry. Coulometry. Fire Assay. Food and Nutritional Analysis Overview. Gas Chromatography Principles. Gravimetry. Indicators Redox. Infrared Spectroscopy Overview. Ion Exchange Oven/iew. Isotope Dilution Analysis. Lipids Fatty Acids. Liquid Chromatography Size-Exclusion. Radiochemical... 

High-performance LC (HPLC) is the technique used most frequently in food analysis for measuring carbohydrates, vitamins, additives (sweeteners, antioxidants, colorants, preservatives, etc.), mycotoxins, amino acids, proteins, tryglicerides in fats and oils, lipids, chiral compounds and pigments, among others (Table 1). Some of these applications will be discussed in this article. 

Application of infrared spectroscopy to food analysis has made possible the highly automated determination of protein content in foodstuffs. Available commercial instruments allow the simultaneous determination of water, lipid, fiber, and protein content in solid or liquid samples with little if any sample preparation and impressive throughput. 

R. Rombaut and K. Dewettinck, Dairy Polar Lipids , in Handbook of Dairy Foods Analysis, eds. L. M. L. NoUet and F. Toldra, CRC Boca Raton, Fla., 2010, p. 189. 

TLC analysis of agricultural products, foods, beverages, and plant constituents is described by Sherma in a review paper. In laboratories throughout the world, TLC is widely used for food analysis and qualitative control. Numerous applications of TLC have been reported in the area of food composition, involving determinations of compounds such as lipids, sugars, amines, vitamins, and organic acids such as amino acids and fatty acids. 

Published applications of TLC or HPTLC are dedicated to different topics in food analysis. With approximately 20% of all published method in the last 50 years, the analysis of dyes and pigments are the largest part of application followed by analysis of fatty acids, lipids, phospholipids and mycotoxins [162, 163], Although neither paper nor thin-layer chromatography plays a major role for routine analysis of berry anthoeyanins the value of these methods for research oriented work should never be imderestimated. 

One of the simplest and most efficient approaches for aroma isolation is direct solvent extraction. The major limitation of this method is that it is most useful on foods that do not contain any lipids. If the food contains lipids, the lipids will also be extracted along with the aroma constituents, and they must be separated from each other prior to further analysis. Aroma constituents can be separated from fat-containing solvent extracts via techniques such as molecular distillation, steam distillation, and dynamic headspace. 

As a first requirement, the sample analyzed should represent as closely as possible the lipid composition of the whole matrix from which it was taken furthermore, sample preparation should be carried out in such an environment as to minimize any changes in lipid properties prior to analysis. In food analysis, proper sampling of the lipid fraction requires knowledge of the physical structure and location of the major lipids in the sample, and the choice of the most adequate procedure depends on the t)q)e of food being analyzed, the nature of the lipid fraction, as well as the analytical procedure applied for the extraction. Foods consisting almost entirely of lipids, such as vegetable oils, often require little, if any, sample preparation prior to analysis. Qn the other hand, for more complex foods, such as meat or milk, extraction and purification of the lipid fraction is necessary prior to analysis. Official methods have been developed, which recommend the sample preparation and extraction procedures to be followed for a specific t)q5e of food. Solvent extraction methods are usually used, to separate lipids from water-soluble food components, prior to chromatographic analysis these are described in the sections that follow. A number of steps are usually required, prior to the solvent xtraction of lipids from a matrix ... 

Mondello L, Tranchida PQ, Stanek V, Jandera P, Dugo G, Dugo P. Silver-ion reversed-phase comprehensive two-dimensional liquid chromatography combined with mass spectrometric detection in lipidic food analysis. J Chromatogr A. 2005 1086 91-8. 

Before analysis, lipids from solid foods are extracted with either a single, nonpolar solvent or a mixture of several organic solvents, such as hexane/2-propanol or chloroform/methanol, followed (if necessary) by sample cleanup procedures. In case of liquid foods (such as oils), the extraction step is often unnecessary, so that the samples can be injected directly into the LC system. 

Monodimensional LC separations are often insufficient to resolve all the lipids of interest in food analysis however, a full analysis of these samples may be attained by combining two independent separation steps with different selectivity, enhancing the resolving power of LC. Following this idea, different comprehensive two-dimensional LC approaches combined with MS have been described for the complete separation of triacylglycerols [16,17]. 

In practice, the non-volatile lipophihc compounds that accompany true lipids in both natural and manufactured products are also classified as lipids. They are termed compounds accompanying lipids (formerly called Kpoids) in food chemistry, and unsaponifiable lipophilic substances in food analysis. Their chemical structure is different and often these compounds do not even contain bound fatty acids. This group includes a large number of lipophilic compounds, for example some terpenoids, especially... 

Oxidation decreases the quality of foods by producing low-molecular-weight off-flavor compounds, as well as by destroying essential nutrients, and it produces toxic compounds and dimers or polymers of lipids and proteins, which in turn contribute to diseases and accelerate the aging process. Its measurement is a leading objective of food analysis. Evaluating lipid oxidation status is a challenging task due to a number of facts. 

Care should be taken to minimize changes in the fatty acid composition of the food before analysis. Lipids are susceptible to enzymic lipolysis and UFA are susceptible to enzymic and nonenzymic oxidation. Therefore, food samples should be kept at low temperamres ( 20°C or lower), preferably under an atmosphere of nitrogen or in an oxygen-impermeable wrap, before extraction. 

To obtain a total fatty acid profile, to include co3 fatty acids, and other potentially beneficial fatty acids such as GLA, the approach is normally straightforward and involves extraction of lipids in the presence of an appropriate, derivatization of fatty acids to methyl esters, and analysis by GC. Appropriate extraction methods, depending on the type of food and lipids presents, must be employed to extract the total lipids efficiently. An alternative is to hydrolyze the sample directly to release all the fatty acids in the free form followed by derivatisation. An appropriate methylation step is required. Alkaline methods are milder, but will only derivatize EFA. Acidic methods are used to derivatize samples containing FFA with or without EFA. Separation of FAME can normally be achieved on Carbowax type columns of medium length, but samples such as milk fats or PHVO, containing complex mixtures of trans fatty acids, require longer polar columns and may require the use of additional techniques. Milk fats also contain SCFA and specific precautions or adaptations of protocols are necessary for their analysis. 

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