Fatty acids, volatile, extraction

Where the fat in a meat or meat product sample is to be characterized in terms of the fatty acid profile, extraction of the fat with chloroform/methanol is required. This solvent mixture, while it may not give complete fat extraction, is used to ensure no chemical change to the lipids and the extraction of phospholipids. Fatty acid analysis of the extracted fat is undertaken by formation of volatile methyl esters of the fatty acids (ISO 5509 2000) and determination by gas chromatography (ISO 5508 1990). 

Ortiz Moreno, A., Dorantes, L., Galindez, J., and Guzman, R. I. 2003. Effect of different extraction methods on fatty acids, volatile compounds, and physical and chemical properties of avocado (Persea americana mill.) oil. J. Agric. Food Chem. 51 2216-2221. 

Eatty acids from commercial fats and oils, such as peanut oil, are extracted with methanolic NaOH and made volatile by derivatizing with a solution of methanol/BE3. Separations are carried out using a capillary 5% phenylmethyl silicone column with MS detection. By searching the associated spectral library students are able to identify the fatty acids present in their sample. Quantitative analysis is by external standards. 

The study of biochemical natural products has also been aided through the application of two-dimensional GC. In many studies, it has been observed that volatile organic compounds from plants (for example, in fruits) show species-specific distributions in chiral abundances. Observations have shown that related species produce similar compounds, but at differing ratios, and the study of such distributions yields information on speciation and plant genetics. In particular, the determination of hydroxyl fatty acid adducts produced from bacterial processes has been a successful application. In the reported applications, enantiomeric determination of polyhydroxyl alkanoic acids extracted from intracellular regions has been enabled (45). 

Cyanomethane, commonly known as acetonitrile, CH3CN, is a toxic volatile liquid that is used as a solvent to purify steriods and to extract fatty acids from fish oils. Acetonitrile can be synthesized from methyl isonitrile by the isomerization reaction CH,NC(g) - CH3CN(g). 

In-fibre derivatisation/SPME has been reported for the analysis of polar analytes. Derivatisation allows target analytes to be converted to less polar and more volatile species prior to GC analysis. In-fibre derivatisation with diazomethane was applied to long-chain (Ci6, Cig) fatty acids in aqueous solutions. Initially, the polyacrylate fibre was placed in an aqueous sample containing the fatty acids. After sufficient extraction time,... 

GC-C-IRMS instrumentation enables the compound-specific isotope analysis of individual organic compounds, for example, n-alkanes, fatty acids, sterols and amino acids, extracted and purified from bulk organic materials. The principle caveat of compound-specific work is the requirement for chemical modification, or derivatisation, of compounds containing polar functional groups primarily to enhance their volatility prior to introduction to the GC-C-IRMS instrument. Figure 14.7 summarises the most commonly employed procedures for derivatisation of polar, nonvolatile compounds for compound-specific stable isotope analysis using GC-C-IRMS. 

The transesterification of sucrose has been performed with a fatty acid ester of a volatile alcohol in the presence of an alkaline catalyst in a dipolar, aprotic solvent.142 The reaction of sucrose (293 mmoles) with methyl dodecanoate (293 mmoles) in A/,N-dimethylformamide in the presence of sodium methoxide in a pressure bomb for 8 h at 130° gave, after solvent extraction and crystallization, sucrose mono(dodecanoate) (m.p. 72-80° [a]D+52°) in 50% yield.142 Commercialization of these sucrose esters has so far been limited, in part because of the use of expensive solvents, and, in part, because solvent remaining in the product makes it unsuitable for use as a food emulsifier. In view of this situation, methods have been developed in which the use of toxic and expensive solvents has been avoided. 

Methods have been described for the determination of total fatty acids in raw sewage sludge. These methods [30-32] require a concentration steps such as simple distillation, steam distillation, evaporation, or extraction [33-35] which resulted in great losses of the volatile matter [36, 37],... 

Procedures for the isolation and characterization of trace gases and odorants in the dust from pig houses are given by SCHAEFER et al. (29), HAMMOND et al.(30) and TRAVIS and ELLIOTT (31). Alcoholic solvents were found to be effective for the extraction of volatile fatty acids and phenols from the dust of hen (32) and pig houses (33), (34). Today, gas chromatography is usually used for the separation and identification of the trace gases. Table IV gives a literature review of compounds identified in the dust of pig houses. There are only very few reports on investigations on the dust from hen houses (32). 

This may find application in several areas. The first example is the homogenization of animal tissues in a high-speed blender, which enables a homogeneous sample to be obtained for subsequent analysis. This is used, for example, in the analysis of arsenic or copper in liver (Ross, 1990). A second area is the extraction of volatile fatty acids from silage. Typically, 10 g fresh silage is homogenized for between 1 and 10 min with 100 ml water in a blender before filtration (Lessard et ai, 1961). The last area is the dry... 

An extensive list of volatile compounds in apples and other fruits was included in a review by Nursten (222). White (223) reported that the principal components of the aroma of apples were alcohols (92% ) methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-l-propa-nol, 2-methyl-l-butanol, and 1-hexanol. The other constituents included 6% carbonyl compounds and 2% esters. Later, MacGregor et al. (224) tentatively identified 30 volatile components of McIntosh apple juice including four aldehydes, one ketone, 11 alcohols, 10 esters, and four fatty acids. The major organic volatiles in several different extractants of Delicious apple essence were identified and quantitatively estimated by Schultz et al. (225). They reported from sensory tests that low molecular weight alcohols contributed little to apple aroma. Flath et al. (226) identified... 

Jennings et al (228) fractionated an extract from Bartlett pears into 32 volatile components of which five were found to contribute significantly to the characteristic pear aroma. Later studies indicated that esters of trans-2 cis-4 decadienoic acid and hexyl acetate were significant components of the Bartlett pear aroma (229, 230). More recently, numerous volatiles of Bartlett pears were separated and identified including esters of methyl, ethyl, propyl, butyl, and hexyl alcohols, and Cio to Ci8 fatty acids (231, 232). 

Reports a standardized method for direct determination of TBA value in oils, fats, and lipid extracts. Unlike distillation and extraction methods, this technique determines total reactive substances without previous isolation of the volatile fraction. Furthermore, the solvent of choice is organic (l-butanol) rather than aqueous. This protocol is reported as the official (AOCS) method to determine TBA value (direct method) of animal and vegetable fats and oils, fatty acids and their esters, partial glycol esters, and similar materials. 

Despite the relatively low percentage content of extractives (Table II), they very often influence wood properties and thus play a role in utilization. Advantages accrue from the presence of colored and volatile extractives which provide esthetic values. Some of the phenolic compounds provide resistance to insect and fungal attack. Other extractives provide useful products. From tall oil, products such as turpentine, rosin and fatty acids are produced. In addition, tannins, camphor, gum arabic, natural rubber and flavonoids are some of the many products from extractives. 

Lipid decomposition volatiles. Reactions of sugar and amino acids give rise to odor profiles that are, at best, common to all cooked or roasted meats. The water soluble materials extracted from chicken, pork, or beef give reasonably similar meat flavor. To develop a species specific aroma one needs to study the lipid fraction and the volatiles produced from those lipids. The work of Hornstein and Crowe (10) reported that the free fatty acids and carbonyls generated by heating will establish the specific species flavor profiles. 

Two oat varieties were studied with respect to their oil content. The composition of these SCCO2 extracted oils, with regard to fatty acids, free fatty acids, phosphorus and thermal stability has previously been reported (Fors and Eriksson, submitted for publication 1988). Volatile compounds were isolated from the oat oils by molecular vacuum distillation. The fractions obtained were transferred to aqueous alkali and extracted by CH2CI2. The adjustment in pH was made to remove fatty acids which could otherwise interfere with the later work. Moreover, it is well established that many heterocycles are important flavor compounds in heated food items. These compounds are normally isolated in the basic fraction. The isolates were analysed by chemical and sensory methods. 

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