Document Detail


Methods for analysis of conjugated linoleic acids and trans-18:1 isomers in dairy fats by using a combination of gas chromatography, silver-ion thin-layer chromatography/gas chromatography, and silver-ion liquid chromatography.
MedLine Citation:
PMID:  15164853     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Conjugated linoleic acids (CLA) are octadecadienoic acids (18:2) that have a conjugated double-bond system. Interest in these compounds has expanded since CLA were found to be associated with a number of physiological and pathological responses such as cancer, metastases, atherosclerosis, diabetes, immunity, and body fat/protein composition. The main sources of these conjugated fatty acids are dairy fats. Rumen bacteria convert polyunsaturated fatty acids, especially linoleic and linolenic acids, to CLA and numerous trans- containing mono- and diunsaturated fatty acids. It has been established that an additional route of CLA synthesis in ruminants and monogastric animals, including humans, occurs via delta9 desaturation of the trans-18:1 isomers. To date, a total of 6 positional CLA isomers have been found in dairy fats, each occurring in 4 geometric forms (cis,trans; trans,cis; cis,cis; and trans,trans) for a total of 24. All of these CLA isomers can be resolved only by a combination of gas chromatography (GC), using 100 m highly polar capillary columns, and silver-ion liquid chromatography, using 3 of these 25 cm columns in series. Complete analysis of all the trans-18:1 isomers requires prior isolation of trans monoenes by silver-ion thin-layer chromatography (TLC), followed by GC analysis using the same 100 m capillary columns operated at low temperatures starting from 120 degrees C. These analytical techniques are required to assess the purity of commercial CLA preparations, because their purity will affect the interpretation of any physiological and/or biochemical response obtained. Prior assessment of CLA preparations by TLC is also recommended to determine the presence of any other impurities. The availability of pure CLA isomers will permit the evaluation and analysis of individual CLA isomers for their nutritional and biological activity in model systems, animals, and humans. These techniques are also essential to evaluate dairy fats for their content of specific CLA isomers and to help design experimental diets to increase the level of the desired CLA isomers in dairy fats. These improved techniques are further required to evaluate the CLA profile in monogastric animals fed commercial CLA preparations for CLA enrichment of animal products. This is particularly important because absorption and metabolism will alter the ingested-CLA profile in the animal fed.
Authors:
Cristina Cruz-Hernandez; Zeyuan Deng; Jianqiang Zhou; Arthur R Hill; Martin P Yurawecz; Pierluigi Delmonte; Magdi M Mossoba; Michael E R Dugan; John K G Kramer
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of AOAC International     Volume:  87     ISSN:  1060-3271     ISO Abbreviation:  J AOAC Int     Publication Date:    2004 Mar-Apr
Date Detail:
Created Date:  2004-05-28     Completed Date:  2004-08-24     Revised Date:  2008-03-17    
Medline Journal Info:
Nlm Unique ID:  9215446     Medline TA:  J AOAC Int     Country:  United States    
Other Details:
Languages:  eng     Pagination:  545-62     Citation Subset:  IM    
Affiliation:
Agriculture and Agri-Food Canada, Food Research Program, 93 Stone Rd West, Guelph, Ontario, Canada.
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MeSH Terms
Descriptor/Qualifier:
Animals
Cheese / analysis*
Chromatography, Gas
Chromatography, Liquid
Chromatography, Thin Layer
Linoleic Acids, Conjugated / analysis*
Milk / chemistry*
Trans Fatty Acids / analysis*
Chemical
Reg. No./Substance:
0/Linoleic Acids, Conjugated; 0/Trans Fatty Acids

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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