Stability of cyclopropane and conjugated linoleic acids during fatty acid quantification in lactic acid bacteria

Abstract

Seven methods commonly used for fatty acid analysis of microorganisms and foods were compared to establish the best for the analysis of lyophilized lactic acid bacteria. One of these methods involves fat extraction followed by methylation of fatty acids, while the other methods use a direct methylation of the samples, under different operating conditions (e.g., reaction temperature and time, reagents, and pH). Fatty acid methyl esters were identified by gas chromatography-mass spectrometry and quantified by on-column capillary gas chromatography. Two reliable methods for the analysis of fatty acids in bacteria were selected and further improved. They guarantee high recovery of classes of fragile fatty acids, such as cyclopropane and conjugated acids, and a high degree of methylation for all types of fatty acid esters. These two direct methylation methods have already been successfully applied to the analysis of fatty acids in foods. They represent a rapid and highly reliable alternative to classical time- and solvent-consuming methods and they give the fatty acid profile and the amount of each fatty acid. Using these methods, conjugated linoleic acids were identified and quantified in lactic acid bacteria.

Effects of Polyunsaturated Fatty Acids in Growth Medium on Lipid Composition and on Physicochemical Surface Properties of Lactobacilli

“…Linoleic acid, although fairly uncommon, has been identified in cellular fatty acids of lactobacilli, the proportions ranging from trace amounts up to 20% (3,6,7). In the present study, we did not identify this parent n-6 PUFA in bacterial fatty acids of three analyzed lactobacilli grown in standard MRS medium (without PUFA supplementation), although ␥-linolenic acid and eicosapentaenoic acid were identified in all lactobacilli.…”

“…The fourth major group of fatty acids in the present study was 19:cyc, especially dihydrosterculic acid. Previous reports regarded dihydrosterculic and lactobacillic acids, formed by methylenation of oleic and vaccenic acids, respectively, as the major fatty acids in lactobacilli (3,7,10,20). Even though lactobacillic acid is the most frequently reported fatty acid in lactobacilli, we did not identify it in L. delbrueckii subsp.…”

“…Most of the previous reports presented 18:1 without further identifying different isoforms, e.g., oleic and vaccenic acids. These octadecanoic acids seem to be the most predominant in lactobacilli, making up 14 to 67% of the total fatty acids (3,5,7,17). The fairly substantial variation in the results most likely is due to different culture conditions (e.g., temperature, incubation time, culture medium, and strain differences).…”

Study on Lipid Fractions of Streptococcus thermophilus by TLC, GC and GC/MS Techniques

“…This result could be explained by the incorporation of exogenous fatty acids, deriving from the original matrix (i.e., milk) where the bacteria grew before their isolation. To our knowledge the presence of the short chain fatty acids has hardly ever been observed by other authors on lipids extracted from lactic acid bacteria [17]. This lack of information could be due to either the adoption of GC operative conditions not being suitable for the separation of these low boiling point compounds, or the evaluation of non-dairy foodborne strains [5,9,11,12,16,31].…”

“…It is known that microbial fatty acid composition is dependent upon several factors and it is often modified in response to environmental physicochemical parameters such as oxygen, temperature, nutrients, growth phase and pH value [7][8][9][10][11][12][13][14][15][16]. Different analytical procedures have been applied for the determination of bacterial fatty acids: acid or alkaline direct transesterification of the cells [17], methylation of the whole fat extracted, preceded or not by saponification [4,5,8,12,16]. Gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS) and pyrolysis/mass spectrometry were further applied to identify and quantify the different fatty acids as methylesters (FAME).…”