Chromatographic and Molecular Insights into Fatty Acid Profiles of Thermophilic Lactobacillus Strains: Influence of Tween 80TM Supplementation

The molecular fatty acid (FA) profiles of seven certified thermophilic <i>Lactobacillus</i> strains, including the influence of an extracellular source of oleic acid (as Tween 80^TM), were characterised using advanced chromatographic and spectrometric methods. Cyclic and conjugated fatty acids were identified by GC-MS using co-injections with authentic standards, ECL, and diagnostic EI ions, with a secondary confirmation using literature data. Additionally, the molecular-level characterisation of fatty acid profiles of bacterial cells was summarised using the latest analytical approaches, highlighting inconsistencies and differences reported in previous studies. Six saturated fatty acids, two single-branched fatty acids with iso and anteiso structures, one hydroxy fatty acid, nine unsaturated fatty acids with one double bond, two fatty acids with unsaturated double bonds, six fatty acids with conjugated bonds, and three fatty acids with a cyclic part in the carbon chain were identified. Within these fatty acids, we also demonstrated the limitations of molecular chromatographic resolution and structural discrimination, which impacted the effective identification of fatty acids in our research. We confirmed the significant differences in terms of the identification of C18:1,<i>cis-</i>9 and C18:1,<i>cis-</i>11 acids, as well as cycC19:0,<i>cis-</i>10,11, and cycC19:0,<i>cis-</i>9,10 acids. The observations at the molecular-physiological interface related to the lack of growth of <i>L. acidophilus</i> strains and the visibly reduced growth of <i>L. delbrueckii</i> subsp. <i>lactis</i> ATCC 4797 in the MRS without the addition of Tween 80^TM allowed us to confirm that the exclusion of this medium is useful in differentiating the lactobacilli.