Effect of pH on growth and fatty acid composition ofLactobacillus büchneri andLactobacillus fermentum

Growth and fatty acid composition of two lactobacilli,Lactobacillus büchneri andLactobacillus fermentum, were studied at different pHs of the media in a small-scale fermenter with particular interest in lactobacillic acid production of the cultures. Generally, the total fatty acid content of the bacterial cells increased with increasing culture age. The production of lactobacillic acid was affected in the two lactobacilli by both culture age and pH of the media, but in a very different manner. In L.büchneri cultures, the relative proportion of lactobacillic acid was highest when the pH was lowest (pH 4.5), whereas inL. fermentum cultures, the proportion of lactobacillic acid was highest at pH 7.0. The pH of the medium affected not only the relative proportion of lactobacillic acid, but also biomass production and total fatty acid accumulation of the cultures. Thus, by controlling the pH of the cultures, the volumetric yield of lactobacillic acid could be improved considerably compared to cultures without pH control.     

Conformational analysis XX—13C NMR studies of saturated heterocycles 5—substituent effects on the 13C chemical shifts of methyl substituted 1,3-dithiolanes

The ¹³C NMR chemical shifts for 1,3-dithiolane and 13 methyl substituted derivatives are reported. Substituent effects are derived and compared with those for cyclopentanes and 1,3-dioxolanes. The magnitude and variety of the substituent effects are best explained with the aid of a half-chair conformation where the S-1? C-2? S-3 plane passes between C-4 and C-5.     

Nuclear magnetic resonance studies on the conformational,effects of alkyl-substituted 1,3-oxathiolanes 1–3

The ¹H NMR spectra of a number of alkyl-substituted 1,3-oxathiolanes were recorded and analysed. The NMR data were employed to predict the configurations and most probable conformations of the 1,3-oxathiolane ring and also to estimate the conformational free energy values of the pseudoaxial substituents in the different positions. Some of the compounds studied were epimeric and able to equilibrate. The energy parameters obtained from chemical shifts and vicinal coupling constants were found to be in excellent agreement with the results derived from equilibration experiments.