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Branched chain fatty acids (BCFAs) are fatty acids substituted with alkyl groups. Many of them are chiral and therefore occur in two enantiomeric forms. This review describes their occurrence in Nature, their biosynthesis, their properties as flavours, and their enzymatic kinetic resolution. Many lipases are able to separate the enantiomers of BCFAs, in hydrolysis, esterification or transesterification reactions. Very often, the stereoselectivity of these reactions is remarkably high, even when the chiral carbon atom is remote from the carboxylic acid group.

The application of enantioselective micelles in ultrafiltration systems can be an alternative route to meet the increasing demand for enantiopure products. We have studied the separation of d,l-phenylalanine (Phe) by cholesteryl-l-glutamate:Cu^II (CLG:Cu^II) anchored in nonionic micelles (intrinsic enantioselectivity αD/L,int = 1.9). A cascaded system is needed to complete the separation, as a single stage is insufficient to obtain >99% optically pure products. It is shown that the complexation and decomplexation processes are not instantaneous; hence, elucidation of the complexation kinetics is essential to the design of a multistage system. Linear driving force (LDF) models describe both the complexation and decomplexation rates of enantiomers. It can be concluded that the complexation rates of d- and l-Phe, (32 ± 11) × 10^-5 s^-1 and (28 ± 14) × 10^-5 s^-1, respectively, are not limited by enantiomer diffusion in the hydrophilic shell of the micelles. Consequently, the formation and rearrangement of the chelate complexes must be rate-limiting. In addition, decomplexation of both enantiomers is even slower, on the order of 10^-6 s^-1. Fortunately, ultrafiltration experiments indicate that a rapid exchange rate of bound l-Phe by unbound d-Phe improves the decomplexation of l-Phe to (360 ± 250) × 10^-5 mM^-1 s^-1. This exchange process can be described by a second-order LDF model.

Many enantiomer separation systems are studied to meet the increasing demand for enantiopure compounds. One way to obtain pure enantiomers is to apply enantioselective micelles in ultrafiltration systems. We have studied the separation of phenylalanine (Phe) enantiomers by the ultrafiltration of nonselective nonionic micelles containing selector molecules, cholesteryl-l-glutamate:Cu^II (CLG:Cu^II). Because the net charges of enantiomer and CLG are pH-dependent, it is foreseen that pH will be an important factor in the design of a cascaded separation process that yields enantiopure products. Experiments at pH 7, 9, and 11 showed that the complexation can be described by multicomponent Langmuir isotherms. The CLG enantioselectivity for d-Phe increases with decreasing pH, being 1.4, 1.7, and 1.9 for pH 11, 9, and 7, respectively. Accordingly, the saturation concentration and the affinity constants decrease with decreasing pH, finally resulting in no complexation at pH 6. To design an economically attractive separation process, the regeneration of d-Phe-saturated micelles leaving the multistage system is inevitable. Regeneration, i.e., recovery of enantioselective micelles for reuse, is possible at pH ≤ 4. To keep salt production to a minimum, the shift in pH between the separation and regeneration processes must be minimized. Therefore, a separation process at pH 7 seems most attractive.

The production of active dried starter cultures can be influenced at several levels in the production process. In this paper the following process factors are discussed:  osmotic stress during growth and cell density prior to drying. Contradicting results are reported in the literature on the influence of osmotic stress during growth on the residual activity after drying. The combined approach in which two process factors were studied at a time resulted in an explanation for the discrepancy in earlier work. The cell density prior to drying had an important influence on the glucose fermenting activity after drying. Residual activities ranging from 0.10 to 0.83 were achieved using initial cell densities between 0.025 and 0.23 g of cell/g of sample, respectively. The drying tolerance of cells grown with osmotic stress of 1 M NaCl was low (residual activity = 0.06) and was not related to the cell density prior to drying. The influence of osmotic stress during growth on the drying tolerance of Lactobacillus plantarum was dependent on the cell density prior to drying.