Alternative Ernährungsformen: Allgemeine Aspekte und vegetarische Kostformen.

Alternative diets (AD) differ from the current common mixed diet; AD are recommended as a permanent diet. These diets are based on ethical, philosophical and health promoting principles and lead to very different recommendations for food selection. Even within a particular AD there is usually a broad spectrum of versions, so that a general evaluation is only possible to a limited extent. This is also true for single AD. Vegetarian diets and partly paleo-diets have been investigated to a reasonable extent. Plant based diets are appropriate as permanent diets and offer health benefits as compared with currently practiced diets (risk reduction of cancers by 10-18% and of heart diseases by 30%; favorable effect on blood pressure and lipid profile; no risk reduction on cancer and total mortality). Vegan diets have to be critically assessed: they are linked to an increased risk of deficits for single nutrients (vitamin B12, iodine and as the case may be. calcium and long chain omega-3 fatty acids), if suitable supplements or fortified foods are not consumed.

Uptake of iron by Kluyveromyces marxianus DSM 5422 cultivated in a whey-based medium.

The ability of Kluyveromyces marxianus for converting lactose into ethyl acetate offers a chance for the economical reuse of whey. Iron plays a significant role in this process as ester synthesis requires a low intracellular iron content, xFe . The iron content in turn is decreased by growth due to cell expansion and increased by iron uptake. Thus, the iron-uptake rate, ψ, is important for the considered process. Iron uptake by K. marxianus DSM 5422 was studied in aerobic cultivation on a whey-borne medium with varied initial iron content, in part combined with a feed of iron under intensive growth conditions. A possible precipitation of iron that would pretend iron uptake was verified not to have occurred. Regularly measured dissolved iron concentrations, CFe,L , allowed the xFe and ψ parameters to be obtained by model-based iron balancing. The achieved data were used for establishing a ψ(CFe,L , xFe ) model. Mathematical simulations based on this iron-uptake model reproduced the performed cultivation processes. The created iron-uptake model allows for a future predictive system to be developed for the optimization of biotechnological ester production.

Formation of ethyl acetate by Kluyveromyces marxianus on whey during aerobic batch and chemostat cultivation at iron limitation.

The ability of Kluyveromyces marxianus to convert lactose into ethyl acetate offers a chance for an economic reuse of whey. Former experiments with K. marxianus DSM 5422 proved limitation of growth by iron (Fe) or copper as a precondition for significant ester synthesis. Several aerobic batch and chemostat cultivations were done with whey-borne media of a variable Fe content for exploring the effect of Fe on growth, the Fe content of biomass, and metabolite synthesis. At low Fe doses, Fe was the growth-limiting factor, the available Fe was completely absorbed by the yeasts, and the biomass formation linearly depended on the Fe dose governed by a minimum Fe content in the yeasts, x (Fe,min). At batch conditions, x (Fe,min) was 8.8 µg/g, while during chemostat cultivation at D = 0.15 h(-1), it was 23 µg/g. At high Fe doses, sugar was the growth-limiting factor, Fe was more or less absorbed, and the formed biomass became constant. Significant amounts of ethyl acetate were only formed at Fe limitation while high Fe doses suppressed ester formation. Analysis of formed metabolites such as glycerol, pyruvate, acetate, ethanol, ethyl acetate, isocitrate, 2-oxoglutarate, succinate, and malate during chemostat cultivation allowed some interpretation of the Fe-dependent mechanism of ester synthesis; formation of ethyl acetate from acetyl-SCoA and ethanol is obviously initiated by a diminished metabolic flux of acetyl-SCoA into the citrate cycle and by a limited oxidation of NADH in the respiratory chain since Fe is required for the function of aconitase, succinate dehydrogenase, and the electron-transferring proteins.