Abstract
A new yeast wild-type Yarrowia lipolytica isolate presented efficient growth on glycerol. During flask cultures, nitrogen limitation led to the secretion of sugar-alcohols as the major metabolites of the process (mannitol, arabitol and erythritol), whereas insignificant quantities of citrate were synthesized. Although in some instances high initial glycerol concentrations were employed (≈150 g/L), remarkable glycerol assimilation and polyol secretion was observed. Total polyols ≈ 52 g/L (conversion yield on glycerol consumed = 0.43 g/g) was recorded in the flask experiments. The sugar-alcohol production bioprocess was successfully simulated with the aid of a modified Velhlust–Aggelis model that fitted very well with the experimental data, while optimized parameter values seemed to be quite consistent. In bioreactor trials, a noticeable metabolic shift towards citric acid production was observed, while simultaneously insignificant polyol quantities were produced. In fed-batch bioreactor experiments, a total citric acid quantity ≈ 102 g/L was recorded—one of the highest in the literature for wild-type Y. lipolytica strains. This metabolic transition was due to higher oxygen saturation into the medium that occurred in the bioreactor experiments compared with the flasks. Cellular lipids produced in the bioreactor trial contained higher concentrations of unsaturated fatty acids compared with those produced in flasks.
Highlights
The constant and continuous decrease in non-renewable energy feedstocks and the concomitant rise in the price of crude oil have resulted in the increment of scientific interest concerning the discovery and study of “renewable” types of energy sources
The choice of Gly0 ≈ 100 g/L was based on the results indicated in Table 1; precisely, in flask cultures with this Gly0 concentration, glycerol was almost completely consumed by the microorganism in a not excessively high incubation time (c. 180 h), while DCWmax concentration was substantially high not being seriously influenced by the inhibition exerted due to high Gly0 concentrations into the medium
A maximum total citric acid quantity of ≈102 g/L, one of the highest in the literature for wild-type Y. lipolytica strains, was recorded in a successful fed-batch experiment with glycerol employed as the substrate
Summary
The constant and continuous decrease in non-renewable energy feedstocks and the concomitant rise in the price of crude oil have resulted in the increment of scientific interest concerning the discovery and study of “renewable” types of energy sources. Alky-esters of fatty acids esterified with low-molecular weight alcohols) and bioethanol are considered as the most important and interesting types of biofuels [1,2,3,4,5]. The synthesis of the above-mentioned biofuels is connected with the production of concentrated glycerol-containing waters, which are the principal side-products of these processes. Besides bioethanol production, important quantities of glycerol-containing. Sci. 2020, 10, 7373 water can be generated as side products in various alcoholic beverages’ production facilities; for instance, during the typical ethanol fermentation process, ethanol is separated via distillation
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