Efficient growth of Kluyveromyces marxianus biomass used as a biocatalyst in the sustainable production of ethyl acetate

Abstract

Background: Whey is just turning from a waste of milk processing to a renewable raw material in biotechnology for producing single-cell protein, bio-ethanol, or ethyl acetate as an economic alternative. Conversion of whey-borne sugar into ethyl acetate requires yeast biomass as a biocatalyst. A high cell concentration results in a quick ester synthesis, but biomass growth means consumption of sugar at the expense of ester production. Efficient and cost-saving biomass production is thus a practical requirement. Whey is poor in nitrogen and has therefore to be supplemented with a bioavailable N source. Methods: Several aerobic growth tests were performed with Kluyveromyces marxianus DSM 5422 as a potent producer of ethyl acetate in whey-borne media supplemented with various N sources. Preliminary tests were done in shake flasks while detailed studies were performed in a stirred bioreactor.

STUDY OF INCREASING THE PRODUCTION OF VOLATILE FLAVOR COMPOUNDS BY THE YEAST Kluyveromyces marxianus THROUGH OPTIMIZATION OF CARBON AND NITROGEN SOURCES

“…This may due to the rapid consumption of ammonium which leads to an ionic imbalance and acidification in the medium. The growth of yeast can be effected by such acidification in the medium (Löser et al 2015). In the present study, availability of both organic and inorganic nitrogen sources in the growth medium showed the preference of yeast for the organic nitrogen source.…”

“…In a similar manner, supplementing the whey medium with yeast extract or yeast extract plus ammonium sulphate increased the biomass concentration of K. marxianus in comparison to the control and supplementing with only ammonium (Parrondo et al 2009). A production of yeast biomass and the right balance between yeast growth and synthesis of total volatile flavor compounds are important factors for the economy of the total volatile compounds (Löser et al 2015). This balance can be optimized by using such kind of statistical approaches applied in this study.…”

“…On the contrary, increasing concentration of glucose enhanced the ethanol production in the fermentation medium (p<0.01). Nitrogen-limited growth can regulate yeast metabolism and provoke ethanol formation at aerobic conditions stated by Löser et al (2015), previously. Similarly, YE and glucose had a significant effect on the production of fusel alcohols (2-PE and isoamyl alcohol) by K. marxianus.…”

“…Cell dry weights (g L -1 ) were obtained by separating the yeasts from a defined volume of suspension via centrifugation (at 7000 rpm for 10 min), washing the pellet twice with distilled water, drying at 103 °C until constant weight and cooled to room temperature in a desiccator before weighing (Löser et al 2015).…”

“…Therefore, it is important to assess what kind of flavor compounds are synthesized by K. marxianus when growing on defined and/or semidefined culture medium rather than growing on waste stream (Gethins et al 2015). Medium composition especially carbon and nitrogen sources, is one of the critical factor for both growth and production flavor compounds by yeasts (Fabre et al 1998;Gethins et al 2015;Löser et al 2015). Hence, to obtain high biomass and metabolite productivities, it is important to find appropriate types of nutrients and their optimum concentrations in growth medium of the yeast (Manera et al 2008;Fonseca et al 2013;Yilmaztekin et al 2013).…”