Selection of yeast strain and fermentation conditions for high‐yield ethanol production from lactose and concentrated whey

Abstract

A total of 65 yeast strains were screened for their ability to grow and ferment lactose in a standard DURHAM tube test at 30 "C. Based on the kinetic parameters for lactose and whey lactose fermentations in shake flask cultures, the strain Condidu pseudotropicdis 65 was chosen for further studies. Some of the cultural parameters affecting ethanolic fermentations on lactose were standardized. At an initial lactose concentration of 1oOLI20 g/l in the medium containing concentrated whey or lactose, at 40 OC and within 48 h, the selected strain reached an ethanol concentration of 41-59 g/l, an ethanol productivity of 1.3-3.0 g/l/h, a lactose consumption of 99%, an ethanol yield 0.4-0.49 d g and a biomass yield of 0.027 dg.

Fermentation of deproteinized cheese whey powder solutions to ethanol by engineered Saccharomyces cerevisiae: effect of supplementation with corn steep liquor and repeated-batch operation with biomass recycling by flocculation

“…Among the works on whey fermentation by natural lactose-fermenting yeasts, a few report higher ethanol titers but considerably lower productivities [9,22] compared to this work. Conversely, some report higher productivity but lower ethanol titer [11,12,17,46]. Only two papers report simultaneously higher ethanol titer and higher productivity [20,43] than obtained in this work.…”

“…Accordingly, several authors have reported substrate inhibition effects on ethanol production and/or yeast growth, particularly at high initial lactose concentrations (150-200 g/l), for Kluyveromyces spp. [20,[35][36][37]43] and Candida pseudotropicalis [11,46]. The high ash content (particularly sodium and potassium) in concentrated whey has also been reported to inhibit yeast growth and ethanol formation by Kluyveromyces spp.…”

“…A repeated-batch process was stably operated during five consecutive fermentation runs in an air-lift bioreactor with cell recycling by flocculation (without a costly centrifugation step) and without the need for pH control system. concentrations during repeated-batch fermentations of concentrated whey supplemented with 10 g/l CSL in the air-lift bioreactor: run 1 (squares); run 2 (triangles); run 3 (diamonds); run 4 (circles); run 5 (inverted triangles) Table 3 Comparison of studies on batch ethanol production from whey using recombinant S. cerevisiae [99 [46] Values were either collected directly from the reference or calculated from the data provided in the reference; the best condition (maximizing ethanol titer and/or productivity) in each reference was selected a…”

Improved bioethanol production in an engineered Kluyveromyces lactis strain shifted from respiratory to fermentative metabolism by deletion of NDI1

“…Although the yield obtained with the NRRL‐Y1140 strain seems high for a respiratory yeast, the distribution between respiratory and fermentative metabolism in wild‐type K. lactis is dependent on oxygen availability (González‐Siso et al ., ; Guimarães et al ., ) and low levels of oxygen in these cultures favour fermentation. Similar ethanol yields in whey than those reached by the NRRL‐Y1140 strain in this work were obtained by other authors in fermentative conditions with other Kluyveromyces strains (Szczodrak et al ., ; Guimarães et al ., ).…”