3.5. Fed-batch cultivation in the fermentor
According to the results of initial shaken cultures, the C. tropicalis, P. stipitis and C. guilliermondii strains were chosen for fedbatch cultivations in a benchtop fermentor. The mean of the 3 cultivation results expressed as the ‘‘net’’ (with the subtracted amount of inoculum) biomass concentration in the fermentor [g DM] is shown in the Figure below (see Fig. 3). During 10 h of cultivation, the ‘‘net biomass’’ (biomass without seed yeast) content increased from 0 g DM (24 g DM of the inoculum was subtracted) to 45.4(±4.43) g DM for C. tropicalis, 54.7(±6.35) g DM for P. stipitis, and 43.6(±5.87) g DM for C. guilliermondii in the fermentor. The crude protein content in the dry matter of C. tropicalis biomass obtained after 10 h of fed-batch cultivation was 47.8(±2.34)%.For P. stipitis and C. guilliermondii cells protein content in dry matter was 45.6(±3.76)% and 49.2(±4.14)%, respectively. Pessoa et al. (1996), after cultivating the C. tropicalis IZ 1824 strain in a 1 dm3 bioreactor, obtained up to 10.1 g DM dm3 by
using sugar cane hydrolysate containing 25.4 g of reducing sugars
in 1 dm3. In our research, the yeast biomass in the range of 45.4–54.5 g DM, obtained from 2.8 dm3 of hydrolysate (containing 65.8 g of saccharides possible to be utilised dm3 ) is a very promising result. The crude protein content is close to the values presented in the literature for fodder yeast (Harrison, 1993; Reed and Nagodawithana, 1991). It should also be noted that both the yield and protein content depend on many factors, including yeast strain, medium composition, cultivation conditions and postcultivation operations such as drying and storage.