Various fungal species can degrade lignocellulolytic materials with their enzyme cocktails composed of cellulolytic and lignolytic enzymes. In this work, seven fungal species (Mucor indicus DSM 2185, Paecilomyces variotii CBS 372.70, Myceliophthora thermophila CBS 663.74, Thielavia terrestris CBS 456.75, Botryosphaeria dothidea JCM 2738, Fusarium oxysporum f.sp. langenariae JCM 9293, and Fusarium verticillioides JCM 23107) and four nutrient media were used in the screening for effective lignocellulose degrading enzymes. From the seven tested fungi, F. oxysporum and F. verticilliodes, along with nutrient medium 4, were selected as the best medium and producers of lignocellulolytic enzymes based on the determined xylanase (>4 U mg⁻¹) and glucanase activity (≈2 U mg⁻¹). Nutrient medium 4 supplemented with pretreated corn cobs was used in the production of lignocellulolytic enzymes by sequential solid-state and submerged cultivation of F. oxysporum, F. verticilliodes, and a mixed culture of both strains. F. oxysporum showed 6 times higher exoglucanase activity (3.33 U mg⁻¹) after 5 days of cultivation in comparison with F. verticillioides (0.55 U mg⁻¹). F. oxysporum also showed 2 times more endoglucanase activity (0.33 U mg⁻¹). The mixed culture cultivation showed similar endo- and exoglucanase activities compared to F. oxysporum (0.35 U mg⁻¹; 7.84 U mg⁻¹). Maximum xylanase activity was achieved after 7 days of cultivation of F. verticilliodes (≈16 U mg⁻¹), while F. oxysporum showed maximum activity after 9 days that was around 2 times lower compared to that of F. verticilliodes. The mixed culture achieved maximum xylanase activity after only 4 days, but the specific activity was similar to activities observed for F. oxysporum. It can be concluded that both fungal strains can be used as producers of enzyme cocktails for the degradation of lignocellulose containing raw materials, and that corn cobs can be used as an inducer for enzyme production.

Water kefir is a product obtained through the fermentation of sucrose solution, usually with some kind of dried fruit addition, by a combined culture of micro-organisms which are contained within kefir grains. Its popularity is rising because of the simplicity of its preparation and its anti-inflammatory, antioxidant, probiotic, and antibacterial effects. In this research, the water kefir production was studied in 250 mL jars, as well as in a horizontal rotating tubular bioreactor (HRTB). The first part of the research was conducted in smaller-scale (jars), wherein the optimal fruit and fruit portions were determined. These experiments included the addition of dried plums, apricots, raisins, dates, cranberries, papaya, and figs into 150 mL of initial sugar solution. Also, the optimal ratio between dried fruit and sucrose solution (0.2) at the beginning of the bioprocess was determined. The second part of this research was conducted using HRTB. The experiments in the HRTB were carried out by using different operational modes (constant or interval bioreactor rotation). A total of six different bioreactor setups were used, and in all experiments, figs were added at the beginning of the bioprocess (0.2 ratio between dried figs and sucrose solution). On the basis of the obtained results, the interval bioreactor rotation mode proved to be the better HRTB mode for the production of the water kefir, as the yield of the main fermentation products was higher, and their ratios were the most adequate for the quality of water kefir drink. The optimal results were obtained via HRTB setup 3/57 (3 min rotation, 57 min pause within 1 h) and rotation speed of 3 rpm. Furthermore, it is clear that HRTB has great potential for water kefir production due to the fact that HRTB experiments showed shorter fermentation times (at least five times) than water kefir production in jars.

Alternative to the use of fossil fuels are biofuels (e.g., bioethanol, biodiesel and biogas), which are more environmentally friendly and which can be produced from different renewable resources. In this investigation, bioethanol production from raw sugar beet cossettes (semi-solid substrate) by yeast Saccharomyces cerevisiae in a horizontal rotating tubular bioreactor (HRTB) was studied. Obtained results show that HRTB rotation mode (constant or interval) and rotation speed have considerable impact on the efficiency of bioethanol production in the HRTB. The main goal of this research was to develop a non-structural mathematical model of bioethanol production from raw sugar beet cossettes in the HRTB. The established mathematical model of bioethanol production in the HRTB describes substrate utilization and product formation (glycerol, ethanol and acetate) and presumes negative impact of high substrate concentration on the working microorganism (substrate inhibition) by using Andrews inhibition kinetics. All simulations of bioethanol production in the HRTB were performed by using Berkeley Madonna software, version 8.3.14 (Berkeley Madonna, Berkeley, CA, USA). The established non-structural bioprocess model describes relatively well the bioethanol production from raw sugar beet cossettes in the HRTB.

Research background. An innovative integrated bioprocess system for bioethanol production from raw sugar beet cossettes (SBC) and arabitol from remaining exhausted sugar beet cossettes (ESBC) was studied. This integrated three-stage bioprocess system is an example of the biorefinery concept to maximise the use of raw SBC for the production of high value-added products such as sugar alcohols and bioethanol. Experimental approach. The first stage of the integrated bioprocess system was simultaneous sugar extraction from SBC and its alcoholic fermentation to produce bioethanol in an integrated bioreactor system (vertical column bioreactor and stirred tank bioreactor) containing a high-density suspension of yeast Saccharomyces cerevisiae (30 g/L). The second stage was the pretreatment of ESBC with dilute sulfuric acid to release fermentable sugars. The resulting liquid hydrolysate of ESBC was used in the third stage as a nutrient medium for arabitol production by non-Saccharomyces yeasts (Spathaspora passalidarum CBS 10155 and Spathaspora arborariae CBS 11463). Results and conclusions. The obtained results show that the efficiency of bioethanol production increased with increasing temperature and prolonged residence time in the integrated bioreactor system. The maximum bioethanol production efficiency (87.22 %) was observed at a time of 60 min and a temperature of 36 °C. Further increase in residence time (above 60 min) did not result in the significant increase of bioethanol production efficiency. Weak acid hydrolysis was used for ESBC pretreatment and the highest sugar yield was reached at 200 °C and residence time of 1 min. The inhibitors of the weak acid pretreatment were produced below bioprocess inhibition threshold. The use of the obtained liqiud phase of ESBC hydrolysate for the production of arabitol in the stirred tank bioreactor under constant aeration clearly showed that S. passalidarum CBS 10155 with 8.48 g/L of arabitol (YP/S=0.603 g/g and bioprocess productivity of 0.176 g/(L·h)) is a better arabitol producer than Spathaspora arborariae CBS 10155. Novelty and scientific contribution. An innovative integrated bioprocess system for the production of bioethanol and arabitol was developed based on the biorefinery concept. This three-stage bioprocess system shows great potential for maximum use of SBC as a feedstock for bioethanol and arabitol production and it could be an example of a sustainable ‘zero waste’ production system.

Utilization of various biomasses as raw materials in biorefineries represents a promising alternative for the production of valuable chemicals and biofuels. This study investigates the potential of the fungus Mucor indicus DSM 2158, cultivated on media containing the liquid phase of grass hydrolysates (LGH) and various nitrogen sources (yeast extract and corn steep liquor), for the production of valuable metabolites, such as ethanol, chitin, chitosan, and fatty acids. The ethanol yield varied depending on the cultivation media and conditions. The highest substrate-into-ethanol conversion coefficients (0.14–0.2 g g⁻¹) were achieved during M. indicus cultivation on the LGH medium containing 5 g L⁻¹ CSL in Erlenmeyer flasks and a bubble column bioreactor. In these cultivations, the highest fungal biomass concentrations (5.61–5.91 g L⁻¹) were also observed. In flask cultivations, the highest content of total lipids in fungal dry biomass (15.76%) was observed. The obtained fungal biomass contained up to 22 fatty acids, with oleic acid (≈50%) being the most predominant. Chitin and chitosan yields were from 0.1 g g⁻¹ to 0.3 g g⁻¹ of dry biomass depending on the cultivation media and conditions. The residual media from the cultivation of M. indicus were used for the growth of the non-sulfur purple bacterium Rhodovulum adriaticum DSM 2781. Cultivations of R. adriaticum DSM 2781 on the residual media, in Erlenmeyer flasks and a stirred-tank bioreactor, resulted in a biomass yield of 0.50 to 2.26 g L⁻¹. After extraction of bacterial biomass, total pigments (expressed as bacteriochlorophyll-a) were obtained in the range from 1.8 to 48.1 mg g⁻¹ dry biomass depending on the media and cultivation conditions. The highest titer of bacteriochlorophyll-a was achieved during cultivation on the exhausted LGH medium with 5 g L⁻¹ yeast extract. The established biorefinery system has to be optimized in order to reach capacity for transfer to a larger scale.