Factors Affecting Volatile Phenol Production During Fermentations with Pure and Mixed Cultures of Dekkera bruxellensis and Saccharomyces cerevisiae

U radu je ispitan utjecaj etanola i prekursora hidroksicimetne kiseline i vinilnog fenola na biosintezu hlapljivih fenola u fermentacijama s mješovitim i čistim kulturama kvasaca Saccharomyces cerevisiae i Dekkera bruxellensis. Analizirana su tri različita soja D. bruxellensis koja su pokazala jedinstveni profil proizvodnje hlapljivih fenola u fermentacijama s mješovitom i čistom kulturom kvasaca. Rezultati su pokazali da je u biosintezi s mješovitom kulturom, u usporedbi s čistom kulturom D. bruxellensis, nastalo manje vinilnog fenola, a više etilnog fenola. Prekursori vinilnog fenola značajno inhibiraju rast kvasca S. cerevisiae te proizvodnju etilnog fenola. Geni što kodiraju enzime kumarat dekarboksilazu i vinilfenol reduktazu u kvascu D. bruxellensis pokazuju jači odziv na prekursore vinilnog fenola u usporedbi s hidroksicimetnom kiselinom. Veće su koncentracije vinilnog fenola u stanicama kvasaca imale jači citotoksični učinak od hidroksicimetne kiseline. Utvrđeno je također da su male koncentracije etanola potakle veću proizvodnju hlapljivih fenola u fermentacijama s kvascima S. cerevisiae i D. bruxellensis, što je potvrđeno i ekspresijom gena što kodiraju kumarat dekarboksilazu u kvascu D. bruxellensis.The paper examines the impact of ethanol, and hidroxycinnamic and vinylphenol precursors on the production of volatile phenols in fermentations of mixed and pure cultures of yeasts Saccharomyces cerevisiae and Dekkera bruxellensis. Three different D. bruxellensis strains were examined and they all showed a unique volatile phenol production pattern in the fermentations of pure and mixed cultures. Generally, the results showed that in mixed culture fermentations less vinylphenols and more ethylphenols were produced in comparison with D. bruxellensis pure culture fermentations. Vinylphenol precursors significantly inhibited the growth of S. cerevisiae and the production of ethylphenols. Nevertheless, it was found that D. bruxellensis genes encoding for enzymes coumaric acid decarboxylase (CAD) and vinylphenol reductase (VPR) are more responsive to vinylphenol precursors in comparison with hidroxycinnamic acids. Consequently, higher concentrations of vinylphenols in the cell were found to be more cytotoxic than hidroxycinnamic acids. In general, low ethanol concentrations induced higher production of volatile phenols by S. cerevisiae and D. bruxellensis. This was confirmed with the expression pattern of gene encoding for CAD of D. bruxellensis

The influence of mixed fermentations of yeasts Saccharomyces cerevisiae and Dekkera bruxellensis on the biosynthesis of aromatic compounds

Vpliv mešane fermentacije kvasovk Saccharomyces cerevisiae in Dekkera bruxellensis na biosintezo aromatskih snov

A novel rotation generator of hydrodynamic cavitation for the fibeillation of long conifer fibers in paper production

Refining of cellulose pulp is a critical step in obtaining high quality paper characteristics, however, this process is slow and costly especially for refining longer conifer fibers which are the preferred source for high quality paper production and give the paper its strength. In this study, we have applied a novel rotation generator of hydrodynamic cavitation for refining conifer rich pulp samples. Our results show that the device is capable of generating intense shear forces and multiple zones of developed cavitation and is successful in increasing the drainage rate of high consistency pulp (3%). The paper produced by means of the obtained pulp has higher quality because of its higher tensile index (50.5 kN m kg-1) and burst index (3 kPa m2 g-1). These physical parameters were sufficient for newsprint paper and other paper/board quality manufacture. In addition, this laboratory scale rotation generator proved to be economically efficient in comparison to the routinely employed laboratory beaters. To our knowledge, this is the first example of using hydrodynamic cavitation for the refinement of softwood fiber pulp of standard industrial consistencies (3%)

Kavitacija kot potencialna tehnologija za revitalizacijo odpadnih voda: primer povečanega sproščanja hranil iz odpadnega biološkega mulja papirne industrije

Wastewater recycling and sludge removal in the paper industry account for about 60 % of all process costs. New and environmentally friendly wastewater treatment techniques are, therefore, continually being developed. Cavitation exploitation is currently a well-investigated topic that is also interesting for the paper production industry. This study investigates efficiency of hydrodynamic cavitation alone and in combination with the addition of NaOH for the treatment of secondary pulp and paper mill sludge in order to enhance nutrient release. First, two laboratory-scale devices were tested: the blow-through and the rotating hydrodynamic cavitation generator. The latter set-up proved to be more efficient: therefore, further experiments were performed on its pilot-scale version. The results showed an increase of soluble chemical oxygen demand (CODs) by 514 mg/L, total nitrogen (Nt) by 17.4 mg/L, and total phosphorous (Pt) by 2.3 mg/L. To further increase nutrient release combination of cavitation and sludge sample alkalinization was tested. The addition of NaOH and 30 min cavitation of secondary sludge (500 L) significantly improved CODs and Nt release by 2400 mg/L and 120 mg/L, respectively. Microbiological photos revealed a definite disintegration of sludge flocks. According to our estimates, 1.9 kg of released CODs from alkaline pre-treated and cavitated sludge would cost only one euro

Application of (super)cavitation for the recycling of process waters in paper producing industry

In paper production industry, microbial contaminations of process waters are common and can cause damage to paper products and equipment as well as the occurrence of pathogens in the end products. Chlorine omission has led to the usage of costly reagents and products of lower mechanical quality. In this study, we have tested a rotation generator equipped with two sets of rotor and stator assemblies to generate developed cavitation (unsteady cloud shedding with pressure pulsations) or supercavitation (a steady cavity in chocked cavitation conditions) for the destruction of a persistent bacteria Bacillus subtilis. Our results showed that only supercavitation was effective and was further employed for the treatment of waters isolated from an enclosed water recycle system in a paper producing plant. The water quality was monitored and assessed according to the chemical (COD, redox potential and dissolved oxygen), physical (settleable solids, insolubles and colour intensity) and biological methods (yeasts, aerobic and anaerobic bacteria, bacterial spores and moulds). After one hour of treatment, a strong 4 logs reduction was achieved for the anaerobic sulphate reducing bacteria and for the yeastsa 3 logs reduction for the aerobic bacteriaand a 1.3 logs reduction for the heat resistant bacterial spores. A 22% reduction in COD and an increase in the redox potential (37%) were observed. Sediments were reduced by 50% and the insoluble particles by 67%. For bacterial destruction in real industrial process waters, the rotation generator of supercavitation spent 4 times less electrical energy in comparison to the previously published cavitation treatments inside the Venturi constriction design. In paper production industry, microbial contaminations of process waters are common and can cause damage to paper products and equipment as well as the occurrence of pathogens in the end products. Chlorine omission has led to the usage of costly reagents and products of lower mechanical quality. In this study, we have tested a rotation generator equipped with two sets of rotor and stator assemblies to generate developed cavitation (unsteady cloud shedding with pressure pulsations) or supercavitation (a steady cavity in chocked cavitation conditions) for the destruction of a persistent bacteria Bacillus subtilis. Our results showed that only supercavitation was effective and was further employed for the treatment of waters isolated from an enclosed water recycle system in a paper producing plant. The water quality was monitored and assessed according to the chemical (COD, redox potential and dissolved oxygen), physical (settleable solids, insolubles and colour intensity) and biological methods (yeasts, aerobic and anaerobic bacteria, bacterial spores and moulds). After one hour of treatment, a strong 4 logs reduction was achieved for the anaerobic sulphate reducing bacteria and for the yeastsa 3 logs reduction for the aerobic bacteriaand a 1.3 logs reduction for the heat resistant bacterial spores. A 22% reduction in COD and an increase in the redox potential (37%) were observed. Sediments were reduced by 50% and the insoluble particles by 67%. For bacterial destruction in real industrial process waters, the rotation generator of supercavitation spent 4 times less electrical energy in comparison to the previously published cavitation treatments inside the Venturi constriction design

Removal of bacteria Legionella pneumophila, Escherichia coli, and Bacillus subtilis by (super)cavitation

In sufficient concentrations, the pathogenic bacteria L. pneumophila can cause a respiratory illness that is known as the "Legionnaires" disease. Moreover, toxic Shiga strains of bacteria E. coli can cause life-threatening hemolytic-uremic syndrome. Because of the recent restrictions imposed on the usage of chlorine, outbreaks of these two bacterial species have become more common. In this study we have developed a novel rotation generator and its effectiveness against bacteria Legionella pneumophila and Escherichia coli was tested for various types of hydrodynamic cavitation (attached steady cavitation, developed unsteady cavitation and supercavitation). The results show that the supercavitation was the only effective form of cavitation. It enabled more than 3 logs reductions for both bacterial species and was also effective against a more persistent Gram positive bacteria, B. subtilis. The deactivation mechanism is at present unknown. It is proposed that when bacterial cells enter a supercavitation cavity, an immediate pressure drop occurs and this results in bursting of the cellular membrane. The new rotation generator that induced supercavitation proved to be economically and microbiologically far more effective than the classical Venturi section (super)cavitation