Fermentation, Volume 4, Issue 2 (June 2018) – 28 articles

Τable olive is one of the main fermented vegetable worldwide and can be processed as treated or natural product. Lactic Acid Bacteria (LAB) are responsible for the fermentation of treated olives. The aim of this work was to study the technological characteristics and the potential probiotic properties of LAB isolated from Cypriot green table olives. This is the first comprehensive report on the isolation and characterization of LAB isolates retrieved from Cypriot green table olives. From a collection of 92 isolates from spontaneously fermenting green olives, 64 g positive isolates were firstly identified to genus level using biochemical tests, and secondly to species level using multiplex species specific polymerase chain reaction (PCR) amplifications of the sodA gene. Moreover, each of our isolates were tested for their technological and probiotics properties, as well as for their safety characteristics, using biochemical and molecular methods, in order to be used as starter cultures. Finally, to discriminate the most promising isolates on the base of their technological and probiotics properties, Principal component analysis was used. All the isolates were identified as Enteroccocus faecium, having interesting technological properties, while pathogenicity determinants were absent. Principal component analysis showed that some isolates had a combination of the tested parameters. These findings demonstrate that enteroccoci from Cypriot table olives should be considered as a new source of potential starter cultures for fermented products, having possibly promising technological and probiotic attributes. Full article

Transcription factors are key regulatory proteins in all living beings. In fungi, transcription factors include either broad-domain regulatory proteins that affect the expression of many genes involved in biosynthetic processes, or proteins encoded by cluster-associated (also called pathway-specific) regulatory genes. Belonging to the most interesting transcription factors in fungi are binuclear zinc finger proteins. In addition to the transcription factors in the strict sense, other proteins play a very important role in the expression of genes for primary and secondary metabolism in fungi, such as winged helix regulators, the LaeA protein and the velvet complex. LaeA appears to be involved in heterochromatin reorganization, and the velvet complex proteins, which are nuclear factors that associate with LaeA, also have a determining role in both differentiation (sporulation) and secondary metabolite biosynthesis. The genes involved in the biosynthesis of β-lactam antibiotics are well known and serve as an excellent model to understand the transcriptional control of genes involved in the biosynthesis of secondary metabolites. Interaction between different regulatory proteins in the promoter regions may represent a cross-talk regulation between different gene clusters. Full article

Cyanobacteria and microalgae have been cultivated only for a limited number of bioactive compounds or biotechnological applications such as for carotenoids; essential omega-3 fatty acids; phycobilipigments; live cells, unprocessed or minimally processed complete biomass as aqua feed, animal feed and human health supplements as rich sources of proteins, carbohydrates, pigments, vitamins and minerals. However, cyanobacteria and microalgae have been reported through several research investigations as a potential source for various bioactive molecules with marketable nutraceutical and pharmaceutical properties. Therefore, more cultivation of cyanobacteria and microalgae species are waiting for new biotechnological applications. At present, the global demand for microalgal applications is focused on biofuels including biodiesel and bioethanol apart from a handful (mentioned above) of bioactive compounds which are mostly used as nutraceuticals. Thus, microalgal biorefinery is growing rapidly for multiple commodities production from both conventional and photobioreactor-based cultivation for biomass feedstocks for various biotechnological applications. This review presents the cultivation aspects of selected cyanobacteria and microalgae for commercial purposes. Full article

High initial glucose concentrations may inhibit glucose utilization and decrease ethanol fermentation efficiency. To minimize substrate inhibition, the effects of feeding yeast with different glucose concentrations on the ethanol production by batch and fed-batch cultures in a 5-L fermentor were investigated. When a batch culture system with Saccharomyces cerevisiae was used for ethanol fermentation with glucose concentrations ranging 10–260 g/L, as a result, 0.2–7.0 g/L biomass and 5.1–115.0 g/L ethanol were obtained. However, substrate inhibition was observed with the initial glucose concentrations greater than 200 g/L in the fermentative media. When a fed-batch culture system (an initial glucose concentration of 180 g/L and total glucose concentration of 260 g/L) was performed, the maximum ethanol concentrations and ethanol yield were significantly higher than those of the batch cultures. The cell biomass, maximum ethanol concentration, and ethanol yields for the fed-batch fermentation cultures were 8.3 g/L, 130.1 g/L and 51% (100% of the theoretical value), respectively. The results indicated that high ethanol concentration and ethanol yield could be achieved by the fed-batch cultures with total glucose concentrations up to 260 g/L. Full article

Caulobacter crescentus is a gram-negative bacterium that can utilize xylose as a substrate using the Weimberg pathway, which converts xylose to α-ketoglutarate in five steps without carbon loss. This is an interesting pathway for heterologous expression in other organisms in order to enable xylose utilization in biorefinery processes. C. crescentus was grown on xylose, arabinose and glucose, and maximum specific growth rates determined for the three substrates were 0.11 h⁻¹, 0.05 h⁻¹, and 0.15 h⁻¹ respectively. Growth was found to be significantly inhibited at sugar concentration of 20 g L⁻¹, shown primarily by an increased lag phase. Enzyme activity assays showed that the Weimberg pathway was active in cells grown, not only on xylose but also on arabinose. No activity was found for growth on glucose. Furthermore, substantial amounts of α-ketoglutarate—up to a yield of 0.4 g g⁻¹—was excreted during growth on xylose, but no other extracellular intermediates in the Weimberg pathway were detected during growth on xylose. Apparently, C. crescentus is not well adapted for efficient growth on high xylose levels, and responds by an extended lag phase and secretion of α-ketoglutarate. Full article

Clinical needs for novel antifungal agents have increased due to the increase of people with a compromised immune system, the appearance of resistant fungi, and infections by unusual yeasts. The search for new molecular targets for antifungals has generated considerable research, especially using modern omics methods (genomics, genome-wide collections of mutants, and proteomics) and bioinformatics approaches. Recently, micro- and nanoscale approaches have been introduced in antifungal drug discovery. Microfluidic platforms have been developed, since they have a number of advantages compared to traditional multiwell-plate screening, such as low reagent consumption, the manipulation of a large number of cells simultaneously and independently, and ease of integrating numerous analytical standard operations and large-scale integration. Automated high-throughput antifungal drug screening is achievable by massive parallel processing. Various microfluidic antimicrobial susceptibility testing (AST) methods have been developed, since they can provide the result in a short time-frame, which is necessary for personalized medicine in the clinic. New nanosensors, based on detecting the nanomotions of cells, have been developed to further decrease the time to test antifungal susceptibility to a few minutes. Finally, nanoparticles (especially, silver nanoparticles) that demonstrated antifungal activity are reviewed. Full article

In food processing, temperature is a key parameter affecting product quality and energy consumption. The efficiency of temperature control depends on the data provided by sensors installed in the production device. In the wine industry, temperature sensor placement inside the tanks is usually predetermined by the tank manufacturers. Winemakers rely on these measurements and configure their temperature control accordingly, not knowing whether the monitored values really represent the wine’s bulk temperature. To address this problem, we developed an end-user software which 1. allows winemakers or tank manufacturers to identify optimal sensor locations for customizable tank geometries and 2. allows for comparisons between actual and optimal sensor placements. The analysis is based on numerical simulations of a user-defined cooling scenario. Case studies involving two different tanks showed good agreement between experimental data and simulations. Implemented based on the scientific Linux operating system gmlinux, the application solely relies on open-source software that is available free of charge. Full article

Development of a counter-selection method for phenylalanine auxotrophy could be a useful tool in the repertoire of yeast genetics. Fluorinated and sulfurated precursors of phenylalanine were tested for toxicity in Saccharomyces cerevisiae. One such precursor, 4-fluorophenylpyruvate (FPP), was found to be toxic to several strains from the Saccharomyces and Candida genera. Toxicity was partially dependent on ARO8 and ARO9, and correlated with a strain’s ability to convert FPP into 4-fluorophenylalanine (FPA). Thus, strains with deletions in ARO8 and ARO9, having a mild phenylalanine auxotrophy, could be separated from a culture of wild-type strains using FPP. Tetrad analysis suggests FPP resistance in one strain is due to two genes. Strains resistant to FPA have previously been shown to exhibit increased phenylethanol production. However, FPP resistant isolates did not follow this trend. These results suggest that FPP could effectively be used for counter-selection but not for enhanced phenylethanol production. Full article

To better understand the effects of host selection on gut acetogens and their potential role in syngas fermentation, the composition and hydrogenotrophic features of acetogen populations in cow and sheep rumens, rabbit ceca, and horse feces were studied. The acetogens detected in horses and rabbits were more phylogenetically diverse than those in cows and sheep, suggesting that the host species plays an important role in shaping gut acetogen populations. Acetogen enrichments from these animals presented good capacities to use hydrogen, with acetate as the major end product. Minor propionate, butyrate, and isovalerate were also produced. During 48 h of incubation, acetogen enrichments from horse consumed 4.75 moles of H₂ to every 1 mole of acetate—significantly lower than rabbits, cows, and sheep (5.17, 5.53, and 5.23 moles, respectively) (p < 0.05)—and produced significantly more butyrate (p < 0.05). Enrichments from cows and sheep produced significantly higher amounts of propionate when compared to rabbits or horses (p < 0.05); enrichments from sheep produced the highest amounts of isovalerate (p < 0.05). These short chain fatty acids are important precursors for the synthesis of biofuel products, suggesting that gut contents of herbivores may be promising sources for harvesting functional acetogens for biofuel production. Full article

Red wines ferment in contact with skins to extract polyphenols and anthocyanins that help build, establish, and stabilize color. Concentration and composition vary among genera, species, and cultivars. For this study, 11 grapes representing Vitis vinifera (Cabernet Sauvignon, Merlot, Cabernet Franc, Barbera, Syrah, Petite Sirah, Mourvedre), Vitis labrusca (Concord), Muscadinia rotundifolia (Noble), and French-American hybrids (Marquette, Chambourcin) were selected. All cultivars were fermented on skins while color extraction was monitored daily. Each grape was also extracted using six different methods (microwave, and ultrasound assisted, Glorie procedure, ITV Standard (Institut Technique de la Vigne et du Vin), AWRI method (Australian Wine and Research Institute), solvent extraction of skins) and compared to color characteristics of the wines produced by fermentation. Results show that the extraction pattern varies among cultivars. Post-fermentation maceration, pressing, and sulfur dioxide addition lead to color loss up to 68 percent of the original maximum with the highest loss for native American grapes and hybrid varieties. Extraction procedures over-estimate color in the finished wine but are more accurate if compared to peak extraction levels during fermentation. Color loss and suitability of different extraction procedures to predict color characteristics of fermented wine strongly depend on the complexity of the anthocyanin spectrum and therefore the cultivar used. Full article

The quality of beer relies on the activity of fermenting yeasts, not only for their good fermentation yield-efficiency, but also for their influence on beer aroma, since most of the aromatic compounds are intermediate metabolites and by-products of yeast metabolism. Beer production is a traditional process, in which Saccharomyces is the sole microbial component, and any deviation is considered a flaw. However, nowadays the brewing sector is faced with an increasing demand for innovative products, and it is diffusing the use of uncharacterized autochthonous starter cultures, spontaneous fermentation, or non-Saccharomyces starters, which leads to the production of distinctive and unusual products. Attempts to obtain products with more complex sensory characteristics have led one to prospect for non-conventional yeasts, i.e., non-Saccharomyces yeasts. These generally are characterized by low fermentation yields and are more sensitive to ethanol stress, but they provide a distinctive aroma and flavor. Furthermore, non-conventional yeasts can be used for the production of low-alcohol/non-alcoholic and light beers. This review aims to present the main findings about the role of traditional and non-conventional yeasts in brewing, demonstrating the wide choice of available yeasts, which represents a new biotechnological approach with which to target the characteristics of beer and to produce different or even totally new beer styles. Full article

Verdicchio, Passerina and Pecorino are native grape cultivars of the Marche region, cultivated in winemaking area of Ascoli Piceno, in central Italy. In particular, Passerina and Pecorino varieties have been abandoned and forgotten for a long time and only in recent years are rediscovered and appreciated. Here, two indigenous yeasts, isolated from grapes of Verdicchio and Pecorino varieties and identified as Saccharomyces cerevisiae, were evaluated and compared with commercial starters cultures widely used for the vinification of Piceno DOC (Denominazione Origine Controllata) area at industrial scale. A polyphasic approach, including yeast genotyping, phenotypic traits evaluation and fermentative performance in natural grape juice, was applied to evaluate the fitness of strains. Using interdelta primers, the two selected cultures showed a unique profile while the results of microvinifications showed that both indigenous strains exhibited good enological parameters and fermentative aptitude comparable with that shown by commercial strains used as controls. The profile of volatile compounds of wines of indigenous strains was characterized by a significant high production of isoamyl acetate and ethyl esters at 22 °C and phenyl ethyl acetate at 16 °C. Overall results indicate that the two indigenous selected yeasts showed a genetic and phenotypic specificity and they could be profitably used to characterize the Piceno DOC area wines. Full article

The world market of citric acid (CA) is one of the largest and fastest growing markets in the biotechnological industry. Microbiological processes for CA production have usually used the mycelial fungi Aspergillus niger as a producer and molasses as a carbon source. In this paper, we propose methods for CA production from renewable carbon substrates (rapeseed oil, glucose, glycerol, ethanol, glycerol-containing waste of biodiesel industry and glucose-containing aspen waste) by the mutant strain Yarrowia lipolytica NG40/UV5. It was revealed that Y. lipolytica grew and synthesized CA using all tested raw materials. The obtained results are sufficient for industrial use of most of the raw materials studied for CA production. Using rapeseed oil, ethanol and raw glycerol (which is an important feedstock of biodiesel production), a high CA production (100–140 g L⁻¹) was achieved. Full article

Insoluble fiber (IF) recovered from the enzyme-assisted aqueous extraction process (EAEP) of soybeans is a fraction rich in carbohydrates and proteins. It can be used to enhance ethanol production in an integrated corn-soy biorefinery, which combines EAEP with traditional corn-based ethanol processing. The present study evaluated IF as a substrate for ethanol production. The effects of treatment of IF (soaking in aqueous ammonia (SAA), liquid hot water (LHW), and enzymatic hydrolysis), primarily simultaneous saccharification and co-fermentation (SSCF), as well as scaling up (250 mL to 60 L) on ethanol production from IF alone or a corn and IF slurry were investigated. Enzymatic hydrolysis (pectinase, cellulase, and xylanase, each added at 5% soy solids during simultaneous saccharification and fermentation/SSCF) was the best treatment to maximize ethanol production from IF. Ethanol yield almost doubled when SSCF of IF was performed with Saccharomyces cerevisiae and Escherichia coli KO11. Addition of IF in dry-grind corn fermentation increased the ethanol production rate (~31%), but low ethanol tolerance of E. coli KO11 was a limiting factor for employing SSCF in combination corn and IF fermentation. Nonlinear Monod modeling accurately predicted the effect of ethanol concentration on E. coli KO11 growth kinetics by Hanes-Woolf linearization. Collectively, the results from this study suggest a potential of IF as a substrate, alone or in dry-grind corn fermentation, where it enhances the ethanol production rate. IF can be incorporated in the current bioethanol industry with no added capital investment, except enzymes. Full article

Vast amounts of information can be obtained by systematic explorations of synergy between phytochemicals and probiotics, which is required for the development of non-dairy probiotic products, globally. Evidence confirms that the same probiotic strain can have different efficiencies depending on the food matrix. One such functional property, viz., antipathogenicity of the probiotic strain against Shigella was investigated in this study. The potential of two fruit based (apple and sea buckthorn) beverage matrices fortified with Lactobacillus rhamnosus GG (ATCC 53103), against outbreak-causing serotypes of Shigella dysenteriae (ATCC 29026) and Shigella flexneri (ATCC 12022) was evaluated. The originality of this study lies in the fact that the functionality assessment was performed with a more realistic approach under storage conditions from 0–14 days at 4 °C. The finding confirms that Lactobacillus rhamnosus GG (LGG) differs in its potential depending on beverage matrices. Principal Component Analysis (PCA) clustered the matrices based on their pathogen clearance. LGG fortified sea buckthorn beverage matrix showed 99% clearance of S. dysenteriae within the first hour compared to 11% in apple beverage matrix. Interestingly, S. flexneri showed more resistance and was cleared (99%) in the LGG fortified sea buckthorn beverage matrix within three hours compared to 5.6% in apple matrix. Full article

The increasing scarcity of fossil raw materials, together with the need to develop new processes and technology based on renewable sources, and the need to dispose of an increasing amount of biomass-derived waste, have boosted the concept of biorefineries. Both 1G and 2G biorefineries are focused on the obtention of biofuels, chemicals, materials, food and feed from biomass, a renewable resource. Fumaric acid, and most compounds involved in the Kreb cycle, are considered key platform chemicals, not only for being acidulants and additives in the food industry, but also for their prospective use as monomers. This review is focused on the biotechnological processes based on fungi, mainly of the Rhizopus genus, whose main product is fumaric acid, on the process conditions, the bioreactors and modes of operation and on the purification of the acid once it is produced. Full article

Vineyards in Nemea, the most important viticultural zone in Greece, were surveyed for indigenous non-Saccharomyces (NS) yeasts of enological potential. NS populations were isolated from the final stage of alcoholic fermentation and identified by a range of molecular methods. The enological profiles of Hanseniaspora guilliermondii, H. osmophila, Lachancea thermotolerans, Starmerella bacillaris and Torulaspora delbrueckii strains were evaluated. Significant interspecies variation was observed in fermentation kinetics. H. osmophila and T. delbrueckii showed the highest capacity for prompt initiation of fermentation, while S. bacillaris achieved a higher fermentation rate in the second half of the process. Significant differences were also observed in the chemical parameters of NS strains. S. bacillaris SbS42 and T. delbrueckii TdS45 were further evaluated in mixed-culture fermentations with Saccharomyces cerevisiae. NS strains achieved lower population densities than S. cerevisiae. SbS42 exhibited a higher death rate than TdS45. The chemical profiles of different ferments were separated by principal component analysis (PCA). Both NS strains were associated with lower levels of ethanol, when compared to single S. cerevisiae inoculation. TdS45 increased the ethyl acetate levels, while SbS42 caused a different production pattern of higher alcohols. This is the first report to explore the enological potential of NS wine yeast populations from Nemea. Based on prominent enological traits identified, the selected S. bacillaris and T. delbrueckii strains may be further exploited as co-culture starters for improving the quality and enhancing the regional character of local wines. Full article

Ever since plant diseases began causing losses in viticulture, the control of phytopathogenic fungi has become of vital interest for winemakers. The occurrence of novel pests, fungicide resistance, and changed consumer expectations have led to an enormous demand for novel plant protection strategies. As part of integrated protection measures, antagonistic microorganisms have been investigated to a large extent. Such microorganisms can be applied not only in conventional, but also in organic farming as biological control agents (BCA). Particularly, yeasts were found to be interesting candidates for the development of BCA. Many of these eukaryotic microorganisms are found as part of the phylloplane microflora. In this study, we assessed a set of 38 yeast isolates from different habitats, including the guts of termites, for inhibitory effects against some phytopathogenic fungi that have received less attention in earlier studies. The majority of yeasts were found to interfere with fungi infecting grapevine (Eutypa lata, Botrytis cinerea, and Roesleria subterranea), stone fruits (Monilinia fructicola), or rice (Magnaporte oryzae), as well in vitro and in model experiment on fruits. Although most yeast strains secreted glycoside hydrolases and proteases, attempts to demonstrate direct antagonistic activities of lytic enzymes failed. However, in culture filtrates of the termite yeast Papiliotrema odontotermitis OO5, a low molecular thermostable antagonistic factor was detected. Iron depletion as a BCA mechanism was confirmed for strains of Metschnikowia pulcherrima but not for other yeasts. Full article

Polyhydroxyalkanoates (PHA) are microbial biopolyesters utilized as “green plastics”. Their production under controlled conditions resorts to bioreactors operated in different modes. Because PHA biosynthesis constitutes a multiphase process, both feeding strategy and bioreactor operation mode need smart adaptation. Traditional PHA production setups based on batch, repeated batch, fed-batch or cyclic fed-batch processes are often limited in productivity, or display insufficient controllability of polyester composition. For highly diluted substrate streams like is the case of (agro) industrial waste streams, fed-batch enhanced by cell recycling has recently been reported as a viable tool to increase volumetric productivity. As an emerging trend, continuous fermentation processes in single-, two- and multi-stage setups are reported, which bring the kinetics of both microbial growth and PHA accumulation into agreement with process engineering and allow tailoring PHA’s molecular structure. Moreover, we currently witness an increasing number of CO₂-based PHA production processes using cyanobacteria; these light-driven processes resort to photobioreactors similar to those used for microalgae cultivation and can be operated both discontinuously and continuously. This development is parallel to the emerging use of methane and syngas as abundantly available gaseous substrates, which also calls for bioreactor systems with optimized gas transfer. The review sheds light on the challenges of diverse PHA production processes in different bioreactor types and operational regimes using miscellaneous microbial production strains such as extremophilic Archaea, chemoheterotrophic eubacteria and phototrophic cyanobacteria. Particular emphasis is dedicated to the limitations and promises of different bioreactor–strain combinations and to efforts devoted to upscaling these processes to industrially relevant scales. Full article

Sweet sorghum juice is a liquid sugar feedstock that can be produced in non-tropical climates. Utilization of sweet sorghum juice as a feedstock for the production of lysine was investigated utilizing the auxotrophic mutant Corynebacterium glutamicum ATCC 21513 in stirred tank bioreactors. The juice was found to have inadequate nutrients for growth of the auxotroph alone and was supplemented with two levels of yeast extract and peptone. The supplemented juice could support growth and produce lysine from the available sugars. No inhibitory effects of the juice were found on the growth of the organism. The lysine concentrations reach 28.8 g/L in the batch fermentations with complete utilization of the available sugars and a conversion efficiency of 0.23 g/g. Full article

Unlike most fermentation alcohol beverage production processes, brewers recycle their yeast. This is achieved by employing a yeast culture’s: flocculation, adhesion, sedimentation, flotation, and cropping characteristics. As a consequence of yeast recycling, the quality of the cropped yeast culture’s characteristics is critical. However, the other major function of brewer’s yeast is to metabolise wort into ethanol, carbon dioxide, glycerol, and other fermentation products, many of which contribute to beer’s overall flavour characteristics. This review will only focus on brewer’s yeast flocculation characteristics. Full article

Typically, probiotics are consumed in dairy based products such as yogurt. However, given the rise in various diet types, non-dairy alternatives have been developed, such as inoculating fruit juices with probiotics. Lactobacillus rhamnosus GR-1 is a probiotic strain exerting a number of human health benefits such as the prevention of urinary tract infections. Therefore, the objective of this study was to determine the viability of L. rhamnosus GR-1 in apple cider, orange, and grape juice when fortified with either 4% short chain or 4% long chain inulin fiber over 72 h of fermentation and 30 days of refrigerated storage. The secondary objective was to determine consumer acceptability of apple cider and orange juice samples using the hedonic scale. All of the fruit juice samples achieved a mean viable count of at least 10⁷ CFU/mL during 72 h of fermentation and 30 days of refrigerated storage. According to the sensory evaluation, which evaluated samples according to appearance, flavor, texture, and overall acceptability, apple cider juice with long chain inulin fiber proved to have the highest score for all characteristics except appearance. Therefore, this study indicated a potential for probiotic fruit juices as a valid alternative to dairy based probiotic products. Full article

Moderate wine consumption is associated with human health benefits (reduction of cardiovascular risk and neurodegenerative diseases, decrease of onset of certain cancers) attributed to a series of bioactive compounds, mainly polyphenols, with antioxidant power capable of counteracting the negative action of free radicals. Polyphenols are naturally present in the grapes, but an additional amount originates during winemaking. The aim of this work was to assess the ability of four commercial and two indigenous Saccharomyces cerevisiae strains to produce bioactive compounds (tyrosol, hydroxytyrosol, tryptophol, melatonin and glutathione) during alcoholic fermentation. In order to exclude the fraction of antioxidant compounds naturally occurring in grapes, the strains were inoculated in a synthetic must. At the end of fermentation the bioactive compounds were analysed by High-Performance Liquid Chromatography, while antioxidant activity was measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Moreover, freeze-dried samples, originating from the experimental wines, were used to perform ex-vivo assays on cultured cells (RAW 264.7 murine macrophages) with the aim to evaluate their antioxidant and anti-inflammatory activities. The results indicated that the production of the considered bioactive compounds is a strain-specific property; therefore, the different yeast strains utilized during fermentation have different capabilities to modify the antioxidant and anti-inflammatory properties of the wine. Full article

Microalgae cultivation is booming in agriculture, aquaculture, and bioenergy sectors. A wide range of bioactive compounds with attractive properties can be produced with microalgae, including pigments, vitamins, proteins, carbohydrates, and lipids. The biofuel yields from microalgae can exceed the yields obtained with energy crops by 10–100 times. Therefore, such cultivation is promising for the regulation of the biosynthesis of microalagae with phytohormones, which can enhance the production of high-valued bioproducts. This review reports the effect of auxins, abscisic acid, cytokinins, gibberellins, and ethylene on microalgal growth and metabolites, as well as the crosstalk of different phytohormones. The use of phytohormones is also promising because it can also reduce the inputs necessary to grow the selected microalgae and maximize the yields. Full article

The disposal of excess crude glycerol produced by the booming biodiesel industry and wastewater sludge solid waste has become a severe problem, and alternate routes of use and valorization of these waste byproducts are needed. The use of cheaply available wastewater sludge solids in fermentation media is very much desirable to reduce the cost of production. The strains of Yarrowia lipolytica can assimilate a wide array of waste substrates, such as crude glycerol, waste cooking oil, starch wastewater, and cellulosic. This study optimized the concentration of wastewater sludge solids (5–35 g/L) to be used with crude glycerol in fermentation media to produce microbial oil as feedstock for biodiesel production. The results indicated that 20 g/L of sludge solids with 40 g/L of crude glycerol resulted in highest lipid content of 29.35% in 96 h. Further, assuming wet extraction of lipids, it was found that at least 11.2% or higher lipid content is required for this process to have an overall positive net solid waste reduction. Insignificant inhibition was observed by the crude glycerol used in this study as compared to pure glycerol, which proves it to be an adequate source of carbon substrate for lipid production. Full article

The process by which beer is brewed has not changed significantly since its discovery thousands of years ago. Grain is malted, dried, crushed and mixed with hot water to produce wort. Yeast is added to the sweet, viscous wort, after which fermentation occurs. The biochemical events that occur during fermentation reflect the genotype of the yeast strain used, and its phenotypic expression is influenced by the composition of the wort and the conditions established in the fermenting vessel. Although wort is complex and not completely characterized, its content in amino acids indubitably affects the production of some minor metabolic products of fermentation which contribute to the flavour of beer. These metabolic products include higher alcohols, esters, carbonyls and sulfur-containing compounds. The formation of these products is comprehensively reviewed in this paper. Furthermore, the role of amino acids in the beer flavour, in particular their relationships with flavour active compounds, is discussed in light of recent data. Full article

Yeasts are ubiquitous microbes found in virtually all environments. Many yeast species can ferment sugar into ethanol and CO₂, and humans have taken advantage of these characteristics to produce fermented beverages for thousands of years. As a naturally abundant source of fermentable sugar, honey has had a central role in such fermentations since Neolithic times. However, as beverage fermentation has become industrialized, the processes have been streamlined, including the narrow and almost exclusive usage of yeasts in the genus Saccharomyces for fermentation. We set out to identify wild honey- or honey-bee-related yeasts that can be used in honey fermentation. Here, we isolated two strains of Torulaspora delbrueckii from the gut of a locally collected honey bee. Both strains were able to ferment honey sugar into mead but failed to metabolize more than a modest amount of wort sugar in trial beer fermentations. Further, the meads fermented by the T. delbrueckii strains displayed better sensory characteristics than mead fermented by a champagne yeast. The combination of T. delbrueckii and champagne yeast strains was also able to rapidly ferment honey at an industrial scale. Thus, wild yeasts represent a largely untapped reservoir for the introduction of desirable sensory characteristics in fermented beverages such as mead. Full article