Comparative study of the biochemical changes and volatile compound formations during the production of novel whey-based kefir beverages and traditional milk kefir

Cheese whey (CW) and deproteinised cheese whey (DCW) were investigated for their suitability as novel substrates for the production of kefir-like beverages. Lactose consumption, ethanol production, as well as organic acids and volatile compounds formation, were determined during CW and DCW fermentation by kefir grains and compared with values obtained during the production of traditional milk kefir. The results showed that kefir grains were able to utilise lactose from CW and DCW and produce similar amounts of ethanol (7.8–8.3 g/l), lactic acid (5.0 g/l) and acetic acid (0.7 g/l) to those obtained during milk fermentation. In addition, the concentration of higher alcohols (2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-methyl-1-propanol, and 1-propanol), ester (ethyl acetate) and aldehyde (acetaldehyde) in cheese whey-based kefir and milk kefir beverages were also produced in similar amounts. Cheese whey and deproteinised cheese whey may therefore serve as substrates for the production of kefir-like beverages similar to milk kefir.The authors acknowledge the financial support from Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES), CAPES-GRICES and Lactogal for supplying cheese whey powder

Pentanol isomer synthesis in engineered microorganisms

Pentanol isomers such as 2-methyl-1-butanol and 3-methyl-1-butanol are a useful class of chemicals with a potential application as biofuels. They are found as natural by-products of microbial fermentations from amino acid substrates. However, the production titer and yield of the natural processes are too low to be considered for practical applications. Through metabolic engineering, microbial strains for the production of these isomers have been developed, as well as that for 1-pentanol and pentenol. Although the current production levels are still too low for immediate industrial applications, the approach holds significant promise for major breakthroughs in production efficiency

Yeast : the soul of beer’s aroma—a review of flavour-active esters and higher alcohols produced by the brewing yeast

Among the most important factors influencing beer quality is the presence of well-adjusted amounts of higher alcohols and esters. Thus, a heavy body of literature focuses on these substances and on the parameters influencing their production by the brewing yeast. Additionally, the complex metabolic pathways involved in their synthesis require special attention. More than a century of data, mainly in genetic and proteomic fields, has built up enough information to describe in detail each step in the pathway for the synthesis of higher alcohols and their esters, but there is still place for more. Higher alcohols are formed either by anabolism or catabolism (Ehrlich pathway) of amino acids. Esters are formed by enzymatic condensation of organic acids and alcohols. The current paper reviews the up-to-date knowledge in the pathways involving the synthesis of higher alcohols and esters by brewing yeasts. Fermentation parameters affecting yeast response during biosynthesis of these aromatic substances are also fully reviewed.Eduardo Pires gratefully acknowledges the Fundacao para a Ciencia e a Tecnologia (FCT, Portugal) for the PhD fellowship support (SFRH/BD/61777/2009). The financial contributions of the EU FP7 project Ecoefficient Biodegradable Composite Advanced Packaging (EcoBioCAP, grant agreement no. 265669) as well as of the Grant Agency of the Czech Republic (project GACR P503/12/1424) are also gratefully acknowledged. The authors thank the Ministry of Education, Youth and Sports of the Czech Republic (MSM 6046137305) for their financial support

Ca isotope fingerprints of early crust-mantle evolution

Among the most important factors influencing beer quality is the presence of well-adjusted amounts of higher alcohols and esters; as well as the successful reduction of undesirable by-products such as diacetyl. While higher alcohols and esters contribute rather positively to the beer aroma, diacetyl is mostly unwelcome for beer types with lighter taste. Thus, the complex metabolic pathways in yeast responsible for the synthesis of both pleasant and unpleasant by-products of fermentation were given special attention in this last chapter

Yeast genomics on food flavours

The appearance and concentration of the fusel alcohol 3-methyl-1-butanol is important for the flavour of fermented foods. 3-Methyl-1-butanol is formed by yeast during the conversion of L-leucine. Identification of the enzymes and genes involved in the formation of 3-methyl-1-butanol is a major prerequisite to optimize and control the final food flavour. To identify genes involved in this metabolic route, cDNA microarrays were carried out to study yeast gene expression genome-wide. Crosshybridisation with probes from the ‘soy-yeast’ Zygosaccharomycs rouxii, responsible for flavour formation during soysauce fermentation, on Saccharomyces cerevisiae cDNA microarrays, revealed the presence of several Zr genes. However, this group (115 out of ~5000 Zr ORFs) was too small for studying the 3-methyl-1-butanol pathway. Conversely, arraydata of S. cerevisiae resulted in several clues concerning flavour formation. For example BAT2, encoding an enzyme responsible for the first step in the L-leucine breakdown, was strongly expressed in yeast grown on ethanol. In addition to the transcription data, deletion studies revealed that 3-methyl-1-butanol production stopped in S. cerevisiae lacking BAT2, indicating a major role for Bat2p. Furthermore, the microarrays showed that genes involved in branched chain amino acid biosynthesis, but also genes of amine biosynthesis, caboxylic acid- and organic acid metabolism, were altered in expression level. Interestingly, non-branched chain amino acids: aromatic amino acids, serine, arginine, glutamine, homoserine and lycine, superficially unrelated with branched chain amino acids, were also effected when L-leucine was used as nitrogen source. A subgroup of genes was significantly present, which contained regulatory elements for GCN4 and GLN3. GCN4 and GLN3 encoding transcription factors involved in nitrogen metabolism. BAP2 and BAP3, encoding permeases necessary for the uptake of L-leucine, PDX1 and YDL080c, encoding decarboxylases for 4-methyl-2-oxopentanoate and ADH3, ADH5, YMR 318c and YCR105w, encoding alcohol dehydrogenases were also upregulated in S. cerevisiae. Concerning flavour formation from L-leucine, besides 3-methyl-1-butanol, also 4-methyl-2-oxopentanoate, 3-methyl-2-oxobutanoic acid and 3-methylbutyric acid emerged. The combination of metabolite formation and the expression data from cDNA microarrays thus provides strong indications of the existence of alternative pathways. Automated microtiter plates (MTP) fermentations with a pH or/and NaCl range, revealed the optimal fusel alcohol formation at pH 3.0 without NaCl. In addition to this metabolic screening, cDNA microarrays were carried out and showed a total 747 genes, which displayed significantly altered transcription activity at pH 3.0, compared to the standard pH 5.0. Further investigation on this dataset, by the web-tool SGD Gene Ontology (GO) Term Finder revealed that a significant part of these genes had a function in the metabolism of nicotinamides, vitamins, fatty acids, glutamate or carboxylic acids. From this group, 11 genes, BNA6, BNA2, BNA4, BNA3, YOR356W, RPE1, MDH3, CIT1, CIT2, KGD1 and KGD2, were appointed as promising targets for the development of improved production strains, based on their altered gene expression at pH 3.0 and literature research. Further experiments will establish the weight of these identified genes on the final taste of fermented foods

Primary Epstein-Barr virus infection with neurological complications

Item does not contain fulltextSeveral case studies have reported on neurological complications caused by a primary Epstein-Barr virus (EBV) infection. We aimed to investigate the viral loads and the clinical and inflammatory characteristics of this disease entity. We evaluated all 84 cases in which the EBV polymerase chain reaction test (PCR) was requested on cerebrospinal fluid (CSF) for the period 2003-2008. Fourteen patients with proven neuroborreliosis served as the control group. Nine patients were diagnosed with a primary EBV infection and neurological symptoms (median age 36 y; 4 male). Viral DNA copies in CSF were detected by PCR in 7 of 9 patients. The presenting symptoms were meningeal signs, epileptic insults, polyradiculomyelitis, polyradiculitis, and/or sudden cognitive disorders. All EBV cases had a pleocytosis with significantly increased mononuclear leukocytes as compared to the neuroborreliosis group (median 99% interquartile range (96-100%) versus 90% (86-97%). In cases with a primary EBV infection, viral loads ranged from 43 to 3202 copies/ml in CSF and from 61 to 15,595 copies/ml in serum. Seventy-eight percent of the cases had a positive PCR on CSF. This study provides criteria for diagnosing neurological disease during primary EBV infection. Primary EBV infections in immune competent persons can cause a broad range of neurological symptoms, with lymphocytic and monocytic inflammation both in blood and CSF

Genome-wide transcription survey on flavour production in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae is widely used as aroma producer in the preparation of fermented foods and beverages. During food fermentations, secondary metabolites like 3-methyl-1-butanol, 4-methyl-2-oxopentanoate, 3-methyl-2-oxobutanoate and 3-methylbutyrate emerge. These four compounds have a major influence on the final taste of fermented foods. Their presence is influenced by the availability of free branched chained amino acids (BCAA). To study the underlying molecular mechanism of the formation of these compounds, we performed genome-wide transcription analyses with cDNA microarrays. The expression profile of yeast during flavour formation, when cultivated on L-leucine, was compared to the expression profile of cells cultivated on ammonia. In addition, the expression profiles of cells cultivated in a batch culture were compared to cells cultivated under continuous growth conditions. Genome-wide gene analysis of these samples revealed a group of 117 genes, which w! ere more than two-fold up- or down-regulated and significantly altered in gene expression (P < 0.001) under both cultivation conditions. This group included genes encoding enzymes of different amino acid metabolism pathways. The group of the BCAA metabolism was not significantly altered in gene expression. Genes identified with altered expression levels, in only batch or continuous culture fermentions, represented functional groups concerning energy, protein fate, cell cycle and DNA processing. Furthermore, clustering of genome-wide data revealed that the type of cultivation overruled the differences in N-source in the gene-expression profiles. This observation emphasizes the importance of sample history in gene expression analysis.