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      Physiology, ecology and industrial applications of aroma formation in yeast

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          Abstract

          Yeast cells are often employed in industrial fermentation processes for their ability to efficiently convert relatively high concentrations of sugars into ethanol and carbon dioxide. Additionally, fermenting yeast cells produce a wide range of other compounds, including various higher alcohols, carbonyl compounds, phenolic compounds, fatty acid derivatives and sulfur compounds. Interestingly, many of these secondary metabolites are volatile and have pungent aromas that are often vital for product quality. In this review, we summarize the different biochemical pathways underlying aroma production in yeast as well as the relevance of these compounds for industrial applications and the factors that influence their production during fermentation. Additionally, we discuss the different physiological and ecological roles of aroma-active metabolites, including recent findings that point at their role as signaling molecules and attractants for insect vectors.

          Abstract

          This review explores the biochemical pathways leading to production of a wide array of aroma compounds, the various industrial applications that have been developed around use of aroma compounds, as well as the newly uncovered physiological and ecological roles the various compounds may play.

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          Most cited references 362

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          Inhibition of ethanol-producing yeast and bacteria by degradation products produced during pre-treatment of biomass.

          An overview of the different inhibitors formed by pre-treatment of lignocellulosic materials and their inhibition of ethanol production in yeast and bacteria is given. Different high temperature physical pre-treatment methods are available to render the carbohydrates in lignocellulose accessible for ethanol fermentation. The resulting hydrolyzsates contain substances inhibitory to fermentation-depending on both the raw material (biomass) and the pre-treatment applied. An overview of the inhibitory effect on ethanol production by yeast and bacteria is presented. Apart from furans formed by sugar degradation, phenol monomers from lignin degradation are important co-factors in hydrolysate inhibition, and inhibitory effects of these aromatic compounds on different ethanol producing microorganisms is reviewed. The furans and phenols generally inhibited growth and ethanol production rate (Q(EtOH)) but not the ethanol yields (Y(EtOH)) in Saccharomyces cerevisiae. Within the same phenol functional group (aldehyde, ketone, and acid) the inhibition of volumetric ethanol productivity was found to depend on the amount of methoxyl substituents and hence hydrophobicity (log P). Many pentose-utilizing strains Escherichia coli, Pichia stipititis, and Zymomonas mobilis produce ethanol in concentrated hemicellulose liquors but detoxification by overliming is needed. Thermoanaerobacter mathranii A3M3 can grow on pentoses and produce ethanol in hydrolysate without any need for detoxification.
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            Odor coding in the Drosophila antenna.

            Odor coding in the Drosophila antenna is examined by a functional analysis of individual olfactory receptor neurons (ORNs) in vivo. Sixteen distinct classes of ORNs, each with a unique response spectrum to a panel of 47 diverse odors, are identified by extracellular recordings. ORNs exhibit multiple modes of response dynamics: an individual neuron can show either excitatory or inhibitory responses, and can exhibit different modes of termination kinetics, when stimulated with different odors. The 16 ORN classes are combined in stereotyped configurations within seven functional types of basiconic sensilla. One sensillum type contains four ORNs and the others contain two neurons, combined according to a strict pairing rule. We provide a functional map of ORNs, showing that each ORN class is restricted to a particular spatial domain on the antennal surface.
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              The natural history of Caenorhabditis elegans.

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                Author and article information

                Journal
                FEMS Microbiol Rev
                FEMS Microbiol. Rev
                femsre
                FEMS Microbiology Reviews
                Oxford University Press
                0168-6445
                1574-6976
                17 August 2017
                August 2017
                17 August 2017
                : 41
                : Suppl 1
                : S95-S128
                Affiliations
                [1 ]Laboratory for Genetics and Genomics, Centre of Microbial and Plant Genetics (CMPG), KU Leuven, Gaston Geenslaan 1, B-3001 Leuven, Belgium
                [2 ]Laboratory for Systems Biology, VIB Center for Microbiology, Bio-Incubator, Gaston Geenslaan 1, 3001 Leuven, Belgium
                [3 ]Laboratory for Process Microbial Ecology and Bioinspirational Management (PME&BIM), Department of Microbial and Molecular Systems, KU Leuven, Campus De Nayer, Fortsesteenweg 30A B-2860 Sint-Katelijne Waver, Belgium
                Author notes
                Corresponding author: Centre of Microbial and Plant Genetics (CMPG), KU Leuven, VIB Center for Microbiology, Bio-Incubator, Gaston Geenslaan 1, B-3001 Leuven, Belgium. Tel: +32 (0)16 75 1390; E-mail: kevin.verstrepen@ 123456kuleuven.vib.be
                Article
                fux031
                10.1093/femsre/fux031
                5916228
                28830094
                © FEMS 2017.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                Page count
                Pages: 34
                Product
                Funding
                Funded by: ERC 10.13039/501100000781
                Award ID: CoG682009
                Funded by: HFSP 10.13039/100004412
                Award ID: RGP0050/2013
                Categories
                Review Article

                Microbiology & Virology

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