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Influence of Kazachstania spp. on the chemical and sensory profile of red wines
No full textWe report the fermentative traits of two Kazachstania species (K. aerobia and K. servazzii) in non-sterile red wine and the resulting chemical and sensory properties. This builds on our previous work which revealed that Kazachstania spp. increased acetate esters in sterilised white wine. In this study Kazachstania spp. were initially evaluated in laboratory-scale fermentations (500 mL) in Merlot must to assess whether similar increases in chemical/volatile compounds would occur. The impact of malolactic fermentation (MLF) by Oenococcus oeni (VP41) on aroma composition was considered and found to reduce ester profiles in Merlot wines. The sensory implications of sequential inoculation with Kazachstania spp., followed by Saccharomyces cerevisiae, were then evaluated in small-lot fermentations (7 kg) of Shiraz must. Fungal diversity was monitored during early fermentation stages and was influenced by the early implantation of Kazachstania spp., followed by the dominance of S. cerevisiae. The effect of MLF in Shiraz wines was inconclusive due to high ethanol levels providing an inhospitable environment for lactic acid bacteria. When compared to S. cerevisiae alone, Kazachstania spp. significantly increased acetate esters, particularly phenylethyl acetate and isoamyl acetate, in both Merlot and Shiraz. The Shiraz wines fermented with Kazachstania spp. had higher jammy and red fruit aroma/flavour compared to S. cerevisiae (monoculture) wines. No influence was observed on colour one-year post-bottling. Results from this study show the contribution of Kazachstania spp. to the aroma profile of red wines and demonstrate their potential as starter cultures for improving the aromatic complexity of wines.</p
Genomic analysis of Kazachstania aerobia and Kazachstania servazzii reveals duplication of genes related to acetate ester production
No full textKazachstania aerobia and Kazachstania servazzii can affect wine aroma by increasing acetate ester concentrations, most remarkably phenylethyl acetate and isoamyl acetate. The genetic basis of this is unknown, there being little to no sequence data available on the genome architecture. We report for the first time the near-complete genome sequence of the two species using long-read (PacBio) sequencing (K. aerobia 20 contigs, one scaffold; and K. servazzii 22 contigs, one scaffold). The annotated genomes of K. aerobia (12.5 Mb) and K. servazzii (12.3 Mb) were compared to Saccharomyces cerevisiae genomes (laboratory strain S288C and wine strain EC1118). Whilst a comparison of the two Kazachstania spp. genomes revealed few differences between them, divergence was evident in relation to the genes involved in ester biosynthesis, for which gene duplications or absences were apparent. The annotations of these genomes are valuable resources for future research into the evolutionary biology of Kazachstania and other yeast species (comparative genomics) as well as understanding the metabolic processes associated with alcoholic fermentation and the production of secondary 'aromatic' metabolites (transcriptomics, proteomics and metabolomics).</p
Evaluation of indigenous non-Saccharomyces yeasts isolated from a South Australian vineyard for their potential as wine starter cultures
No full textThe use of non-Saccharomyces yeast in conjunction with Saccharomyces cerevisiae in wine fermentation is a growing trend in the wine industry. Non-Saccharomyces, through their distinctive production of secondary metabolites, have the potential to positively contribute to wine sensory profile. To discover new candidate strains for development as starter cultures, indigenous non-Saccharomyces were isolated from un-inoculated fermenting Shiraz musts from a South Australian vineyard (McLaren Vale wine region) and characterised. Among the 77 isolates, 7 species belonging to 5 genera (Kazachstania, Aureobasidium, Meyerozyma, Wickerhamomyces and Torulaspora) were identified by sequencing the internal transcribed spacer regions of the 5.8S rRNA gene (ITS1-5.8S-ITS2 region). The indigenous isolates were evaluated for oenological properties, namely, ethanol tolerance, enzyme activity, and H2S production. To determine their potential industrial use as starter cultures, representative isolates of each species were assessed in a sterile chemically defined grape juice and Viognier grape juice to evaluate their contribution to fermentation kinetics and production of key metabolites, including volatile compounds.</p
Isolation and Characterisation of Yeasts with Biotechnological Properties
Get PDFThe primary aim of this research was to identify and characterise novel non-Saccharomyces
species from a vineyard and assess their potential use as starter cultures, either as an alternative
or complement to Saccharomyces cerevisiae. The first step towards this aim was to access the
vast potential of non-Saccharomyces yeasts to produce desired oenological characteristics
which may be absent in S. cerevisiae with a view towards their application in winemaking. In
particular, their ability to produce high levels of aroma compounds (esters, higher alcohols)
and secrete enzymes (β-glucosidases, esterases, lipases, proteases) releases aroma compounds
from odourless precursors to positively enhance the sensorial profile of wines. The 77 yeast
isolates previously isolated from a South Australian vineyard were identified by sequencing
the internal transcribed space regions of the 5.8S rRNA gene (ITS1-5.8S-ITS2) region. The
isolates consisted of 7 species belonging to 5 genera (Aureobasidium, Kazachstania,
Meyerozyma, Wickerhamomyces and Torulaspora). The indigenous isolates were evaluated for
oenological properties, specifically ethanol tolerance, enzymatic activities, and hydrogen
sulfide production.
To improve the overall wine aroma complexity, research has devised various techniques from
cultivation and harvesting (of grapes) to vinification. One such method is the use of mixed
starter cultures (non-Saccharomyces and S. cerevisiae) to impart distinctive aroma/flavour
profiles. Whilst commercial non-Saccharomyces belonging to Metschnikowia pulcherrima,
Lachancea thermotolerans and Torulaspora delbrueckii are available as commercial wine
starter cultures there is a diverse range of indigenous non-Saccharomyces unexplored. The next
step was to conduct fermentation trials with 17 representative strains from each species in
chemically defined grape juice media (CDGJM). None of the isolates could complete
fermentation (as monocultures) in CDGJM (200 g/L sugar), with T. delbrueckii isolates utilising sugar the fastest, following by Kazachstania aerobia, Kazachstania servazzii and
Wickerhamomyces anomalus. Based on their fermentation profile in CDGJM, 7 isolates were
selected for use in sequential fermentation with a commercial S. cerevisiae strain in sterile
Viognier juice to evaluate their contribution to fermentation kinetics and production of key
metabolites, including volatile compounds. These laboratory-scale fermentations showed that
species belonging to Kazachstania (K. aerobia and K. servazzii) produced wines with elevated
levels of phenylethyl alcohol and isoamyl alcohol, as well as their corresponding acetate esters.
The Kazachstania spp. sequential wines also reduced alcohol (ethanol), by ~1% (v/v)
compared to the S. cerevisiae control.
Because of this interesting result the fermentative efficiency of Kazachstania spp. in non-sterile
red musts (Merlot and Shiraz) was evaluated. Three isolates of Kazachstania spp. (2x K.
aerobia and 1x K. servazzii) were inoculated in sequential fermentations with S. cerevisiae. In
contrast to S. cerevisiae, Kazachstania spp. wines had significantly increased phenylethyl
acetate and isoamyl acetate in both Merlot and Shiraz, as well as increased glycerol
concentrations and decreased ethanol concentration (Merlot only, not in Shiraz due to the high
initial °Brix of Shiraz must). With respect to Shiraz wines, Kazachstania spp. treatments
enhanced the wine sensory appeal; the wines were perceived as ‘jammy’, ‘red fruit’ and higher
aroma intensity compared to S. cerevisiae control (‘cooked vegetable’, ‘earthy’, ‘forest floor’
and ‘savoury’).
In addition to the collection of 77 isolates, 5 isolates belonging to Hanseniaspora uvarum
isolated from a Victorian vineyard were included for characterisation. The effects of H. uvarum
on the terpene content of white wines were initially evaluated in Viognier, which was overall
lower in the sequential wines compared to the S. cerevisiae control. To further validate this phenomenon, tests were conducted in chemically defined grape juice medium spiked with
linalool, and two more aromatic varietals (Muscat and Riesling), which included uninoculated
treatments as negative controls. The results show that H. uvarum neither increased or reduced
the linalool concentrations, except in Riesling which had higher linalool concentration, but still
lower compared to the S. cerevisiae control. These findings suggest that the terpene content in
white wines could be matrix- and/or temperature-dependent.
As Kazachstania spp. consistently produced higher concentrations of acetate esters compared
to S. cerevisiae in both white and red wines, their genomic and metabolic features (particularly
acetate ester biosynthesis) were investigated. Complete genome sequences of K. aerobia and
K. servazzii isolates were obtained at contig level (de novo assembly) based on PacBio
sequencing reads. The genome size and GC content was 12.5 Mb and 35.8% for K. aerobia
and 12.3 Mb and 34.4% for K. servazzii. Furthermore, comparative analyses were performed
with putative orthologous genes involved in acetate ester and higher alcohol formation. Unlike
S. cerevisiae, where both alcohol acetyltransferase (AATase) encoding genes ATF1 and ATF2
are present, both K. aerobia and K. servazzii have only one orthologue in their genome.
This study will expand the knowledge on the application of non-Saccharomyces yeasts in
winemaking, particularly Kazachstania spp. which have demonstrated their potential to be
employed as pure or mixed-starter cultures.Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 202
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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