Dr Joanna Gambetta

Sunburn is a physiological disorder that reduces grape quality and vineyard yield. It is the result of excessive sunlight and high temperatures. As climate change continues to increase air temperatures, reports of sunburn damage in vineyards worldwide are becoming more frequent. Grapes produce secondary metabolites (carotenoids, polyphenols and aroma compounds) to counter photooxidative stress and acclimate to higher radiation environments. This study evaluated changes in these compounds in during ripening when grapes were exposed post-flowering (ED) and at véraison (LD), and compared them to a nondefoliated control (ND). ND contained more a-terpineol and violaxanthin, and the defoliated treatments contained more zeaxanthin, ß-carotene, C6 compounds and flavonoids. ED berries adapted better to higher-light environments, displayed larger changes in secondary metabolite concentrations and lower levels of sunburn damage than LD berries did. The composition of berries with increasing sunburn damage was evaluated for the first time. Berries with no damage had the lowest concentrations of flavonoids and oxidized glutathione, and the highest concentrations of chlorophyll and a-terpineol. As damage increased, destruction of photosynthetic pigments, increase in polyphenols and loss of aroma compounds were evidenced. A significant effect of temperature and developmental stage on grape composition was also observed. This study provides a holistic overview of changes in secondary metabolites experienced by grape berries when exposed to excessive light, how these vary along development and how they affect sunburn incidence.

Aureobasidium pullulans is a yeast-like fungus that produces volatile organic compounds (VOCs) with antifungal properties. VOCs have the potential to trigger the production of intracellular reactive oxygen species (ROS), lipid peroxidation and electrolyte loss in microorganisms. The relationship among A. pullulans VOCs, induced ROS accumulation and electrolyte leakage was investigated in Botrytis cinerea and Alternaria alternata in vitro. Exposure to a mixture of A. pullulans VOCs: ethanol, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-phenylethanol, resulted in electrolyte leakage in both B. cinerea and A. alternata. Fluorescence microscopy using 2',7'-dichlorofluorescein diacetate indicated triggered ROS accumulation in exposed fungal mycelia and the presence of the superoxide radical was evident by intense red fluorescence with dihydroethidium. Partial inhibition of enzymes of the mitochondrial respiratory chain complex I of B. cinerea and A. alternata by pre-treatment with rotenone reduced ROS accumulation in hypha exposed to A. pullulans VOCs and reversed the VOCs inhibition of fungal growth. Scanning electron micrographs revealed that B. cinerea and A. alternata hypha exposed to A. pullulans VOCs had altered cell wall structures. Our findings give insights into the potential mechanisms involved in the antifungal properties of A. pullulans in the suppression of B. cinerea and A. alternata growth in vitro.

Background and Aim: Reduced rainfall during vine dormancy and supplementary irrigation during winter or at spring impact on vine growth partitioning. We assess the implications that induced changes on canopy growth due to soil moisture availability in spring have on fruit and wine composition. Methods and Results: Irrigation strategies were assessed in a vineyard where winter rainfall was excluded and irrigation was applied during winter or at spring during three seasons. Reduced soil moisture in spring increased canopy porosity from flowering and increased the concentration of phenolic substances in the fruit and wine. Colour, aroma intensity and fruit attributes typical of Barossa Shiraz wines were enhanced under more open canopies. When soil moisture was restored in spring by natural rainfall or by supplementary irrigation, vines developed denser canopies and phenolic substances were reduced in the fruit and wines. Irrigation at spring following a dry winter altered wine style and was associated with some negative attributes. Conclusions: Smaller canopies due to reduced water availability at spring improved fruit and wine composition at the expense of yield. Irrigation in spring following a dry winter promoted canopy growth over yield, and impacted negatively on fruit and wine composition. Significance of the Study: These results stress the importance that soil water availability in spring has on defining wine style, and establishes a framework for the adoption of irrigation strategies that may maintain regional style in a context of a changing climate. These responses can be expected in regions with a Mediterranean climate experiencing a reduction in winter rainfall.

The combined biochemical impact of carbon, nitrogen and temperature on the biosynthesis of the antifungal volatile organic compounds (VOCs): ethanol, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-phenylethanol produced by Aureobasidium pullulans A1 and A3 was investigated using a Box¿Behnken experimental design and response surface methodology (RSM). Normalized peak areas derived from solid phase micro extraction-gas chromatography¿mass spectrometry (SPME-GC¿MS) analysis, indicated that initial carbon content had a significant influence on the biosynthesis of ethanol and alcohols with greater than three carbon atoms. This result suggests a dominant activity of the A.¿pullulans anabolic pathway to biosynthesize three higher alcohols via de novo biosynthesis of amino acids from sugar metabolism. Low concentrations of carbon (3¿13 g l-1) with nitrogen as both ammonium and amino acids in the growth medium resulted in a higher number of significant linear and quadratic relationships. Nitrogen availability and growth temperature had significant negative linear and quadratic correlations with VOCs biosynthesis in most instances. Isolate-dependant metabolic response was evident for all abiotic parameters tested on alcohol production. The findings of this study offer new perspectives to improve the production of key antifungal compounds by antagonists in biological control systems.

Sunburn is a physiological disorder that affects the visual and organoleptic properties of grapes. The appearance of brown and necrotic spots severely affects the commercial value of the fruit, and in extreme cases, significantly decreases yield. Depending on the severity of the damage and the driving factors, sunburn on grapes can be classified as sunburn browning (SB) or as sunburn necrosis (SN). Sunburn results from a combination of excessive photosynthetically active radiation (PAR) and UV radiation and temperature that can be exacerbated by other stress factors such as water deficit. Fruit respond to these by activating antioxidant defense mechanisms, de novo synthesis of optical screening compounds and heat-shock proteins as well as through morphological adaptation. This review summarizes the current knowledge on sunburn in grapes and compares it with relevant literature on other fruits. It also discusses the different factors affecting the appearance and degree of sunburn, as well as the biochemical response of grapes to this phenomenon and different potential mitigation strategies. This review proposes further directions for research into sunburn in grapes.

In Latin, 'pulcherrima' is a superlative form of an adjective that translates as beautiful. Apart from being 'the most beautiful' yeast, Metschnikowia pulcherrima has a remarkable potential in production of wines with lower ethanol content. The oenological performance of six M. pulcherrima strains was hereby tested in sequential cultures with Saccharomyces cerevisiae. The best-performing strain MP2 was further characterised in fermentations with different S. cerevisiae inoculation delays in both white grape juice and Chemically Defined Grape Juice Medium (CDGJM). The analysis of main metabolites, undertaken prior to sequential inoculations and upon fermentation completion, highlighted metabolic interactions and carbon sinks other than ethanol in MP2 treatments. Depending on the inoculation delay, MP2 white wines contained between 0.6% and 1.2% (v/v) less ethanol than the S. cerevisiae monoculture, with even larger decreases detected in the CDGJM. The MP2 treatments also contained higher concentrations of TCA cycle by-products (i.e. fumarate and succinate) and glycerol, and lower concentrations of acetic acid. The analysis of volatile compounds showed increased production of acetate esters and higher alcohols in all MP2 wines, alongside other compositional alterations arising from the S. cerevisiae inoculation delay.

Establishing a fine wine image through regional typicality has been of interest to New World wine producing countries like Australia, but previous research mainly involved unoaked experimental wines, which were not reflective of the retail wine market. The regional typicality of commercially available fine Australian wines (FAW) was therefore explored, based on the hypotheses that sensory and chemical composition of varietal fine wines would discriminate by region, and further nuances within region would be explained by drivers of intraregional typicality. Chardonnay wines (2015 vintage) from Margaret River (MR, n = 16) and Yarra Valley (YV, n = 16); and Shiraz wines (2014 vintage) from Barossa Valley (BV, n = 16) and McLaren Vale (MV = 15), were selected for descriptive sensory analysis and underwent profiling of volatiles by gas chromatography-mass spectrometry (GC¿MS). For both grape varieties, there was large variability in wine styles among wines from the same GI, such as fruity/crisp vs oaked Chardonnay and oaky/astringent vs savoury Shiraz. Consequently, human intervention seemed to be an important component of regional/sub-regional typicality, which therefore cannot be determined solely on geographic origin of the fruit. Using a combination of sensory markers and volatile profiles allowed the building of regional typicality models, which are promising, however, consumers may not perceive sub-regional differences based on sensory attributes. Undoubtedly, variation of wine styles emerging across wine regions, vintages, and viticultural and winemaking practices needs to be further explored, but this work created a preliminary sensory and volatile map for future research.

Volatile organic compounds (VOCs) produced by Aureobasidium pullulans were investigated for antagonistic actions against Alternaria alternata and Botrytis cinerea. Conidia germination and colony growth of these two phytopathogens were suppressed by A. pullulans VOCs. A novel experimental setup was devised to directly extract VOCs using solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) from antagonist-pathogen culture headspace. The proposed system is a robust method to quantify microbial VOCs using an internal standard. Multivariate curve resolution-alternating least squares deconvolution of SPME-GC-MS spectra identified fourteen A. pullulans VOCs. 3-Methyl-1-hexanol, acetone, 2-heptanone, ethyl butyrate, 3-methylbutyl acetate and 2-methylpropyl acetate were newly identified in A. pullulans headspace. Partial least squares discriminant analysis models with variable importance in projection and selectivity ratio identified four VOCs (ethanol, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-phenylethanol), with high explanatory power for discrimination between A. pullulans and pathogen. The antifungal activity and synergistic interactions of the four VOCs were evaluated using a Box-Behnken design with response surface modelling. Ethanol and 2-phenylethanol are the key inhibitory A. pullulans VOCs against both B. cinerea and A. alternata. Our findings introduce a novel, robust, quantitative approach for microbial VOCs analyses and give insights into the potential use of A. pullulans VOCs to control B. cinerea and A. alternata.

Rapid analytical methods based on infrared spectroscopy in combination with chemometrics have found wide application in the food and beverage industry. These methods have the potential to qualitatively analyse and classify or authenticate samples including grapes and wines, or be used as a tool for objective decision-making while grapes are still ripening, ultimately offering better control over the winemaking process. Thus, an initial investigation examined the use of attenuated total reflectance (ATR) mid-infrared (MIR) spectroscopy to discriminate Chardonnay grape samples from different geographical origins and industry-allocated quality grades with minimal sample preparation. Classification of samples according to region of origin using partial least squares discriminant analysis (PLS-DA) of the fingerprint region of the MIR spectra (1500¿800¿cm-1) had an overall success rate of 83 and 81% for the 2014 and 2016 vintages, respectively. It was also possible to classify sample quality successfully using this same approach. Correct classification of Chardonnay grapes according to quality grade was of the order of 83% in 2014 and 79% in 2016. The ability to predict juice titratable acidity and total soluble solids was also shown. We have demonstrated the potential use of ATR-MIR as a rapid tool to classify samples according to geographical origins and quality grades, which has implications for authenticity determination and for optimising the streaming of fruit to the most appropriate winemaking processes.

The aim of this work was to investigate how useful the Rate-All-That-Apply (RATA) method with naive consumers is to profile a wide range of wines and how the sensory profiles obtained compare with those of classic descriptive analysis (DA). For this purpose, we conducted two studies. Study 1 presents preliminary work comparing the discrimination ability of RATA, undertaken by 84 naive consumers, with a traditional DA with 11 trained panelists. The vocabulary lists remained the same across the two methods, and the assessment was based on a set of six red table wines (from six different varieties). Study 2 aimed to further elucidate the discrimination ability of RATA with 71 naive consumers compared with traditional DA. It expanded on Study 1 by increasing the number of samples assessed (12 white table wines from six varieties) and by varying the vocabulary between methods (RATA used a generic white wine attribute list and the DA used a panel-generated attribute list). In addition, similarity of sample configuration in the sensory space between RATA and DA was assessed by means of multiple factor analysis (MFA) and regression vector (RV) coefficients. The results of both studies revealed that RATA and DA are highly similar in sample discrimination ability (in terms of number of attributes significantly discriminating among samples). Furthermore, the MFA indicated high agreement in sample configuration between RATA and DA, reinforced by highly significant RV coefficients of 0.97 for Study 1 and 0.92 for Study 2. Overall, this observation supports a trend toward more consumer-centric approaches for sensory profiling and suggests that RATA could be a valid, accurate, and rapid addition to existing profiling methods used for wine.

The yeast Lachancea thermotolerans (previously Kluyveromyces thermotolerans) is a species of large, yet underexplored, oenological potential. This study delivers comprehensive oenological phenomes of 94 L. thermotolerans strains obtained from diverse ecological niches worldwide, classified in nine genetic groups based on their pre-determined microsatellite genotypes. The strains and the genetic groups were compared for their alcoholic fermentation performance, production of primary and secondary metabolites and pH modulation in Chardonnay grape juice fermentations. The common oenological features of L. thermotolerans strains were their glucophilic character, relatively extensive fermentation ability, low production of acetic acid and the formation of lactic acid, which significantly affected the pH of the wines. An untargeted analysis of volatile compounds, used for the first time in a population-scale phenotyping of a non-Saccharomyces yeast, revealed that 58 out of 90 volatiles were affected at an L. thermotolerans strain level. Besides the remarkable extent of intra-specific diversity, our results confirmed the distinct phenotypic performance of L. thermotolerans genetic groups. Together, these observations provide further support for the occurrence of domestication events and allopatric differentiation in L. thermotolerans population.

Chardonnay is a neutral grape variety offering a diversity of wine styles that are popular among con­sumers. The links between wine production methods and Chardonnay wine volatile composition, as determinants of quality, require further elucidation. Over 80 commercial Australian Chardonnay wines were assessed by expert panelists who were asked to define four distinct levels of quality in a blind tasting. Wine aroma volatiles in each wine were analyzed by solid-phase microextraction-gas chromatography-mass spectrometry, and multivariate sta­tistical techniques were used to examine the relationship between volatile composition and quality as defined by the experts. Of 39 aroma compounds quantified, nine volatiles (including cis- and trans-oak lactones, furfural, and diethyl succinate) correlated significantly and positively with Chardonnay wine quality, while 11 volatiles (including fruity esters and monoterpenoids) correlated negatively. Compounds associated with oak contact and malolactic fermentation were present at highest concentrations in higher-quality wines as perceived by wine experts. Lower scores were assigned to younger but less complex wines, which were richer in fruity esters and other grape-derived compounds. A model was developed using partial least squares regression based on these results, which permitted classification of the Chardonnay wines into high-, medium-, and low-quality brackets depending on their relative concentrations of cis- and trans-oak lactone, ethyl lactate, and 2-methyl-1-propanol (positive) and of 1-propanol and 1-hexanol (negative). There was a significant and positive correlation (r = 0.469, p <0.0001) between retail price and quality score, underlying the usefulness of price as an indicator of quality, although it failed to entirely explain quality (as judged by experts) and should therefore be used in conjunction with other quality cues.

Defluviicoccus vanus-related glycogen accumulating organisms (GAO) regularly proliferate in industrial wastewater treatment plants handling high carbon but nitrogen deficient wastes. When GAO dominate, they are associated with poor performance, characterised by slow settling biomass and turbid effluents. Although their ecophysiology has been studied thoroughly in domestic waste treatment plants, little attention has been paid to them in aerobic industrial systems. In this study, the effect of nitrogen addition on GAO carbon metabolism was investigated during an 8 h cycle. Activated sludge dominated by GAO from a winery wastewater sequencing batch reactor was incubated under different carbon to nitrogen (COD:N) ratios (100:1, 60:1 and 20:1) using 13 C ¿ acetate and 15 N ¿ urea. GAO cell assimilation was quantified using FISH-NanoSIMS. The activated sludge community was assessed by 16S rRNA gene profiling, DNA and storage polymer production. Carbon and nitrogen quantification at the cellular level by NanoSIMS revealed that low (COD:N of 100:1) or null nitrogen concentrations enhanced GAO carbon uptake. COD:N ratios of 60:1 and 20:1 reduced GAO carbon uptake and promoted whole microbial community DNA production. Nitrogen dosing at COD:N ratios of 60:1 or higher was demonstrated as feasible strategy for controlling the excessive GAO growth in high COD waste treatment plants.

The relationship between berry chemical composition, region of origin and quality grade was investigated for Chardonnay grapes sourced from vineyards located in seven South Australian Geographical Indications (GI). Measurements of basic chemical parameters, amino acids, elements, and free and bound volatiles were conducted for grapes collected during 2015 and 2016. Multiple factor analysis (MFA) was used to determine the sets of data that best discriminated each GI and quality grade. Important components for the discrimination of grapes based on GI were 2-phenylethanol, benzyl alcohol and C6 compounds, as well as Cu, Zn, and Mg, titratable acidity (TA), total soluble solids (TSS), and pH. Discriminant analysis (DA) based on MFA results correctly classified 100% of the samples into GI in 2015 and 2016. Classification according to grade was achieved based on the results for elements such as Cu, Na, Fe, volatiles including C6 and aryl alcohols, hydrolytically-released volatiles such as (Z)-linalool oxide and vitispirane, pH, TSS, alanine and proline. Correct classification through DA according to grade was 100% for both vintages. Significant correlations were observed between climate, GI, grade, and berry composition. Climate influenced the synthesis of free and bound volatiles as well as amino acids, sugars, and acids, as a result of higher temperatures and precipitation.

Phenolic compounds play a critical role in determining red wine color, taste, flavor, and mouthfeel sensory attributes. Additionally, they contribute to wine aging and provide wine stability. This study evaluated the use of an attenuated total reflection (ATR) mid-infrared (MIR) spectroscopy to measure phenolic compounds in Shiraz wine samples of different quality levels obtained from 24 Australian wine geographical indications. Partial least squares (PLS) regression using the second derivative of the whole MIR spectrum produced the coefficient of determination (R2) in calibration and standard error in cross-validation (SECV) for different attributes. In particular, SO2-resistant pigments had R2 = 0.58 (SECV=0.58 au), total anthocyanins had R2 = 0.61 (SECV=32 mg/L), wine color density had R2 = 0.51 (SECV=0.56 au), and total phenolics had R2 = 0.60 (SECV=5.7 au). These results demonstrated the potential use of ATR-MIR spectroscopy with PLS regression as a rapid method to measure important parameters related to red wine phenolic composition and wine quality.

Two rosé wines, representing a tropical and a fruity/floral style, were chosen from a previous study for further exploration by aroma extract dilution analysis (AEDA) and quantitative analysis. Volatiles were extracted using either liquid-liquid extraction (LLE) followed by solvent-assisted flavor evaporation (SAFE) or a recently developed dynamic headspace (HS) sampling method utilizing solid-phase extraction (SPE) cartridges. AEDA was conducted using gas chromatography-mass spectrometry/olfactometry (GC-MS/O) and a total of 51 aroma compounds with a flavor dilution (FD) factor =3 were detected. Quantitative analysis of 92 volatiles was undertaken in both wines for calculation of odor activity values. The fruity and floral wine style was mostly driven by 2-phenylethanol, ß-damascenone, and a range of esters, whereas 3-SHA and several volatile acids were seen as essential for the tropical style. When extraction methods were compared, HS-SPE was as efficient as SAFE for extracting most esters and higher alcohols, which were associated with fruity and floral characters, but it was difficult to capture volatiles with greater polarity or higher boiling point that may still be important to perceived wine aroma.

Wine quality depends upon the composition of the grapes used in its production, which in turn depends on the weather and soil of the growing region together with viticultural practices. Region is used by many winemakers as a proxy for quality but objective quality measures are lacking. This study examined the compositional aspects of Chardonnay wines produced with berries from different regions. Through descriptive analysis, distinct sensory profiles were recognised for three diverse regions in South Australia (Adelaide Hills, Eden Valley, Riverland), which helped to pinpoint compounds relating to higher- and lower-quality Chardonnay wines. Correlations between the content of elements, fatty acids, free volatiles and conjugated glycosides in berries from different quality levels, and the composition of their corresponding wines, were investigated. Higher berry concentrations of linalool, (E)-linalool oxide, (Z)-3-hexen-1-ol, decanoic acid, vitispirane, Cu, Zn, and behenic acid, and lower °Brix and pH levels were related to higher quality wines.