 IVES 9 IVES Conference Series 9 The use of fluorescence spectroscopy to develop a variability index and measure grape heterogeneity

The use of fluorescence spectroscopy to develop a variability index and measure grape heterogeneity

Abstract

AIM This work aims to investigate fluorescence spectroscopy as a tool to assess grape homogenates to discriminate between samples of varying maturities and to develop an index to objectively characterise the level of grape heterogeneity present in any given vineyard.

METHODS Cabernet-Sauvignon grape bunches were sampled every ten days from veraison through to harvest from the Coonawarra Geographical Indication of South Australia in 2020. After sorting into maturity classes using density baths,1 berries were homogenised and an Aqualog spectrophotometer was used to record the excitation emission matrix (EEM)2 of each maturity class at each sample date. The pre-processed EEM data underwent parallel factor analysis (PARAFAC) to identify the relevant fluorescence regions that discriminated samples based on maturity. The grape homogenate EEM dataset was then used to formulate a variability index.

RESULTS Chlorophyll and anthocyanin fluorescence signals were identified from EEM data at excitation wavelengths in the range 250 – 700 nm and emission wavelengths between 400 – 800 nm in grape homogenate samples using PARAFAC. Discrimination between samples depending on maturity was achieved using PARAFAC. The variability index was calculated and levels of grape heterogeneity were quantified.

CONCLUSIONS

This work demonstrated the possibility of using grape homogenate EEM data, particularly in the region of chlorophyll and anthocyanin fluorescence, to objectively measure grape heterogeneity by developing a variability index. Grape heterogeneity has been shown to impact Cabernet-Sauvignon wine chemical profile and sensory characteristics.3 Therefore, a tool to analyse grape heterogeneity within a winery could aid viticultural and winemaking decisions to achieve wines of targeted quality and style.

DOI:

Publication date: September 7, 2021

Issue: Macrowine 2021

Type: Article

Authors

Claire Armstrong

Australian Research Council Training Centre for Innovative Wine Production, The University of Adelaide. ,Adam GILMORE, HORIBA Instruments Inc., Piscataway, United States. Paul BOSS, CSIRO Agriculture and Food and Australian Research Council Training Centre for Innovative Wine Production, The University of Adelaide. Vinay PAGAY, Australian Research Council Training Centre for Innovative Wine Production, The University of Adelaide. David JEFFERY, Australian Research Council Training Centre for Innovative Wine Production, The University of Adelaide.

Contact the author

Keywords

chemometrics, colour, grape maturity, parafac, vineyard variability

Citation

New ways of grape pomaces valorization: production of functional beverages or nutraceuticals

The wine industry generates each year 20 million tons of by-products. Among them grape pomaces represent a big part that can be considered as a source of potentially bioactive molecules such as polyphenols. Kombucha fermentation is an ancestral process which allow to increase the biological properties of tea by the action of a microbial consortium formed by yeasts and bacteria called scoby.

OTA DEGRADATION BY BACTERIAL LACCASEST

Laccases from lactic acid bacteria (LAB) are described as multicopper oxidase enzymes with copper union sites. Among their applications, phenolic compounds’ oxidation and biogenic amines’ degradation, have been described. Besides, the role of LAB in the toxicity reduction of ochratoxin A (OTA) has been reported (Fuchs et al., 2008; Luz et al., 2018). Fungal laccases, but not bacterial laccases, have been screened for OTA and mycotoxins’ degradation (Loi et al., 2018). OTA is a mycotoxin produced by some fungal species, such as Penicillium and Aspergillus sp., which infect grape bunches used for winemaking.

Estimating bulk stomatal conductance of grapevine canopies

In response to changes in their environment, grapevines regulate transpiration using various physiological mechanisms that alter conductance of water through the soil-plant-atmosphere continuum. Expressed as bulk stomatal conductance at the canopy scale, it varies diurnally in response to changes in vapor pressure deficit and net radiation, and over the season to changes in soil water deficits and hydraulic conductivity of both soil and plant. It is necessary to characterize the response of conductance to these variables to better model how vine transpiration also responds to these variables. Furthermore, to be relevant for vineyard-scale modeling, conductance is best characterized using data collected in a vineyard setting. Applying a crop canopy energy flux model developed by Shuttleworth and Wallace, bulk stomatal conductance was estimated using measurements of individual vine sap flow, temperature and humidity within the vine canopy, and estimates of net radiation absorbed by the vine canopy. These measurements were taken on several vines in a non-irrigated vineyard in Bordeaux France, using equipment that did not interfere with ongoing vineyard operations. An inverted Penman-Monteith equation was then used to calculate bulk stomatal conductance on 15-minute intervals from July to mid-September 2020. Time-series plots show significant diurnal variation and seasonal decreases in conductance, with overall values similar to those in the literature. Global sensitivity analysis using non-parametric regression found transpiration flux and vapor pressure deficit to be the most important input variables to the calculation of bulk stomatal conductance, with absorbed net radiation and bulk boundary layer conductance being much less important. Conversely, bulk stomatal conductance was one of the most important inputs when calculating vine transpiration, further emphasizing the need for characterizing its response to environmental changes for use in vineyard water use modeling.

Wine metabolomics and sensory profile in relation to terroir: A case study focusing on different wine-growing areas of Piacenza Province (Italy)

Aim: In this work, we have optimized a robust methodology for investigating possible correlations between the phytochemical profile of wine and the terroir (including the climate), considering the specific wine-growing area. In particular, the untargeted metabolomic and sensorial profiles of Gutturnio DOC commercial wines (both still and “frizzante” types) from different production areas in the Piacenza province were determined. The geographical areas taken into consideration for this study consisted in Val Tidone, Val Nure and Val d’Arda.

The influence of the soil on the phenolic composition of both grapes and wines : “the Grenache observatory”

La composition fine des raisins de Grenache noir est mal connue. Il est généralement admis une certaine variabilité de comportement de ce cépage qui se manifeste principalement sur la couleur des vins. De nombreux facteurs peuvent être à l’origine de cette variabilité : matériel végétal, pratiques culturales, types de vinification et terroir. Un travail de recherche concernant ce cépage a été engagé dans la Vallée du Rhône.