A novel approach to upgrade infrared spectroscopy calibrations for nutritional contents in fresh grapevine organs

[EN] Infrared spectroscopy is widely used in viticulture. Spectroscopy correlates spectral properties with reference data to obtain calibrations later used to predict the analyte content in new samples with a single spectral measurement. However, the main limitation lies in generating the reference data required to build robust prediction calibrations. This study proposes a data generation strategy to obtain reference data for larger spectral datasets. A reduced sample set was used to develop initial calibrations. These initial cali-brations were subsequently applied to predict the reference data in larger spectral datasets. Calibrations for nitrogen, carbon, and hydrogen content were then attempted using the larger generated datasets. The initial nitrogen calibrations per organ showed coefficients of determination in validation (R2val) between 80.08 and 89.93%. The root mean square errors of prediction (RMSEP) ranged from 0.10 to 0.18% dry matter, and the residual predictive deviations in validation (RPD) were between 2.27 and 3.19. The larger predicted datasets showed improved prediction accuracy with coefficients of determination in validation values above 91.79%, root mean square errors of prediction below 0.14% dry matter, and residual predictive deviations in validation above 3.49. The carbon calibrations showed, on average, a 20% increase in the coefficient of determination in validation decreased root mean square errors of prediction and increased residual predictive deviations in validation. The hydrogen calibrations showed a similar increase in prediction accuracy. The results showed the suitability of using reduced sample sets to generate the reference data of larger datasets capable of yielding more accurate prediction calibrations.& COPY; 2023 IAgrE. Published by Elsevier Ltd. All rights reserved.The authors gratefully acknowledge the Oppenheimer Me- morial Trust, for the local scholarship (OMT Award Ref. 21579/02) awarded to Ms Elizma van Wyngaard.Van Wyngaard, E.; Blancquaert, E.; Nieuwoudt, H.; Aleixandre Tudo, J. (2023). A novel approach to upgrade infrared spectroscopy calibrations for nutritional contents in fresh grapevine organs. Biosystems Engineering. 232:141-154. https://doi.org/10.1016/j.biosystemseng.2023.07.00814115423

Data-driven Determination of Disease Markers’ Threshold Values in Rot-affected Wine Grapes

Grapevine bunch rot is detrimental to grape and wine quality. Traditionally, detecting and quantifyingthe severity of rot infection is executed visually. This study aimed at defining local, area-specific thresholdvalues of rot-associated disease markers. This is a first step towards making informed decisions aboutthe quality of grapes delivered at winery intake. Viticulturists visually assessed on-vine rot infection innine white wine grape cultivars. Results showed that severity ratings were consistent between assessors.Chemical analyses of the grape must from these assessed samples were done. Multiple factor analysis (MFA)showed that rot severity was positively correlated with glycerol, alcohol, gluconic acid and acetic acidconcentrations. As severity increased, gluconic acid, glycerol, alcohol, Brix, acetic acid and total titratableacidity (TA) concentrations also increased. Following the probability chosen for sensitivity and specificity,grape rot indicators’ threshold values in white grape must are as follow: Alcohol ≥ 0.10 %v/v; acetic acid≥ 0.17 g/L; glycerol ≥ 0.79 g/L; gluconic acid ≥ 0.99 g/L; TA ≥ 8.86 g/L. Statistical determined thresholdvalues differentiating between rot-affected and healthy grape must, would eliminate the subjectivity andbias associated with visual assessments

Infrared spectroscopy and chemometric applications for the qualitative and quantitastive investigation of grapevine organs.

[EN] The fourth agricultural revolution is leading us into a time of using data science as a tool to implement precision viticulture. Infrared spectroscopy provides the means for rapid and large-scale data collection to achieve this goal. The non-invasive applications of infrared spectroscopy in grapevines are still in its infancy, but recent studies have reported its feasibility. This review examines near infrared and mid infrared spectroscopy for the qualitative and quantitative investigation of intact grapevine organs. Qualitative applications, with the focus on using spectral data for categorization purposes, is discussed. The quantitative applications discussed in this review focuses on the methods associated with carbohydrates, nitrogen, and amino acids, using both invasive and non-invasive means of sample measurement. Few studies have investigated the use of infrared spectroscopy for the direct measurement of intact, fresh, and unfrozen grapevine organs such as berries or leaves, and these studies are examined in depth. The chemometric procedures associated with qualitative and quantitative infrared techniques are discussed, followed by the critical evaluation of the future prospects that could be expected in the field.The authors gratefully acknowledge the Oppenheimer Memorial Trust. A local scholarship (OMT Award Ref. 21579/01) was awarded to EW.Wyngaard, EV.; Blancquaert, E.; Nieuwouldt, H.; Aleixandre Tudo, J. (2021). Infrared spectroscopy and chemometric applications for the qualitative and quantitastive investigation of grapevine organs. Frontiers in Plant Science. 12:1-16. https://doi.org/10.3389/fpls.2021.7232471161

An exploratory study of urban South African consumers’ perceptions of wine and wine consumption: focus on social, emotional, and functional factors

International audienceWine is of great economic and cultural significance for South Africa, but some population groups were until relatively recently denied equal access to wine and alcohol products. The South African wine industry has launched various campaigns in recent years that aimed at portraying wine as an acceptable and attractive choice when alcohol consumption is considered. It is therefore appropriate now to investigate whether these endeavors of the South African wine industry have resulted in particular consumer behavior and preferences that could serve as input to enhance strategies when marketing to South African consumers. This study uses the thematic analysis method to identify themes that could be of value for wine marketers. To collect data for the study, a total of 44 consumers were assigned to 6 focus groups. Eight main themes driving consumer choices emerged from the data: journey and role of life-stage, context of consumption, conceptualizations, barriers, price and purchasing, bottle closures, health, sensory perception, and cultivars. The influences of gender and ethnicity on consumers’ perceptions of wine and wine consumption were investigated. Gender produced the biggest differences in respect of respondents’ perceptions about wine and wine consumption whilst ethnicity did not appear to be of any significance

Optimisation of PLS Calibrations for Filtered and Untreated Samples towards In-Line Monitoring of Phenolic Extraction during Red-Wine Fermentations

Infrared spectroscopy provides an efficient, robust, and multivariate means to measure phenolic levels during red-wine fermentations. However, its use is currently limited to off-line sampling. In this study, partial least squares (PLS) regression was used to investigate the possibility of using spectral data from minimally pre-treated or untreated samples for the optimisation of prediction calibrations towards an in-line monitoring set-up. The evaluation of the model performance was conducted using a variety of metrics. Limits of detection and quantification of the PLS calibrations were used to assess the ability of the models to predict lower levels of phenolics from the start of fermentation. The calibrations were shown to be useful for the quantification of phenolic compounds and phenolic parameters with minimal or no sample pre-treatment during red-wine fermentation. Upon evaluation of performance, the calibrations built for attenuated-transmission Fourier-transform mid-infrared (ATR-FT-MIR) and diffuse-reflectance Fourier-transform near-infrared (DR-FT-NIR) were shown to be the most suitable spectroscopy techniques for eventual application in an automated and in-line system with values for limits of detection and quantification being suitable for the entire duration of fermentation

Optimisation of PLS Calibrations for Filtered and Untreated Samples towards In-Line Monitoring of Phenolic Extraction during Red-Wine Fermentations

Infrared spectroscopy provides an efficient, robust, and multivariate means to measure phenolic levels during red-wine fermentations. However, its use is currently limited to off-line sampling. In this study, partial least squares (PLS) regression was used to investigate the possibility of using spectral data from minimally pre-treated or untreated samples for the optimisation of prediction calibrations towards an in-line monitoring set-up. The evaluation of the model performance was conducted using a variety of metrics. Limits of detection and quantification of the PLS calibrations were used to assess the ability of the models to predict lower levels of phenolics from the start of fermentation. The calibrations were shown to be useful for the quantification of phenolic compounds and phenolic parameters with minimal or no sample pre-treatment during red-wine fermentation. Upon evaluation of performance, the calibrations built for attenuated-transmission Fourier-transform mid-infrared (ATR-FT-MIR) and diffuse-reflectance Fourier-transform near-infrared (DR-FT-NIR) were shown to be the most suitable spectroscopy techniques for eventual application in an automated and in-line system with values for limits of detection and quantification being suitable for the entire duration of fermentation