Helene Nieuwoudt

Stellenbosch University, Viticulture and Oenology, Faculty Member

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Address: Stellenbosch, Western Cape, South Africa

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Papers by Helene Nieuwoudt

Mealiness in ‘Forelle’ pears: relationship between TSS and prediction based on FT-NIR spectroscopy

Acta Horticulturae, 2018

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Introducing samples from target orchards improves prediction performance of Vis/NIRS models of citrus fruit quality measured at harvest

by Lembe Samukelo Magwaza and Helene Nieuwoudt

Robustness of calibration models has become a critical issue in visible to near infrared spectros... more Robustness of calibration models has become a critical issue in visible to near infrared spectroscopy (Vis/NIRS) and an active area of research in postharvest technology. An important consideration in developing fruit spectral and model libraries is to ensure that calibration data sets represent variability of target prediction samples. A way to achieve this is by adding few samples from the target site (spiking) followed by recalibration of models. This study reports the effects of spiking calibration models with samples from a target orchard on prediction performance. Vis/NIRS signals of fruit from four orchards in the Western Cape Province in South Africa were acquired on freshly harvested ‘Nules Clementine’ mandarin (Citrus reticulata Blanco.) fruit using a LabSpec® spectrophotometer. Reference rind dry matter (DM) content was measured after 8 weeks of storage at 8±0.5°C. Partial least squares (PLS) regression with full cross validation was used to develop calibration models. Th...

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Comparison of pivot profile© to frequency of attribute citation: Analysis of complex products with trained assessors

Food Quality and Preference, Sep 1, 2020

Abstract Pivot© profile (PP), a method which compares samples to a reference (pivot), has shown p... more Abstract Pivot© profile (PP), a method which compares samples to a reference (pivot), has shown profiling potential for complex matrices. However, various aspects require further investigation. This study’s aim was to compare PP to frequency of attribute citation (FC) considering individual judges’ data and sample set complexity. A trained panel analysed three wine sets with different within-set product similarity levels. The stability of the PP sensory space was tested by changing the pivot. PP and FC results were compared using RV coefficients. Confidence ellipses on correspondence analysis (CA) plots were constructed to consider individual judges’ data. CA plots constructed from different pivot PP data sets, were less similar to each other, than to CA plots of FC data, for the set with medium and the set with high within-set variation. The most profound differences were observed for the set with the high within-set variation. PP configurations of the set with low within-set variation, were more similar to each other than to FC configurations. Higher explained variance was obtained with PP than FC, but confidence ellipses overlapped more frequently indicating fewer significant differences between samples. PP and FC data were comparable for the set with medium within-set variation. From this study’s results PP is recommended for wine profiling if medium within-set variation between samples exist but not when sample sets with low or high within-set variation are profiled. PP is recommended over FC for comparative studies where a reference sample is required for example during benchmarking or for aging and shelf-life studies.