Browsing by Author "Afonso, Andreia M."
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- Non-destructive follow-up of ‘Jintao’ kiwifruit ripening through VIS-NIR spectroscopy – individual vs. average calibration model’s predictionsPublication . Afonso, Andreia M.; Antunes, Maria Dulce; Cruz, Sandra; Cavaco, A. M.; Guerra, Rui Manuel Farinha das NevesVisible/near infrared spectroscopy (Vis-NIRS) was used to monitor the yellow-fleshed kiwifruit (Actinidia chinensis Planch 'Jintao') ripening on two selected orchards along 13 weeks, from pre-harvest to the late harvest. Calibration models for several Internal Quality Attibutes (IQA) were built from the spectral data of 375 individual kiwifruit. The analyzed IQA were L*, a* and b* from the CIELAB color space, hue angle, chroma, firmness, dry matter (DM), soluble solids content (SSC), juice pH and titratable acidity (TA). Different pre-processing methods were tested for the construction of PLS calibration models. SSC and Hue were the best performing models with a correlation coefficient of 0.81 and 0.88, and root mean square error of prediction (RMSEP) of 1.27% and 1.95 degrees, respectively. The interpretation of the models in terms of the known absorption bands and the impact of signal to noise ratio (SNR) in them is discussed. The calibration models were used to perform average predictions of the IQA on orchard subareas, for each day of the experiment. These average predictions were compared with the IQA's average reference values on the same subareas and days. The model's metrics improved significantly through the averaging procedure, with RMSEP = 0.26-0.36% and R-2 = 0.99 for SSC; and RMSEP = 0.42 degrees - 0.56 degrees and R-2 = 1 for Hue. Since orchard management is done essentially through averages and not individual values, this result reinforces the applicability of the NIR technology for follow-up of fruit ripening in the tree.
- Non-invasive monitoring of kiwifruit ripeningPublication . Afonso, Andreia M.; Guerra, Rui; Antunes, Maria DulceThis thesis aims to explore the use of Visible and Near-Infrared Diffuse Reflectance Spectroscopy (VisNIR-DRS) in monitoring the ripening of two kiwifruit species, a yellow- (Actinidia chinensis Planch 'Jintao') and a green-fleshed (Actinidia deliciosa Liang et Ferguson 'Hayward'). The technique used in this study relies on correlating spectra with fruit internal quality attributes (IQA). However, low correlations in VisNIR-DRS causes problems in generalizing calibration models to new data. Therefore, the study was designed to test VisNIR-DRS in difficult real field conditions. Two orchards were monitored for each cultivar over two years, enabling internal (IV) and external validation (EV) on four independent datasets. The first part of the study focused on characterizing the time evolution of IQA during ripening. The second part involved developing calibration models for each IQA, based on the data from the first year. The results showed that it is possible to obtain highquality predictions for the IQA's daily averages from medium-quality models. The third part involved the two years' data. Variable selection and orthogonal signal correction were employed to improve the performance of the models, although only the IV performance improved, indicating that these widely recommended techniques are of little value in the context of stringent EV. Usual calibration transfer between the spectrometers used in each year was impossible in the absence of common samples. Therefore, a normalization approach based on daily average spectra was used, resulting in improved model performance. Lastly, the fourth part addressed the time variation of IQA in cold-stored kiwifruit, along with sensory data and their correlation with the spectra. According to the results of this study, VisNIR-DRS is a promising and important tool for kiwifruit industry since can be used to follow non-destructively the kiwifruit ripening, either on-tree or during storage, in a higher number of fruit samples and in less time.
- Ripening assessment of ‘Ortanique’ (Citrus reticulata Blanco x Citrus sinensis (L) Osbeck) on tree by SW-NIR reflectance spectroscopy-based calibration modelsPublication . Pires, Rosa; Guerra, Rui Manuel Farinha das Neves; Cruz, Sandra; Antunes, MDC; Brazio, António; Afonso, Andreia M.; Daniel, Mariana; Panagopoulos, Thomas; Gonçalves, Isabel; Cavaco, Ana M.The aim of this study was the non-destructive assessment of ‘Ortanique’ (Citrus reticulata Blanco x Citrus sinensis (L) Osbeck) ripening, based on the prediction of internal quality attributes (IQA) by short-wave near-infrared reflectance spectroscopy (SW-NIRS) calibration models. Spectra from fruit of 50 trees located in two different orchards, were acquired on tree using a customized portable visible near-infrared (vis-NIR) system. Partial least squares (PLS) was used to build the various IQA calibration models. The models were tested through internal validation (IV) and external validation (EV). Generally, the IV results were always superior to those of EV: regarding IV, a high regression coefficient (R2) and low root mean square error of prediction (RMSEP) were achieved, revealing a good predictive performance for juice pH (R2 = 0.80; RMSEP = 0.10; SDR = 2.23), soluble solids content (SSC) (R2 = 0.79; RMSEP = 0.75 %; SDR = 2.27), titratable acidity (TA) (R2 = 0.73; RMSEP = 0.24 % citric acid; SDR = 1.94) and the maturation index (MI) (R2 = 0.80; RMSEP = 1.38; SDR = 2.2). The best EV predictions were obtained for TA (R2 = 0.69; RMSEP = 0.38 % citric acid; SDR = 1.24), and MI (R2 = 0.69; RMSEP = 2.07; SDR = 1.49). Calibration models for glucose, fructose and sucrose showed medium-coarse predictions for both validation strategies. A detailed investigation of MI models was performed, to understand the causes of their poor EV results. In the context of EV, model updating strategies were explored by using some validation samples to improve the calibration model. The methods of bias correction and spiking were tested, showing a clear improvement in the predictions.
- Sensory evaluation and spectra evolution of two kiwifruit cultivars during cold storagePublication . Afonso, Andreia M.; Guerra, Rui; Cruz, Sandra; Antunes, Maria D.Kiwifruit consumption has increased due to its rich nutritional properties. Although ‘Hayward’ continues to be the main cultivar, others, such as yellow fleshed ‘Jintao’, are of increasing interest. The objective of this research was to evaluate the acceptability and storage performance of these two cultivars. Sensory evaluation of green ‘Hayward’ and yellow ‘Jintao’ kiwifruit were performed along cold storage for three seasons/years to follow the organoleptic characteristics through ripening, as well as the acquisition of their spectra by Vis-NIR. For ‘Jintao’ were performed two sensory evaluations per year at 2.5- and 4.5-months’ storage and for ‘Hayward’ at 2.5-, 4.5- and 5.5-months’ storage. The nonparametric Mann–Whitney test and Kruskal–Wallis ANOVA were performed to test the significant differences between the mean ranks among the storage time. A non-metric multidimensional scaling plot method using the ALSCAL algorithm in a seven-point Likert scale was applied to determine the relationships in the data, and a new approach using the receiver operating characteristic (ROC) analysis was tested. The last revealed that, for both cultivars, sweetness, acidity and texture were the variables with better scores for General flavor. Aroma was also important on ‘Jintao’. A strong correlation between soluble solids content (SSC) and reflectance was found for both cultivars, with the 635–780 nm range being the most important. Regarding firmness, a good correlation with reflectance spectra was observed, particularly in ‘Hayward’ kiwifruit. Based on these results, Vis-NIR can be an objective alternative to explore for determination of the optimum eating-ripe stage.
- Spatiotemporal modelling of the quality and ripening of two cultivars of "Algarve Citrus" orchards at different edaphoclimatic conditionsPublication . Cavaco, Ana M.; Cruz, Sandra P.; Antunes, M. Dulce; Guerra, Rui; Pires, Rosa; Afonso, Andreia M.; Brazio, António; Silva, Leonardo; Lucas, Marcia Rosendo; Daniel, Mariana; Panagopoulos, ThomasAlgarve Citrus are non-climacteric Protected Geographical Indication (PGI) commodities. They are harvested with minimal levels of juice content (>35 %), soluble solids content (SSC) (>10 %) and maturation index (MI) (>8), as required by the respective PGI normative reference. These internal quality attributes (IQA) are usually determined in small samples of fruit collected from the orchards close to harvest. This study aimed to use geostatistics to help predict the optimal harvest date (OHD) of two sweet orange (Citrus sinensis (L.) Osbeck) cultivars, namely, 'Newhall', and 'Valencia Late', at two different edaphoclimatic conditions observed in the locations of Quarteira, at the coast, and Paderne, near a mountainous area. Two orchards of 0.5-0.7 ha per cultivar were chosen and a total of 25 trees were georeferenced within each orchard, comprising 100 sampling points/trees. Firmness, juice content, SSC and MI of fruit were determined through time. In general, the fruit grown in Quarteira showed higher SSC and MI and lower firmness values, ripening two months earlier than those grown in Paderne, although the full effect of the various edaphoclimatic factors on these results are not fully understood. However, geospatial modelling of ripening has shown a large variability within the orchards, with some IQA evolution patterns observed in some orchards and/or cultivars but not in the others. Specifically, 1) a negative correlation between the firmness and MI spatial patterns; 2) a variable decay rate of firmness, much faster in Paderne for 'Valencia Late'; 3) local minima in juice content, below 35 %, observed in restricted spatial areas and in specific time periods, and which were clearer in 'Newhall'. These local variations highlight the need for an optimized management based on geospatial modelling. For example, the variable decay rate of firmness must be taken into account during fruit harvest and postharvest handling. On the other side, the observation of localized plots with juice content below 35 % must be contextualized in the broader picture of the entire orchard which, in the present study, always had consistent temporal average level above 35 %. This study has provided evidence that fruit ripening variability should be considered in the site-specific orchard management of citrus to optimize their harvest date.