Browsing by Author "da Silva, J. M."
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- A possibility for non-invasive diagnosis of superficial scald in 'Rocha' pear based on chlorophyll a fluorescence, colorimetry, and the relation between alpha-farnesene and conjugated trienolsPublication . Guerra, Rui Manuel Farinha das Neves; Garde, I. V.; Antunes, Maria Dulce; da Silva, J. M.; Antunes, Rosário; Cavaco, A. M.This study aimed to identify physiological markers in superficially scalded 'Rocha' pear (Pyrus communis L 'Rocha') that would relate to chlorophyll a fluorescence (CF), allowing a non-invasive diagnosis of the disorder. Conditions chosen before shelf life provided two fruit groups with different developing patterns and severity of superficial scald: T fruit fully developed the disorder in storage, while C fruit developed it progressively throughout shelf life. Principal component analysis (PCA) of all the measured variables, and simple linear correlations among several major parameters and scald index (SI)/shelf life showed that scald and ripening/aging were concurring processes, and that it was not possible to isolate a particular variable that could deliver a direct non-invasive diagnosis of the disorder. For both fruit groups the SI resulted from the balance between the reducing power (OD200) and the content of conjugated trienols (CTos) and alpha-farnesene (alpha-Farn) in the fruit peel. At OD200 > 150 there was a linear relationship between CTos and OD200, suggesting that the level of antioxidants was self-adjusted in order to compensate the CTos level. However, at OD200 < 150 this relationship disappeared. A consistent linear relationship between dos and alpha-Farn existed throughout shelf life in both fruit groups, contrarily to the early storage stage, when those compounds do not relate linearly. The CF variables F-0, F-v/F-m, and the colorimetric variables, L* and h degrees were used in multi-linear regressions with other physiological variables. The regressions were made on one of the fruit groups and validated through the other. Reliable regressions to alpha-Farn and CTos were obtained (R approximate to 0.6; rmsec approximate to rmsep). Our results suggest that a model based on CF and colorimetric parameters could be used to diagnose non-invasively both the contents and the relationship between alpha-Farn and CTos and hence the stage of scald development. (C) 2011 Elsevier By. All rights reserved.
- A Preliminary Approach to the Prediction of 'Rocha' Pear Skin Pigments by Vis/NIR Reflectance SpectroscopyPublication . Cavaco, A. M.; Antunes, Maria Dulce; da Silva, J. M.; Guerra, Rui Manuel Farinha das Neves'Rocha' pear (Pyrus communis L.) is an exclusively Portuguese certified pear cultivar commercialized worldwide. Mature unripe 'Rocha' pears were obtained from COOPVAL (Cadaval, Portugal) after 8 months at -0.5 degrees C, 94-96% RH and CA (2% O-2+0.5% CO2). Then, they were maintained in a dark room at 20+/-2 degrees C and 70% RH to simulate shelf life. For three weeks these fruit were followed along using Vis/NIR reflectance spectroscopy in the wavelength range of 400 to 950 nm, and their colour and firmness were evaluated by standard techniques. 'Rocha' pear firmness decreased significantly during shelf life, paralleled by the yellowing of the fruit skin (increase in a(star) and Hue angle). Pigments were extracted from fruit skin and assayed spectrophotometrically. Both Chla and Chlb contents decreased along ripening in shelf life, while contents of carotenoids remained constant. Vis/NIR reflectance spectra were correlated with the respective fruit skin pigments content by PLS. Prediction models were obtained for Chl (a, b, a+b), but not for carotenoids. Models were reasonably significant in regression terms [r(Chla)=0.898; r(Chlb)=0.897; r(Chla+b)=0.918], but the respective SDR (standard deviation ratio = standard deviation of the validation set/RMSEP)(2.2 (Chla), 2.3 (Chlb), 2.2 (Chla+b)) suggest that only a coarse quantitative prediction is possible for all models. Although Chla model required a higher number of latent variables [Lv(Chla)= 6; Lv(Chlb or Chla+b)= 3], similarity between RMSEC and RMSEP was lower for the other parameters [Chla: 4.6 and 4.6 g m(-2) Chlb: 3.9 and 2.3 g m(-2), Chla+b: 7.3 and 6.7 g m(-2)]. A better performance for these models has been expected, because most of the differences found in the Vis/NIR spectra in shelf life were in the Chl absorption region. However, only a coarse prediction capability was found. Thus, the data obtained suggest that changes on the background around 670 nm decrease the prediction capability of the PLS model and should be further investigated.
- Chlorophyll a Fluorescence: a Fast and Low-Cost Tool to Detect Superficial Scald in 'Rocha' Pear (Pyrus communis L. 'Rocha')?Publication . Garde, I.; Antunes, Maria Dulce; da Silva, J. M.; Guerra, Rui Manuel Farinha das Neves; Cavaco, A. M.This study aimed to test whether the chlorophyll a (Chla) fluorescence determined by a low-cost non-modulated fluorometer could provide fast, reliable and non-invasive estimators of superficial scald in 'Rocha' pear (Pyrus communis L. 'Rocha'). Fruit were harvested before the optimal maturation stage and cold stored under normal atmosphere for 7 months (NA: 0 degrees C, 90-95% RH) and 2 in controlled atmosphere (CA: 0 degrees C, 90-95% RH, 1.5 kPaO(2) + 0.5 kPa CO2) (T), or harvested at the optimal maturation stage and cold stored for 9 months under CA (C). Then, they were transferred to shelf-life conditions (22+/-2 degrees C, 70% RH) and followed for 7 d. Chla fluorescence, scald index (SI), ripening attributes, alpha-farnesene, conjugated trienols, and photosynthetic pigments were determined for each pear in both groups. Conditions chosen before shelf-life did not prevent the subsequent ripening of any fruit, but changed dramatically the superficial scald development pattern: in C fruit, the disorder developed progressively during shelf-life, whereas in T fruit, it peaked during storage. C fruit exhibited a significant negative correlation (R=-0.65; p<0.05) between Fv/Fm and scald development, but not with ripening (R=-0.15; p<0.05). As expected, the opposite was observed in T fruit, in which only a low, positive, yet significant correlation was found between Fv/Fm and ripening (R=0.44; p<0.05). The multiple regression approach using Fv/Fm and other Chla fluorescence parameters produced an equation from which we calculated the 'predicted' scald index in C fruit. This correlated clearly (R=0.73; p<0.05) with the real values visually assessed. If color values a*, b* and Hue were included in this multiple regression, the correlation was significantly enhanced (0.91; p<0.05). Although preliminary, this study has shown that basic Chla fluorescence parameters are valuable estimators of superficial scald in 'Rocha' pear and might be used in the early detection of the disorder.
- Preliminary Results on the Non-Destructive Determination of Pear (Pyrus communis L.) cv. Rocha Ripeness by Visible/Near Infrared Reflectance SpectroscopyPublication . Cavaco, A. M.; Antunes, Maria Dulce; da Silva, J. M.; Guerra, Rui Manuel Farinha das NevesPear (Pyrus communis L.), cv. Rocha was rapidly adopted by consumers due to its inherent quality and currently has great acceptance in both national and international markets, being mainly produced in the west region of Portugal. We report here a first approach to the use of the non-intrusive method of Visible/Near Infrared Reflectance Spectroscopy (Vis/NIRS) to estimate the ripeness of pear cv. Rocha. Mature unripe pears obtained from Frutoeste (Mafra, Portugal) after a six-month cold-storage, were maintained in a dark room at circa 20 degrees C during three weeks. They were followed using the Vis/NIRS in the wavelength band between 400 and 950 nm with two different configurations for the spectra acquisition, namely the Integrating Sphere (IS) and the Partial Transmittance (PT). The diffuse reflectance spectra obtained by the two configurations were compared with the respective fruit ripening parameters (colour, firmness, soluble solids content and % dry matter), determined through the standard techniques. Concerning the rough estimation of ripening parameters, data suggested an increase in both the intensity in the green to red band and pulp %dry matter, but a decreasing firmness. All other parameters remained constant. Relatively to the optical results, we have observed that the PT spectra exhibited clearer features than the IS spectra, especially from 700 nm onwards. This is probably due to the fact that the PT configuration probes more deeply into the fruit pulp. Three peaks at 600 (circa 30%), 725 and 812 nm (both at circa 50%) and a minimum at 675 nm, were identified in both IS and PT spectra. The values of reflectance peaks were approximately constant during ripening, but they moved to slightly lower wavelengths in the second week. A significant increase (circa 3-fold) in the minimal diffuse reflectance was observed in the second week, most probably associated partially, to a decrease in the fruit peel chlorophyll content.
- 'Rocha' pear firmness predicted by a Vis/NIR segmented modelPublication . Cavaco, A. M.; Pinto, Patricia IS; Antunes, Maria Dulce; da Silva, J. M.; Guerra, Rui Manuel Farinha das NevesWe present a segmented partial least squares (PLS) prediction model for firmness of 'Rocha' pear (Pyres communis L) during fruit ripening under shelf-life conditions. Pears were collected from three different orchards. Orchard I provided the pears for model calibration and internal validation (set 1). These were transferred to shelf-life in the dark at 20 +/- 2 degrees C and 70% RH, immediately after harvest. External validation was performed on the pears from the other two orchards (sets 2 and 3), which were stored under different conditions before shelf-life. Fruit was followed in the shelf-life period by visible/near infrared reflectance spectroscopy (Vis/NIRS) in the range 400-950 nm. The correlation between firmness and the reflectance at some wavelength bands was markedly different depending on ripening stage. A segmented partial least squares model was then constructed to predict firmness. This PLS model has two segments: (1) unripe and ripening/ripe pears (high firmness); (2) over-ripe pears (low firmness). The prediction is done in two steps. First, a full range model (full model) is applied. When the full model prediction gives a low firmness value, then the over-ripe model is applied to refine the prediction. The full model is reasonably significant in regression terms, robust, but allows only a coarse quantitative prediction (standard deviation ratio, SDR = 2.48, 1.50 and 2.40 for sets 1, 2 and 3, respectively). Also, RMSEP% = 139%, 91% and 56%, indicating large relative errors at low firmness values. The segmented model improved moderately the correlation, and the values of RMSEC, RMSEP and SDR: it improved significantly the RMSEP% (29%, 55% and 31%), providing an improvement of the relative prediction errors at low firmness values. This method improves the ordinary PLS models. Finally, we tested whether chlorophyll alone was enough for a predictive model for firmness, but the results showed that the absorption of chlorophyll alone does not explain the performance of the PLS models. (C) 2008 Elsevier B.V. All rights reserved.