Manuela Zude

Spectrophotometric analyses of chlorophyll and single carotenoids during fruit development of tomato ( Solanum lycopersicum L.) by means of iterative multiple linear regression analysis

When using spectrophotometric transmittance readings of fruit extracts, the analysis of single carotenoids is difficult because of coinciding absorption bands of the various carotenoids and chlorophylls present in the solution. Aimed at the separate analyses of pigments, an iteratively applied linear regression was developed based on spectral profiles of pigment standards. The iterative approach was validated by dilution series of pigments and compared with commonly applied equation systems. High coefficients of determination and low measuring uncertainties were found for chlorophyll a and b (R(2) > or = 0.99, root mean square error RMSE < or = 10%). Carotenoids were separately analyzed with R(2) = 0.99, R(2) = 0.96, and R(2) = 0.98 for lycopene, beta-carotene, and lutein, respectively. The approach based on the spectral profiles provided low measuring uncertainties even if lutein was additionally present in the solutions, which was not possible with common data analyses. Subjecting tomato tissues (Solanum lycopersicum L.) to the iterative approach, contents of in vivo measured pigments were calculated with R(2) = 0.82, R(2) = 0.84, R(2) = 0.67, and R(2) = 0.03 for chlorophyll a and b, lycopene, and beta-carotene, respectively.

Approach for non-destructive pigment analysis in model liquids and carrots by means of time-of-flight and multi-wavelength remittance readings.

Non-destructive spectroscopy in the visible and near infrared wavelength range has been introduced for analyzing absorbing compounds in fruit and vegetables. A drawback of the method appears due to the measuring principle, where photons detected in the diffusive tissue are influenced by the sample absorption but also scattering properties leading to variation in the photon pathlength. In the present work, distribution of time-of-flight reading was used to calculate the effective pathlength between source and detector. Using this information in addition to the spectral intensities obtained with common continuous wave spectroscopy, Lambert-Beer law was applied for analyzing absolute pigment contents. The method was tested for liquid phantoms mimicking the optical properties of fresh fruit and vegetables. Lambert-Beer law using a constant pathlength as well as combined application of the intensity at a specific wavelength and the effective pathlength resulted in low calibration errors with r(2)>0.98. Applying the two calibrations on phantoms mimicking changes in the scattering properties resulted in validation results of r(2)=0.47 and 0.64, respectively. Improved results by using the effective pathlength were confirmed on real-world samples. The carrot carotenoids analysis resulted in validation results of r(2)=0.66 and 0.74, respectively, while the measuring uncertainty was reduced from 18.10 to 9.62%. Multivariate calibrations using the entire carrot spectra and data pre-processing aiming the reduction of scattering effects resulted in slightly lower measuring uncertainty by comparison. In the sensor fusion approach proposed, however, no expensive spectrophotometer is required and the phenomenon of varying optical properties of the sample is characterized.

Non-destructive evaluation of apple fruit maturity on the tree.

Non-Destructive Evaluation of Apple Fruit Maturity on the Tree The evaluation of apple fruit maturity (Malus domestica Borkh.) is based on destructive analyses, analysing starch conversion, fruit flesh firmness and Brix value. Specific threshold values exist for each cultivar and according to post-harvest treatment and storage. A rapid non-destructive method to evaluate the fruit maturity could be very important to obtain more reliable results. Since miniaturised spectrometer modules were available, visible/near infrared spectroscopy has been used to build up portable spectrometer equipment. Measurements were carried in weekly intervals on three cultivars in a commercial orchard in 2003 to 2005 during the period from August to October. The fruit maturity stage was described by two non-destructive spectral indices i) the chlorophyll decrease and ii) the anthocyanins increase. Both indices demonstrated the high variability of fruit maturity stage in orchard. The characteristics of several apple cultivars could be used to evaluate the actual differences in maturity stage. The spectral indices pointed out the influence of fruit yield and of temperature on the fruit maturity. Niedestrukcyjna Ocena Stopnia Dojrzałości Jabłek Na Jabłoni Ocena stopnia dojrzałości jabłek (Malus domestiuca Borkh.) jest oparta na destrukcyjnych analizach, dotyczących przemian chemicznych skrobi, jędrności miąższu w skali Brixa. Specyficzne wartości progowe są określone dla każdej odmiany w zależności od pozbiorczego traktowania i przechowywania. Szybka, niedestrukcyjna metoda do oceny stopnia dojrzałości jabłek mogłaby być pomocna do otrzymania bardziej wiarygodnych wyników. Do konstrukcji przenośnego spektrometru wykorzystano zminimalizowane moduły spektrometryczne w oparciu o spektroskopię w zakresie widma widzialnego i bliskiej podczerwieni. Pomiary były wykonywane w odstępach tygodniowych na trzech odmianach w sadzie przemysłowym w latach 2003 - 2005, w okresie od sierpnia do października. Stopień dojrzałości owoców był określany na podstawie dwóch niedesktrukcyjnych wskaźników spektralnych: i) spadku poziomu chlorofilu ii) wzrostu poziomu antocyjanów. Obydwa wskaźniki uwidoczniły wysoką różnorodność stopnia dojrzałości owoców w sadzie. Cechy charakterystyczne kilku odmian jabłek zostały wykorzystane do oceny rzeczywistych różnic w stopniu dojrzałości owoców. Spektralne wskaźniki wyraźnie wykazały wpływ wysokości plonu i temperatury na dojrzewanie owoców.

A Computational Model for Path Loss in Wireless Sensor Networks in Orchard Environments

A computational model for radio wave propagation through tree orchards is presented. Trees are modeled as collections of branches, geometrically approximated by cylinders, whose dimensions are determined on the basis of measurements in a cherry orchard. Tree canopies are modeled as dielectric spheres of appropriate size. A single row of trees was modeled by creating copies of a representative tree model positioned on top of a rectangular, lossy dielectric slab that simulated the ground. The complete scattering model, including soil and trees, enhanced by periodicity conditions corresponding to the array, was characterized via a commercial computational software tool for simulating the wave propagation by means of the Finite Element Method. The attenuation of the simulated signal was compared to measurements taken in the cherry orchard, using two ZigBee receiver-transmitter modules. Near the top of the tree canopies (at 3 m), the predicted attenuation was close to the measured one—just slightly underestimated. However, at 1.5 m the solver underestimated the measured attenuation significantly, especially when leaves were present and, as distances grew longer. This suggests that the effects of scattering from neighboring tree rows need to be incorporated into the model. However, complex geometries result in ill conditioned linear systems that affect the solvers convergence.

The Detection of Quality Deterioration of Apple Juice by Near Infrared and Fluorescence Spectroscopy

Processing and storage of apple juice often triggers quality deterioration regarding nutritional valuable compounds and unfavourable color changes resulting from browning. Fluorescence and near-infrared (NIR) spectroscopy were applied to detect such quality loss in apple juice. Juice samples were produced from Malus x domestica ’Pinova’, stored at 20 °C for 4 days or heated at 80 °C for 10 min and stored at the same conditions. The quality of apple juice was measured by standard parameters such as soluble solids content, pH, CIE L*, a*, and b* values. Juice fluorescence spectra were recorded with fluorescence excitation at 250, 266, 355, and 408 nm and emission at 280-899 nm resulting in an excitationemission- matrix (EEM) of 1240×4 for each sample. The NIR transmittance spectra were recorded in the wavelength range 900-1350 nm. The often used color b*-value for monitoring browning was correlated with the EEM variation and a reasonable calibration was built by means of n-way partial least squares (N-PLS) regression. The correlation coefficients were >0.9 in all treatments. NIR spectra were sensitive for predicting soluble solids content, but had poor capability to measure the color deterioration. Results indicated that the combination of NIR spectra and fluorescence EEM can be used to monitor the quality deterioration of apple juice.

Shifted excitation Raman difference spectroscopy: a potential tool for outdoor measurements in precision agriculture

In this work we present Shifted Excitation Raman Difference Spectroscopy (SERDS) as a potential spectroscopic tool for outdoor measurements in precision agriculture. A dual-wavelength diode laser at 785 nm is used as an excitation light source which provides an optical power up to 100 mW in cw-operation. Both emission lines for SERDS show single mode operation with a spectral width of ≤ 11 pm and a spectral distance of about 10 cm-1 over the whole power range. Raman experiments on apples are carried out and show Raman signals from wax layer and β-carotene. Raman investigations under daylight conditions are performed to simulate outdoor measurements. Here, polystyrene (PS) is used as test sample. A broadband signal together with narrow absorption lines of water vapor and Fraunhofer lines of singly ionized calcium (Ca II) mask the Raman lines of PS. Only the strong Raman signal at 999 cm-1 is visible. SERDS efficiently separates the Raman signals of PS from the background signals and a 14-fold improvement of the signal-tobackground noise ratio is achieved.

Methoden für die präzise obstbauliche Produktion

Der Ansatz von Precision Horticulture im Obstbau lehnt sich an das aus dem Ackerbau stammende Konzept der Prazisionslandwirtschaft bzw. der teilflachenspezifischen Bewirtschaftung an. Hierbei sollen prazise an das individuelle Geholzwachstum angepasste Pflegemasnahmen die bislang praktizierte einheitliche Behandlung aller Baume in einer Anlage ablosen. Voraussetzungen hierfur sind u. a. Bodenkarten und Informationen zum Pflanzenwachstum. Das Ziel ist es, den informationsgestutzten Obstbau voranzutreiben und durch ein raumlich und zeitlich differenziertes Management eine effizientere und nachhaltigere Bewirtschaftung zu erreichen.

In-situ analysis of fruit anthocyanins by means of total internal reflectance, continuous wave and time-resolved spectroscopy

In sweet cherry (Prunus avium), the red pigmentation is correlated with the fruit maturity stage and can be measured by non-invasive spectroscopy. In the present study, the influence of varying fruit scattering coefficients on the fruit remittance spectrum (cw) were corrected with the effective pathlength and refractive index in the fruit tissue obtained with distribution of time-of-flight (DTOF) readings and total internal reflection fluorescence (TIRF) analysis, respectively. The approach was validated on fruits providing variation in the scattering coefficient outside the calibration sample set. In the validation, the measuring uncertainty when non-invasively analyzing fruits with cw method in comparison with combined application of cw, DTOF, and TIRF measurements showed an increase in r2 up to 22.7 % with, however, high errors in all approaches.

Schnelle Qualitätsbewertung von Früchten mit Hilfe der Bildverarbeitung

Machine vision systems are integrated into many sorting lines designed to grade fruits and vegetables. Additionally, in newly installed sorting lines spectroscopic analysis methods within the visible range and with NIR spectroscopy are being used for grading produce on fruit dry matter and refractrometric soluble solids content. As a source of light, low-cost silicon based detectors and halogen lamps are used, which cover a wavelength spectrum of up to 1100 nm. Monochromatic laser diodes could provide a new method of sorting according to fruit flesh firmness in the future. This was tested on kiwi fruits. In the laboratory setup the three classes “soft”, “premium” and “hard” were distinguished with a 16.3% misclassification error. The data processing takes less than 70 ms per image on a personal computer (AMD64, 2.19GHz) which makes the technique suitable for commercial online assessment.

Corrigendum to “Non-invasive spectrophotometric sensing of carrot quality from harvest to consumption” [Postharvest Biol. Technol. 45 (2007) 30–37]

Fig. 4. Scatter plots of carrot -carotene contents analyzed by means of destructive chromatographic analysis and non-invasive spectrometry in remission mode applying a PLS model on SNV preprocessed data (A), y = a + bx (a = 782.54465, b = 0.77334513, Rcal = 0.87); and DOSC pre-processed data (B), y = a + bx (a = 130.82529, b = 0.96472452, Rcal = 0.97). The 95% prediction (outer lines) and confidence (inner lines) intervals of linear regression are shown.