Tesis:
Development of on line NMR applications for fruit internal qualiry.
- Autor: HERNANDEZ SANCHEZ, Natalia
- Título: Development of on line NMR applications for fruit internal qualiry.
- Fecha: 2006
- Materia: Sin materia definida
- Escuela: E.T.S. DE INGENIEROS AGRONOMOS
- Departamentos: INGENIERIA RURAL
- Acceso electrónico:
- Director/a 1º: BARREIRO ELORZA, Pilar
- Director/a 2º: RUIZ CABELLO OSUNA, Jesús María
- Resumen: Fruits and vegetables are purchased by the consumers blindly to their internal attributes due to the lack of reliable information. Recently a demand is placed by the industry for the development of on-line equipments that provide internal quality evaluation based on non-destructive techniques, as to engage consumer fidelity. Nuclear Magnetic Resonance (NMR) has shown to be a promising technique for dynamic Spectrometry and 1-D MR images. The aim of this research has been to develop a feasible non-destructive procedure for detecting undesirable characteristics in citrus and pears under on-line conditions based on NMR techniques. Experimental dynamic work using MRI has been performed on a Bruker BIOSPEC 47/40 (4.7 Tesla). NMR Relaxometry (0.1 Tesla, 0.235 Tesla, 0.55 Tesla, 2.35 Tesla, 4.7 Tesla and 7 Tesla) and NMR Diffusion (0.235 Tesla, 0.55 Tesla and 7 Tesla) have been used as auxiliary exploratory techniques under static conditions. A devoted conveyor belt to move the fruit through the NMR spectrometer was constructed during this Thesis. Axial Fast Low Angle SHot (FLASH) T2*-weighted MR images were obtained from whole oranges moving at 54 and 100 mm/s in order to detect those fruits presenting freeze injuries and seeds in their respective studies. Coronal FLASH T2-weighted MR images were obtained from whole moving mandarins at 54 mm/s in order to identify seed containing fruits compared to seedless ones. As for pears, coronal FLASH MR images both T2- and PD-weighted were obtained when whole fruits were conveyed at 54 mm/s in order to detect those samples affected by internal browning. T2 maps were obtained from entire pears, (T1-T2) and (T2-D) correlation spectra were obtained from tissue pieces get a wider insight on tissue alteration in order to guide the MRI experiments. The acquisition of axial MR images involved image blurring due to superimposition of signals from different excited slices. Coronal images overcame superimposition problems although drove the development of devoted algorithms for automatic correction of the motion-induced artefacts. Image processing was performed by applying especially developed algorithms that extracted a number of features characterizing the sample under inspection. Further analysis over such features provided threshold values for the segregation of fruits with poor internal quality. Most relevant results can be summarized as follows: Axial FLASH imaging is a suitable technique for the detection of freeze injury in oranges when conveyed at 54 mm/s and 100 mm/s. The percentage of signal hypointense tissue in relation to the whole tissue provided respective thresholds. Axial FLASH imaging is a suitable technique for the on-line detection of oranges containing more than one seed when conveyed at 54 mm/s belt speed. The percentage of signal hypointense tissue in relation to the whole tissue is the most reliable feature for seed identification. The results obtained from the acquisition of axial MR images of moving samples are greatly influenced by the image blurring. The acquisition of coronal MR images involved a noticeable improvement in the quality of the images acquired under dynamic conditions since the motion correction procedure achieves a high level of blurring deletion.%&/ü An algorithm devoted to the correction of motion artefacts has provided successful results as those features extracted from motion corrected images are statistically indistinguishable from those of the static ones as stated by ANOVA.%&/ü Coronal FLASH imaging is a suitable technique for the on-line identification of seed containing mandarins. The maximum radius and the perimeter of the seeds-axis area have been addressed as the most relevant features for classification of the samples into their corresponding classes. Internal browning in "Blanquilla" pears is a postharvest disorder that may be identified by MRI. Changes in microscopic structure associated to the disorder development are reflected in NMR relaxometry (T1, T2), diffusivity (D), and proton-weighted density. Coronal FLASH imaging is a suitable technique for the on-line identification of internal browning in pears. Histogram-based features have allowed achieving high percentages of correctly classified fruits. It has been demonstrated that it is feasible to perform a straightforward transfer of available models developed under static conditions towards on-line conditions.