In this research, the potential of using a multi-spectral imaging system was investigated for detecting bruises on ‘Golden Delicious’ apples. For this purpose, a hyperspectral imaging system has been ...built in the spectral region between 400 and 1000
nm. Based on the principal components analysis for the hyperspectral images, four wavebands were selected for a multi-spectral imaging test. The principal components analysis on the multi-spectral images gave very similar results as on the hyperspectral images. The second and third principal components scores images were found to be suitable for identifying the presence of bruises. An image processing and classification algorithm based on moments thresholding was developed. The classification results indicated that, for the sample population used in this experiment, about 93% of the non-bruised apples were recognised as sound. An accuracy of about 86% was achieved for detecting bruises, although all the bruised regions were found to remain in the images after moments thresholding.
The impulse response method is often used to measure firmness of spherical fruits. In this method the fruit is excited using an impact hammer and the response signal is captured using a microphone. ...This vibration response signal is subsequently analysed and related to the firmness of the fruit. In our work the effect of the shape of pears on their resonant frequencies is investigated using finite element (FE) modal analysis. Fifty differently shaped 3D FE meshes of ‘Conference’ pears were generated using a geometrical modelling system. The FE model was validated, and found to be sufficiently accurate. The length/maximal diameter (
L/
D) ratio and the Fourier descriptors were used as shape descriptors. A strong linear relationship (
r
2>0.84) was found between the third normalised Fourier descriptor (F3) and the resonant frequencies. A weak linear relation was detected using the
L/
D and the other normalised Fourier descriptors. A simulation of firmness measurements based on the calculated resonant frequency values was carried out to estimate the Young's (
E) modulus of the pear as a measure of its firmness. The estimated error with these simulations was found to be 31.44,
8.02 and 3.82% if the bending, the compression and the oblate–prolate modes were measured and the
L/
D was used as a shape descriptor. If F3 was used, the following error values were found: 6.0% for the bending, 3.39% for compression and 3.38% for the oblate–prolate modes. The results of this study may help in the development of a non-destructive firmness sensor for non-spherical fruits.
The accuracy and applicability of different methods for estimating resistance to gas diffusion through the analysis of the efflux of preloaded inert gas out of a fruit were critically assessed. The ...inert gas neon was introduced as a good replacement for the non-inert gas ethane. A sensitivity analysis was carried out to determine the importance of the different parameters and indicated the importance of the internal free space volume and of the fruit surface area. Experiments with fruit of two apple and two pear cultivars confirmed that the results obtained with non-linear regression were more accurate. The largest resistance to gas diffusion was found in ‘Doyenné du Comice’ pears, followed by ‘Conference’ pears and ‘Braeburn’ apples, and the lowest value was found for ‘Jonica’ apples. Storage duration did not influence the resistance to gas diffusion except for ‘Doyenné du Comice’ pears where a significant increase in resistance to gas diffusion during storage was found. Harvest date had no influence on resistance to gas diffusion.
A model-based approach to design periodic thermal treatments for surface decontamination of strawberries, and fruit in general, was developed. The model accounts for the actual shape of the ...strawberry, surface decontamination kinetics and temperature-related product quality objectives. Conduction heat transfer was coupled with a first-order kinetic model for microbial inactivation at the surface of strawberries. The thermophysical properties were estimated based on the chemical composition of strawberries, and the inactivation properties of
Botrytis cinerea were used. The heat transfer model was validated based on immersion experiments of strawberries in pure water at different temperatures.
The effect of different periodic heating cycles on the internal temperature distribution was expressed by means of a thermal product state functional, in which temperature increases were exponentially penalised. Computer simulations revealed that heating cycles with a small period length minimise the overall product temperature increase and, hence, reduce the level of quality losses. In this way large temperature variations are limited to the product boundary. This model-based approach provides a postharvest engineering tool for design and fine tuning of surface decontamination processes and equipment.
Pears are one of the most important fruits in Europe. There are a number of varieties that are of economic importance. Growers want to have control over the harvesting and (long term) storage ...conditions in order to bring fruit of optimal quality to the consumers. In this contribution a number of pear properties are discussed that affect the quality and the quality evolution of pears. Measurement techniques for quality before and after harvest are also discussed. They include non-destructive acoustic measurements, X-ray tomography and MRI. Pear shape is non-spherical which has implications for non-destructive firmness measurement. It also plays a role in the diffusion and exchange of respiratory gasses with the surroundings. If storage conditions are not properly maintained then severe storage disorders may occur.
Summary A 670nm, 3 mW solid‐state laser diode module has been used as light source to monitor quality changes of tomatoes (c.v. Trust) stored at room temperature for 8 days. The scattering images ...were captured and the total number of pixels in the image was taken as an indicator of fruit ripeness. Non‐destructive acoustic and traditional compression tests were used to determine the firmness of tomatoes. The results showed significant differences in image size (number of pixels) for tomatoes at different maturity stages. The image size increased during the storage period. Fruit firmness showed a negative correlation with the image size. The soft tomato corresponds to a larger image size. A second order polynomial equation expressed the relationship between the stiffness factor and the size of scattering image (r2≈ 0.62). The system has the potential to be used to evaluate the ripeness of tomato fruits.
Starch conversion into sugars is one of the most important indicators for predicting the optimal harvest dates for apples. The starch conversion is usually assessed using an iodine test, in which cut ...fruit are dipped in iodine solution and stain patterns are rated. A methodology based on the image analysis of iodine-treated apple slices was used to quantify the uncertainty on the traditional starch index measurements. Considering the subjective interpretation of different inspectors, the errors for certain image assignments were up to 60%. The averaged values of index assignments of groups of images, however, were for most starch indices not significantly different. It was noticed that the subjective interpretation was related to the high number of indices on the chart, the non-linear scale and a sequence disorder of the reference chart. A modified logistic model was proposed to represent the sigmoidal starch index pattern during the preharvest period by two model parameters. Based on these two parameters, and the recommended starch index at harvest, the optimal harvest date was determined. With this technique, the orchard and cultivar effects were analysed.
A steady state variance propagation algorithm is derived to investigate the effect of stochastic air temperature disturbances on the variability of the temperature field inside refrigerated fruits ...during cold storage conditions. The disturbances are modelled by continuous-time autoregressive processes of variable order. The algorithm is based on the finite element formulation of the heat conduction equation and involves the numerical solution of matrix equations of the Lyapunov and Sylvester type. As an example, the cold storage of pineapple has been considered. It is shown that disturbances of different order but with the same scale of fluctuation result in comparable centre temperature variances.
A steady state variance propagation algorithm is derived to investigate the effect of stochastic air temperature disturbances on the variability of the temperature field inside refrigerated fruits ...during cold storage conditions. The disturbances are modelled by continuous-time autoregressive processes of variable order. The algorithm is based on the finite element formulation of the heat conduction equation and involves the numerical solution of matrix equations of the Lyapunov and Sylvester type. As an example, the cold storage of pineapple has been considered. It is shown that disturbances of different order but with the same scale of fluctuation result in comparable centre temperature variances.
Un dérivé d'algorithme de la variance de la propagation en régime permanent a été utilisé pour étudier l'effect des perturbations de température de l'air stochastiques à l'intérieur de fruits lors de leur entreposage frigorifique. Modélisation des perturbations était effectuée par des procédés autorégressifs d'ordre variable en continu. L'algorithme est basé sur la formulation par éléments finis de l'équation de la conduction de la chaleur et comprend la résolution numérique des équations de matrice du type Lyapunov et Sylvester. L'exemple de l'entreposage de l'ananas a été utilisé. Il a été montré que les perturbations d'ampleurs différentes mais avec la même échelle de fluctuation donnent des variances de température comparables au coeur des fruits.
