Victor Vicent

University of Dar es Salaam, Chemical and mining, Alumnus

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Caractérisation expérimentale et modélisation de la microstructure de produits alimentaires surgelés soumis aux phénomènes de recristallisation et de sublimation : Application aux produits végétaux

La congélation est utilisée pour préserver la qualité des aliments et prolonger leur durée de vie... more La congélation est utilisée pour préserver la qualité des aliments et prolonger leur durée de vie. Cependant, leur microstructure peut changer avec la formation et l’évolution des cristaux de glace en cours de congélation et de stockage, conduisant à une modification de leur qualité. Il existe peu de données 3D sur les évolutions de la microstructure des produits congelés, or ces informations pourraient être utiles pour optimiser les processus de congélation et de stockage. Les travaux de recherche effectués dans cette thèse ont appliqué à la fois des approches d'imagerie micro-tomographique et de modélisation mathématique pour une meilleure compréhension des interactions procédés-microstructure-qualité dans les fruits et légumes, selon les conditions de congélation et de stockage.Une méthode de visualisation et de traitement d’images micro-tomographiques à rayons X a été développée. Elle est basée sur une acquisition des images à l’état congelé et une segmentation à partir des ...

Imaging and modeling of the microstructure of frozen foods during recrystallization and sublimation : A case study on plant-based products

Institut agronomique, vétérinaire et forestier de France ; Université catholique de Louvain (1970-....), Apr 25, 2019

Applicability of X-ray microtomography for characterizing the microstructure of frozen apple during storage

X-ray microtomography (X-ray micro-CT) was applied to visualise the change of 3D microstructure d... more X-ray microtomography (X-ray micro-CT) was applied to visualise the change of 3D microstructure during freezing of 'Jonagold' apple at a pixel resolution of 3.83 µm. To better understand the microstructure evolution during freezing, pore size distributions were carefully analysed. This work highlighted the applicability of X-ray micro-CT to visualise the microstructure evolution in frozen apple samples subjected to three different freezing protocols (at -6°C, -12°C, -20°C). Freezing process was done directly on cooling mounted on micro-CT system that allows one to follow the structure of the materials in frozen state. It was observed that slow rate of heat removal at -6°C damages cellular tissue of apple considerably as noted on the spatial irregularity of pores. Instead; slightly damaging of apple tissues was observed for the latter two freezing protocols (i.e. at -12°C and -20°C). From this study, we manage to show the application of X-ray micro-CT to reveal and quantify t...

Understanding the microstructure of frozen apple during storage using X-ray micro CT system

Quality changes kinetics of apple tissue during frozen storage with temperature fluctuations

International Journal of Refrigeration, 2018

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  Quality changes in apple tissue were studied during frozen storage.  Temperature fluctuations significantly affect the apple quality during storage.  The quality data were fitted to first order kinetics.  A developed kinetic model can be used to predict the apple quality evolution.

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A new method developed to characterize the 3D microstructure of frozen apple using X-ray micro-CT

Journal of Food Engineering, 2017

Non-destructive imaging techniques have become indispensable to improve insights into the microst... more Non-destructive imaging techniques have become indispensable to improve insights into the microstructural changes occurring in fruit tissue during freezing. Here, apple cortex tissue samples were frozen using different freezing rates: (i) slow freezing (2.0 °C per min.), (ii) intermediate freezing (12.6 °C per min.) and fast freezing (18.5 °C per min.). Temperature-controlled X-ray micro-CT was optimized and then applied to visualize and quantify the 3D microstructure and ice crystal distribution at a pixel resolution of 3.8 μm. Ice crystal size distributions with mean equivalent diameters of about 41 ± 3.5 μm, 55 ± 7.4 μm and 71 ± 9.6 μm were obtained for the fast, intermediate and slow freezing rates, respectively. A new imaging methodology was developed and validated to allow segmentation of the ice crystals in frozen apple tissue using the X-ray attenuation coefficients of the reference model samples, i.e. frozen pure water and concentrated apple juice.

Modelling Biological Variation in the Skin Background Colour of 'Jonagold' Apples During Controlled Atmosphere Storage

Acta Horticulturae, 2015

Skin background colour is a very important quality aspect in the grading of 'Jonagold' apples, wi... more Skin background colour is a very important quality aspect in the grading of 'Jonagold' apples, with consumers usually preferring fruit with a green background colour. However, apple handlers are usually faced with large fruit-to-fruit variability of background colour within a population of fruit. In this study, a stochastic modelling approach is used to describe how the initial fruit-to-fruit variability in the background colour of 'Jonagold' apples present at harvest, propagates throughout the postharvest chain. Two hundred fruit were harvested and stored at 1 or 4°C, under different controlled atmosphere (CA) conditions for six months. The fruit were taken out of storage every two months, and the background colour and the ethylene production of individual fruit were measured. At the end of the six months storage, the fruit were placed in shelf life conditions for 15 days, during which skin background colour and ethylene production were measured every five days. A mathematical model was developed to describe the postharvest loss of the skin greenness of apples during CA storage, by assuming that the loss is principally due to chlorophyll breakdown, the rate of which is dependent on the endogenous ethylene concentration within the fruit. The stochastic model parameters in the model were identified, and by treating these parameters as fruitspecific parameters, the model could describe more than 93% of the data for the individual fruit. By considering these fruit-specific parameters as stochastic parameters, the Monte Carlo method was used to describe the propagation of the fruit-to-fruit variability of the background colour of 'Jonagold' apples within a population. The model developed in this study can be used to predict how the initial fruit-to-fruit variability within a batch of apple will propagate throughout the postharvest chain.

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Managing biological variation in skin background colour along the postharvest chain of ‘Jonagold’ apples

Postharvest Biology and Technology, 2014

Skin background colour is an important quality aspect in the grading of Jonagold apples, with con... more Skin background colour is an important quality aspect in the grading of Jonagold apples, with consumers usually preferring fruit with a green background colour. However, apple handlers are usually faced with large fruit-to-fruit variability of background colour within a population of fruit. In this study, a stochastic modelling approach was used to describe how the initial fruit-to-fruit variability in the background colour of Jonagold apples present at harvest, propagates throughout the postharvest chain. Two hundred and twenty Jonagold apple fruit were harvested and stored at 1 ºC or 4 ºC, under different controlled atmosphere (CA) conditions for six months, followed by two weeks exposure to shelf life conditions, during which the background colour and ethylene production of the individual fruit were measured. A kinetic model was developed to describe the postharvest loss of skin greenness, by assuming that the loss was principally due to chlorophyll breakdown, the rate of which was dependent on the endogenous ethylene concentration. Stochastic model parameters were identified, and by treating these parameters as fruit-specific, the model could account for more than 95 % of the variability of the data. By treating the stochastic model parameters as random factors, the Monte Carlo method was used to model and describe the propagation of the fruit-to-fruit variability of the background colour within a population of fruit. The model developed in this study can allow better management of variability in quality along the postharvest chain, by predicting how the initial fruit-tofruit variability within a batch of apple will propagate throughout the postharvest chain, as a function of storage and shelf life conditions.

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Pectin modifications and the role of pectin-degrading enzymes during postharvest softening of Jonagold apples

Food Chemistry, 2014

This study aimed at understanding softening in Jonagold apple (Malus Â domestica Borkh.) fruits, ... more This study aimed at understanding softening in Jonagold apple (Malus Â domestica Borkh.) fruits, by investigating pectin modifications and the evolution of pectin-modifying enzymes during postharvest storage and ripening. Jonagold apples were harvested at commercial maturity and stored at different temperatures and controlled atmosphere conditions for 6 months, followed by exposure to ambient shelf life conditions (20°C under air) for 2 weeks. The composition of the pectic material was analysed. Furthermore, the firmness and the ethylene production of the apples were assessed. Generally, the main changes in pectin composition associated with the loss of firmness during ripening in Jonagold apples were a loss of side chains neutral sugars, increased water solubility and decreased molar mass. Also, the activities of four important enzymes possibly involved in apple softening, b-galactosidase, a-arabinofuranosidase, polygalacturonase and pectin methylesterase, were measured. Pectin-related enzyme activities highly correlated with ethylene production, but not always with pectin modifications.

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Effect of dynamic storage temperatures on microstructure of frozen carrot imaged by X-ray Computed Tomography

Temperature abuses are often encountered during cold storage and distribution chain of food produ... more Temperature abuses are often encountered during cold storage and distribution chain of food products such as frozen vegetables. The subsequent ice recrystallization results in microstructural changes, which is closely linked to the final vegetable quality. In this work, X-ray µCT was used to visualize and quantify 3D ice crystal changes in carrot over a period of two months of frozen storage with dynamic change of temperatures. The results obtained revealed a significant increase in ice crystal size during the storage period, simultaneous to a significant reduction in ice crystal count number. The 3D data on ice crystals acquired within this work provide a better insight for the description of microstructure evolution, and for a better control of cold storage sector of frozen vegetable.

Modeling ice recrystallization in frozen carrot tissue during storage under dynamic temperature conditions

Journal of Food Engineering

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