Olivier Rouaud

École Nationale Vétérinaire, Agroalimentaire et de l'Alimentation Nantes-Atlantique | Oniris · Department of Food Processing, Management and Sustainable Development

This study aimed to model an innovative process of pulsed microwave assisted freezing (MAF), which was expected to improve frozen product quality. The phase change model was based on spherical ice crystal growth and an original enthalpy formulation. The objective was to understand better the thermal interactions between microwaves and a product bei...

Among innovative freezing processes, electromagnetic wave assistance during freezing has received great attention in recent years. The literature provides interesting studies indicating that smaller ice crystals may be obtained during freezing with the assistance of microwaves. In the companion paper, we designed a laboratory scale prototype to per...

An original device dedicated to additive manufacturing was developed to pre-bake cake batter. Its originality lies in the fact that pre-baking is ensured by ohmic heating implemented in a rectangular channel equipped with two parallel electrodes. Experiments and numerical studies were carried out and benchmarked. The rheological properties of the c...

This paper reviews the results of frosting, defrosting and frost management research that have been reported over the past fifty years. The literature can be split into three categories: frost formation and properties, frost effect and frost management techniques, and those for different geometries and under different conditions. The aim is to prov...

The purpose of this study was to experimentally investigate the enhancement of forced convection heat transfer by corona wind in a channel scaled to potential future drying systems. An experimental rig was designed to investigate the thermal and dynamic effects of electro-hydrodynamic (EHD) induced air flow on the grounded bottom wall. The primary...

Microwave sterilization has seen many innovative solutions to solve its primary problem of non-uniform heating. Since its initial studies in the late 1940s, there were solutions that were put forward to address, such as using mechanical holders to contain the inner pressure of the package with food materials, use of fluids instead of mechanical hol...

The measurement of dielectric properties of foods is essential in the design and control of microwave drying systems as they describe the capability of a material to absorb, transmit and reflect electromagnetic energy. The dielectric properties of selected low-moisture products (corn starch, curry, paprika, rice grain and wheat grain) were evaluate...

In most soft wheat products such as cakes, baking powder (BP) plays an important role in achieving the desired product volume through batter aeration by the release of CO2 during baking. However, the optimization of a blend of constituents in BP is minimally documented, especially the selection of acids, which is often supported by the suppliers ba...

Drying is a very old process designed to remove water from food products to extend their self-life, among many benefits. Because convective drying is a very energy-intensive process, novel drying technologies have to be studied to give rise to more efficient and economical dryers. Based on recent experimental and numerical studies, combining electr...

This chapter presents the basic physical concepts related to the application of electrotechnologies dedicated to bioprocessing with focus on food processing. General guidelines, process parameters, and product properties are detailed with the different heating mechanisms applicable to microwave (MW), radiofrequency, and ohmic heating (OH) processes...

The formation of frost on heat exchangers is a phenomenon that appears during specific operating conditions. The presence of frost often incurs a decrease in the amount of cooling performance, resulting in the need for defrost cycles. In this paper, we are interested in the conditions of deep (quick) freezing in industrial freezers characterized by...

The aim of this study was to develop an innovative process dedicated to enhancing the quality of frozen food using microwaves. A microwave assisted freezing device was designed at the laboratory scale to perform experiments in controlled conditions. Small samples of methylcellulose gels were frozen using nitrogen gas in a TE10 waveguide, where micr...

Industrial thawing of raw tuna fishes for the canning industry is of great importance in the global economy. Due to the heat transfer limitations within large sample pieces, these processes need to be improved to reduce fluid and energy consumption. In this work, the water immersion thawing process of yellowfin tuna was studied from both experiment...

Gestion du givre dans les surgélateurs industriels ( Thesis objective and Work progress)

The main aim of this study was to develop a continuous microwave treatment system of whey proteins and then apply this process at 37 °C, 50 °C, 65 °C and 70 °C to achieve pepsinolysis and produce extensively hydrolysed bovine whey protein hydrolysates with low allergenic properties. The microwave process was compared to a conventional thermal treat...

Pour améliorer la qualité de congélation d’un gel modèle, une assistance micro-ondes a été utilisée pour perturber le changement d’état de l’eau dans le but de former de plus petits cristaux de glace. Un prototype à l’échelle laboratoire a été fabriqué pour contrôler au mieux les conditions opératoires. La qualité de congélation a été déterminée pa...

A 3D numerical model was developed to study the heat and mass transfer in a commercial-sized crustless sandwich bread. The objective was to locate the sensitive spots (high and low temperature locations) during a potential industrial baking and to know more about the impact of the process on the final water content of the product. The model was val...

Dielectric properties of a variety of foodstuffs were measured during freezing and thawing conditions, and are presented here as functions of temperature. Measurements were done with the Agilent 85070 high temperature dielectric probe. The differences in characteristics of the graphs resulting from cooling and thawing are discussed. A specific mode...

Crystallization of water and food systems may be affected by electric and magnetic fields. In this review paper, the crystallization of water and food systems assisted by DC voltage (DC-V) is compiled based on existing literature. Two ways of applying DC-V during electrocrystallization can be identified, namely charge flow (CF) conditions with elec...

Proofing of bread dough was studied under ohmic heating for a target temperature of 35 °C. An experimental device based on PLC monitoring was developed to study the effect of heating rates and voltages on the proofing process. Conventional and ohmic heating-assisted proofing were compared; the results showed that the process itself had no impact on...

Bread dough baking was investigated using ohmic heating technology. An experimental system was set up for the measurement of the electrical conductivity of bread dough during heating. The influence of temperature, salt content and degree of fermentation (porosity) on the electrical conductivity of dough was investigated. It was observed that it inc...

Pour étudier l’impact thermique d’un champ électrique induit par des micro-ondes lors d’un procédé de congélation, nous avons développé un modèle numérique couplant l’équation de la chaleur aux équations de Maxwell. Le modèle a d’abord été validé à partir de données de la littérature, puis exploité pour mettre en évidence le rôle de la durée des pu...

Electrohydrodynamic convective drying (EHD drying) is a novel drying method used to enhance forced convection drying (FC drying) by using a wire-electrode to create an electrostatic field. In a previous study, the efficiency of EHD drying (using three different wire-electrode configurations) was compared to classical FC drying by measuring the dryi...

EHD drying (Electrohydrodynamic convective drying) is a novel drying method used to enhance FC drying (forced convection drying) by using a wire-electrode to create an electrostatic field. In this work we studied the dehydration of a food product by means of FC verses EHD drying using three different wire-electrode configurations determined by a prio...

The objectives of this work were to evaluate the advantages brought by using cryogenic freezing in comparison to blast air freezing with respect to weight losses and freezing times during food freezing. A mathematical model was then developed to predict the freezing time and the weight loss of food during freezing in very low ambient temperature. T...

Electrohydrodynamic (EHD) drying is a novel drying method used to enhance forced convective drying by using a wire-electrode to create an electrostatic field. In this study, it was hypothesized that an EHD enhanced forced convective drying process will not only increase the drying rate, but also the exergetic efficiency. A transient exergetic effic...

In this study, the in vivo allergenicity of bovine beta-lactoglobulin (BLG) in peptic whey protein hydrolysates generated during microwave and conventional heating treatments was assessed. The allergenicity of the hydrolysates was explored by studying the reaction of the murine jejunum from previously immunised Balb/c mice to treated BLG in an Ussi...

ElectroHydroDynamic (EHD) drying reduces energy consumption and increases heat transfer by producing an ionic wind through a corona discharge. An experimental study was conducted to measure the heat transfer coefficient (h) at the surface of a heated plate in an airflow channel with EHD. Air at varying velocity entered the channel at controlled psy...

In this study, a proposed method for selecting a tracer for particle imaging velocimetry (PIV) measurement in electrohydrodynamics flows was developed. To begin with, several published studies were identified that exploit different tracers, such as oil smoke, cigarette smoke and titanium dioxide (TiO2). An assortment of tracers was then selected ba...

A specific equipment, made of an assembly of 10-20 vertical metal pins, has been implemented to assess the crusty texture of French breads by a so called multi-indentation test. It was connected to a force sensor set on a material testing machine in the range [0; 100 N]. The height of each pin was adjustable to the irregular surface of the crust of...

The present study concerns the estimation of the dielectric properties of both frozen and defrosted materials during a microwave tempering and heating process. A continuous wave at 2.45 GHz is fed into a rectangular waveguide and the sample, made of methylcellulose gel, fills the whole cross-section of the guide. Temperatures are detected within bo...

In this paper, a reduced order mechanistic model is proposed for the evolution of temperature and humidity during French bread baking. The model parameters are identified using experimental data. The resulting model is then used to estimate the potential energy saving that can be obtained using jet impingement technology when used to increase the h...

Effect of combined microwave (MW) and enzymatic hydrolysis on the human immunoglobulin E (IgE)-binding properties of β-lactoglobulin (β-lg) and other whey proteins (WP) was investigated. Separated β-lg and full whey protein isolate (WPI) were hydrolyzed with trypsin, chymotrypsin, mixture of trypsin/chymotrypsin, and pepsin at three microwave po...

The present study is dedicated to the estimation of internal temperatures within a foodstuff during microwave tempering, in presence of unknown dielectric properties. The solution consists in a software sensor based on a model issued from the closed form solutions of Maxwell's equations coupled with the conduction heat equation solved by finite dif...

The present study is dedicated to the estimation of internal temperatures within a foodstuff during microwave tempering, in the presence of unknown dielectric properties. The solution consists of a software sensor based on a model originating from the closed-form solutions of Maxwell's equations coupled with the conduction heat equation solved by f...

Industrial microwave ovens are widely used in agri-food and chemical applications. Resonant cavities are used to speed up chemical reactions and have the advantage to be small sized and efficient in terms of microwave distribution. These multimode cavities are considered as batch ovens where a small amount of products is treated. Rotating plates ar...

In the first part of the paper (Floury, J., Camier, B. Rousseau, F., Lopez, C., Tissier, J. P., & Famelart, M. H. (2009) Reducing salt level in food: Part 1. controlled manufacture of model cheese systems and their structure-texture relationships. LWT – Food Science and Technology 49(10), 1611–1620), a model cheese matrix presenting different textu...

This study deals with the analytical and numerical solutions of the heat source term because of microwave heating for high and low dielectric materials in 1D and 2D configurations. The authors compare closed-form expressions dedicated to microwave power calculation to numerical simulations. A comprehensive and accurate analysis of the microwave pow...

Industries using energy-intensive processes are being forced to explore ways for reducing their energy consumption. In the food industry, air drying is one of the more energy-consuming processes. To reduce the energy consumption during this operation, alternative processes should be investigated. One promising alternative consists in the electrohyd...

This study deals with a numerical and experimental investigation of a microwave heating process in frozen and defrosted zones. The microwave power generation is computed either from Maxwell's equations or Lambert's law. For the two different approaches, a finite element method is used to design a 2D heat transfer model. The heat source term depends...

Microencapsulation by solvent evaporation technique is widely used in pharmaceutical industries. It facilitates a controlled release of a drug, which has many clinical benefits. Water insoluble polymers are used as encapsulation matrix using this technique. Biodegradable polymer PLGA (poly(lactic-co-glycolic acid)) is frequently used as encapsulati...

This work concerns the thermal decontamination of the surface of a food by hot air with the objective of inactivating the bacteria located at the surface. This heat treatment is considered to be intense and short, compared to more conventional drying processes. In order to predict the surface temperature, a coupled heat and mass transfer model was...

Air is usually used in drying process despite the fact that it is a poor heat transfer medium. In order to improve the drying efficiency and reduce the energy consumption during such a thermal food process, alternative processes should be investigated. One promising alternative consists in the ElectroHydroDynamic (EHD) enhancement of heat and mass...

The majority of data relating heat treatments to thermal death kinetics has previously been obtained by carrying out in vitro tests on small samples of microorganisms in growth medium or food slurries. However, strong evidence exists that suggests microbial death on heat-treated food surfaces cannot be predicted accurately from such systems. An app...

Heat treatments are recommended to decontaminate the surfaces of food. An ideal thermal treatment consists in carrying the superficial layer of food at a predetermined temperature according to a ramping period, an eventual plateau, and a decreasing period. An advanced process control solution is required to force the superficial temperature to perf...

A numerical thermal model was previously developed to take into account heat transfers by convection, radiation and evaporation during the heating and cooling of a solid food product by a jet of air. It has been coupled with another model which describes the transfer of water inside the product. The response of the coupled model to a variation of t...

The coupled heat-water model presented in paper I is used to calculate the temperature and water activity at the surface of an unwrapped lean beef meat sample subjected to changing temperature conditions. Variation in a(w) during heat treatment was determined from weight loss measurements. Surface temperature and water activity predicted by the cou...

The mass transfer and the influence of sudden external perturbations on the behavior of an air curtain are evaluated by means of experimental and numerical studies. The air curtain, consisting of a plane air jet, is combined with a laminar flow unit. They constitute an "open" protection device intended to protect a localized area against any extern...

This study deals with numerical and experimental investigations of a microwave thawing process. The heating due to the microwaves is considered as a source term into the heat equation. The microwave power generation is calculated either from Maxwell's equations and Lambert's law using COMSOL ® 3.2. For those two different approaches, the heat sourc...

Clean rooms are widely used in food-processing industries to guarantee the quality of food products. To maintain the desired cleanliness class in these large and complex enclosures, high ventilation rates are usually used. The recommended air change rates, based on empirical formulas, generate large energy consumptions and do not always guarantee t...

An assessment is made on the influence of external perturbations on an original minienvironment intended for food manufacturing. The minienvironment is a working unit where local displacement ventilation for clean room condition is applied. It consists of a unidirectional flow and an air curtain. Using the particle image velocimetry technique veloc...

Although plane air jets are often used as dynamic barriers to separate two environments, only a few works have explored their sensitivity to perturbations. We investigated the influence of sharp changes of pressure on the flow field of a device designed to avoid air-borne contamination. Laser tomography and tracer gas experiments clearly indicate t...

This work deals with the assessment of the airflow in a food-processing clean room. The flow pattern inside the working area of a pilot scale clean room was numerically investigated using a computational fluid dynamics code based on a finite volume formulation. Two versions of the k-epsilon turbulence model were tested: the standard and the RNG ver...