Bertrand Broyart

Predicting colour kinetics during cracker baking

Abstract The topic of this investigation covers the study of the kinetics of colour formation during the baking of crackers in a static electrically heated oven. Methods for measuring the kinetics of variation of product temperature, water content and surface colour (assessed in CIE 1976 (L ∗ , a ∗ , b ∗ ) system) are described. An appropriate experimental set-up was developed and experiments with increasing baking times were realised in order to reconstitute the whole baking profiles. The validity of this method was proved using continuous temperature recordings. Experimental recordings of cracker surface lightness during baking show first an enlightenment and subsequently a darkening phase. The darkening phase is initiated when the product temperature reaches a critical value in the range of 105–115 °C. A kinetic model was developed in order to predict the lightness variation of the cracker surface using the product temperature and moisture content variations during baking. The evolution of lightness appears to follow a firstorder kinetic influenced by these two parameters.

Modelling heat and mass transfer during the continuous baking of biscuits

Abstract A steady-state mathematical model to calculate heat and mass transfers during the baking of thin cereal products (biscuit type) in a continuous, indirect, gas-fired oven, is presented. The basic principles and equations of the model are discussed. The temperature and composition of the baking atmosphere and biscuit on a transversal oven section are assumed to be uniform. The model takes account of heat transfer by radiation, convection and conduction as well as product–water phase change. For mass balances, the model takes account of the possible condensation of steam from baking atmosphere to product surface and product drying. An experimental study performed on a continuous, indirect, gas-fired, pilot plant oven for biscuit baking was used to validate the model, and good agreement was obtained between predicted and measured values.

Modelling of Moisture Transfer in a Composite Food: Dynamic Water Properties in an Intermediate aw Porous Product in Contact with High aw Filling

Moisture migration is a common problem in many composite food systems where compartments of high/low water activity are adjacent. Water diffuses from the high into the low water activity compartment leading to irreversible texture loss. Moisture distribution in a model multi-compartment food (agar gel/sponge-cake) was experimentally evaluated at 20°C by measuring moisture content profiles as a function of time. A mathematical model was developed to simulate moisture transport within agar gel and sponge-cake. The transport and equilibrium properties of water for each compartment (water diffusivity and sorption isotherm) are important factors required for calculations and modelling. They were evaluated using an independent water vapour sorption experiment. Moisture diffusivity within sponge-cake (∼1 × 10 -10 to 1 x 10 -9 m 2 s -1 ) was rate-limiting for moisture transport and varied with moisture content. This behaviour may be related to the decrease of sponge-cake porosity with moisture content increase. The model was then validated with various initial a w for agar gel.

Validation of a Method of Determination of Apparent Diffusivity Versus Composition in Solids

Abstract A method is presented for computing the values of apparent diffusivity in solids with respect to the concentration of the diffusing substance (water or sodium chloride). This method does not require any assumption upon the mathematical relationship between diffusivity and concentration. It can be applied to experimental measurements of local concentration versus position within the solid (profiles) with relatively few measurements (circa 10) and a mathematical smoothing of the experimental data by using an artificial neural network model. The method was first validated on simulated data obtained by using a constant diffusivity value and on experimental profiles when the relation between diffusivity and concentration was given. It was then applied to original experimental moisture profiles obtained by putting gelatin gels with different initial moisture contents into contact for up to 14 days. The method was also successfully applied to five sets of experimental moisture and sodium chloride profiles taken from the literature and obtained from different food products. Apparent diffusivities calculated by our method were found in agreement with those obtained by authors using different numerical methods to compute the diffusivity values.

Physical Model of Heat and Mass Transfer in a Spouted Bed Coffee Roaster

A key step in coffee processing is roasting, where green coffee beans are heated at high temperatures (over 190°C), initiating a series of complex chemical reactions. This process can be divided in two phases (drying < 160°C and roasting > 160°C). Therefore, the quality of coffee is highly correlated with bean temperature during roasting. The aim of this work is to measure and model coffee bean temperature and moisture content during the roasting process, in order to determine on-line quality of the product allowing the control of the process. A spouted bed roaster, using hot air flow as heating medium, was developed. The surface and center bean temperature, as well as input and output air temperatures, were measured on-line. At each minute interval of roasting, samples of coffee beans were taken to measure the moisture content. A dynamical model, which takes in account heat and mass transfer at the surface and inside of the beans, is proposed. This model, where only the water diffusivity in the bean was adjusted, gave a good prediction of bean temperature (center and surface), average moisture content, and output air temperature for all the experiments. However, in the industry, only the output air temperature can be measured. Consequently, this model could assist in on-line determination of the bean temperature and hence constitutes the first stage in developing a smart sensor for on-line checking including quality control.

Effect of Temperature on Moisture Barrier Efficiency of Monoglyceride Edible Films in Cereal-Based Composite Foods

ABSTRACT The effects of temperature on moisture transfer within a composite food consisting of a sponge cake (SC) separated from a high moisture content agar gel (AG) by an acetylated monoglyceride (AMG1 and AMG2) film were investigated through moisture content profile experiments. A diffusion model was successfully used to predict moisture transfer within various composite foods (AG/SC, AG/AMG1/SC, and AG/AMG2/SC). The barrier efficiencies of the two hydrophobic films studied were reduced by temperature increase due to activation of diffusivity and equilibrium water sorption. Despite the low melting point of highly acetylated monoglyceride films, their barrier efficiency appeared to be less sensitive to temperature than monoglyceride films with a lower degree of acetylation. Consequently, in poor storage temperature conditions, these latter monoglyceride films seemed to be more effective in enhancing the shelf-life of the composite food studied here.

Impact of Lipid Phase on Water Transfer in Food

Apparent water diffusivity has been studied on an emulsified food model made of gelatin and hydrogenized vegetable fat. Lipid content was varied from 0 to 50% w/w and three particle mean diameters were generated (40, 110, and 400 μm) in gelatin samples containing 75 g of water per 100 g of fat-free sample. In joined compartment experiments, fatty hydrated gels were dehydrated in contact with either a dry pure gelatin compartment or an industrial sponge cake. Water content profiles were used to determine the apparent water diffusivity value using Ruiz Cabrera et al.s method,[ 1 ] which takes gel shrinkage into account.