M. Marcotte

Rheological properties of selected hydrocolloids as a function of concentration and temperature

Abstract In this study, rheological properties of several food hydrocolloids (carrageenan, pectin, gelatin, starch and xanthan) were evaluated using a rotational viscometer at three concentrations (1–6%, depending on the type of hydrocolloid) and four temperatures (20, 40, 60 and 80°C). Samples were subjected to a programmed shear rate increasing linearly from 0 to 300 s−1 in 3 min, followed by a steady shear at 300 s−1 for 10 min and finally a linearly decreasing shear rate from 300 s−1 to 0 in 3 min. Experiments were performed in duplicate. In general, the power law model fitted most of the experimental results. Xanthan gum and carrageenan (at 20oC) were exceptions, characterized by a yield stress and hence the rheograms were fitted with the Herschel-Bulkley model. Furthermore, gelatin showed a Newtonian behavior. Three models (power, exponential and polynomial) were used to evaluate the concentration effect on apparent viscosity. Arrhenius model was used to describe the temperature effect. Among the samples, carrageenan showed the most temperature dependency and xanthan gum, the least.

Osmotically-Induced Mass Transfer in Plant Storage Tissues: A Mathematical Model. Part I*

Abstract A mathematical model incorporating cell membrane characteristics for the simulation of water and solute fluxes in complex cellular structures is developed. The overall transport of material in the supporting matrix is considered using relationships associated with an extended form of the second-degree Fickian equation. The interaction of the cells with their immediate environment is described by transport relationships based on irreversible thermodynamics. Because of the complexity of biological tissue structures, a simplified geometrical analogue of the actual cellular matrix is used. This analogue represents the main features of the actual tissue, i.e. apoplastic and symplastic transport, cell volume changes, tissue shrinkage and internal volumetric rearrangements. The mathematical model has been used to simulate movement of water and diffusible permeating and ron-permeating solutes in discs of beet roots and potato tubers. The influence of various cellular and tissue properties on the dynamics of mass transport phenomena occurring in the cellular structures was studied. These simulations will be presented in Part II of this study.

Neural networks for predicting thermal conductivity of bakery products

An artificial neural network (ANN) approach was used to model the thermal conductivity of bakery products as a function of product moisture content, temperature and apparent density. The bakery products considered in this work were bread, bread dough, French bread, yellow cake, tortilla chip, whole wheat dough, baked chapati and cup cake. Data on thermal conductivity of bakery products were obtained from the literature for a wide range of product moisture contents, temperatures and apparent densities resulted from different baking conditions. In developing the ANN model, several configurations were evaluated. The optimal ANN model was found to be a network with six neurons in each of the two hidden layers. This optimal model was capable of predicting the thermal conductivity values of various bakery products for a wide range of conditions with a mean relative error of 10%, a mean absolute error of less than 0.02 W/m K and a standard error of about 0.003 W/m K. The simplest ANN model, which had one hidden layer and two neurons, predicted thermal conductivity values with a mean relative error of less than 15%.

Ohmic heating behaviour and electrical conductivity of two-phase food systems

Abstract Ohmic heating behaviour and electrical conductivity (EC) of two-phase food systems were studied. Food systems were comprised of a liquid phase using 4% w/w starch solution with 0.5% w/w salt, and a solid phase containing carrot puree and cubes of different sizes (6 and 13 mm) in different concentrations (30 and 50% w/w). A set of experiments was carried out for a wide range of particle concentrations from 0 to 60% w/w. With respect to the particle location, experiments were conducted using 30% w/w cubes (6 mm) placed in parallel, in series and in well-mixed conditions with the liquid phase. Ohmic heating was applied to the food systems using a static cell (20-mm-long Teflon cylinder with 35 mm diameter and 25 mm wall thickness) at a constant voltage gradient of 12.5 V/cm. Electrical conductivity values were calculated as a function of particle size, concentration, location and temperature. It was observed that the heating time increased along with particle size and concentration. Overall values of EC ranged from 0.2 to 1.8 S/m, increasing with the process temperature as it ranged from 20–80 °C, and decreasing as particle size or concentration increased. With respect to the particle location within the ohmic cell, the thermal behaviour was different when the two phases were in parallel, in series or in mixed condition. However, there was no significant difference between overall values of EC when liquid and solid phases were separated as compared with the mixed condition.

High-pressure destruction kinetics of Clostridium sporogenes spores in ground beef at elevated temperatures

High pressure (HP) is an alternative technique for thermal sterilization of foods with minimum quality loss. HP destruction kinetics of bacterial spores is essential to establishing sterilization process, but knowledge in this field is still very limited. In this study, destruction kinetics was investigated using Clostridium sporogenes PA 3679 (ATCC7955) spores in extra-lean ground beef (5 g each sealed in a sterile plastic bag). Duplicated samples were subjected to HP treatments at 700, 800 and 900 MPa in a HP system equipped with a Polyoxymethylene insulator to maintain constant temperatures at 80, 90 and 100 degrees C during pressure-holding time. The kinetic parameters of the spores (D- and Z-values) were evaluated at these pressures and temperatures. For the pressure from 700 to 900 MPa, D-values ranged from 15.8 to 7.0 and 1.5 to 0.63 min at 80 and 100 degrees C, respectively. The pressure resistance of Z(T)(P) value was 520-563 MPa at 80-100 degrees C. The temperature resistance of Z(P)(T) value was 19.1-19.7 degrees C at 700-900 MPa, much higher than that at atmospheric condition (12.4 degrees C). A regression model was generated which can be used to predict D-value or the death time of a minimum process under given pressure and temperature conditions. HP treatment with elevated temperatures can destroy bacterial spores with a shorter time or lower temperature than conventional thermal processing. This study provides useful information for the achievement of a safe HP sterilization process.

Modeling the moisture diffusivity in a baking cake

Abstract Full factorial baking (drying) test was performed with five levels of initial moisture contents (0.369, 0.431, 0.539, 0.611 and 0.707 d.b.) of cake batter and four levels of oven temperatures (40, 70, 100 and 200 °C) in duplicate. The moisture diffusivity ( D e ) was then evaluated through the first falling rate period from plotting the dimensionless moisture ratio against time on a semi-log scale. For this moving boundary problem, simple volume compensation method was applied to the analytical solution. The moisture diffusivity was 9.0×10 −11 to 4.4×10 −8 m 2 /s for the industrial cake batter during baking. As porosity ( e ) and temperature ( T ) of the batter increased the moisture diffusivity increased. The semi-empirical model developed was D e =29.6 e exp(−8020.5/ T ).

Kinetics and Quality Aspects of Canadian Blueberries and Cranberries Dried by Osmo-Convective Method

Blueberries and cranberries were dried using a hybrid technology consisting of pretreatment, osmotic dehydration, and convective drying. The performance of this hybrid technology was evaluated in terms of quality attributes such as color, taste, rehydration ratio, water activity, as well as sugar and anthocyanins content. Of thirteen different pretreatment methods tested for cranberries, cutting the berries in halves was the simplest and the best one. No pretreatment was needed for blueberries. Osmotic dehydration was performed in batch and continuous modes using sugar solution of 67.5–70°Brix. Convective drying was then carried out in a fluidized bed, a pulsed fluidized bed, or a vibrated fluidized bed. Quality profiles for both berries were determined after each step of such a hybrid technology and compared with quality of berries dried in the vibrated fluidized bed and freeze dryer. Recommendations for full-scale processing are given.

Thermal and Physical Properties of Bakery Products

Referee: Dr. M R. Okos, Department of Agricultural Engineering, Purdue University, West Lafayette, IN 47907 This article reviews the measurement techniques, prediction models, and data on thermo-physical properties of bakery products: specific heat, thermal conductivity, thermal diffusivity, and density. Over the last decade, investigation has focused more on thermo-physical properties of nonbread bakery products. Both commonly used and new measurement techniques for thermo-physical properties reported in the publication are presented with directions for their proper use. Data and prediction models are tabulated for the range of moisture content and temperature of the bakery products.

Cake baking in tunnel type multi-zone industrial ovens Part II. Evaluation of quality parameters

Abstract In addition to characterization of baking conditions during industrial cake baking, some important quality parameters, such as texture, color, density and viscosity of the cake batter were evaluated during baking in two different multi-zone industrial scale ovens: gas fired band oven and electric powered mold oven. The flow behavior of all batters was pseudo-plastic with a yield stress. The average moisture removal rates (3.59×10−4–1.40×10−3 kg H2O/kg solid s) of cakes fell between those of cookies and breads. During baking, pH increased and then decreased at the late stage of baking. Batter positions (side or center) on the band were not critical for quality parameters with the exception of moisture content. Most color changes occurred 1/4–3/4 way through the baking. After 21 days of storage, the hardness of all cakes increased 1.8–3 times the original value.

Cake baking in tunnel type multi-zone industrial ovens Part I. Characterization of baking conditions

Abstract Baking conditions were observed for two different multi-zone industrial scale ovens: a gas fired band oven and an electric powered mold oven. In each zone of both ovens, parameters measured were: internal temperature profile, air velocity absolute humidity and oven wall temperature. Air temperatures were higher close to the oven wall than at the center of ovens tested. Absolute air humidity in the gas fired band oven (0.0545–0.246 kg H2O/kg dry air) was higher than in the electric fired mold oven (0.0207–0.0505 kg H2O/kg dry air). The relative air velocities in the ovens were 0–0.437 m/s, which resulted in convective heat transfer coefficients of 5.7–7.4 W/m2K and mass transfer coefficients of 3.94×10−8-5.12×10−8 kg/m2 s Pa. The average rate of total energy transferred to each product was 71992–85339 W. A proportion of 26–38.4% was the sensible heat absorbed with 61.6%–74% of the heat absorbed as the latent heat of vaporization of moisture. Radiative heat was responsible for 66.2–81.5% of the heat delivered to the top surface of products for cake baking in direct fired industrial ovens.