Rodolfo H. Mascheroni

Mass transfer during osmotic dehydration of pineapple

The diffusion coefficients of water and solutes are important parameters in the analysis, design and optimisation of an osmotic dehydration process. This work estimated by Fick’s Law the diffusion coefficients of water and sucrose during the osmotic dehydration of slices of pineapple fruit in sucrose solution at different temperatures. In addition, it analysed the effect of the change in thickness (shrinkage) during the process, and the use of higher order terms in the analytical solution. The model results were in good agreement with experimental data of water loss and solid gain. The best fit was found when the shrinkage was considered in a simple model based on the solution of Fick’s Law. The equilibrium water content ranged between 34 and 36% for a 60% w/w sucrose solution and was practically independent of temperature. Equilibrium sugar content increased from 45 to 54% as the temperature rose from 30 to 50°C. Thickness variation was found to be independent of temperature and was only dependent on water content.

Quality evaluation of foodstuffs frozen in a cryomechanical freezer

Fil: Agnelli, Miriam Eliana. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos; Argentina

Modeling of Microwave Drying of Fruits

Heat and mass transfer in foods during microwave drying was studied experimentally and theoretically through mathematical modeling. The food was considered as a system with physical properties that can vary with composition, structure, and temperature. Inner heat generation due to transformation of the electromagnetic energy was accounted for by using the approximation of Lamberts law. Two successive stages were considered: material heating that was followed by liquid evaporation. The coupled system of partial differential equations was coded in Matlab 6.5 (Mathworks, Natick, MA) and used to simulate the experimental runs of pear slices drying in a household microwave oven. Predicted temperature histories at the surface and center of the slab as well as mass loss during drying were in good agreement with experimental results.

Monitoring of Weight Losses in Meat Products during Freezing and Frozen Storage

During freezing and frozen storage, the surface of unpackaged food is exposed to mass transfer exchange with the environment. Ice sublimes forming a dry, porous layer altering the sensory characteristics of the foods. This work describes the design and use of an experimental equipment with controlled operating conditions to quantify weight losses during refrigeration, freezing and frozen storage. Experiments were carried out with several meat products (hamburgers, meat balls, beef cylinders and chicken slabs) under different air conditions: temperature (- 40 to - 20°C), relative humidity (50—95%) and air velocity (1—5 m/s). Weight loss occurred during freezing ranged between 0.28 and 2.98%, meanwhile the global values corresponding to both stages (freezing plus storage up to reach 1200 min of refrigeration) ranged between 1.67 and 6.15%. Good agreement was found between experimental data for the different products tested and data from a numerical model developed in previous work. The results demonstrated that surface dehydration degree should be regarded as an important quality parameter to take into account and to quantify.

Freezing time predictions for regular shaped foods: a simplified graphical method

Abstract A graphical method is proposed for the estimation of freezing times of foods been developed from the predictions of a numerical model which solves the heat balance for a food undergoing freezing. The method is valid for foods with different shapes (flat plate, cylinder and sphere) and covers a wide range of working conditions for industrial freezers. It also enables the prediction to be made for any given end temperature in the thermal centre of the food. Freezing times predicted by this method have been compared with published experimental data, giving an average error in the predicted values of only 4%.

Study and comparison of different drying processes for dehydration of raspberries

ABSTRACT The aim of the present study was to evaluate and compare different drying methods (microwave, hot air + microwave, and osmotic dehydration + microwave) in raspberries (cv. Heritage). A portion of raspberries was pretreated with osmotic dehydration (60°Brix sucrose solution at 20°C for 360 min) and another with hot air drying (HAD) (1.5 m/s air speed at 60°C for 300 min). Pretreated raspberries were then dried by microwave and at three different intensities (3.5, 7.5, and 11 W/g). Physicochemical properties (moisture content, water activity, and drying rate) and quality parameters (optical properties, mechanical properties, antioxidant capacity, and rehydration capacity) of dried raspberries were evaluated. Results showed that the microwave drying (MWD) at 7.5 W/g (50 min and final temperature of 79 ± 5.1°C) allowed a high yield of dried raspberries. The combined processes were not efficient to accelerate the decrease of moisture content, due to the low drying rate of the pretreatments. In terms of quality, none of the drying processes allowed a high retention of the antioxidant capacity. However, they allowed an appropriate rehydration performance. The combination of HAD with MWD allowed obtaining a good appearance and desirable texture on the dried product. Thus, this last option seems to be the best among the drying methods tested, but additional studies are required to improve the efficiency of the process and the effect on the antioxidant capacity during drying.

Equilibrium Moisture Characteristics of High Oleic Sunflower Seeds and Kernels

Abstract The equilibrium moisture content (EMC) characteristics of high oleic sunflower seeds and kernels between 10 and 55°C were determined by equilibrating the samples to known relative humidities (RH) above saturated salt solutions. EMC of the kernels was lower than that of seeds in the range of 11 to 96% ERH and at 25 and 40°C. Hysteresis effect was found for the EMC properties of seeds and kernels at 25°C. Four EMC–ERH models (modified Henderson, Chung-Pfost, Halsey, and Guggenheim–Anderson–de Boer) and their estimated parameters were evaluated for goodness of fit. GAB and Halsey equations showed the best fitting of experimental data although GAB equation adjusted for temperature described the EMC data the best. Components of the seed as oil content or hull/kernel ratio did not explain the slight differences in EMC found between the varieties.

Comparison of two alternatives of combined drying to process blueberries (O'Neal): Evaluation of the final quality

ABSTRACT In this work, we examined and compared two combined alternatives for the drying of blueberries (O’Neal). Pretreatments of osmotic dehydration (60°Brix sucrose solution at 40°C for 6 h) and hot air drying (HAD) (60°C, 2.5 m/s for 90 min) were performed to reach the same water content. Pretreated blueberries were then dried by microwave at different microwave output power values: 562.5, 622.5, and 750 W. The combined drying processes were also compared with HAD alone (control). The effects of the processes over blueberries were studied in terms of decrease in water content, drying rate (DR), mechanical properties (firmness and stiffness), optical properties (L*, a*, and hue angle (h)), antioxidant capacity, and rehydration capacity. The hot air–microwave drying decreased the process time and presented a high drying rate compared with the osmotic dehydration–microwave processes and the control drying. In terms of quality, the antioxidant and rehydration capacities were the most affected. The results showed that the best drying method to obtain the desired final product was the hot air–microwave drying (750 W).

Generalized Correlations for Characteristic Variables and Thermophysical Properties of Osmotically Dehydrated Fruits

Based on experiments on osmotic dehydration of different fruits, with diverse dehydrating solutions and working conditions, and on an extensive search of the literature on osmotic dehydration, general linear correlations between water content (WC) and soluble solids (SS) content of fruits dehydrated in sugar or alcohol solutions have been developed for each type of fruit that allows characterization of both properties with only one rapid determination of either property. A linear regression for SS vs. WC including all of the experimental data for the seven types of fruits tested (apple, strawberry, pear, kiwi, plum, nectarine, and melon) and the five solutes used in those experiments (sucrose, glucose, xylitol, sorbitol, polyethylene glycol) was obtained with a high regression coefficient. Based on experimental data determined in this work in the range −40 to 40°C, correlations are established between heat capacity and enthalpy with water content and temperature for both fresh strawberries and strawberries that were osmotically dehydrated in different solutions. In addition, general polynomial correlations for the initial freezing temperature of fresh and osmotically dehydrated fruits as a function of water content and type of dehydrating solute are proposed.

Application of Transfer Functions to the Thermal Processing of Sweet and Sour Cherries Preserves: Influence of Particle and Container Sizes

The conditions of thermal processing of fruit preserves packed in transparent glass containers have great importance from the point of view of the final product appearance. Process simulation can allow to predict the quality of the product and its possible degradation. This work applied the transfer function method to simulate the pasteurisation of whole sweet and sour cherries canned in glass containers, with a 25 °Brix sucrose solution as covering liquid, and the predicted results were experimentally tested. The influence of fruit and container diameters on the treatment times was analysed. Kinetic models for enzyme degradation were coupled to the prediction model as examples of the possibilities of optimising the whole pasteurisation process. The accuracy (average error in predicted temperatures: 2.1%) of the simulation method was satisfactory for practical purposes, its use resulted simple and fast, and it allowed adjusting of pasteurisation times, even during the process.