Laura Analía Campañone

Weight loss during freezing and storage of unpackaged foods

Dehydration of unwrapped foods occurs during freezing and frozen storage. Coupled heat and mass balances were proposed incorporating solidification of water and sublimation of ice. The mathematical model was solved using an implicit finite-differences method, with a variable grid to follow the moving sublimation front. The model evaluates temperature and water concentration profiles and was used to predict the kinetics of weight loss for different products. Model predictions were favourably compared against experimental data on weight loss during storage of unwrapped meat, potato and tylose.

Modeling and Simulation of Microwave Heating of Foods Under Different Process Schedules

This paper describes the development of a simulation model for heating of foods in microwave ovens and its uses to optimize food heating strategies. The solution of the coupled energy and mass microscopic balances considers the electromagnetic energy absorption as well as temperature-dependent thermal, transport, and dielectric properties. The microscopic balances are highly nonlinear coupled differential equations, which were solved using finite element software (Comsol Multiphysics). Maxwell equations were employed in order to describe the interaction between electromagnetic radiation and food. The mathematical model allowed the evaluation of the effect of product size and composition in the temperature profiles that developed inside the food that was radiated either on one or both sides. In order to improve the nonuniform temperature profiles that occurred within foods under continuous operation, different operation schemes were evaluated: intermittent cycles, joint action of microwaves with air impingement, and the effect of interference of electromagnetic waves.

Modeling of Microwave Drying of Fruits. Part II: Effect of Osmotic Pretreatment on the Microwave Dehydration Process

The heat and mass transfer during the combined process of osmotic–microwave drying (OD-MWD) of fruits was studied theoretically and experimentally through modeling and numerical simulation. With the aim of describing the transport phenomena involved in the combined dehydration process, the mass and energy microscopic balances were set out. For the first step (OD), two models with different levels of complexity were proposed, an osmotic–diffusive and a countercurrent flow diffusive model. For MWD, the energy and mass balances were solved, using moisture- and temperature-dependent properties; inner heat generation due to transformation of the electromagnetic energy was accounted for by using the approximation of Lamberts law. The numerical solution obtained from OD was incorporated as initial values for the simulation of MWD. The model validation was satisfactorily carried out in pears, both fresh and osmodehydrated for 2xa0h in sucrose solutions and then irradiated in a microwave oven at 500xa0W. From the res...

Experimental study of the application of edible coatings in pumpkin sticks submitted to osmotic dehydration

ABSTRACT Osmotic dehydration (OD) improves the organoleptic characteristics of products; nevertheless, depending on the product, the incorporation of great amounts of solute can be undesirable to consumers. The application of hydrogel coatings would overcome this, acting as a barrier to solute entering the product. An alginate–calcium chloride barrier system (A-CC) was tested with or without pretreatment of Ca2+ as a firmness agent applied to pumpkin sticks. Products were dehydrated in sucrose and glucose solutions (40 and 60% w/w). Different parameters were estimated such as soluble solids uptake, water content, and weight reduction; in addition, texture and microstructural changes were studied. The A-CC configuration complies with the barrier function to solids uptake from the dehydrating solution in case of 60% of sucrose, allowing water exit from the vegetal matrix. The pretreatment with Ca2+ contributed to the retention of product firmness. Integrity, adhesiveness, and thickness of the A-CC system during the OD process were evaluated by environmental scanning electron microscopy (ESEM). In this case, the coating thickness reduction was according to the product weight reduction, indicating that the coated product was dehydrated as an integrated system.

Numerical solution of coupled mass and energy balances during osmotic microwave dehydration

The mass and energy transfer during osmotic microwave drying (OD-MWD) process was studied theoretically by modeling and numerical simulation. With the aim to describe the transport phenomena that occurs during the combined dehydration process, the mass and energy microscopic balances were solved. An osmotic-diffusional model was used for osmotic dehydration (OD). On the other hand, the microwave drying (MWD) was modeled solving the mass and heat balances, using properties as function of temperature, moisture and soluble solids content. The obtained balances form highly coupled non-linear differential equations that were solved applying numerical methods. For osmotic dehydration, the mass balances formed coupled ordinary differential equations that were solved using the Fourth-order Runge Kutta method. In the case of microwave drying, the balances constituted partial differential equations, which were solved through Crank-Nicolson implicit finite differences method. The numerical methods were coded in Matlab 7.2 (Mathworks, Natick, MA). The developed mathematical model allows predict the temperature and moisture evolution through the combined dehydration process. Mathematical subject classification: Primary: 06B10; Secondary: 06D05.

Análisis digital de imágenes para evaluar el encogimiento de fresas sometidas a tecnologías emergentes de procesamiento

In fruits, strawberries in particular, appearance is an attribute of great importance. Appearance, which can be defined by color, shape, size and visual texture, not only determines the degree of maturation or the presence or absence of impurities, but also indicates the application of technological processes or prolonged storage conditions. In most cases, an excessive shrinkage of fruits negatively affects the preference and acceptance of these products by consumers. Particularly, in the case of dehydrated fruits, the geometric modifications (shape and size) caused by the process are a matter of great concern to the industry. Traditional techniques for monitoring physical and physico-chemical parameters of quality usually are time consuming, costly, laborious, invasive and impracticable during in-line monitoring at the industry. Computer vision techniques and digital image analysis are an attractive and economical alternative to evaluate the appearance changes of foodstuffs during processing. Therefore, the present work aims the evaluation and correlation of morphological characteristics area ( A ), by digital image analysis techniques, and thickness ( L ) measured by caliber in strawberries subjected to combined treatments that include application of edible coatings (alginate-lactate), osmotic dehydration (sucrose, 60 oB, 40 oC, 4h) and microwave assisted drying (1,2 W/g). Related to thickness, reductions of 60% (retention 40%) were obtained for fresh (FR+MW) and fresh coated (FR_R+MW) samples. OD pre-treated samples (DO+MW and DO_R+MW) reached values of 37% (retention 63%). The digital processing of images showed cross sectional area reductions up to 56% for FR+MW and FR_R+MW samples, being significatively higher (up to 18%) for samples previously osmo-dehydrated (DO+MW and DO_R+MW). By correlating the L and A percentage retention, during MW-drying, excellent correlations were attained for FR+MW and FR_R+MW samples (R 2 : 97 and 98%).

Application of osmotic dehydration and microwave drying to strawberries coated with edible films

Abstract Osmotic dehydration (OD) is one of the conventional methods to increase the shelf-life of vegetables and fruits. However, the operating conditions can adversely affect the organoleptic and nutritional quality of fresh products due to the high sugar uptake during processing and the loss of water-soluble constituents to the osmotic medium. The application of edible films has attracted interest due to their ability to reduce the entry of solutes and simultaneously increase the removal of water during OD treatments. Microwave (MW) is one of the most effective emerging technologies to accelerate dehydration processes in vegetable matrices. This aspect is particularly relevant in strawberries, given its high content in bioactive and nutritional compounds. Thus, the aim of this paper was to assess the influence of edible film application (alginate–lactate) in strawberry slabs during combined OD-microwaves dehydration processes. Samples of 1u2009cm thickness were treated with sucrose solution (60°Bx, 40u2009°C, 4u2009h) and then were dehydrated in a microwave oven (1.2u2009W/g). The application of alginate–lactate edible films resulted in similar weight and water losses but lower solids gain compared to uncoated samples during OD treatment. OD pre-treated MW-dried strawberry slabs with moisture contents up to 0.15u2009kg dry basis were obtained after 100u2009min of MW drying. Besides, the effective diffusional coefficient (De) was estimated for MW drying process, values ranged from 4.5 to 8.8 10−10 m2/s when shrinkage effect was considered, and from 1.1 to 2.3 10−9 m2/s for constant thickness assumption.