Showing papers by "Amparo Chiralt published in 2003"

Food dehydration and product structure

Abstract: Dehydration of biological material is a controlled effort to preserve the structure or create a new one that serves for functional purposes. In this context, food dehydration is revisited from the perspective of recent advances in food materials science, knowledge from desiccation in Nature, microstructural probing, novel processing technologies and deeper insights into drying mechanisms, among others. The role of structure in dehydrated products appears evident to understand transport mechanisms and to design functional properties. Some approaches and research topics in structure of dehydrated products are presented and discussed.

Modelling of dehydration-rehydration of orange slices in combined microwave/air drying

Abstract: The development of new citrus products, such as dry products for direct use or for rehydration, is interesting to promote their consumption. Combined microwaves (MW)–air (2 m/s, 60 °C) drying of orange slices has been studied in terms of process kinetics and of the rehydration capability as affected by the applied MW power (0, 0.17, 0.36, 0.69 and 0.88 W/g). Drying curves were modelled considering two periods, with different kinetic constants, related with the effective water diffusivity. These constants increased linearly with the applied MW power and, despite the low levels of MW power used, a sharp reduction in drying time of orange slices was obtained. Rehydration behaviour of orange slices was modelled through Peleg's and Weibull's equations. No differences in rehydrating behaviour were observed as a function of the applied MW power. So, the highest level, which was limited to avoid sample browning, will be recommended to reduce the drying time.

Transport Mechanisms in Osmotic Dehydration: The Role of the Structure

Abstract: Osmotic dehydration promotes water release from a cellular material immersed in a concentrated solution, while a simultaneous external solute uptake happens. Mass transfer occurs during this operation through different mechanisms to a different extent depending on process variables. The action of the different mechanisms, balanced by controlling those variables, makes possible to achieve a specific dewatering-solute uptake ratio in the final product. Mechanisms involved in mass transfer during osmodehydration of cellular tissues depend on the structural level of the tissue. The external broken cells can be easily impregnated by the external solution, and in the intercellular spaces, bulk flow of solution, water and solute diffusion occur. The bulk flow is promoted due to capillary pressure in processes carried out at atmospheric pressure. Nevertheless, when vacuum is applied to the system, capillary impregnation is promoted and when the atmospheric pressure is restored, pores are extensively flooded with the external solution and depending on the applied compression ratio. Mass transport in the intercellular spaces is mainly responsible for solute gain. At cellular level, cell wall and membranes act as non-selective and selective barriers respectively to mass transport and the transmembrane flux is responsible for most of the cell-to-cell water transport during osmotic dehydration of tissues. (A)

Food Matrix Engineering: The Use of the Water-Structure-Functionality Ensemble in Dried Food Product Development

Abstract: The structured food systems (i.e. cellular tissues) are dissipative structures whose functionality mainly concerns their properties (physico-chemical properties, chemical and biochemical reactions), external interactions with surroundings (interactions with micro-organisms, heat and mass transport pathway) and especially, their interactions with consumers (nutritional value, quality, taste and flavour, texture, appearance: size, shape, colour). Dehydration or rehydration processes concern heat and mass transport phenomena (water, solutes) coupled with micro and macrostructure changes both producing important effects on food functionality. Control of these changes is the major concern in food product development. This control must be applied not only to the changes in physico-chemical properties but also to those related with consumers' issues. Food matrix engineering is a branch of food engineering which aims to apply the knowledge of the food matrix composition, structure and properties to promote and control adequate changes which can improve some sensorial and/or functional properties in the food. These changes, which are caused by some basic operations, are related to the phenomena of heat and mass transfer, vaporization-condensation, internal gas or liquid release, structure deformation-relaxation and phase transitions in matrix components, and are usually coupled throughout the operation's progress. The final product may be a new product with improved composition and sensorial properties and/or more stability. All these concepts are discussed in this paper using several examples related to the application of combined food dehydration techniques. (A)

Effect of Blanching and Vacuum Pulse Application on Osmotic Dehydration of Pear

Abstract: Osmotic dehydration of pear cylinders (var. blanquilla) was studied by analysing the effect of blanching pre-treatment and the application of a vacuum pulse on the kinetics and yield of the process and on product quality (colour and mechanical behaviour). Fresh and stem-blanched samples were treated with 65 °Brix sucrose at atmospheric pressure and by applying a vacuum pulse (50 mbar for 5 min). The influence of the sugar gain and water loss fluxes, and the tissue structural response to the vacuum pulse, on the total mass and volume losses of the samples has been discussed. Blanching implied an increase in the mass transfer rate in pear tissue. Vacuum pulse in blanched samples resulted in more volume compression than sample impregnation with the external solution due to the sample softening by thermal effect and to the partial gas release during its thermal expansion. This provoked the greatest volume losses and a reduction of the ratio of sugar gain to water loss, where the highest values reached were for non-blanched ...(A)

Structure and color changes due to thermal treatments in desalted cod

Abstract: Cod (Gadus morhua) has a great importance in some European countries, either due to fish production and exportation volume or because of its high consumption. Desalted cod (3.94 ± 0.04% salt content and 73.49 ± 0.06% water content) has a limited shelf-life due to the microbial activity and the autolytic proteolysis affecting product texture. Thermal treatments can be used to preserve the cod, but these can cause changes in color, fish muscle tenderization through protein denaturation and collagen breakdown. In this research, steam blanching (5 min), water blanching (1 min) and microwave heating (5 W/g, 2 min) were applied to desalted cod. The effect of these treatments on color (CIEL*a*b* coordinates), mechanical properties (shear and TPA tests) and microstructure of cod were analyzed. Thermally treated cod were lighter, slightly yellowed and softer. From color data and microstructural observations, heat induced changes in cod were a little smaller than in microwave heated cod.

Kinetics of Solute Gain and Water Loss During Osmotic Dehydration of Orange Slices

Abstract: The effect of the osmotic solution (sucrose and dextrose syrups) on the kinetics and process yield was evaluated on osmotic dehydration of orange (Valencia Late var.). Processes were carried out at 30 C, using 35, 45, 55 and 65 Brix solutions and by applying a vacuum pulse (100 mbar for 10 min) at the beginning of the process. Kinetics of sugar gain-water loss and mass changes were analysed by separately considering peel and pulp fractions of orange slices. Mass transport properties of orange slices in osmotic treatments were different for pulp and peel fractions due to the different contributions of the mechanisms involved. Faster water and solute transport were observed in the peel impregnated with the osmotic solution. Sugar gain in sucrose solutions was enhanced in comparison with dextrose treatments, whereas diffusional water loss was faster in samples treated with dextrose. These effects made the process yield higher for sucrose treatments. An increase in the osmotic solution concentration implied higher mass transport rates, but did not notably affect process yield. (A)

Influence of operating conditions on sensory quality of minimally processed osmotically dehydrated guava

Abstract: The influence of solution temperature (T), process time (t) and pressure regimen (P) on the sensory quality of minimally processed, osmotically dehydrated guava was analyzed. The study encompassed these values of each independent variable: T-30, 40 and 50C; t-60, 120 and 180 min, and P-atmospheric pressure, pulsed vacuum (5 min under vacuum, then atmospheric pressure) and continuous vacuum. The product was sensorially evaluated for color, flavor and firmness. Results were processed by means of the Design Expert version 5 software. Temperature, time and pressure regimen were shown to significantly influence the product's flavor. No effect of the factors on the fruit's color and firmness could be demonstrated. At the cellular level the tissues of guava treated at 40C for 60 min under pulsed vacuum are not significantly altered.

Special Issue on the International Conference Iberdesh 2002: Process, Structure and Functionality

Abstract: Over the years water management and foods has been a major topic in the Sub-programme XI Treatment and Conservation of Foods of the Ibero-American CYTED programme in Science and Technology. Since 1985 successive projects on intermediate moisture foods, combined methods technology and minimal processing have positioned the subject and researchers of the region at the forefront of scientific and technological advances. Dehydration is perhaps the oldest technology used by man to stabilize foods and a preferred way by nature to preserve life on earth (e.g., dry seeds). Drying is also a very important industrial operation accounting for 10–25% of the total energy used in manufacturing processworldwide. Sun-dryinghasbeenused for centuries virtually unchanged to preserve fruits, vegetables, meat and fish in developing countries establishing a huge market for traditional dried products. At the same time, food engineers are examining novel alternatives to make the process more energyand time-efficient, for example, using radiation sources often combined with conventional systems, to spur heat and mass transfer. Nevertheless, food dehydration goes beyond removing water fast and at low cost: it has to do with structure and functionality of materials as well. Recent trends in many areas of science and technology attempt to couple the process of water removal with desirable properties of the dry product. Biotechnologists are interested in protecting the activity of labile and expensive biomolecules in their transit to and during storage in the solid state. The pharmaceutical industry is concerned with the long-term efficacy and the controlled release of drugs in our bodies. Biologists and plant physiologists are making deep inroads in the understanding of the mechanisms of molecular protection and adaptation involved in drought resistance in plants and anhydrobiosis. Simultaneously, high-resolution, non-intrusive techniques for visualising and characterizing structures and methods to precisely measure physical properties in situ are becoming available. New concepts borrowed from food materials science, such as the rubbery-glass transition, find application in the interpretation of the structural and chemical stability of dried tissue foods and powders. Iberdesh 2002: Process, Structure and Functionality, an international conference held in Valencia (Spain) in September 2002, was intended from the outset to be an unorthodox meeting on the science of drying. It had as major objective to revisit the important subject of dehydration from a much wider perspective than usual and to explore with no limits possible avenues and opportunities for cross-fertilisation. Micro-structure, glass-transition, hydrodynamicmechanisms of transport, fractals, wetting, pharma products, resurrection plants, etc. are some of the keywords that accompany the papers presented as a vivid example of the wide scope of subjects covered. This special issue of the International Journal of Food Science and Technology includes the full text of all invited presentations at the meeting. As international coordinator of CYTED project XI.13 StructureProperty Relationships in Dehydration and Storage of Dried Foods my gratitude goes to the CYTED Programme and the Universidad Politécnica de Valencia for their logistic and financial support, to the Editorial Committee of the journal for the opportunity to achieve a widespread dissemination of the ideas discussed, and last but not least, to the invited lecturers who travelled long distances and submitted their manuscripts on time. We hope that the food technology community will appreciate the effort involved and enjoy the contents of this special issue.