Pedro Fito

Modelling of vacuum osmotic dehydration of food

Abstract Vacuum osmotic dehydration leads to some advantages as compared with atmospheric osmotic dehydration. The influence of vacuum treatment is very important on the kinetics of the mass transfer phenomena, especially concerning water loss and weight reduction of food during osmotic treatment. This effect of vacuum application cannot be explained only on the basis of diffusional and osmotic transport mechanisms. So, a hydrodynamic mechanism has been proposed and experimentally analysed. Taking this new mechanism into account, a more accurate approach to the modelling of the vacuum osmotic dehydration operation may be done.

Vacuum impregnation and osmotic dehydration in matrix engineering: Application in functional fresh food development

Abstract Health benefits are one of the specific issues that will greatly influence the food industry in the next few years. Functional foods are products that may provide a health benefit beyond the traditional content of nutrients, or through other added physiologically active components (PAC). Fruits and vegetables are increasingly being consumed because of their appreciated nutritional and fresh properties. The enrichment of these products with minerals, vitamins or other PAC can be a good choice to develop functional foods. Vacuum impregnation (VI) allows to introduce controlled quantities of a solution in the porous structure of fruit and vegetable (matrix). This solution can contain PAC, a w or pH depressors, antimicrobials, etc., in order to formulate functional, stable, fresh-like products. The feasibility of VI for a great quantity of fruits and vegetables is discussed by means of analysing their response to VI. Porosity and VI effectiveness of impregnated products were observed by Cryo-SEM. A model to determine the concentration level of PAC in the impregnating solution was established in order to formulate functional foods with different calcium and iron salts which could represent a determined percentage of the recommended daily intake of these minerals.

Development of probiotic-enriched dried fruits by vacuum impregnation

Abstract In this study an attempt is made to combine the beneficial effects of probiotics with fruit and vegetables by applying the vacuum impregnation process. Apple cylinders were impregnated either with commercial apple juice containing Saccharomyces cerevisiae , and with whole milk or apple juice containing 10 7 or 10 8 cfu/ml of Lactobacillus casei (spp. rhamnosus). Impregnated apple samples contained around 10 7 cfu/g. In order to increase stability and to assure fruit preservation, impregnated apple samples were air dried at 40 °C to a water content of 0.037 kg water/kg dry matter and stored at room temperature for two months. The content of L. casei viable cells in dried and stored product was greater than 10 6 cfu/g. This concentration level of probiotics is similar to that in commercial dairy products.

Calcium fortification of vegetables by vacuum impregnation interactions with cellular matrix

Calcium fortification of vegetables by applying vacuum impregnation (VI) is an alternative in developing functional foods. Nevertheless, calcium ions can interact with the plant tissue, modifying its mechanical and vacuum impregnation responses. These effects were studied in eggplant, oyster mushroom and carrot samples. Sample VI was carried out with isotonic solutions containing (i) sucrose and calcium lactate and (ii) sucrose. From the analysis of sample impregnation and deformation levels, the slight influence of Ca presence on the impregnation behaviour of these products could be concluded. Nevertheless, mechanical behaviour of eggplant and carrot were notably affected by calcium, although no significant effects were observed in oyster mushroom (without pectin in their cell architecture). Energy dispersive X-ray microanalysis (EDXMA) in impregnated products showed that calcium impregnation occurs in the intercellular spaces of eggplant and oyster mushroom and in xylem of carrot.

Use of vacuum impregnation in food salting process

Salting is an ancient preservation method, usually used separately or in combination with other processes such as air drying and pH lowering. Traditional salting processes are divided into brining and dry salting, each of them specifically applied for particular products. In this work, the use of brine vacuum impregnation (BVI) instead of dry salting or brine immersion (BI) at atmospheric pressure is discussed. The influence of different process variables (length of vacuum pressure period, temperature, sample structure and dimensions) is analysed, in terms of kinetic data and process yields, for meat (ham and tasajo), fish (salmon and cod) and cheese (Manchego type cheese). In general, BVI processes imply a notable reduction of salting time, increasing the process yields in line with the greater values of the ratio salt gain to water loss. Likewise, samples lose natural gas or liquid phases entrapped in their structure and reach a flatter salt concentration profile than that obtained in the conventional salting methods.

DRYING KINETICS OF APPLE CYLINDERS UNDER COMBINED HOT AIR–MICROWAVE DEHYDRATION

Abstract Apple cylinders (Granny Smith) were dried in a combined hot air–microwave system. Drying experiments were carried out at various air temperatures (25, 30, 40 and 50 °C) combined with different levels of microwave incident power (0, 3, 5, 7 and 10 W/g) until 0.11 (d.b.) moisture content was obtained. Vacuum impregnation with an isotonic solution was used as a pretreatment before drying. Sample weight changes were determined for different drying conditions. When drying with combined air–microwave system, the drying rate curve could be divided in four periods limited by four critical points. An empirical model was proposed to estimate the drying kinetic constants as a function of the air temperature and the microwave power level for both sorts of samples, fresh apples and impregnated apples. At the end of the process different tissue matrices were obtained depending on the different drying conditions.

Non-diffusional mechanisms occurring during vacuum osmotic dehydration

Abstract The non-diffusional mass transfer in operations where porous food is immersed in a liquid and submitted to vacuum conditions is analysed in this study. The liquid penetration in the food pores due to pressure gradients have been mathematically modelled. An experimental verification of the resulting equations is presented.

Changes in mechanical properties throughout osmotic processes: Cryoprotectant effect

Abstract In osmotic dehydration of fruits, physical and chemical changes occurring throughout the process provoke changes in the product texture and appearance to a different degree depending on the process conditions and product characteristics. Nevertheless, water content reduction and sugar gain have been observed to have some cryoprotectant effects on colour and texture in several fruits. In this work, the specific influence of osmotic treatments with sucrose solutions at 30°C on mechanical properties of mango, kiwi and strawberry are discussed. The combined effect of blanching and vacuum impregnation is analysed in mango. The influence of osmotic solution concentration and vacuum impregnation on kiwi fruit is discussed and the effect of osmotic dehydration, as compared with air drying is analysed in strawberry. In all cases, changes in mechanical properties of fresh and pre-dehydrated fruits due to freezing–thawing are compared in order to quantify the cryoprotectant effect of the osmotic treatment.

Vacuum impregnation for development of new dehydrated products

Vacuum impregnation (VI) of structured foods implies the partial release of gas from pores and its substitution by an external liquid. Therefore, important changes in physicochemical and structural properties take place in the food and these affect its behavior in drying operations (air-drying (AD) and/or osmotic dehydration (OD)). The adequate control of VI prior to dehydration may be used as a tool both to improve mass transfer and to develop engineered products. In order to evaluate this alternative, the effectiveness of VI as a tool in porous matrix formulation is analyzed. Likewise, its influence on some physical and transport properties of the plant tissue and the relevant changes induced in osmotic and convective drying processes are discussed, since these are probably the most interesting alternative processes to lengthen the impregnated product shelf-life. Improved yield of some dehydration processes, such as fruit candyin, when VI is applied at the beginning, is also discussed in terms of the cell network relaxation mechanism, responsible for hydrodynamic tissue impregnation.

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.