Amparo Chiralt

Recent Advances in Edible Coatings for Fresh and Minimally Processed Fruits

The development of new edible coatings with improved functionality and performance for fresh and minimally processed fruits is one of the challenges of the post harvest industry. In the past few years, research efforts have focused on the design of new eco-friendly coatings based on biodegradable polymers, which not only reduce the requirements of packaging but also lead to the conversion of by-products of the food industry into value added film-forming components. This work reviews the different coating formulations and applications available at present, as well as the main results of the most recent investigations carried out on the topic. Traditionally, edible coatings have been used as a barrier to minimize water loss and delay the natural senescence of coated fruits through selective permeability to gases. However, the new generation of edible coatings is being especially designed to allow the incorporation and/or controlled release of antioxidants, vitamins, nutraceuticals, and natural antimicrobial agents by means of the application of promising technologies such as nanoencapsulation and the layer-by-layer assembly.

Coupling of hydrodynamic mechanism and deformation-relaxation phenomena during vacuum treatments in solid porous food-liquid systems

The aim of this work is to extend the hydrodynamic mechanism (HDM) analysis, initially considered with no occurrence of deformations in the solid matrix, to the case of coupling HDM and deformation-relaxation phenomena (DRP). The mathematical model developed in a previous paper regarding HDM, has been extended, taking into account the possibility of solid matrix deformations because of the expansion and compression of the gas occluded into the porous structure. An experimental procedure has also been developed to assure the proposed mathematical model. The first experimental results affirm that HDM and DRP couple during the pressure changes in porous solid-liquid systems, and that the coupling itself has an important influence on the final values of mass transferred by HDM and permanent deformations in the solid food.

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.

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.

Effect of cross-linking using aldehydes on properties of glutenin-rich films

The effect of cross-linking agents glutaraldehyde (GTA), glyoxal (GLY) and formaldehyde (FA) on relevant properties of films based on a glutenin-rich fraction from commercial wheat gluten was studied. The gliadin-rich fraction was separated from glutenin-rich fraction using 70% (v/v) aqueous ethanol solution. The 70% ethanol-insoluble fraction (glutenin-rich fraction) was dispersed in 50% (v/v) aqueous ethanol at 40 °C and pH 5. GTA, GLY or FA was added in concentrations of 2, 4 and 8% (g/100 g dry protein) to the film-forming solution. Glycerol was used as plasticizer. Films were cast and dried at 23 °C and 40% RH (relative humidity) for 10 h. Mechanical and water vapour barrier properties, color, water sorption isotherms and glass transition temperature of control and cross-linked films were evaluated. Water vapour permeability values decreased by around 30% when FA, GTA or GLY were incorporated. The highest tensile strength values were obtained using FA, followed by GTA and GLY. Glass transition temperature of cross-linked films shifts to slightly higher values when cross-linking agents were used. Films treated with GTA and GLY were darker with a yellowish color. Addition of concentrations up to 2% of cross-linker did not modify the properties of the films. Water sorption behaviour of control and cross-linked films did not differ.

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.

Influence of sucrose solution concentration on kinetics and yield during osmotic dehydration of mango

The effect of the sucrose solution concentration on the process kinetics and yield during osmotic dehydration of mango (Kent var.) cylinders has been studied. Processes were carried out at 30 °C, using 35, 45, 55 and 65 °Brix sucrose, at atmospheric pressure (osmotic dehydration) and by applying a vacuum pulse (50 mbar for 10 min) at the beginning of the process (pulsed vacuum osmotic dehydration, PVOD). Kinetics of sugar gain, and water loss, as well as changes in sample mass and volume was analysed. Effective diffusion coefficients in the fruit liquid phase were also estimated. Microstructure of the mango samples after 15 min of PVOD treatments were examined by scanning electron microscopy. Effective diffusion coefficient in the fruit liquid phase increased when sucrose concentration decreased and was always higher in pulsed vacuum osmotic processes. These give rise to tissue impregnation with sucrose solution to an exceptional extent for the treatment with 45 °Brix, which induces a very high sugar gain-water loss ratio.

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.