Osmotic dehydration effects on major and minor components of chestnut (Castanea sativa Mill.) slices

Osmotic dehydration: More than water loss and solid gain

The immersion of food in a hypertonic solution results in an osmotic dehydration process (OD) with the loss of water (WL) from the food to the solution and the gain of solids from the solution (SG) by the food. For this reason, OD is commonly used to produce semi-dehydrated or enriched foods by incorporation. Although the most of OD studies are focused on the WL and SG processes, many publications addresses the physicochemical and nutritional changes resulting from OD in the food matrix and in the osmotic solution. Such changes must be handled in order to improve the quality of the product. This work is a compilation of publications with this approach.

Pomegranate arils osmotic dehydration: effect of pre-drying on mass transfer

In this work, the effect of ambient drying prior to osmotic dehydration (OD) of Tunisian pomegranate arils has been investigated. The whole fruit was pre-dried under ambient climate conditions, 20 °C and a climate humidity of 66%, until obtaining hard peels. Fresh and pre-dried pomegranate arils were dehydrated in sucrose osmotic solution at optimized conditions (50 °Brix, 40 °C, 440 rpm, foodstuff to solution weight ratio of 1:4 and 420 min). Water and solute transfer during OD where monitored. Mass transfer kinetics were modeled according to Peleg equation. This model showed a relatively good fitting of experimental data of both fresh and pre-dried samples. The pre-drying prior to OD of pomegranate arils gave lower solid gain. The sucrose uptake was about 0.403, 0.173, 0.116 g/g of dry matter for 81%, 70%, 59% initial moisture content, respectively. The highest water loss to solid gain ratio was obtained for dehydrated pomegranate arils of 70% initial moisture content. Effective diffusion coefficients were determined using the analytical solution of Fick's second law. The effective diffusion coefficients decrease with decreasing arils moisture contents. The average effective diffusion coefficients were 8.3 × 10^-9 and 4.6 × 10^-9 m² s^-1 for water loss and solid gain, respectively.

Use of ultrasound for dehydration of mangoes (Mangifera indica L.): kinetic modeling of ultrasound-assisted osmotic dehydration and convective air-drying

This work evaluated the production of dehydrated mangoes (Mangifera indica L.) and the effectiveness of ultrasonic-assisted osmotic dehydration on the drying kinetics of mangoes. Cube shaped mango samples were pretreated using ultrasound-assisted osmotic dehydration (UAOD) and dried in a circulating drying oven. An experimental design was created to evaluate the effect of pretreatment time and osmotic solution concentration on the water loss and sugar gain in the osmotic dehydration and on the drying time. The ultrasonic pretreatment was carried out in a bath ultrasound operating at 25 kHz and outputting 55 W/m³ of power. Osmotic solution ranging from 0 to 500 kg sucrose/m³ was applied in the treatments, and air drying was carried out at 60 °C. A mathematical model was developed for the osmotic pretreatment, and Fick's law was used to model the air-drying process. The mass transfer coefficients were estimated for the ultrasonic-assisted osmotic dehydration, and the apparent water diffusivity was estimated for the air-drying process. The mass transfer coefficient ranged from 0.017 to 0.109 m²/s and the resistance to mass transfer at the surface ranged from 0.26 × 10^-6 to 1.22 × 10^-6 m²/s on the UAOD, while the apparent water diffusivity during air drying ranged from 5.94 × 10^-9 to 8.41 × 10^-9 m²/s. Mangoes presented a different behavior when compared to other fruits. The ultrasonic pretreatment was effective only when associated with an osmotic solution at 500 kg sucrose/m³.

Modelling dehydration of apricot in a non-conventional multi-component osmotic solution: effect on mass transfer kinetics and quality characteristics

The quality and preservation of fresh-cut fruits can be improved by applying mild, non-thermal pre-treatments, such as osmotic dehydration (OD). The aim was to model the effect of OD on mass transfer and quality preservation. Apricot pieces were immersed in multi-component solutions comprising glycerol, erythritol, steviol glucosides and mineral salts, at various time-temperature conditions (25-45 °C for 3-240 min, w_fruit/w_solution = 1/5). Water loss (WL), solid gain (SG), water activity (a_w) as well as main quality indices (colour, texture) were measured during OD. OD apricot exhibited higher quality retention (acceptable level of colour change, increased firmness) suggesting that OD can be an effective pre-processing step in the production of innovative products. A second degree polynomial model was developed, describing the effect of processing conditions and glycerol concentration on WL, SG, a_w, colour and texture of osmotically dehydrated apricots, and ANOVA was applied to identify the factors that significantly affect the aforementioned parameters.