Mass transfer kenetics in infusion of phenolic compounds extracted from grape pomace into Aloe vera gel by osmotic dehydration

The current study was carried out to investigate the kinetics of infusion of phenolic compounds extracted from grape pomace (Argol) into Aloe vera gel cylinders. Aloe vera gel was treated at 50 °C in different osmotic solution with (40, 50 and 60) % sucrose plus (10, 20 and 30) % Argol, for 0–120 min. The fruit to solution ratio was kept 1:4 (w/w) during all experiments. A two parameters model was used for prediction of kinetics of mass transfer and values of equilibrium moisture loss and solid gain. Moisture and solid effective diffusivities were estimated using Fick’s second law of diffusion. Results showed that Azuara model has the potential for estimating the equilibrium points. In addition, a good correlation between predicted and experimental values were obtained by this model. Besides, moisture and solid effective diffusivities increased by increasing sucrose solution and Argol from 40 to 50 percentage and 10 to 20 percentages, respectively. Moisture and solid diffusivities were found in the range of 0.61–4.23×10−9 m2/s and 2.13 –2.77 × 10−9 m2/s, respectively. Functional food is an emerging field in food science due to its increasing popularity with health-conscious consumers and the ability of marketers to create new interest in existing products. New by-product application should be investigated to have a positive environmental impact or to turn them into useful products. The use of by-product such as the grape juice pomace (Argol), results in the return of these valuable sources into the food cycle as well as an improvement in nutritional value and functional products in the food industry. Red grape (Vitis vinifera L.) pomace contains a large amount of polyphenolic compounds, therefore extraction of bioactive compounds promote human health. It is not as easy to mix the functional ingredient in the solid system as it is, in the case of the powder and liquid products. With the help of osmotic dehydration, many researchers have demonstrated the infusion of active compounds such as mineral, phenolic compounds, curcuminoids, probiotics and vitamins into solid food tissue. Fruits such as aloe vera, which have a short shelf life and are suitable system models for infusion of phenolic compounds during osmotic dehydration. Osmotic dehydration can prove useful in drying aloe vera (Aloe Barbadensis Miller) which contains several nutritional compounds, including polysaccharides, phenolics, antioxidants, vitamins, enzymes, minerals, and so forth. The phenomenon of osmotic dehydration can be modeled by the fundamentals of mass transfer that describe the origin of the diffusive forces that are involved in and control these processes. A two-parameter equation of Azuara was used to predict the kinetics of osmotic dehydration and the final equilibrium point. The internal mass transfer occurring during osmotic dehydration of food is usually represented by Fick’s second law which is the best known phenomenological model to represent the diffusional mechanism is the model of Crank, consisting of a set of solutions of Fick’s law of diffusion for different geometries, boundary conditions and initial conditions. To date, there is no research on mass transfer during osmotic dehydration of aloe vera. Therefore, the objective of the present work was the infusion of Argol phenolic compounds in alo vera gel through osmotic dehydration treatment to investigate mass transfer during osmotic treatment. Material and methods: The Aloe Vera was added to agar and shaped into cylindrical pieces (20×20 mm). Afterwards the pieces were floated in a solution of sugar (40, 50 and 60) percentage and Argol (10, 20 and 30) percentage. The weight ratio of osmotic medium to fruit sample was 4:1 to avoid significant dilution of the medium and subsequent decrease of the driving force during the process. The experiment was performed with constant temperature of 50 °C. Samples were removed from the solution at 30, 60, 90, 180, and 120 min of immersion, drained and the excess of solution at the surface was removed with absorbent paper. Afterward, the dehydrated samples from each group were drained and blotted with absorbent paper to remove excess solution. Each assay was made in triplicate. Weight and moisture content of the samples, and moisture loss (ML) and solid gain (SG) were calculated. The curves of moisture loss and salt gain as a function of time were constructed using experimental data. A two parameters model was used for prediction of kinetics of mass transfer and values of equilibrium moisture loss and solid gain. Moisture and solid effective diffusivities were estimated by using Fick’s second law of diffusion. Results showed that in all of the studied conditions, the levels of moisture loss and solid gain had a non-linear increase with more floatation time in the solution. Moreover, the absorption rate of solid gain was faster in the beginning but eventually slowed down. Azuara model has the potential in estimating the equilibrium points. In addition, a good correlation between predicted and experimental values was obtained by this model. Besides, increasing the concentration of sucrose and Argol from 40% to 50% and 10% to 20% respectively, the coefficient of effective penetration for both parameters (water loss and solid substance absorption) improved. In addition, the coefficient of effective penetration displayed that different levels of sucrose and Argol had a notable effect on this coefficient.