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Osmotic dehydration (OD) is a method to partially reduce moisture of food, aiming to improve the shelf life and the stability of the products. The mass transfer that occurs during this process can be enhanced with the application of reduced pressure in the first minutes of the osmotic dehydration (pulsed vacuum osmotic dehydration - PVOD). The present work aimed to study the vacuum effect on the kinetics of osmotic dehydration of vegetables (carrot, eggplant and beetroot) in terms of water loss, solids gain and water activity, in ternary solution. Moreover, mathematical modeling of experimental data obtained from the osmotic processes, was employed for correlating the mass transfer of the food product under the different conditions. An intensification of mass transfer was observed for carrot and eggplant in the vacuum treatments. This was related to their porous structure. The present work demonstrated a lack of fit of Fick’s second law for describing the dehydration kinetics of the eggplant.

Tomato is one of the most cultivated vegetables, playing important role in the human feed. Due to its characteristics and composition, tomatoes present reduced shelf life, and preservative techniques are required. In this study, response surface methodology was used to optimize process conditions during the osmotic dehydration (OD) of tomato slices, through the desirability function. Optimization factors were absolute pressure (21-89 kPa), vacuum application period (7-15 min), and osmotic solution water activity (0.893-0.943), while investigated responses were sodium incorporation (NaI), water loss (WL), solid gain (SG), weight reduction (WR), and osmodehydrated product water activity (ODaw). The optimized conditions were achieved, and a further hot-air drying (HAD) was conducted at different temperatures and air velocities. During the OD, lower absolute pressure, and osmotic solution water activity led to lower NaI and higher WL and WR. Shorter drying time and higher diffusivity were obtained at higher temperature and air velocity, during the HAD. The dried tomato slices with sodium incorporation reduction were evaluated with regard to the final water activity, rehydration and color, in which no significant differences (p > 0.05) were observed between the treatments.

Pulsed vacuum osmotic dehydration (PVOD) is a widely used technique for reducing moisture content and water activity in biological products. This study aimed to analyze the effect of vacuum application (VA) on PVOD of beetroot, carrot, and eggplant slices, with respect to chemical (moisture, water activity, specific pigments, polyphenols, and sodium content), optical (color), mechanical (shrinkage, maximum stress, and elasticity), and structural (microstructure) properties. PVOD was conducted at three different vacuum pressures (0, 40, and 80 kPa, for 10 min), during a total process time of 300 min. Osmotic processing was performed at 35 °C by using a ternary osmotic solution [40% sucrose + 10% sodium chloride (w/w)]. Eggplant and carrot samples were more sensitive to VA, compared to beetroot. This was related to their porous and less compact structure. In general, VA reduced the moisture content and water activity and preserved the carotenoid content. VA caused loss of betalain and phenolic acid, favored sodium uptake, and induced significant changes in the optical, mechanical, and structural properties, compared to the osmotic processing conducted at atmospheric pressure.

A desidratacao osmotica assistida por pulso de vacuo (PVOD – pulsed vacuum osmotic dehydration) e um processo eficiente para obtencao de alimentos parcialmente desidratados. Devido ao seu elevado teor de umidade os figos precisam ser conservados de alguma maneira. O presente trabalho teve como objetivo avaliar o efeito da concentracao da solucao de sacarose (46,6 a 63,4 °B) e de sua temperatura (31,6 e 48,4 °C) assim como, o tempo de pulso de vacuo aplicado a PVOD (74 mmHg, 0 a 40 min) na incorporacao de materia seca e reducao do teor de agua. A desidratacao osmotica foi realizada por 300 min com proporcao amostra/solucao de 1:10 (m/m). O planejamento experimental utilizado foi um delineamento composto central rotacional 2 3 , incluindo 6 pontos axiais e 4 repeticoes no ponto central, totalizando 18 experimentos. O aumento do tempo de pulso de vacuo apresentou efeitos significativos na reducao do teor de umidade e incorporacao de materia seca.