Pulsed Vacuum Osmotic Dehydration Research Articles

Secagem por microondas a vácuo de Yacon pré-tratado por desidratação osmótica pulsada como alternativa de preservação de fruto-oligosacarídeos

ABSTRACT Yacon, a perennial plant from the Andean region, is particularly rich in fructo-oligosaccharides (FOS) and inulin. However, these saccharides are rapidly hydrolyzed after harvest, affecting the functional characteristics of yacon. Therefore, a preservation technology such as drying is warranted to preserve the FOS content of yacon products during the off-season. To this end, we dried yacon slices, either untreated or pretreated with pulsed vacuum osmotic dehydration (PVOD), in a microwave vacuum (MWV). PVOD was performed using a sorbitol solution (38 °Brix, 35 °C, and 681 mmHg during the first 10 min). A three-level experimental design with three initial power densities (PDs) of 3.6, 6.3, and 9.9 W.g−1 and three vacuum pressures (VPs) of 0, 300, and 600 mmHg was employed to perform the MWV drying experiments. FOS content, drying kinetics, diffusivity, shrinkage, yacon temperature, and rehydration were investigated. We observed that during PVOD, as microwave PD increased, the drying time, moisture, and water activity decreased. Moreover, an increase in PD positively affected FOS retention, diffusivity, temperature, and shrinkage. Furthermore, VP significantly affected FOS retention in pretreated samples and facilitated drying. In addition, microwaves with a higher PD increased the effective diffusivity and facilitated FOS retention. VP also affected the drying and FOS retention of pretreated samples. In general, yacon browning was observed under all treatment conditions, independent of pretreatment. For osmotically dehydrated samples, processing conditions with a PD of 9.9 W.g−1 and vacuum pressure of 600 mmHg are ideal for drying yacon slices via microwave vacuum, thereby increasing the FOS content by approximately 40%.

Pulsed Vacuum Osmotic Dehydration (PVOD) of Fermented Beetroot: Modeling and Optimization by Response Surface Methodology (RSM)

AbstractFermented beetroots can be osmotically dehydrated and then dried to make a nutritious snack known as fermented beet chips. To ensure the best product quality, it is necessary to determine optimal parameters of osmotic dehydration. Therefore, the aim of this study was to determine the optimal parameters of pulsed vacuum osmotic dehydration (PVOD) of fermented beetroot slices. The response surface methodology (RSM) was employed to optimize PVOD and improve the efficiency of the process. The experimental parameters considered: (T) processing temperature (20 < T < 40 °C), (SC) sugar concentration (40 < SC < 60%), (VT) vacuum impregnation time (10 < VT < 50 min), and (ST) slice thickness (2 < ST < 6 mm). PVOD was optimized in terms of properties of beetroot tissue (hardness, HT, redness, a*T, water loss, WL, solid gain, SG) and osmotic solution (dry matter content, DMS, redness, a*S). The optimum qualities of beetroot tissue (HT = 202.0 N, a*T = 11.8, WL = 55.5%, SG = 7.1%) and osmotic solution (DMS = 57.3%, a*S = 38.9) were obtained at T = 20 °C, SC = 60%, VT = 10 min, ST = 6 mm and T = 40 °C, SC = 60%, VT = 50 min, ST = 2 mm, respectively. The beet tissue obtained by PVOD in optimal parameters was characterized by 2.58 ± 0.21 kg H2O/kg DM moisture content (MCF), 4.64 ± 0.37 mg GA/g DM total polyphenols (TPC), 2.2 ± 0.2 mg TE/g DM ferric reducing antioxidant power (FRAP), 1125 ± 10 kg/m3 density (ρT), and 4.29 ± 0.24 total color change (ΔE*) compared to material before PVOD. 2D and 3D images of the beetroot surface structure allowed to observe the collapse of the structure and the appearance of a semi-transparent coating (most likely a sugar solution) on the material after PVOD.

Combined Pulsed Vacuum Osmotic Dehydration and Convective Air-Drying Process of Jambolan Fruits.

Jambolan (Syzygium cumini) is a native fruit from Asia that has adapted well to the tropical climate of the Amazonian region. However, due to its limited annual availability and high perishability, the jambolan fruit is still underexploited. Thus, this study aimed to preserve the jambolan through a combined process of pulsed vacuum osmotic dehydration (PVOD) and convective air-drying and to monitor the total phenolic contents (TPCs) and total monomeric anthocyanins (TMAs) during these processes. To this end, jambolan fruits were pretreated with increasing PVOD times. After monitoring of moisture loss, solid gain, weight reduction, water activity, TPC, and TMA, pretreated (PT) and non-pretreated (NPT) fruits underwent convective air-drying (50-70 °C). The PVOD reduced half of the water present in the fruits; nonetheless, PVOD decreased the TPC and TMA over time. The increase in air-drying temperature shortened the drying time for both NPT and PT jambolan, and PVOD reduced even further the drying time of the fruits. Moreover, the fruits pretreated and dried at 60 °C showed promising results, potentially being a good alternative to extend the fruit's shelf life and make it available throughout the year.

Dried yacon with high fructooligosaccharide content

AbstractThe convective drying of yacon was investigated (40–70°C). Pulsed vacuum osmotic dehydration (PVOD) (sorbitol 38 °Brix, 35°C, 681 mmHg in the first 10 min) as pretreatment was tested. Drying behavior, energy consumption, diffusivity, fructooligosaccharide (FOS) retention, shrinkage, water activity, shrinkage, and color were measured. Fick's model was adequate for drying kinetics adjustment, mainly for untreated samples with shrinkage consideration. PVOD pretreated dried yacon was a less shrunken product in a shorter drying time with up to 60% FOS retention. Nevertheless, the best tested condition for FOS retention (88%) was the convective drying at 60°C without PVOD application.Practical ApplicationsThe yacon is a seasonal plant that presents high concentrations of functional compounds. Like most vegetables, its shelf life is short and storage difficult. Therefore, improved techniques for conservation are required. The present paper evaluates the effects of drying temperature on the production of fresh and osmodehydrated yacon slices during convective drying. This study could offer an interesting response to the changes promoted by these processes, relating to the modifications to the physicochemical properties of osmodehydrated yacon.

Drying of ‘yacon’ pretreated by pulsed vacuum osmotic dehydration

ABSTRACT In this study, the ‘yacon’ was dried using pulsed vacuum osmotic dehydration as pretreatment followed by vacuum drying (at different temperatures) or convective drying. The use of osmotic dehydration and vacuum drying had their influence evaluated concerning drying kinetics and quality of the final product, considering fructan retention, color, and water activity. Fick’s second law and Page’s equation were suitable for the fitting of drying evolution. It was observed that higher temperatures (60 °C) resulted in shorter drying time, higher diffusivity, and higher fructan retention when compared to 40 and 50 °C. The osmotic pretreatment and the vacuum drying differed in fructan retention (p ≤ 0.05). Moreover, the dried product, osmotically pretreated, presented a shorter drying time. The best condition was vacuum drying at 60 ºC, preceded by pulsed vacuum osmotic dehydration that resulted in fructan retention of approximately 38% in a quicker, higher diffusivity and lighter color product concerning the other tested conditions.

Drying of persimmon fruit (Diospyros kaki L.) pretreated by different osmotic processes

AbstractPersimmon is a short shelf life fruit with interesting potential for application in different industrial segments. The immersion of food in a hypertonic (30 and 45 °Brix) or even hypotonic medium can be used as a pretreatment for the drying process. In this study, the convective drying of persimmons was preceded by osmotic dehydration (OD) with fructose in a standard atmosphere, pulsed vacuum osmotic dehydration (PVOD), ultrasound (US)‐assisted OD, and US pretreatment in distilled water. Pretreatment times were 0, 10, and 30 min. The samples were subjected to convective drying at 40 and 60°C, 0.5 m s−1. The effects of the pretreatments on the drying kinetics, volumetric shrinkage, and rehydration capacity were investigated. Fick's model and the Dincer and Dost model were used to fit the drying evolution. In addition to the influence of the osmotic solution concentration, moisture content and solid gain were functions of the treatment type. Convective drying required 260–740 min. The use of PVOD and US pretreatments resulted in the shortest drying times. The dried fruits showed particular characteristics with each different pretreatment. Both tested models presented satisfactory adjustments, but Fick's model was the best approach. In general, the treatments caused structural modifications in the persimmon fruits that modified the drying kinetics and the properties of the dried food.Practical ApplicationsConvective drying is a food processing method used to extend the shelf life of fruits, such as persimmons. The use of pretreatments is an interesting strategy to improve the drying process. However, the combination of these technologies can influence drying kinetics. Therefore, the use of mathematical models is important to represent the behavior of these processes.

Modeling mass transfer during osmotic dehydration of different vegetable structures under vacuum conditions

Abstract 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.

MODELING AND OPTIMIZATION OF THE PULSED VACUUM OSMOTIC DEHYDRATION (PVOD) PROCESS OF CARROTS IN A TERNARY SOLUTION BY RESPONSE SURFACE METHODOLOGY

Optimization of the pulsed vacuum osmotic dehydration (PVOD) process of carrot slices in a ternary solution was carried out using the response surface methodology. During PVOD, the vacuum pulse was applied at the beginning of the process for 10 min at a reduced pressure of 500 mm of Hg throughout all the experiments. After that, the osmotic dehydration process was continued at atmospheric pressure according to the central composite rotatable design (CCRD). The effects of temperature (35-55oC), sugar concentration (40-50oBrix), salt concentration (5-15%) and osmosis time restored at atmospheric pressure (10-240 min) on the responses viz. water loss (WL), solute gain (SG) and colour difference (∆E) of the dehydrated samples were assessed and statistically optimized through the desirability function approach. The models obtained for water loss, solute gain and colour difference were found suitable to describe the experimental data. It was found that the time restored at atmospheric pressure has the most significant effect on the responses at the 95% confidence level. The optimum condition was found at a temperature of 50oC, sugar concentration of 45.47oBrix, salt concentration of 7.50%, and restoration time of 67.50 min. At these optimum conditions, the water loss, solute gain and colour difference were 42.61%, 10.42% and 4.38, respectively. The predicted optimum values for independent linear variables were validated by performing triplicate experiments and the simulated data were come across similar with the experimental ones.

Pulsed vacuum pickling (PVP) of garlic cloves: Mass transfer kinetics and quality attributes

Due to special taste and medicinal properties, pickled sweat-sour garlic is one of the most popular garlic-based functional foods in China. The traditional pickling method of garlic is tedious, time consuming, laborious, low efficient, and easily influenced by environmental factors and microorganisms. In the present study, garlic cloves were subjected to two pickling methods: osmotic dehydration at atmospheric conditions (OD) and pulsed vacuum osmotic dehydration (PVOD). Pulsed vacuum impregnation was applied in order to evaluate the possibility of enhancement of pickling efficiency and quality of final product. The effect of OD and PVOD on mass transfer kinetics of sodium chloride, sucrose and acetic acid as well as quality attributes (color parameters such as L*, a*, b*, and thiosulfinates content) of pickled sweet and sour garlic cloves was investigated. Results indicate that PVOD promoted mass transfer of sodium chloride and acetic acid compared to the traditional OD method. However, there was no significant effect on mass transfer of sugar. PVOD significantly decreased thiosulfinates content (from 4.49 mg/mL to 1.91 mg/mL) and L* values (from 66.72 to 45.85) of garlic. During PVOD of garlic, samples gradually turned from white color to the desired amber color during the PVOD process. The findings of current work indicate that PVOD is a promising technique for garlic pickling as it enhances mass transfer and accelerates the degradation of thiosulfinates content in garlic.

Comparison of pulsed vacuum and ultrasound osmotic dehydration on drying of Chinese ginger (Zingiber officinale Roscoe): Drying characteristics, antioxidant capacity, and volatile profiles.

The effects of pulsed vacuum osmotic dehydration (PVOD) and ultrasound osmotic dehydration (USOD) on drying characteristics and quality attributes of ginger were investigated. PVOD was subjected to pulsed vacuum at 13 kPa for 30 min, and USOD was subjected to ultrasound with the frequency of 40 kHz for 30 min. After PVOD and USOD treatments, the samples were then dried at intermittent microwave & air‐drying oven with an output of 700 W and temperature of 60°C to the final moisture content of 0.12 g water/g d.w. The results showed PVOD and USOD treatments could improve the total phenolic contents by −1.8% to 16.4%, total flavonoid content by 7.7%–18.7%, DPPH radical scavenging by 9.5%–12.2%, and ABTS+ antioxidant activity by 17.8%–27.4%, although they prolonged the later stages drying of ginger. Besides, the PVOD‐ and USOD‐pretreated dried samples had less brownings than the untreated‐dried samples which could be attributed to the inactivation of polyphenol oxidase (PPO) and peroxidase (POD). The PPO activity was significantly reduced in the PVOD and USOD ginger, whereas POD activity was decreased in USOD ginger but increased in PVOD ginger. Moreover, PVOD pretreatment also led to a better preservation of volatile profiles and cell structure than USOD treatment. Therefore, both PVOD and USOD are effective pretreatments for drying of ginger.

Kinetics of the pulsed vacuum osmotic dehydration of green fig (Ficus carica L.)

The fig (Ficus carica L.) is a fruit native to the Mediterranean region. However, it has spread worldwide. Osmotic dehydration is used to reduce the moisture content in food, preserving its main characteristics. This study aimed to obtain the kinetics of the water loss, solid gain and water activity of green figs that were cut transversely and osmotically dehydrated in different sucrose solutions (40, 50 and 60 °Brix). The osmotic dehydration occurred at 40 °C, with a vacuum pulse of 74 mmHg in the first 5 min of the process in a total time of 240 min. The ratio of sample:solution was kept constant at 1:10 (weight/weight). Periodically, the samples were weighed to calculate the kinetics of water loss, solid gain, and water activity. The increase in the concentration of the sucrose solution from 40 to 60 °Brix promoted a percentage increase of water loss from 8.14 ± 0.80 to 12.80 ± 0.50%, of solid gain (0.89 ± 0.31 to 1.42 ± 0.70%), and the reduction of water activity (0.93 ± 0.02 to 0.91 ± 0.01). The mathematical models of Peleg and Azuara were tested for fitting the kinetics of water loss and solid gain. Both the mathematical models of Peleg and Azuara presented good fitness to the experimental data. However, the latter was more adequate (higher r2 and lower error), with predicted equilibrium conditions closer to the experimental values.

Comparison between Artificial Neural Network model and mathematical models for drying kinetics of osmotically dehydrated and fresh figs under open sun drying

AbstractIn this study, drying kinetics of figs (Ficus carica L) under open sun drying (OSD) was compared with using Artificial Neural Network (ANN) model and mathematical models. Pulsed vacuum osmotic dehydration (PVOD) was applied as a pretreatment. In experiments, whole figs (Sarılop variety) were immersed in sucrose solution at 50°Brix and 50 °C with a ratio of solution/food was 4:1 for 180 min. Vacuum impregnation was applied at 253 mbar for 15 min. Shrinkage effect was considered, also. Results showed that PVOD reduced drying time of figs. The mean of Deff values of PVOD treated and fresh figs were obtained as 2.55 × 10−10 m2/s and 2.36 × 10−10 m2/s, respectively. It was found that present model was the best drying model with the highest correlation coefficient (R2) values among the mathematical models whereas ANN model had a higher correlation coefficient (R2 = 0.9999) values than the mathematical models for both PVOD treated and fresh figs.Practical applicationsDried figs have an economic income for Turkey and Turkey is the biggest dried fig producer and exporter in the World. Drying of figs is very important phenomena because figs have a short harvesting time. Figs are widely dried under open sun because this method has low operating cost. OD method is used before drying step and provides reducing drying time. This study presents experimental results of osmotically dehydrated and fresh figs under open sun drying. Drying kinetics of figs were modeled with empirical and semiempirical models under shrinkage consideration. Shrinkage of fresh and osmotically dehydrated figs during the drying were mathematically modeled thus these correlations can be helpful for researchers. Also, a new mathematical model was established and this model had more accuracy than other mathematical models. The ANN model was used for the prediction of drying curves of figs in different operating conditions.

Pulsed Vacuum Osmotic Dehydration of Beetroot, Carrot and Eggplant Slices: Effect of Vacuum Pressure on the Quality Parameters

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.

Reuse of sorbitol solution in pulsed vacuum osmotic dehydration of yacon (Smallanthus sonchifolius)

The osmotic solution (OS) used in pulsed vacuum osmotic dehydration (PVOD) could represent an environmental problem. The reuse of the solution minimizes the cost, but has to consider the properties of the dehydrated product and the solution itself. The reuse of sorbitol solution, 38 kg/100 kg solution, in 15 successive PVOD of yacon slices (35°C, 300 min) was studied. The evaluation was based on alterations of soluble solids, water activity, pH, turbidity, electrical conductivity, viscosity, density, color, and microbiological stability. The weight loss, moisture content, and soluble solids of the food were also evaluated. Among the OS characteristics, only the color, electrical conductivity, and turbidity of the solution changed significantly, alterations that could be reduced with filtration. The food properties were not significantly affected. The microbiological content was retained in acceptable levels. The reuse of the sorbitol solution could be performed without relevant alterations in the food or the solution. Practical applications The osmotic solution is used in osmotic dehydration to promote a partial removal of the moisture content of the food. However, after the osmotic process, the solution is diluted and contains native solutes from the food. For obtaining a dehydrated product within a standard production, the solution should also present standard characteristics. This works presents the evolution of some analysis as soluble solids, water activity, pH, turbidity, electrical conductivity, viscosity, density, color, and microbiological stability in a solution of sorbitol. Sorbitol solution is an alternative to sucrose for obtaining semidehydrated products with glycemic index. It was shown that the solution could be used for at least 15 times in yacon dehydration.

Microwave, convective, and intermittent microwave-convective drying of pulsed vacuum osmodehydrated pumpkin slices

The drying of pumpkin slices (Cucurbita moschata Duch.) by microwave, convective, and intermittent microwave–convective techniques was studied. The samples were pretreated by blanching followed by pulsed vacuum osmotic dehydration. The microwave output power was 780 W. Air temperatures were 30 °C and 60 °C and air velocities were 2.22 and 4.44 m s−1. The final moisture content was set at 0.08 kg [H2O] kg−1 [dry matter]. The drying kinetics were obtained and fitted with the Fick's model and the Page's empirical correlation. Color, water activity, shrinkage, and rehydration were evaluated. Shorter drying times, higher diffusivity and better color quality were obtained by employing microwave. Convective experiments carried out to higher water activity and lower shrinkage. For describing the drying behavior, the better adjustment was reached by the Page's empirical correlation. Practical applications The pumpkin (Cucurbita moschata Duch.) is well known as an important source of carotenoids, vitamins and minerals. After the harvest, techniques are required to assist the preservation of fruits, once they present high moisture contents. Microwave drying is an alternative method to preserve temperature-sensitive compounds and to economize energy and time. Microwave energy combined with other drying methods can improve the drying efficiency as well as the quality of food products which is far better than that achievable by the application of each method alone. This study investigates the efficacy of convective, microwave and intermittent microwave–convective drying techniques for osmodehydrated pumpkin slices. The mathematical models provide information about the processes. It was also evaluated the changes on physical characteristics of the product after drying.

Effects of pulsed vacuum osmotic dehydration (PVOD) on drying kinetics of figs (Ficus carica L)

Abstract Drying kinetics of non-pretreated (fresh) and pretreated Sarilop (Ficus carica L.) variety figs were compared. In experiments, figs were performed as a whole (unsliced and unpeeled). Pretreatment was pulsed vacuum osmotic dehydration (PVOD). Osmotic dehydration was performed in sucrose solution at 50 °Brix and 50 °C with a solution/fruit mass ratio of 4/1. Vacuum impregnation in osmotic dehydration was applied at 130 mbar for 15 min then the osmotic treatment continued at atmospheric pressure for 165 min, therefore the total pretreatment period lasted for 180 min (15 min (130 mbar) + 165 min (Patm)). Pretreated and non-pretreated figs were dried at 55, 65 and 75 °C in a convective oven. Results showed that increasing of drying temperature shortened the drying time for both non-pretreated and pretreated figs. Drying period of pre-treated figs lasted shorter than non-pretreated figs, thus PVOD shortened the drying period. Non-pretreated (fresh) figs had greater shrinkage than the pretreated figs. Effective moisture diffusivity (Deff) values of pretreated figs are greater than the non-pretreated figs during the drying at all three temperatures. Deff increased with drying temperature for both pretreated and non-pretreated figs. Deff values of non-pretreated and pretreated figs ranged 2.75·10− 10–5.69·10− 10 m2/s and 3.57·10− 10–10.25·10− 10 m2/s, respectively. Activation energy (Ea) of non-pretreated and pretreated figs were obtained 34.68 (kJ/mol) and 50.27 (kJ/mol), respectively. Also, sensory evaluation of color, flavor, odor, texture and overall acceptability of the samples was made. Industrial relevance The use of PVOD technique is relevant for food industry. So that, PVOD treatment shortened the drying period of figs. Thus, this result can cause the economic advantage as reducing the further costs for drying process. Additionally, results of sensory evaluation show that there was no significant difference (p > 0.05) between the pretreated and traditional dried figs except for flavor. Sensory properties of pretreated figs may be improved by changing conditions of pretreatment.

Optimization of pulsed vacuum osmotic dehydration of the cape gooseberry (Physalis peruviana L.) using the response surface methodology

The objective of this study was to optimize mass transfer during pulsed vacuum osmotic dehydration (PVOD) of cape gooseberries (Physalis peruviana L.) by means of the surface response methodology. The effects of the factors temperature (25-45°C), solids (50-70°Brix), rotation speed (60-100 rpm), pressure (50-100 mbar) and number of vacuum pulses (1-3) on osmotic dehydration, weight reduction percentage (WR), water loss percentage (WL), and solid gain percentage (SG%) were assessed. Sucrose syrup at a 5/1 syrup/fruit ratio was used for 2 h. The results provided 45°C, 70°Brix, 99.99 rpm, 98.92 mbar and 2.87 pulse vacuum, for a WR of47.52%, WL of 21.12%, and SG of 118.40% as the optimal conditions. Mathematic models were adjusted to the optimal conditions to describe the PVOD kinetics of cape gooseberries. Azuara's penetration empiric model, a phenomenological model from the solution of Fick's second law, and Peleg's empiric model were used. The latter adjusted better to the experiment data.

Osmotic dehydration of yacon (Smallanthus sonchifolius): Optimization for fructan retention

Yacon presents prebiotic and hypoglycemic properties with a high fructan content. Pulsed vacuum osmotic dehydration (PVOD) is a process that can reduce water activity with small variations in nutritional properties. Yacon slices were dehydrated with two different solutions: fructose and sorbitol. The experiments were based on a central composite rotational design and the optimum condition set for the highest retention of fructans. The PVOD experiments were performed in 300 min, with vacuum pulse in the first 10 min. The independent variables were temperature (24–44 °C), vacuum pressure (49.4–200.6 mmHg) and osmotic solution concentration (22.0–60.8 °Brix). The dependent variables were fructan retention, weight reduction, water loss, solid gain, water activity and total color difference. The highest fructan retention was obtained with sorbitol, ranging from 28.13 to 82.03%, in contrast to the range of 2.79–39.48% obtained for the sample dehydrated with fructose. The optimum PVOD condition with sorbitol was concentration of 38 °Brix, temperature of 35 °C and vacuum pressure of 74 mmHg. For PVOD with fructose, the best results were obtained with a solution concentration of 35 °Brix, temperature between 24 and 30 °C and vacuum pulse above 100 mmHg.

Pulsed vacuum osmotic dehydration of tomatoes: Sodium incorporation reduction and kinetics modeling

Semi-dehydrated food is obtained via osmotic dehydration (OD). The influence of the osmotic agent (27.5% sucrose or maltodextrin combined with 10.0% of NaCl, 40 °C) with/without the application of a vacuum pulse (VP) (100 mbar, 20 min) on the NaCl incorporation and on the kinetics of water loss (WL), solid gain (SG), and water activity (aw) were studied in the OD of sliced tomatoes. The kinetics of the WL and SG were evaluated and fitted with diffusive and hydrodynamic models. The NaCl incorporation was 25% lower in the maltodextrin-NaCl solution (MN) compared to the sucrose-NaCl solution (SN). The MN reduced that incorporation compared to the SN. Moreover, the salt incorporation was significantly reduced (by approximately 50%) by using a VP in the osmotic process, which was independent of the ternary solution. The variable effective diffusivity improved the fitness of the OD kinetics with respect to the constant diffusivity or the modelling of the hydrodynamic mechanism. The large reduction of NaCl incorporation obtained in the present work, which was mainly due to the use of a VP, suggests that more attention is necessary in studies of OD with vacuum pulse involving the immersion of food in a ternary.

Optimisation of the pulsed vacuum osmotic dehydration of cladodes of fodder palm

SummaryFodder palm, a great source of nutrients for human and animals, grows even in arid climates. Pulsed vacuum osmotic dehydration is an efficient process for obtaining semidehydrated food. It was used to slice cladodes of fodder palm. The independent variables used were temperature (30–50 °C), pulsed vacuum pressure (50–150 mbar) and NaCl concentration (5–15 g per 100 g solution). The response variables were water activity (aw), moisture content (X), colour parameters, water loss (WL), solid gain (SG) and weight reduction (WR). The pulsed vacuum osmotic dehydration process was optimised for minimum values of aw, X and SG, and maximum values of chroma. The experimental data obtained with the optimum condition (100 mbar; 10 gNaCl per 100 g solution, 44 °C) were near the estimated ones. For example, WL, aw and ∆E, and their error were 8.15 g per 100 g, 11%; 0.985, 0.3% and 6.15, 15.2%, respectively.