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

Fodder 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 (a_w), 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 a_w, 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, a_w and ?E, and their error were 8.15 g per 100 g, 11%; 0.985, 0.3% and 6.15, 15.2%, respectively.     

真空、脉冲真空、超声波对芒果渗透脱水的影响

为研究真空、脉冲真空和超声波对芒果渗透脱水动力学的影响,将大小为26mm×26mm×5mm的块状样品浸于65°Brix果葡糖浆溶液中,渗透脱水处理180min。结果表明,菲克扩散模型能很好地描述渗透脱水过程中芒果失水率和固增率的变化规律;真空、脉冲真空和超声波均促进了水分和固形物的扩散,其中超声波作用使水分扩散系数具有最大值,而真空处理导致了固形物扩散系数最高。     

Changes in apple liquid phase concentration throughout equilibrium in osmotic dehydration

ABSTRACT:  Previous results on apple tissue equilibration during osmotic dehydration showed that, at very long processing times, the solute concentrations of the fruit liquid phase and the osmotic solution were the same. In the present study, changes in apple liquid phase composition throughout equilibrium in osmotic dehydration were analyzed and modeled. Results showed that, by the time osmosed samples reached the maximum weight and volume loss, solute concentration of the fruit liquid phase was higher than that of the osmotic solution. The reported overconcentration could be explained in terms of the apple structure shrinkage that occurred during the osmotic dehydration with highly concentrated osmotic solutions due to the elastic response of the food structure to the loss of water and intake of solutes. The fruit liquid phase overconcentration rate was observed to depend on the concentration of the osmotic solution, the processing temperature, the sample size, and shape of the cellular tissue.     

Effect of osmotic dehydration on dielectric properties,microwave vacuum drying kinetics and quality of mangosteen

Mangosteen (Garcinia mangostana Linn.) with and without osmotic dehydration (OD) in sucrose solution was dried by microwave vacuum drying at 1200, 1440 and 1680 W. Because of water loss (49.12–49.98 g 100 g^?1) and solid gain (9.31–11.62 g 100 g^?1) during OD, dielectric constant, loss factor and loss tangent of mangosteen were significantly increased (P ≤ 0.05) to 24.82–25.12, 11.52–14.18 and 0.47–0.50, respectively. With the decreased initial moisture content and the modified dielectric properties, drying time of osmotically dehydrated mangosteen was shorter than that of mangosteen without OD. Moreover, an increase in microwave power enhanced drying kinetics. With OD, Tg of dried mangosteen was increased from ?7.01, ?3.00 to 11.11–25.96 °C. Hardness and lightness (seedless part) were significantly increased (P ≤ 0.05). Structure of dried seedless mangosteen was well protected, resulting in the improved rehydration ability (P ≤ 0.05). Nonetheless, rehydration ability of the mangosteen containing seed was not improved (P > 0.05).     

Comparison of diffusion of fructo-oligosaccharide components during vacuum impregnation and osmotic dehydration

The osmotic behaviour of fructo-oligosaccharides was investigated during osmotic dehydration of apple cubes. The effect of vacuum impregnation on discrete diffusion coefficient (D _eff) of oligomers was scrutinised. D _eff were determined using the solution of Fick’s unsteady-state diffusion equation developed by Rastogi and Raghavarao. The moisture content decreases logarithmically irrespective of the type of treatment. The applied vacuum does not influence the rate of decrease of moisture content, but it reduces the water content. There are not significant differences among the D _eff of oligomers. Vacuum impregnation has no effect on D _eff values, which are in narrow range of the order of 10⁻⁹ m² s⁻¹ in the observed set of unit operation parameters. The prediction by the used model is acceptable in all cases especially in traditional osmotic dehydration, where the relative standard deviation (RSD) is less than 10%, and it also demonstrates the altered mechanism of vacuum impregnation by the increased RSD values.     

Prediction of mass transfer kinetics during osmotic dehydration of apples using neural networks

An artificial neural network (ANN) model was developed for the prediction of water loss (WL) and solid gain (SG) in osmotic dehydration of apple cylinders using a wide variety of data from the literature to make it more general. This model mathematically correlates six processing variables (temperature and concentration of osmotic solution, immersion time, surface area, solution to fruit mass ratio and agitation level) with WL and SG. The optimal ANN consisted of one hidden layer with four neurons. This model was able to predict WL and SG in a wide range of processing variables with a mean square error of 13.9 and 4.4, and regression coefficient of 0.96 and 0.89, respectively, in testing step. This ANN model performs better when compared to linear multi-variable regression. The wide range of processing variables considered for the formulation of this model, and its easy implementation in a spreadsheet using a set of equations, make it very useful and practical for process design and control.     

Modelling of mass transfer and texture evaluation during osmotic dehydration of melon under vacuum

The influence of vacuum time and solution concentration on mass transfer and mechanical properties of osmodehydrated melon cubes has been studied. Pulsed vacuum osmotic dehydration (PVOD) was carried out at 30 °C for 4 h, using sucrose solutions (40, 50 or 60°Brix) and applying a vacuum pulse (100 mbar for 5, 10 or 15 min). Kinetics of water loss, solid gain and stress at rupture were analysed, as well as effective diffusivities using the hydrodynamic model. The increase in solution concentration favoured water removal, but no significant effect of vacuum time was observed. The use of less concentrated solutions coupled to the action of vacuum pulse resulted in greater solid uptake. Samples subjected to PVOD using 60°Brix sucrose solution presented greater water loss, lower sugar uptake and better maintenance of fresh fruit texture throughout the process. Diffusion coefficients estimated by the hydrodynamic model showed a good fit to the experimental data.     

Effect of osmotic dehydration on the drying kinetics and quality of cashew apple

The effect of different osmotic pretreatments on cashew apple drying kinetics and product quality were investigated. The osmotic pretreatment was carried out in an incubator at constant temperature and agitation. The drying process was conducted in a fixed bed dryer at different temperatures and constant air velocity. Experimental data were fitted successfully using the Page and the two‐term exponential models for dried fresh and pretreated fruit, respectively. It was found that drying rates of osmosed fruits decreased owing to the presence of infused solutes. Evaluation of the final product was performed by means of ascorbic acid content, water activity and sensorial test. The osmotic pretreated samples showed the highest vitamin C losses and the lowest water activity. The samples pretreated in sucrose solution had the highest acceptance.     

Application of Weibull distribution model to describe the vacuum pulse osmotic dehydration of sardine sheets

Application of Weibull frequency distribution model was investigated for predicting the moisture and salt contents of sardine sheets during vacuum pulse osmotic dehydration using brine at different concentrations (0.15-0.27 g NaCl/g), temperatures (30-38 °C), and applying a vacuum pulse at 11.0 kPa for 10 min. The high regression coefficients (R²>0.99) and low mean relative error (<10%) indicated the acceptability of Weibull model for predicting both moisture and salt contents. The scale parameters for moisture and salt contents as a function of temperature all followed an Arrhenius relationship. Models for scale and shape parameters for moisture and salt contents as a function of brine concentration and temperature were found.     

真空脱水对花生油挥发性物质的影响

采用顶空固相微萃取结合气相色谱-质谱联用技术(HS-SPME-GC-MS),以对苯甲酚为内标物,对花生油在真空脱水过程中挥发性物质的变化进行了半定量研究。结果表明:真空脱水可以有效脱除花生油中的水分,真空脱水5 min即能脱去花生油中约50%的水分;真空脱水15 min之内,花生油挥发性物质的总量基本保持不变,但继续延长脱水时间,花生油所保有的挥发性物质总量的损失将增大;绝大部分挥发性物质在15 min的真空脱水时间内变化不大,但具有甜香味风味特征的苯乙醛、麦芽酚等挥发性物质含量随着脱水时间的延长呈近似线性的下降趋势。综合来看,真空脱水能够在保护花生油挥发性物质的前提下起到有效脱水的效果。     

Determination of water effective diffusion coefficient of sardine sheets during vacuum pulse osmotic dehydration

The water effective diffusion coefficient of sardine sheets during vacuum pulse osmotic dehydration was determined. Sardine sheets (20.1×15.0×6.4 mm³) were osmotic dehydrated at brine concentrations between 0.15 and 0.27 g NaCl/g, and temperatures between 32 and 38 °C. The water effective diffusion coefficient ranged approximately from 1.46×10⁻¹⁰ m²/s to 2.41×10⁻¹⁰ m²/s. In general, diffusion coefficient increased with increasing concentration and temperature. Dependence on temperature followed an Arrhenius relationship, regardless of concentration Diffusion coefficient at 0.18 g NaCl/g was found to be the most temperature sensitive (E_a=39.62 kJ/mol) while that at 0.15 g NaCl/g was the least temperature sensitive (E_a=23.67 kJ/mol). The water effective diffusion coefficient was empirically correlated with concentration and temperature of osmotic solution. A high degree of correlation was observed between predicted and experimental values of the water effective diffusion coefficient (R²=0.856).     

Mass transfer kinetics during osmotic dehydration of pomegranate arils

The mass transfer kinetics during osmotic dehydration of pomegranate arils in osmotic solution of sucrose was studied to increase palatability and shelf life of arils. The freezing of the whole pomegranate at -18 °C was carried out prior to osmotic dehydration to increase the permeability of the outer cellular layer of the arils. The osmotic solution concentrations used were 40, 50, 60°Bx, osmotic solution temperatures were 35, 45, 55 °C. The fruit to solution ratio was kept 1:4 (w/w) during all the experiments and the process duration varied from 0 to 240 min. Azuara model and Peleg model were the best fitted as compared to other models for water loss and solute gain of pomegranate arils, respectively. Generalized Exponential Model had an excellent fit for water loss ratio and solute gain ratio of pomegranate arils. Effective moisture diffusivity of water as well as solute was estimated using the analytical solution of Fick's law of diffusion. For above conditions of osmotic dehydration, average effective diffusivity of water loss and solute gain varied from 2.718 × 10(-10) to 5.124 × 10(-10) m(2)/s and 1.471 × 10(-10) to 5.147 × 10(-10) m(2)/s, respectively. The final product was successfully utilized in some nutritional formulations such as ice cream and bakery products.     

Optimisation of vacuum pulse osmotic dehydration of blanched pumpkin

Pulsed vacuum osmotic dehydration (PVOD) is an efficient process for obtaining semi‐dehydrated food. The effects of temperature (30–50°C), solute concentration (NaCl 0–15 kg per 100 kg solution, sucrose, 15–35 kg per 100 kg solution) and vacuum pulse application (50–150 mbar and 5–15 min) on water loss (WL), solid gain (SG), water activity (a_w) and total colour difference (?E) of previously blanched pumpkin slices were assessed through Plackett–Burman experimental design. Temperature was not statistically significant in the process. Later, with the aid of a central composite design (CCD), it was found that concentration of sucrose and NaCl was influent on the WL, SG, a_w and ?E, and the pressure and time of application of vacuum were influent on WL and SG. The optimal conditions of process were stabilised with the desirable function, and the simulated data were similar from the experimental ones.     

Effect of ultrasound‐assisted osmotic dehydration on cell structure of sapotas

BACKGROUND: Drying is a traditional way of fruit preservation. Because of the high energy costs associated with air‐drying, osmotic dehydration is often applied as a pretreatment to reduce air‐drying time. Ultrasound is an emerging technology with several applications in food processing. The effect of ultrasound on fruit tissue depends on the tissue structure and composition, and ultrasound might be beneficial to improve air‐drying efficiency, with consequent reduction in process costs. In this study the effect of ultrasound and ultrasound‐assisted osmotic dehydration on sapota tissue structure was evaluated. RESULTS: Ultrasound induced cell disruption and breakdown of cells with high phenolic content (dense cells) and also induced elongation of parenchyma cells. Ultrasound application combined with high osmotic gradient enhanced water loss and solid gain because of the formation of microscopic channels. Ultrasound‐assisted osmotic dehydration induced gradual distortion of the shape of cells, cell breakdown and formation of microscopic channels. Micrographs of the fruit tissue showed that ultrasound preferentially affected dense cells. CONCLUSION: Ultrasonic pretreatment was able to preserve the tissue structure of the fruit when distilled water was used as liquid medium. The application of ultrasound‐assisted osmotic dehydration resulted in severe changes in the tissue structure of the fruit, with consequent increase in the effective water diffusivity, because of the formation of microscopic channels and cell rupture. Copyright © 2009 Society of Chemical Industry     

Effect of osmotic dehydration and vacuum impregnation on respiration rate of cut strawberries

Respiration rate in terms of O₂ consumption and CO₂ production was determined in strawberry halves, both fresh-cut and vacuum impregnated with an isotonic solution. The experimental measurements were also carried out in osmodehydrated samples for different concentration levels (to 30 °Brix) at atmospheric pressure and by applying a vacuum pulse. Changes throughout time of O₂ and CO₂ concentration in the headspace of chambers containing the samples were analysed to determine respiration rates. The effect of temperature on respiration rate in fresh-cut and impregnated samples showed sigmoid behaviour where a sharp increase in respiration levels occurred between 5 and 10 °C. Osmodehydration treatments resulted in a great decrease in O₂ consumption but no notable changes in CO₂ generation, which suggests that anaerobic biochemical pathway became dominant respiration mode due to the treatments. Production of ethanol and acetaldehyde was detected in these cases in agreement with the anaerobic process.     

辣椒果肉的渗透脱水效果研究

研究了不同渗透溶液对辣椒果肉的脱水效果,从失水率、固形物增加率、含盐量和色泽变化等方面综合分析了不同浓度的纯糖溶液(50%和65%)、纯盐溶液(10%和20%)和糖盐混合溶液(10%盐,50%糖)的作用效果。结果表明,蔗糖和盐混合溶液的脱水效果最好,8h的失水率可以达到54.20%,可溶性固形物增加率仅有7.53%,且含盐量更是低于纯盐溶液的含盐量变化,只增加了2.62g/100g干基。在渗透后的颜色方面,混合溶液渗透后的变化差异没有纯溶液渗透后的明显。     

樱桃番茄渗透预处理热风干燥特性研究

为了提高干制品的营养保留率和品质,进行了渗透预处理联合热风干燥的工艺路线的实验研究。以樱桃番茄为例,分别对不同浓度(50%,70%)蔗糖溶液常压渗透以及真空渗透处理后热风干燥的干燥时间、干燥速率、样品体积比、Vc保留率、硬度、颜色等参数分别进行测定和比较。结果表明:渗透预处理可以除去新鲜樱桃番茄中的大部分自由水,从而减少其热风干燥时间,使产品在高温中的暴露时间减少,从而缩短整体干制时间、提高干制效率及营养品质。经渗透预处理的樱桃番茄干制产品的体积比和Vc保留率要比直接热风干燥的产品增加,而硬度大大下降;其中经浓度为50蔗糖溶液真空渗透预处理后干燥产品的体积比、Vc保留率以及硬度是直接70℃热风干燥的1.72、2.26和0.12倍;而且产品的色泽更加接近新鲜原料,使产品的口感和感官品质更好。研究表明,渗透预处理联合热风干燥是1种很有发展前景的制干工艺。     

Comparative behaviour of cellulosic and starchy plant materials during osmotic dehydration

Osmotic dehydration studies on two cellulosic plant materials—Golden Delicious and Cox apple—and two starchy plant materials—banana and potato—showed that the amount and rate of water loss occurred in the following descending order: Golden Delicious > Cox > potato > banana. Temperature, concentration and immersion time of samples in the osmotic solution played a significant effect on amount and rate of water loss in all commodities in a descending order as follows: 55 > 40 > 32.2 °C; 0.70 > 0.60 > 0.50 > 0.40 g kg^?1; and 30 > 60 > 90 > 120 min, respectively. A corresponding uptake of solids from the osmotic solution occurred, the rate been greatest over the first 30 min, before declining significantly thereafter. The diffusion coefficients for water loss (D_{eff, w}) measured by the method of slopes on the water loss rate curves conducted at 32.2, 40 and 55 °C for 0.40, 0.50, 0.60 and 0.70 g kg^?1 sucrose concentration solutions were higher for cellulosic plant materials than starchy plant materials. Significant variations occurred in efficiency index (WL/SG) between cellulosic and starchy plant materials. Copyright © 2007 Society of Chemical Industry