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。     

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.     

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).     

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 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。     

Drying of plums (Prunus sp,c.v Gulfblaze) treated with KCl in the field and subjected to pulsed vacuum osmotic dehydration

The pulsed vacuum osmotic dehydration (PVOD) promotes more homogeneous concentration profiles in the product and quality improvement of several fruits. The objective of this work was to study the drying of plums submitted to treatments of plants manure with KCl and PVOD (5” c.a., 10 min). Experimental planning was done with the following independent variables: doses of KCl (400, 700 and 1000 g/plant), concentration of sucrose solution (40; 50 and 60 ºBrix) and drying temperature (50, 60 and 70C). The tested variables were: color, shrinkage, visual quality and rehydration. Temperature leads to a skin browning at fruit pulps and lower visual quality. The treatment with KCl leads to final products with lower moisture content. The higher the values of all the independent variables, the lower the shrinkage and the rehydration capacity. Plums submitted to convective drying with previous PVOD promote a new product with good visual quality and satisfactory shrinkage.     

果蔬渗透脱水的研究进展及应用前景

主要论述了果蔬渗透脱水的研究进展 ,总结了影响渗透脱水效果的主要因素 ,概括了渗透脱水在果蔬的品质保持和节能方面的优势 ,它将作为果蔬加工的前处理方法而具有广阔的应用前景。     

Optimisation of osmotic dehydration of 'Tommy Atkins' mango fruit

Osmotic dehydration of mango in sucrose solution as influenced by temperature (30–50 °C), immersion time (60–150 min) and solution concentration (40–60% w/w) was studied through response surface methodology. Responses of water loss and solid gain were fitted to polynomials, with multiple correlation coefficients ranging from 0.72 to 0.95, respectively. The fitted functions were optimised for maximum water loss and minimised incorporation of solids in order to obtain a product resembling non-processed fruit. Optimum conditions to obtain water removal >25% with solid uptake lower than 6% could be obtained using a 44% (w/w) sucrose solution concentration, temperatures up to 38 °C and immersion times up to 80 min.     

Optimization of osmotic dehydration of melons followed by air-drying

Osmotic dehydration represents a technological alternative to reduce post‐harvest losses of fruits. In this work, the influence of the osmotic solution concentration and osmotic solution to fruit weight ratio was examined on the osmotic dehydration of melons under vacuum. The process of osmotic dehydration followed by air‐drying was studied and modelled so that it could be optimised. The developed model has been validated with experimental data and simulations have shown that how the operating conditions affect the process. An optimisation was done using the model in order to search for the best operating condition that would reduce the total processing time.     

Optimisation of osmotic dehydration process of guavas by response surface methodology and desirability function

Response surface methodology was used to assess the effects of osmotic solution concentration (40–60°Brix), process temperature (20–40 °C) and vacuum pulse application time (0–20 min) at 100 mbar on water loss (WL), weight reduction (WR), solid gain (SG), water activity (a_w), colour parameters and mechanical properties of guava slices. Optimal process conditions were determined through the desirability function approach and quality characteristics of osmotically dehydrated guavas were analysed. Only models obtained for WL, WR and a_w were suitable to describe the experimental data. The desirability function showed that optimal conditions for osmotic dehydration of guavas were: osmotic solution concentration at 60°Brix, process temperature at 32 °C and 20 min of vacuum pulse application. Under optimal conditions, colour and mechanical properties of treated guavas were similar to fresh fruit, presenting WL of 29.01 g/100 g, WR of 25.91 g/100 g, SG of 3.10 g/100 g and a_w of 0.979.     

Osmodehydration assisted by ohmic heating/pulse vacuum in apples (cv. Fuji): retention of polyphenols during refrigerated storage

Apples are a widely consumed fruit and have a high polyphenol content. The aim of this study was to analyse the combined effects of osmotic dehydration (OD) and ohmic heating (OH) with a pulsed vacuum (PV) on polyphenol retention during the stored refrigeration of apple cubes. Treatments were performed using a 65°Brix sucrose solution at 30, 40 or 50 °C for 120 min, and then, samples were stored for 28 days at 5 °C. OH provides an electric field of 13 V cm^?1, and a pulsed vacuum was applied for 5 min at the beginning of the process. The results indicated that a lower temperature process (30–40 °C) resulted in the retention of more polyphenol compounds after treatment than a higher temperature process (50 °C). Nevertheless, during refrigerated storage, we observed that 50 °C preserved these compounds better due to polyphenol oxidase inactivation. PVOD/OH treatment at 50 °C was determined to be the best retention of polyphenols from the fresh apple for dehydrating apples.