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).     

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 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.     

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。     

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 invert sugar on the drying kinetics and water mobility of osmosed‐air dried cantaloupe

Effect of partially replacing sucrose with invert sugar on drying kinetics of osmosed cantaloupe was evaluated using four levels of invert sugar (0, 5, 10 and 15% (v/v)) to partially replace sucrose syrup at 50 °Brix. The osmosed samples were then dried at 60 °C. The osmosed cantaloupe without invert sugar exhibited the fastest drying rate. The drying rate decreased with increasing amounts of invert sugar. An increase in the degree of water binding to invert sugar is the most likely explanation for this effect and is supported by the observed decrease in the NMR relaxation time. The use of invert sugar could reduce water activity of final product but not significantly improve overall appearance. Six different mathematical models were tested for their goodness of fit with experimental data. Modified Henderson and Pabis model was found to give the best fit and was able to predict the drying time accurately.     

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.     

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.     

干燥方式对脱水菠菜质量特性的影响

为研究不同干燥方法对脱水菠菜理化特性的影响。将样品分别采用热风干燥,微波干燥,真空干燥,微波-真空干燥进行干燥处理,分别测定干燥后叶绿素保存率、维生素C保存率、产品的复水性和质构特性。结果表明,微波-真空干燥脱水菠菜不仅叶绿素保存率和维生素C保存率高,产品的复水性好、质构特性好,而且干燥时间短,是一种较好的脱水菠菜制备方法。     

Mass transfer kinetics during osmotic dehydration of bananas (Musa sapientum,shum.)

Osmotic dehydration is used widely to partially remove water from plant tissues by immersion in a hypertonic solution. In this work, the influence of temperature (25–55 °C), sugar concentration (30–60%) and salt concentration (0–10%) of the osmotic solution was investigated during osmotic dehydration of banana (Musa sapientum, shum.). Mass transfer kinetics were modelled according to Peleg’s equation. Kinetic parameters were evaluated using response surface methodology. Peleg’s equation showed to be suitable for modelling the water removal and solute uptake. Initial rate of water loss and water concentration at equilibrium were influenced by linear factors of the three independent variables. Initial rate of sucrose uptake and sucrose uptake at equilibrium were affected by all factors and interactions. Initial rate of salt uptake and salt concentration at equilibrium showed a positive correlation with temperature and NaCl concentration and a negative correlation with sucrose concentration.     

Polyphenoloxidase (PPO) activity and osmotic dehydration in Granny Smith apple

Osmotic dehydration (OD) permits the preservation of foods via a decrease in water content and an increase in solute concentration. Osmotically dehydrated fruits such as apple are suitable for the manufacture of desserts, cakes, salads, yoghurts, etc. Different microstructural and engineering aspects of OD are already known, but its effects on enzymatic activity are still unknown. This study analyses the activity of polyphenoloxidase (PPO) in fresh Granny Smith apples and the effect that OD by immersion in sucrose‐saturated syrup has on this activity. The low PPO activity found in the edible parenchyma of osmotically dehydrated apples is attributed to penetration by the osmotic agent and flooding of the intercellular spaces, which produces a low moisture content and a limited O₂ concentration in the immediate environment of the enzyme. These results show that OD prevents enzyme–substrate interaction. Thus the low PPO activity would reduce browning of this type of product. Copyright © 2005 Society of Chemical Industry     

Mass transfer kinetics and mathematical modelling of the osmotic dehydration of orange‐fleshed honeydew melon in corn syrup and sucrose solutions

A simple mathematical model to predict dehydration and impregnation process during osmotic dehydration of orange‐fleshed honeydew in sucrose and corn syrup solutions was proposed. Results showed low dispersion and a good fitting capability for WL and SG kinetics. Diffusivity values for WL ranged from 0.96 × 10^?10 to 2.22 × 10^?10 and 1.04 × 10^?10 to 3.10 × 10^?10 m² s^?1 in corn syrup and sucrose solutions, respectively. For SG, the obtained range was 0.72 × 10^?10 to 2.35 × 10^?10 and 0.71 × 10^?10 to 2.46 × 10^?10 m² s^?1 in corn syrup and sucrose solutions, respectively. The half‐life of dehydration rates (t_1/2) was from 30.9 to 71.2 min and from 19.4 to 57.5 min in corn syrup and sucrose solutions, respectively. Diffusivities values obtained according to the proposed model were close to the ones observed from diffusive model; t_1/2 was a promising criterion for the process time definition.     

热风温度对湿腌肉鸡翅根干燥动力学及成品品质的影响

对比分析了不同热风温度（60¹00℃）对肉鸡翅根干燥动力学及成品品质的影响。实验结果表明,湿腌肉鸡翅根热风过程为内部水分扩散的降速干燥过程,含水率及干燥速率的变化均受温度显著影响（p<0.05）;肉鸡翅根的水分有效扩散系数D eff随着热风温度的升高而增大,在60¹00℃内为3.09×10-9¹1.13×10-9m2/s,扩散活化能E a为33.08kJ/mol。对比分析了8种干燥经验模型的回归统计结果,确定Page方程为最佳干燥模型（平均R2=0.9994,平均χ2=0.000041）,可精确预测肉鸡翅根热风过程（60¹00℃）的含水率。成品品质分析表明,热风温度对烤翅成品硬度、咀嚼性及剪切力有显著影响（p<0.05）,而弹性、内聚性及回复性无明显差异（p>0.05）,90℃热风干燥得到的成品硬度、咀嚼性及剪切力均最大;干燥时间对硫代巴比妥酸（TBA）值及酸价的影响要大于热风温度。相关性分析表明,D eff与Page方程的参数k、n值均具有显著正相关性（p<0.05）,咀嚼性与硬度、剪切力均有显著的正相关性（p<0.05）。      

Osmotic dehydration pretreatment for improving the quality attributes of frozen mango: effects of different osmotic solutes and concentrations on the samples

The effect of osmotic dehydration pretreatment on the quality attributes (e.g. colour, hardness, drip loss, vitamin C content and pH) of frozen mango cuboids in different osmotic solutions (sucrose, glucose and maltose) and concentrations (30, 45 and 60% (wt/wt)) was investigated. Results revealed that melting temperature of mango cuboids was affected by both solute type and solid mass fraction. In addition, the dehydrofrozen samples pretreated in maltose had higher quality in vitamin C content (increasing by 23.5–73.0%), colour (colour change reducing by 2.6–39.2%) and drip loss (reducing by 0.7–9.7%) than those pretreated in other osmotic solutions. The cuboids pretreated in glucose displayed higher hardness (increasing by 16.4–36.2%). Based on principal component analysis and group distance, osmotic dehydration in 45% maltose was proposed as the most favourable freezing conditions with the highest sensory score (6.8). The current work indicates osmotic dehydration significantly improves frozen mango quality.     

Modelling osmotic dehydration of lemon slices using new sweeteners

Lemon slices were osmotically dehydrated using the following healthy sweeteners as osmotic agents: tagatose, isomaltulose, oligofructose and aqueous extract of stevia. A kinetic study using a Fickian approach was performed, which also analysed the changes in water activity, total mass, mass of water and mass of soluble solids in lemon slices. The results showed that the greatest value of effective diffusivity (D_e) in osmodehydrated lemon slices was obtained from a combination of oligofructose and stevia [D_e = (10.2 ± 0.3) × 10^?9 m²·s^?1]. However, the level of water activity (a_w) reached with this syrup was the highest (a_w = 0.978 ± 0.004 after 1440 min) meaning that the product might be less stable. Additionally, isomaltulose favoured the total mass loss, whereas tagatose did the opposite. Finally, the syrup recommended for dehydrating lemon slices would be a combination of tagatose, oligofructose and aqueous extract of stevia as its D_e was similar to the value obtained when only oligofructose and stevia were used, but a_w values were lower.     

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.