Adsorption isotherm and heat of sorption of osmotically pretreated and air-dried pineapple slices.

Slabs (1 ×1.5 ×5 cm) of pineapple were immersed in sucrose solutions of 52°B, 60°B and 68°B (w/w) at 25 °C for 12 h. Osmosed pineapple slices were subsequently air-dried at 60 °C for 72 h. Adsorption isotherms of osmo-dried pineapple slices were determined at 20 °C and 40 °C, using the gravimetric-static method. Isotherms were modeled using Brunnauer, Emmet and Teller (BET) and Guggenheim Anderson de Boer (GAB) models. Heat of moisture adsorptions were calculated from adsorption data using the Clausius-Clapeyron equation. Adsorption isotherms of osmo-oven-dried pineapple followed the characteristic type III (J-shape) isotherms. Equilibrium moisture contents at constant water activity decreased with increasing temperature, but crossing of the isotherms occurred at a_w~ 0.86. GAB and BET monolayer moisture decreased with increased temperature. The net isosteric heat increased with decreased moisture content, and decreased with increased sucrose pretreatment concentration of pineapple slices.     

Effects of electrical pretreatment conditions on osmotic dehydration of apple slices: Experimental investigation and simulation

Electrical pretreatments at 9 different conditions consisting of the combination of 3 different voltage gradients (20, 27, and 32 V/cm) and 3 different application times (10, 20, and 30 s) were applied on apple slices. Apple slices were osmotically dehydrated in 50% sucrose solution at 40 °C until their total dry matter content (TDM) reached to 40%. The effect of pretreatment conditions on the change of water loss and solid gain during osmotic dehydration was investigated, and effective diffusion coefficients were determined. The time needed to reach up to 40% TDM content was predicted by using the numeric solution of unsteady state mass transfer equations and diffusion coefficients via MATLAB code written. The electrical pretreatments reduced the osmotic dehydration time by in the range of 26–64%. The final water and solid distributions of apple slices were simulated in ANSYS. Modeling and simulation results were in good agreement with experimental data (p < 0.05).Industrial relevanceSince the electrical pretreatment both shortens the osmotic dehydration time and increases the water removed per unit energy used, its application prior to osmotic dehydration processes in the commercial productions will be economical. The proposed modeling and simulation approach for assessment of the effects of electrical pretreatments on osmotic dehydration characteristics may provide valuable information on the scaling up of these conditions in the industrial scale systems.     

Effect of process variables on the drying rate of mango pulp by Refractance Window

Refractance Window (RW) process is considered a novel and promising drying method, which uses hot water in contact with a polyester film (Mylar) at its bottom face to heat up and dry out a solution spread on the film surface. The aim of this study was to investigate the effect of process variables on the RW drying of mango pulp: water temperature (75, 85 and 95 °C), product thickness (2, 3 and 5 mm) and radiant source (transparent and painted Mylar film). Films' transmissivities to infrared radiation were determined and the drying kinetics of mango pulp with the nine possible pairs of layer thickness and water temperature were assessed. Mylar film was partially transparent to infrared radiation, while the black film (Mylar painted) blocked all infrared radiation emitted from the hot water. RW evaporation capacity was up to 10 kg m^− 2 h^− 1 (pulp with 2 mm, water at 95 °C), indicating a very efficient drying process. RW is more efficient than black film process for pulp thickness up to 3 mm. In fact, this study clearly established that radiative heat transfer contributes to less than 5% of the total amount of energy delivery to food during the RW drying process.     

Rehydration and sorption properties of osmotically pretreated freeze-dried strawberries

The aim of this work was to investigate the influence of osmotic dehydration and type of osmotic solution on selected physical properties of freeze-dried strawberries. Frozen Senga Sengana strawberries were dehydrated in osmotic solution with water activity of about 0.9 (sucrose and glucose solutions and starch syrup). Osmotically dehydrated fruits were frozen and freeze-dried at heating shelf temperature of 30 °C for 24 h.     

Influence of Refractance Window evaporation on quality of juices from small fruits

A new type of evaporator (Refractance Window^® (RW) evaporator) has been developed that operates at atmospheric conditions and uses thermal energy from hot water to concentrate foods. The influence of product temperature and dissolved solids on vitamin C in blueberry juice and color of cranberry juice was evaluated in this new evaporation method in comparison with conventional falling film multi-effect evaporators. During RW evaporation, vitamin C in blueberry juice was reduced by 32% and 48% with product temperatures at 55.5 and 59.0 °C, respectively. Concentration of the same juice from single strength to 65°Brix in an industrial falling film evaporator operating at 68 °C reduced vitamin C content by 70.1%. The color of cranberry juice, defined by the hue angle, was not significantly different between the concentrates from the RW and falling film evaporation methods. Further investigation is needed for complete insights into the mechanism for vitamin C loss in RW evaporation.     

苹果片热风薄层干燥过程中颜色变化的动力学模型

为了研究苹果片在热风薄层干燥过程中的颜色变化规律,分别在60、70、80、90、100℃下对苹果片进行热风薄层干燥处理,以亮度值(L*)、红绿值(a*)、黄蓝值(b*)、总色差(ΔE)、饱和度、褐变指数(BI)等为指标描述苹果片的颜色变化,并分别应用零级和一级反应动力学方程进行数学模型的拟合分析。结果表明,热风薄层干燥过程中,苹果片的L*值随着干燥时间的延长而逐渐降低,而a*值、b*值、ΔE、饱和度、BI值则逐渐升高,且反应速率常数k随着干燥温度的升高而呈现出一定的规律性变化。根据拟合决定系数R2的比较结果,零级反应动力学模型能更好的描述和预测苹果片在热风薄层干燥过程中的L*、a*、b*、ΔE值变化,而饱和度和BI值的变化则更符合一级反应动力学模型。该模型可以对苹果片在热风薄层干燥中的颜色变化进行预测,为优化干燥工艺提供参考。      

Processing and quality characteristics of apple slices under simultaneous infrared dry-blanching and dehydration with continuous heating

This study investigated the effects of various processing parameters on apple slices exposed to infrared (IR) radiation heating in a continuous heating mode for achieving simultaneous infrared dry-blanching and dehydration (SIRDBD). The investigated parameters were radiation intensity, slice thickness and processing time. A three-factor factorial experiment design was conducted to determine the influence of parameters on the heating and drying rates, product temperature, moisture reduction, residual polyphenol oxidase (PPO) and peroxidase (POD) activities and surface color change (ΔE). High radiation intensity and/or thin slices had faster increase of product temperature, and quicker moisture removal and inactivation of PPO and POD, than did low radiation intensity and/or thick slices. The simple page model performed well for describing drying behavior during SIRDBD. The first-order kinetics and the fractional conversion models fitted well for PPO and POD inactivation curves, respectively. Surface color changes of apple slices were mainly due to the decrease of L value and increase of a value, which corresponded to enzymatic browning occurred during the process. To achieve 1 log reduction of POD, the SIRDBD treatments resulted in moisture reductions of 15.35–49.29% and ΔE between 2.030 and 5.518. It has been concluded that SIRDBD with continuous heating could be used as an alternative to the current processing methods for producing high-quality blanched and partially dehydrated fruits and vegetables.     

Effect of calcium salts on the texture,structure and sensory acceptance of osmotically dehydrated guavas

The effect of additives, calcium chloride and calcium lactate (5–25 g kg^?1), on the osmotic dehydration of guavas with sucrose solutions was studied, aiming at the structural preservation of processed fruits. The osmotic process was evaluated from the reduction in weight of the guavas, water loss and solids gain, and the samples were analyzed with respect to calcium content, texture (stress and strain at failure, relaxation time and residual stress), structure by light microscopy and sensory acceptance. Calcium salts had a strong influence on the texture and structure of the processed guavas, resulting in the maintenance of tissue structure when calcium lactate was used at concentrations up to 15 g kg^?1, and calcium chloride was used at 5 g kg^?1. The sensory acceptability of guava was related to the structural and texture results. Calcium treatments did not improve guava's sensory acceptance. Guavas treated with calcium lactate showed good sensory acceptance, presenting slight inferior scores only at concentrations above 20g kg^?1, while CaCl₂ treated guavas showed average scores statistically equal to the sucrose and calcium lactate treated fruits only at 5 g kg^?1. Copyright © 2007 Society of Chemical Industry     

Processing and quality characteristics of apple slices processed under simultaneous infrared dry-blanching and dehydration with intermittent heating

This study investigated the effects of three processing parameters, e.g. product surface temperature, slice thickness and processing time, on blanching and dehydration characteristics of apple slices exposed to simultaneous infrared dry-blanching and dehydration (SIRDBD) with intermittent heating. A three-factor factorial experiment design was conducted to determine the influence of processing parameters on product temperature, moisture reduction, drying rate, residual polyphenol oxidase (PPO) and peroxidase (POD) activities and surface color change. Slice thickness had a significant effect on product quality and processing characteristics, as faster inactivation of enzymes and quicker moisture reduction took place in thinner slices. A Page model performed well for describing drying behavior during the treatment, and first-order kinetics and a biphasic model fit well for PPO and POD inactivation, respectively. Surface color changes (ΔE) of apple slices during prolonged heating resulted from non-enzymatic browning with an increase in b value was observed. In order to achieve a 1 log reduction in POD activity, the process resulted in a reduction in moisture from 20% to 59% and in ΔE from 2.27 to 5.59. It is suggested that SIRDBD with intermittent heating could be used as an alternative to manufacture high quality blanched and partially dehydrated fruits and vegetables.     

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.     

钙处理对干装苹果罐头质地的影响

采用质地多面分析方法(TPA),以清水处理为对照,研究碱性钙(氧化钙、氢氧化钙)、无机钙(氯化钙、碳酸钙、硫酸钙)、有机钙(乳酸钙、醋酸钙、丙酸钙)对干装苹果罐头质地参数(硬度、回复性、弹性指数、咀嚼性、内聚性)的影响,并对TPA参数之间及其与感官品质间的相关性进行了研究。结果表明:与对照相比,除硫酸钙以外,各处理对干装苹果罐头质地均有明显的影响,经碱性钙(氧化钙和氢氧化钙)处理的干装苹果罐头硬度适中,回复性、弹性指数、咀嚼性、内聚性、感官品质均较好。回复性、弹性指数、咀嚼性、内聚性之间的相关性均显著,硬度与感官品质之间呈显著正相关关系。表明碱性钙对干装苹果罐头有较好的作用,并保持良好的质构。      

钙处理对干装苹果罐头质地的影响

采用质地多面分析方法(TPA),以清水处理为对照,研究碱性钙(氧化钙、氢氧化钙)、无机钙(氯化钙、碳酸钙、硫酸钙)、有机钙(乳酸钙、醋酸钙、丙酸钙)对干装苹果罐头质地参数(硬度、回复性、弹性指数、咀嚼性、内聚性)的影响,并对TPA参数之间及其与感官品质间的相关性进行了研究.结果表明:与对照相比,除硫酸钙以外,各处理对干装苹果罐头质地均有明显的影响,经碱性钙(氧化钙和氢氧化钙)处理的干装苹果罐头硬度适中,回复性、弹性指数、咀嚼性、内聚性、感官品质均较好.回复性、弹性指数、咀嚼性、内聚性之间的相关性均显著,硬度与感官品质之间呈显著正相关关系.表明碱性钙对干装苹果罐头有较好的作用,并保持良好的质构.     

Inactivation of Escherichia coli O157:H7 during storage or drying of apple slices pretreated with acidic solutions

Inactivation of Escherichia coli O157:H7 was evaluated on inoculated apple slices without pretreatment or pretreated by immersing in water or acid solutions commonly used to help retain apple color during dehydration, then stored at ambient temperature or dried for 6 h. Half-ring slices (0.6 cm thick) of peeled and cored Gala apples were inoculated by immersion for 30 min in a three-strain composite inoculum of E. coli O157:H7 (7.8-8.0 CFU/g). Inoculated slices received (1) no pre-drying treatment (control); or a 10-min immersion in solutions of (2) sterile water, (3) 2.8% ascorbic acid, (4) 1.7% citric acid, (5) 50% commercial lemon juice, or (6) 50% commercial lemon juice with preservatives. Drained slices were placed in sterile plastic bags and stored at room temperature (25+/-2 degrees C) for up to 6 h or dehydrated (62.8 degrees C) for up to 6 h. Samples were plated on tryptic soy agar (TSA) and sorbitol MacConkey agar (SMAC) for direct enumeration of surviving bacteria at various time intervals. Immersion in sterile water or acidic solutions caused initial bacterial reductions of 0.9-1.3 log CFU/g on apple slices. Between 0 and 6 h of storage at room temperature, slices dipped in acidic solutions showed minor changes in bacterial populations (-0.2 to +0.6 log CFU/g) compared to a 1.1 log CFU/g increase for slices dipped in sterile water. The no treatment samples (control) showed an increase in bacterial populations of 1.3-1.5 CFU/g over the 6-h holding time. For apple slices dried at 62.8 degrees C, bacterial populations were reduced by 2.5 (SMAC) and 3.1 (TSA) log CFU/g in the control (no pre-drying treatment) samples following 6 h dehydration. The slices immersed in sterile water showed a 5.8 (SMAC) and 5.1 (TSA) reduction after 6 h of dehydration. In contrast, after 6 h of dehydration bacterial populations on the four acid-pretreated products were reduced by 6.7-7.3 log CFU/g. The results showed that acidic treatment alone was not effective in destroying E. coli O157:H7 on apple slices but did inhibit growth of the organism during holding before drying. However, pretreatment of the apple slices with common household acidulants enhanced destruction of E. coli O157:H7 during drying compared to slices dried without treatment.     

Fracture properties of stored fresh and osmotically manipulated apple tissue

The purpose of this research was to use single-edge notch three-point bend and cutting tests to evaluate changes in the texture of Granny Smith apples under room temperature storage conditions and to relate these changes to changes in internal structure. Experiments were performed at 1 week intervals over a period of 4 weeks. Specimens were soaked in buffer solutions in order to attain maximum and constant turgor pressure. Confocal microscopy showed that internal air spaces increased and cell adhesion decreased with increased storage time. Fracture toughness (a parameter that quantifies the ease of propagating a crack due to stress concentration at its tip) and cutting energy (the energy required to cleave the bonds in the plane of cutting) did not follow the same patterns. Relative changes in fracture toughness were far larger ( ≈50%) than changes in cutting energy (≈30%) in fresh specimens. However, relative changes in cutting energy (≈30%) were far larger than in fracture toughness (≈5.5%) in soaked specimens. We conclude that in Granny Smith apples, cutting energy is a more sensitive measure of cell adhesion, whereas fracture toughness obtained from bend tests seems to be related more directly to cell turgor pressure. Received: 8 October 1999 / Revised version: 15 December 1999     

Effect of osmotic dehydration with different osmosis agents on water status,texture properties,sugars, and total carotenoid of dehydrated yellow peach slices

The water status, texture properties, sugars, and total carotenoid of dehydrated yellow peach slices pretreated with or without osmotic dehydration (OD) combined with heat pump drying were studied. In this study, different osmotic agents were used, namely, sucrose and isomaltooligosaccharide (IMO) with 30 °Brix for 1, 3, and 5 h. Results showed that the dehydrated samples pretreated by sucrose-OD with the best shape and cell structure showed lower hardness compared to the dehydrated yellow peach slices with IMO-OD pretreatment and without OD pretreatment. Notably, the highest total carotenoid content was found in dehydrated yellow peach slices pretreated by IMO-OD, followed by samples without OD, and samples with sucrose-OD pretreatment. In addition, the lowest a_W (0.517) was obtained in samples with IMO-OD for 5 h, which was beneficial for storage. The assessment of water status and total carotenoid content of dehydrated yellow peach slices showed that IMO-OD pretreatment could better improve the quality of dehydrated fruits. Moreover, the use of IMO in OD treatment was a good alternative to sucrose.     

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.     

Image analysis of osmotically dehydrated fruits: melons dehydration in a ternary system

Osmotic dehydration represents a technological alternative to reduce post-harvest losses of fruits. In this work, the osmotic dehydration of a ternary system (water/sugar/salt) was investigated for melon (Curcumis melo L.) dehydration using image analysis. Three kinds of sugars were used to formulate the osmotic solutions: sucrose, glucose and manitol. The process of osmotic dehydration was studied and the effects of the ternary osmotic system on the fruit shrinkage were investigated using image analysis technique. The experimental study allowed estimating the process parameters of the osmotic dehydration. The results showed the advantage of using high sugar and salt concentrations for the osmotic solution, mild temperatures, and the use of the osmotic treatment to reduce the total processing time to dry the fruit. Image analysis enabled to show how far the solid penetrates inside the fruit and to estimate the shrinkage factor of the fruit during the osmotic dehydration.