Freeze/Thaw Effects on Mass Transfer Rates during Osmotic Dehydration

A model fruit system (apple slices) was studied during osmotic preconcentration in concentrated solutions of corn syrup solids. The effect of freeze/thawing on water removal and solid uptake rates during complimentary osmotic dehydration was examined. Product response to freeze/thawing after partial osmotic dehydration was also explored. Osmotically preconcentrated, frozen/thawed samples did not exhibit a significant change in rate of water loss during complimentary osmotic dehydration. They had sharply higher sugar gain rates compared to controls. The duration of osmotic preconcentration had a significant effect on freeze/thaw induced exudation losses.     

Water Diffusion and Concentration Profiles During Osmodehydration and Storage of Apple Tissue

The objective of this work was to study the mobility of water and sucrose during osmotic dehydration and storage of apple tissue and to conduct an analysis of the behavior of the effective diffusion coefficients determined from concentration profiles. Osmotic dehydration (OD) of apple was carried out at 40°C for 1 h, and the solution: sample ratio was 20:1 (w/w). Samples of 20-mm diameter were extracted from the dehydrated apple immediately after the OD process and after 4 and 24 h of storage at 25 °C. Moisture of these samples and soluble solids content were analyzed. Our results showed, after 1 h of OD, the outer layer of the apple sample lost 0.37 kg water/kg apple and gained 0.30 kg sucrose/kg apple. These values decreased toward the internal layers of the apple. A fine layer of greatly dehydrated cells was formed on the surface around the sample, which determined the mass transfer rate in the whole tissue. Smaller mass transport rates were observed in the development of concentration profiles during storage. Diffusion coefficients obtained for the outer layer after 1 h of OD were 1.53 × 10⁻¹⁰ and 1.05 × 10⁻¹⁰ m²/s for water and sucrose, respectively. The analysis of compositional profiles developed during osmodehydration was a useful tool to get a better understanding of the changes in the water activity of the outer layer of the apple tissue.     

Study of the Pseudo-equilibrium During Osmotic Dehydration of Apples and Its Effect on the Estimation of Water and Sucrose Effective Diffusivity Coefficients

The study of the equilibrium is needed not only for modeling of the osmotic process as a unit operation but also for a better understanding of the mass transfer mechanisms involved in this kind of systems. A true equilibrium state usually takes very long time to achieve; therefore, a pseudo-equilibrium state is often employed. Experimental pseudo-equilibrium states for water loss and solid gain during the osmotic dehydration of apple slices (5?×?50?×?50?mm³) at different osmotic syrup concentrations (30%, 40%, 50%, and 60% (w/w) of sucrose) were evaluated. Four empirical mathematical methods (Slopes, Azuara, Zugarramurdi and Lupín, and Equal concentration) were used in order to calculate the pseudo-equilibrium values obtained and then to compare them against to the experimental ones. Additionally, the effective diffusion coefficients for water and sucrose were calculated by using those pseudo-equilibrium values. Experimental pseudo-equilibrium values increased with concentration of the osmotic syrup, ranged between 24% and 56% for water loss and 11% and 28% for solid gain; the predicted pseudo-equilibrium values followed the same trend. The decreasing order of accuracy for pseudo-equilibrium values and effective diffusion coefficients, among the methodologies evaluated, was Equal concentration method > Azuara method > Slopes method > Zugarramurdi and Lupín method. Although the Equal concentration method has no theoretical accuracy, it is independent of the kinetic data presenting a higher advantage over the other three mathematical methods evaluated.     

Physicochemical Characteristics of Dehydrated Apple Cubes Reconstituted in Sugar Solutions

Water solutions with different sugar compositions and concentrations were used to reconstitute air-dried and freeze-dried apple pieces. The mass transfer was determined between dehydrated fruit pieces and solutions during rehydration as well as some physicochemical properties of the reconstituted apple pieces. Varying the concentration of sugar solutions used for reconstitution medium, made it possible to achieve different levels of water absorption and solids loss or uptake. In addition, water activity (a_w), freezing point, amount of freezable water and firmness correlated linearly with soluble solids content.     

How to deal with visco-elastic properties of cellular tissues during osmotic dehydration

In this work, vacuum impregnated apple discs with different isotonic solutions (sucrose and trehalose) were equilibrated during osmotic dehydration (55°Brix glucose at 40 °C). Changes in sample composition (water and soluble solid contents), weight and volume are analysed. A mathematical model is proposed to describe and quantify the outflow of water from the protoplast as well as the visco-elastic behaviour of the cell. Good correspondence between simulated and measured data of non impregnated samples and samples impregnated with isotonic solutions of sucrose or trehalose during long term osmotic dehydration is obtained. Fitted values of the cell permeability correspond well with tabulated values. Furthermore, also the obtained values of the parameters describing the mechanical properties of the cell wall and Hectian strands seem to reflect the observed structural development of these structures for the different treated samples well.     

Osmotic concentration of potato.

A study was conducted to determine what conditions define the equilibrium state between potato and osmosis solution for an osmosis concentration process. It was shown that at equilibrium, there is an equality of water activity and soluble solids concentration in the potato and in the osmosis solution. Rinsing the surface of the potato after osmotic concentration was shown to significantly reduce solids gain and soluble solids concentration in the potato, thus resulting in a sizeable increase in the potato water activity.
When water loss, solids gain, change of water activity and economics are considered, the optimal conditions for an equilibrium osmosis with sucrose would use a 50% solution at a solution/solids ratio of 4. Uptake of solids during sucrose-based osmosis results in 75% of the soluble solids in the equilibrated potato coming from the osmosis solution. A comparison of various osmosis solutions at a 60% total solids level shows that mixed sucrose-salt solutions give a greater decrease of water activity than the pure sucrose solution, even though the mass transport data are similar, this undoubtedly being due to the uptake of salt.
A model has been developed for calculation of osmosis mass transport data and water activity for osmotic concentration to equilibrium in sucrose solutions for the concentration range 10–70% and solutionlsolids range of 1–10. The mass transport data can be calculated with an average error < 4%. Water activity can also be predicted with good accuracy for the range of parameters normal for osmosis concentration processes. The proposed model was also able to predict osmosis mass transport data and water activity data for short, non-equilibrium osmosis times.     

蓝莓渗透脱水的研究

在不同的渗透温度 ( 4 5～ 65℃ )条件下 ,高果糖浆和蔗糖的有效水分扩散率 (Dm)分别为( 4 90 60～ 5 2 3 66)× 1 0 - 10 m2 /s和 ( 3 5 5 1 8～ 4 0 1 0 9)× 1 0 - 10 m2 /s,有效固形扩散率 (Ds)分别为( 2 7740～ 3 691 5 )× 1 0 - 10 m2 /s和 ( 1 3 1 63～ 2 691 5 )× 1 0 - 10 m2 /s的规律。在渗透脱水处理过程中Dm 和Ds 随处理温度升高而增加。经高果糖浆 ( 70°Brix)渗透脱水的蓝莓的平均体积比随温度升高而稍微下降。其相对密度随温度的升高也略有增加     

Osmotic Dehydration of Nectarines: Influence of the Operating Conditions and Determination of the Effective Diffusion Coefficients

The aim of the present work is to study the kinetics of osmotic dehydration of Caldesi nectarines (Prunus persica var. nectarina) evaluating the effect of osmotic solution concentration, type of solute, temperature, fruit/solute ratio and process time on moisture content, water loss, soluble solids content and solids gain. The process analysis was carried out experimentally and numerically through the mathematical modelling of mass transfer. Hypertonic solutions of glucose syrup and sorbitol (40 and 60 % w/w) were used for dehydration, during 2 h of process at temperatures of 25 and 40 °C, with fruit/osmotic agent ratio of 1:4 and 1:10. Water loss and solids gain showed significant differences depending on the type and concentration of the osmotic agent, process time and fruit/solution ratio. The concentration interacted significantly with all variables; in addition, there was an interaction between the type of osmotic agent and the relationship between fruit and the osmotic agent. The effective diffusion coefficients were obtained from the analytical solution of Fick’s second law applied to flat-plate geometry and by solving the mass transfer microscopic balances by finite element method, taking into account the real geometry of the nectarine pieces. The values obtained from Fick’s law varied between 1.27?×?10^?10 and 1.37?×?10^?08?m²?s^?1 for water and from 1.14?×?10^?10 to 1.08?×?10^?08?m²?s^?1 for soluble solids, while the values calculated by finite elements method ranges were between 0.70?×?10^?09 and 4.80?×?10^?09?m²?s^?1 for water and between 0.26?×?10^?09 and 1.70?×?10^?09?m²?s^?1 for soluble solids. The diffusion coefficients values obtained from the numerical solution are consistent with those published in literature.     

PILOT PLANT FOR OSMOTIC DEHYDRATION OF FRUITS: DESIGN AND EVALUATION

This work proposes a pilot scale equipment for osmotic dehydration (OD) of apple cubes that consists of a novel agitation‐immersion device, a bag filter and a vacuum evaporator to conduct simultaneously the OD process, filtration and reconcentration of the osmotic solution (OS). The functional method analysis was used to design the pilot plant. Apple cubes (～1 cm³) were dehydrated using a 60 ° Brix sucrose syrup OS at 50C and a syrup/fruit ratio of 5. OD was conducted either with or without reconcentration of the OS. During the OD process particles of fruit were eliminated from the OS by filtration and the OS concentration was kept at 60 ° Brix by reconcentration in the evaporator. A comparison of the dehydration parameters of apple cubes obtained at pilot scale to those obtained at laboratory scale was done to evaluate the performance of the pilot equipment. The results show that the proposed set‐up can be suitable for commercial production of osmodehydrated fruits.     

Determination of Lactose and Sucrose Contents of Ice Cream Mix via Enzymatic-Cryoscopic Methodology

A simple method was developed for determining the lactose and sucrose contents of ice cream mix. The method is based on measuring the freezing point depression resulting from incubating samples with invertase (EC 3.2.1.26) and β-galactosidase (EC 3.2.1.23). Sucrose and lactose concentrations are determined separately with each determination requiring 50 units of enzyme and 2 hr of incubation at 37°C. A standard curve for lactose determination was obtained using ice cream mixes containing various amounts of sucrose and corn syrup solids (R²= 0.996, C.V. = 1.2%). A standard curve for sucrose determination was obtained using ice cream mixes containing various amounts of lactose and corn syrup solids (R²= 0.996, C.V. = 1.9%).     

Modelling of mass transfer during osmotic dehydration of apple tissue pre-treated by pulsed electric field

The osmotic dehydration mechanism of apple sample pre-treated by pulsed electric field (PEF) was investigated over a range of 44.5-65 ° Brix sucrose concentrations. Apple disks treated by PEF field of 0.90 kV/cm during a constant time were immersed in sucrose solution at ambient temperature with 3:1 syrup to apple ratio (w/w). Increase of the initial solute concentration and the PEF treatment resulted in acceleration of the osmotic dehydration (OD). The PEF-treated samples had a higher water loss (WL) and higher solid gain (SG) than the untreated samples. The osmotic dehydration kinetics was studied on the basis of two approaches: Fick's unsteady state diffusion equation and a two-exponential kinetic model. The coefficients of effective diffusion of water and solute were calculated. Their values were higher for samples pre-treated electrically. The effect of PEF was more pronounced for the WL comparatively to the SG. The two-exponential kinetic model permits evaluating of both convective and diffusion stages of OD. The PEF pre-treatment accelerates the kinetics of water and solute transfer during convective and diffusion stages of OD.     

DEVELOPMENT OF A SWEETENER FROM BLACK PLUM (VITEX DONIANA) FRUIT

The Black plum (Vitex doniana) fruit was studied in respect of the chemical composition of its edible pulp, and syrup produced by concentration of extracted juice. Organoleptic evaluation was also conducted on the developed syrup. The results show that the edible pulp of the fruit is acidic (PH 5.20), high in moisture (67.9%), sucrose (12.5%) and reducing sugar (7.3%), and fairly rich in vitamin C (28.5 mg/100 g). Temperature of water used for extracting juice from the pulp correlated positively with soluble solids (r=0.86), titratable acidity (r=0.91) and negatively with vitamin C (r=?0.61). The syrup contained higher reducing sugars (51.7%), lower moisture (25.0%), but similar sucrose (12.9%) content compared to the pulp. The soluble solids of the extracted juice and consequently the yield of the syrup varied with water temperature. An optimum temperature of 80°C gave 20% (w/w) syrup per pulp. The syrup compares favorably with sucrose in sensory properties in model foods.     

Effect of syrup concentration,temperature and sample geometry on equilibrium distribution coefficients during osmotic dehydration of mango

The effect of initial sucrose concentration (30–70%), solution temperature (22–90 °C) and sample geometry (cube, slice and wedges) on equilibrium distribution coefficients of mango was investigated during osmotic dehydration. The distribution coefficients for water ranged from 0.908 to 2.12 for cubes, 0.919 to 1.74 for slices and 0.915 to 1.95 for wedges, respectively, while the distribution coefficients for solids varied from 0.520 to 1.183 for cubes, 0.683 to 1.13 for slices and 0.592 to 1.17 for wedges, respectively. The distribution coefficient for water decreased with increasing temperature and surface area, and it increased with the increase in syrup concentration and thickness of the minimum geometric dimension. The distribution coefficient for solids increased with the increase in temperature, and surface area, while it decreased with the increase in syrup concentration, and thickness of minimum geometric dimension. A multiple regression analysis of experimental data was carried out to correlate distribution coefficients with dimensionless temperature, syrup concentration and geometric shape parameters.     

Modeling and Optimization of Microwave Osmotic Dehydration of Apple Cylinders Under Continuous-Flow Spray Mode Processing Conditions

The objective of this study was to model and optimize the mass transfer behavior during microwave osmotic dehydration of apple cylinders under continuous-flow spray mode processing conditions. Data needed for the model development and optimization were obtained using a central composite rotatable experimental design involving sucrose concentration (33.3–66.8°B), temperature (33.3–66.8 °C), flow rate (2,120–3,480 ml/min), and contact times (5–55 min); and the response variables were moisture loss, solids gain, and weight loss. Mass transfer kinetics was evaluated based on the empirical Azuara model and the conventional diffusion model. Diffusivities of both moisture loss (D _m) and solids gain (D _s) obtained from the diffusion model were related to sucrose concentration, temperature, and flow rate. Optimization was evaluated using a desirability function model which could be used with several imposed constraints. The optimum conditions obtained depended on the imposed constraints. A set of constraints involving maximizing moisture loss and weight reduction while keeping the solids gain below 3.5% gave the following optimal conditions: a 30-min osmotic treatment at 65°B, 60 °C, and 2,800 ml/min flow rate yielding a moisture loss of 40.9%, weight reduction of 37.7%, with a solids gain of 3.32%.     

Review characterization of edible films formulated with sodium alginate and low-methoxyl pectin in osmotic dehydration applications

The aim of this work was to evaluate the behaviour of two edible films (sodium alginate and low-methoxyl pectin) under different osmotic conditions (solutions: sucrose, glucose syrup and maltodextrin; concentrations: 40 °Brix and 60 °Brix; temperature 40 °C and processing times: 0.5, 1 and 2 h). From the experimental water loss and solid uptake kinetics, effective diffusion coefficients and the dehydration performance ratio were obtained. The microstructural characteristics of the osmodehydrated films were also analysed using pear as a food matrix. The results showed that films osmodehydrated with maltodextrin and glucose syrup solutions presented higher dehydration performance ratio values than those osmodehydrated with sucrose. A reduction in the thicknesses of edible coatings was observed. The best formulation was sodium alginate 2% and calcium lactate 5% according to the microstructural analysis and structural integrity for at least up to 16 h of osmotic dehydration.     

Osmotic dehydration of apple slices using a sucrose/CaCl2 combination to control spoilage caused by Botrytis cinerea, Colletotrichum acutatum, and Penicillium expansum

The efficacy of sucrose combined with CaCl2 during osmotic dehydration (OD) was tested for the control of Botrytis cinerea, Colletotrichum acutatum, and Penicillium expansum growth on lightly processed apple slices. The objective of this work was to determine whether the addition of CaCl2 in the osmotic solutions would limit the proliferation of fungal decay organisms. Slices were submitted to OD for 1 h at 25 degrees C in solutions containing 5 to 65% sucrose. Calcium chloride was added to a similar set of sucrose solutions at 0 to 8%. Control slices were made of untreated slices, and slices were processed in water. The mass ratio of the slices did not vary when fruit pieces were processed in solutions containing 5 to 65% sucrose. These slices showed a high susceptibility to spoilage compared to the control slices not submitted to OD: a significant twofold and 60% increase in decay area caused by B. cinerea and P. expansum, respectively, was observed when slices were processed in 50% sucrose/0% CaCl2; C. acutatum showed a significant 50% increase in decay area when slices were processed in 20% sucrose/0% CaCl2. Calcium uptake was significantly increased when slices were processed in CaCl2 solutions, and the highest Ca content was observed when processed in 8% CaCl2, reaching 40 times that of the control slices processed in water. Calcium-treated slices were less susceptible to spoilage by all three pathogens, and the most effective combination in reducing apple slice spoilage was 20 to 30% sucrose combined with 2% CaCl2.     

Determination of a thermal process schedule for guava (Psidium guajava Linn.)

A thermal process schedule for guava canned in syrup has been evolved on the basis of inactivation of pectinesterase (PE) which was found to be more heat resistant than peroxidase. The values for thermal inactivation and thermal resistance of PE in syrup homogenate containing guava pulp and sugar syrup in the ratio of 11:6 and total soluble solids content of 20% at pH 4.0 were     respectively. The F value of 1 was equivalent to 1.69 D . In commercial canning, a 2.5 D process is recommended which ensures a microbiologically safe and organoleptically acceptable product.
Process time was calculated both by graphical and formula methods. Calculation by the formula method using slopes of heating and cooling curves plotted on semilog paper by least squares analysis, and f _h/ U :g tables for actual values of j _c gave process times very close to those obtained by the graphical method. The process times required at different initial and processing temperatures are given.
To minimize viscosity increase in the covering syrup during storage, firming of guava in 1% calcium chloride solutions for 30 min prior to canning is suggested. In addition, use of covering syrup containing 0.125% ascorbic acid with or without citric acid (0.06%) yields a product of good colour, texture and flavour.     

Sugar composition of apple juices

Fifty-one samples from 12 geographic growing regions of Turkey and 3 varieties common for production of apple juice concentrate were processed to apple juice and analysed for their sugar composition. Enzymatic analyses was used to determine soluble sugars of apple juice. Glucose, fructose, sucrose, total sugar concentrations (g/l) and total soluble solids (%) of apple juices were ranged, respectively, as follows: 9.30-32.2, 66.10-96.00, 8.5-55.10, 110.90-164.40, 11.80-18.60. Cultivar significantly influenced the content of all the sugar analysed. Significant differences in fructose and sucrose concentrations have also been found between some growing areas.     

渗透方式对真空冷冻干燥芒果细胞结构及品质的影响

为探索渗透方式对冻干芒果细胞结构及品质的影响,本实验以玉芒为原料,在环境温度（20、30 ℃）下采用蔗糖固态渗透（SSD）、液态渗透（LOD）方式处理芒果后再进行真空冷冻干燥,通过测定渗透方式处理后芒果鲜样可溶性固形物、细胞形态以及分析冻干芒果的弹性模量、孔隙度、细胞壁结构、色泽以及V_C、总酚、β-胡萝卜素保留率指标的变化。结果表明:固态渗透芒果可溶性固形物增加量高于液态渗透,液态渗透处理的芒果细胞形态与鲜样（CK）无明显差异,固态渗透随蔗糖添加量的增加可溶性固形物含量和细胞形态皱缩程度增加;固态渗透减少细胞间孔隙度提高芒果弹性模量;傅里叶变换红外光谱结果表明O-H的伸缩震动吸收峰,随着蔗糖添加量的增加,吸收峰强度逐渐增加;低蔗糖固态渗透有利于维持芒果色泽;在环境温度20和30 ℃条件下固态渗透处理的真空冷冻芒果V_C和总酚的保留率高于液态渗透,其中固态渗透SSD20的V_C和总酚保留率最高分别为37.75%、33.37%;固态渗透SSD20处理的真空冷冻芒果的β-胡萝卜素保留率高于液态渗透LOD30,但固态渗透随蔗糖添加量的增加,β-胡萝卜素的保留率逐渐下降。本研究结果发现低蔗糖固态渗透可以有效提高真空冷冻芒果的综合品质,为改善芒果干燥制品品质提供理论参考。     

EFFECT OF CaCl2 AND CONVECTIVE-OSMOTIC DRYING ON TEXTURE AND PREFERENCE OF APPLE

Conventional air‐drying combined with osmotic dehydration was researched as a potential method for drying apple cubes of superior quality. Samples were pretreated with CaCl₂ at different temperatures and times. Pretreated apple cubes were dehydrated in a tray dryer. Then, osmotic dehydration with sucrose solutions was carried out. The curves for osmotic dehydration showed that the gain of solids was higher when 40% of water was removed by convective drying while the loss of weight was lower at the same level of dehydration at 65°Brix. Texture measurements indicated that the temperature of pretreatment affected the hardness and cohesiveness. Hardness values were higher at 40C, while cohesiveness values were lower at the same temperature. The CaCl₂ at a given temperature did not have a significant effect on texture. Sensory evaluation showed that samples pretreated at 25C and osmotically dried at 50°Brix had the higher preference by the judges.