Mass Transfer in Strawberry Tissue During Osmotic Treatment I: Microstructural Changes

ABSTRACT: Microstructural changes in strawberry tissue were quantified during osmotic treatment (OT) with sucrose solutions in concentrations of 15 to 65 (% w/w). The response-surface method was used to determine how the process variables (processing time and concentration) influence cellular shrinkage and cell destruction. With regard to the concentration of the osmotic solution, the kinetics of cell destruction followed a 1st-order model. The diffusional approach for modelling water transport in a layer of cells inside the strawberry tissue showed that water diffusivity is related to the concentration of the sucrose solution. Water diffusivity ranged from 16 ± 2 10⁻¹² to 6.2 ± 0.6 10^12.2 m²/s with sucrose solutions in concentrations between 15 and 65 (% w/w).     

Evaluation of Mass Transfer Mechanisms During Osmotic Treatment of Plant Materials

ABSTRACT: The proportion of intact, damaged, and ruptured (non-intact) cells (Zp) due to osmotic stress during osmotic treatment of potato was monitored using electrophysical measurement based on electrical impedance analysis. Osmotic stress on potato cell culture made cell membranes shrink thereby damaging the cells. The proportion of the ruptured and shrunk cells within the samples increased with the increase in concentration of solute in the osmotic solution. The osmotic removal of water from thin potato slices started at a critical osmotic pressure. Once the critical osmotic pressure was exceeded, mass transfer was rapid and the cells lost substantial amounts of water due to rupture of cell membranes.     

Transmembrane Mass Transfer in Carrot Protoplasts during Osmotic Treatment

Minimized experiments with Confocal Scanning Laser Microscopy were used to describe mass transfer of isolated carrot protoplasts from at the usual conditions of the Osmotic Treatments (OT). Carrot protoplasts during OT with 30, 40 and 50% sucrose solutions were monitored. The ratio of cellular volume before and after OT with 30, 40 and 50% sucrose solutions was 0.86 ± 0.12, 0.41 ± 0.04 and 0.17 ± 0.02, respectively. Trans‐membrane water flux was determined from cellular shrinkage, and the coefficient for water membrane permeability was (5.2 ± 0.9) 10^‐6 mol²/Jm²s. To describe water transport in protoplasts at transient conditions, the diffusional approach was used. The effective water diffusivity during OT with 50% sucrose solutions was in the (0.8‐1.8) 10^‐12 m²/s range.     

Electronic Nose to Detect Strawberry Aroma Changes During Osmotic Dehydration

ABSTRACT:  An electronic nose was used to detect the aroma evolution of strawberry fruits, cultivar "Camarosa," during the osmotic dehydration in sorbitol and sucrose solutions. Strawberry slices were subjected to osmotic dehydration at 30 °C for 1, 2, 4, and 6 h using either 60% sucrose or 60% sorbitol solutions. Volatile compounds of fresh and processed strawberry slices were analyzed by electronic nose and gas chromatography. Electronic nose was able to reveal changes in the aroma profile during processing and permitted differentiation between dehydrated strawberry samples obtained by different osmotic treatments. The electronic nose has the advantage of being simple, rapid, and nondestructive. Such characteristics and the promising results of this work suggested that this device could be a useful and innovative tool to monitor strawberry aroma changes during osmotic dehydration, providing real-time information about the effects of processing conditions and allowing the optimization of technological parameters.     

Accelerated Mass Transfer During Osmotic Dehydration of High Intensity Electrical Field Pulse Pretreated Carrots

High intensity electrical field pulse (0.22 to 1.60 kV/cm) pretreatment was tested to accelerate the osmotic dehydration of carrot. Applied energy in the range of 0.04 to 2.25 kJ/kg, increased cell disintegration index in the range of 0.09 to 0.84 with < 1 °C rise in the product temperature. The effective diffusion coefficients of water and solute, determined using a Fickian diffusion model, increased exponentially with electric field strength according to D = A exp(-B/E). The rise in effective diffusion coefficient may be attributed to an increase in cell wall permeability, facilitating transport of water and solute. Such increase was evidenced by cell disintegration index and softening of product.     

Enhanced Mass Transfer During Osmotic Dehydration of High Pressure Treated Pineapple

High pressure pretreatment (100–700 MPa) was applied to enhance mass transfer rates during osmotic dehydration of pineapples and accelerate the process. Experimentally determined diffusivity values, based on a Fickian model, increased fourfold for water and twofold for sugar. Diffusivity values were correlated with pretreatment pressure by an equation of the form D=A exp(–B/P), which suggests that diffusivity would level after an initial increase in pressure. The increase was attributed to breaking-up of cells walls which facilitated the transport of water. Evidence for the extent of cell wall break-up with applied pressure was based on differential interference contrast microscopic examination of tissue. Preliminary experiments on rehydration characteristics showed high pressure pretreated samples did not absorb as much water as controls.     

不同小分子糖渗透草莓的传质动力学及对真空冷冻干燥草莓品质的影响

为系统地了解不同小分子糖特别是低聚糖和糖醇对草莓的渗透行为以及不同小分子糖对真空冷冻干燥草莓品质的影响,本研究利用两种数学模型对10 种常见小分子糖（白利度为40 °Brix）的渗透动力学进行拟合,并进一步对渗糖处理后真空冷冻干燥草莓的理化特性进行表征。结果表明,Weibull模型更适用于描述渗糖处理后草莓的可溶性固形物增量（solid gain,SG）,而Peleg模型可以更好地描述草莓的水分去除量（water loss,WL）。经不同糖渗透处理结束后,草莓的SG差异较大,山梨糖醇可以使草莓的SG达到6.84 g/100 g,是低聚异麦芽糖的6.16 倍。此外,渗糖处理的草莓硬度得到普遍提高（94.58%～223.23%）;葡萄糖、果糖、山梨糖醇渗透处理组的脆度分别降低了16.70%、20.74%、41.45%,低聚果糖渗透处理后的草莓质构特性与蔗糖最为接近。综合考虑渗透效率、感官营养品质和生产成本,低聚果糖是蔗糖在果蔬渗透处理方面的一种潜在替代品。     

罗非鱼片渗透处理中的水分传递特性

为了研究水产食品原料在不同的渗透处理条件下的水分传递规律,本实验选择了罗非鱼片为研究对象,采用食盐溶液作为渗透液,在改变渗透液浓度、固液比和鱼片厚度的条件下,研究了罗非鱼片的水分迁移变化特性.结果表明,鱼片在10%浓度的盐水溶液中表现为吸水增重,在20%以上的盐水中才会出现渗透脱水现象;在渗透液浓度和鱼片厚度不变的条件下,鱼片的脱水率随着固液比的增大而升高;同时厚度对鱼片脱水率的影响与渗透时间有关,渗透时间的延长会降低较薄鱼片的脱水率.     

Effect of osmotic stress on microstructure and mass transfer in onion and strawberry tissue

We investigated the structural changes in onion epidermis and strawberry cortex tissue due to osmotic stress during osmotic treatment (OT) with sucrose solutions of concentrations ranging from 300 to 600 g kg^?1. We used miniaturised experiments with confocal scanning laser microscopy (CSLM) to monitor microstructural changes—cellular shrinkage and viability—during OT. The overall cellular shrinkage of these plant tissues was not significantly different under the same conditions of osmotic stress. For onion epidermis we determined the transmembrane water flux from the cellular shrinkage and found that the coefficient of water membrane permeability was (1.0 ± 0.39) × 10^?6 mol² J^?1 m^?2 s^?1. Osmotic stress did not affect the cellular viability of onion epidermis but significantly reduced the viability of protoplasts of strawberry in the whole range of solution concentrations. We used Fick's unsteady state second‐order diffusion equation to describe cellular water transport under transient conditions. The pseudo‐diffusional approximation led to water diffusivity values in the range (3–10) × 10^?12 m² s^?1 for both onion epidermis and strawberry cortex tissue. The concentration of the solution did not significantly affect the values of effective water diffusivity, which indicated the primary role of the plasma membrane during the initial stages of OT. Copyright © 2003 Society of Chemical Industry     

超声场强化渗透脱水传质机理模型研究

研究超声场强化芋头渗透脱水,探讨芋头失水速率和干物质增加率随溶液质量浓度、温度、超声功率、材料厚度以及超声场下处理时间段的变化规律。分析超声空化泡在相间的传质过程,由此建立超声空化气泡强化相间传质数学模型Km≈ DABπtmRδAfφ(BI－cf2)(A为经验常数(10-8～10-15m2);B、C为超声波作用液体的有关常数,数量值分别在1014、106左右;f为声波频率/s-1;DAB为扩散系数/(m2/s) ;tm为时间/s;R为半径/m;δ为边界层厚度/m;φ为半径为R的气泡数占生成空化气泡总数百分比;I为声强/(W/cm2)),与实验结果相吻合,能较好地描述超声空化泡在液体中的传质行为。该关系式为超声波强化传质过程提供了理论依据。     

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.     

超声波强化菠萝渗透脱水工艺

研究超声波强化菠萝渗透脱水的工艺过程。结果表明超声波强化菠萝渗透脱水的优化工艺条件：超声波频率中(48.1kHz)、超声波功率300W、糖液质量分数60%、糖液温度60℃、超声波作用时间40min,在此工艺条件下菠萝脱水率可达到41.41%。超声波强化技术能提高菠萝渗透脱水过程中的传质速率,缩短脱水时间。     

Evaluation of Mass Exchange During Osmotic Dehydration of Plum Using Response Surface Methodology

Water loss (WL), solid gain (SG), weight reduction (WR) and shrinkage were quantitatively investigated during osmotic dehydration of plum using response surface methodology with the sucrose concentration (30–60g/100 g sample), temperature of sucrose solution (40–60°C) and immersion time (60–240 min). Experiments were designed according to Central Composite Rotatable Design with these three factors. For each response, second order polynomial models were developed using multiple linear regression analysis. With respect to water loss, solid gain, weight reduction and shrinkage, both linear and quadratic effects of four variables were found to be significant. In most cases, an increase of sucrose concentration, temperature and immersion time increased WL, SG, WR and shrinkage, except the increasing of immersion time for osmotic treatment has no effect on shrinkage. It was found that immersion time and temperature were the most significant factors affecting the WL during osmotic dehydration of plum followed by concentration of sucrose solution. This was also true for WR. Effect of temperature and time were more pronounced for SG than the concentration of sucrose solution.     

热处理对袋装草莓果保鲜效果的影响

研究了袋装草莓果经 40℃热处理后在室温 ( 2 2± 2 )℃贮藏过程中呼吸强度和化学成分的变化。结果表明 ,热处理可降低草莓果贮藏期间的腐烂率和减少抗坏血酸、还原糖和有机酸含量的损失。以热处理 3 0min的效果最明显 ,且对草莓呼吸的刺激作用最小     

Increased Mass Transfer during Osmotic Dehydration of γ-Irradiated Potatoes

ABSTRACT: γy-irradiation pretreatment was tested to accelerate the osmotic dehydration of potato. Applied irradiation in the range of 3.0 to 12.0 kGy resulted in decrease in hardness of the potato sample, as indicated by texture profile analysis. The effective diffusion coefficients (D) of water and solute determined using a Fickian diffusion model increased exponentially with doses of γ-irradiation (G) according to an equation of the form D = A exp(-B/G), where A and B are constants. The microstructures of irradiated potato samples resulted in swelling and aggregation of starch granules as well as breaking up of cell wall structure, leading to channeling effect, facilitating transport of water from the tissue and solute into it.     

Solute Transfer in Osmotic Dehydration of Vegetable Foods: A Review

While various mechanisms have been proposed for the water transfer during osmotic dehydration (OD), little progress has been made to understand the mechanisms of solute transfer during osmotic dehydration. The transfer of solutes has been often described only by the diffusion mechanism; however, numerous evidences suggest the participation of a variety of mechanisms. This review deals with the main issues of solute transfer in the OD of vegetables. In this context, several studies suggest that during OD of fruits and vegetables, the migration of solutes is not influenced by diffusion. Thus, new theories that may explain the solute transport are analyzed, considering the influence of the plant microstructure and its interaction with the physicochemical properties of osmotic liquid media. In particular, the surface adhesion phenomenon is analyzed and discussed, as a possible mechanism present during the transfer of solutes in OD.     

不同强度的冷激处理对草莓保鲜效果的研究

本实验以"丰香"草莓为材料,研究了不同强度的冷激处理对果实贮藏期间品质的影响.结果表明,0℃冰水混合物处理1h可以明显的延缓草莓果实的后熟过程,推迟了草莓果实的变色,降低了呼吸速率和丙二醛的含量,冷激处理还可以抑制果实可滴定酸、VC、可溶性固形物和花色苷含量的下降,从而延缓了果实的成熟衰老.     

芒果片真空预处理联合超声辅助渗透脱水的传质动力学及品质分析

为解决芒果果脯生产过程中传质效率低、加工时间长的问题,该文研究了脉冲真空预处理联合超声辅助渗透脱水对芒果传质动力学、质量特性和微观结构的影响。结果表明：脉冲真空预处理联合超声辅助渗透脱水组的芒果失水率（54.43%）最高,较常规渗透脱水、脉冲真空预处理渗透脱水、超声辅助渗透脱水组分别高45.85%、14.06%、29.38%,增固率（12.81%）较常规渗透脱水、超声辅助渗透脱水、脉冲真空预处理渗透脱水组分别高90.03%、53.43%、32.06%。用Azuara模型拟合渗透脱水过程中失水率和增固率的变化,高回归系数（R2>0.97）和低RMSE表明Azuara模型可以较好拟合芒果渗透脱水过程,预测脉冲真空预处理联合超声辅助渗透脱水组的平衡脱水率、增固率最高,分别为65.06%和23.35%。测定色泽和质构,发现超声辅助渗透脱水组、脉冲真空预处理联合超声辅助渗透脱水组芒果硬度值显著低于常规渗透脱水组和脉冲真空预处理渗透脱水组（p<0.05）,而芒果色泽得到了较好保护。通过扫描电镜的观察,发现超声处理使芒果细胞壁塌陷与变形、细胞横截面积变小、微孔增多。此外,真空对芒果硬度和微观结构的影响均较小。综上,脉冲真空预处理联合超声辅助渗透脱水通过改变芒果细胞结构、增加传质微通道,提高了渗透脱水的效率,缩短加工时间,可以较好保护芒果色泽,但会导致硬度的下降。     

Osmotic Dehydration of Tomato in Sucrose Solutions: Fick's Law Classical Modeling

ABSTRACT:  Osmotic dehydration of tomato was modeled by the classical Fick's law including shrinkage, convective resistance at the interface and the presence of water bulk flow. Tomato slices having 8 mm thickness were osmotically dehydrated in sucrose solutions at 50, 60, and 70 °Brix and at 35, 45, and 55 °C. Other experiments were done in a 70 °Brix sucrose solution at 35 °C with tomato slices of 4, 6, and 8 mm thickness and at different motion levels (velocities 0, 0.053, and 0.107 m/s). Tomato weight, water content, and °Brix of the products were measured as a function of processing time (20, 40, 80, 160, and 320 min). Results showed that temperature, concentration, thickness, and solution movement significantly influenced water loss and sucrose gain during the osmotic dehydration of tomato. The model predicted the modifications of soluble solid content and water content as a function of time in close agreement with the experimental data. Experimental Sherwood number correlations for sucrose and water were determined as Sh _s = 1.3 Re ^0.5 Sc _s^0.15 and Sh _w = 0.11 Re ^0.5 Sc _w^0.5, respectively. The effective diffusion coefficients of water (4.97 10⁻¹¹– 2.10 10⁻¹⁰ m²/s) and sucrose (3.18 10⁻¹¹– 1.69 10⁻¹⁰ m²/s) depended only on temperature through an Arrhenius-type relationship.     

热空气处理对草莓果实品质和抗氧化活性的影响

研究热空气处理（45 ℃,3.5 h）对草莓在20 ℃、4 d贮藏期间果实品质、抗氧化活性及相关基因表达的影响。结果表明,热空气处理可以显著抑制果实腐烂的发生,延缓果实硬度、总黄酮、总酚和VC含量的下降,抑制花青素的积累,保持较高的DPPH自由基清除能力和还原力。另外,热处理可显著促进果实中黄酮醇合酶、查耳酮合酶和苯丙氨酸解氨酶基因的表达,而抑制β-木糖苷酶和花青素合酶基因的表达。这些结果表明,热空气处理可以通过调控相关基因的表达,较好地保持果实的品质和抗氧化活性。