果蔬渗透脱水过程中的传质模型及其应用研究

主要介绍了果蔬渗透脱水过程中的传质模型,如Peleg模型、Page模型、Fick第二定律和Weibull分布函数。此外,就各个模型在果蔬渗透脱水过程中的应用进行了详细阐述,同时对传质模型在果蔬保鲜方面的应用进行了展望。     

莴笋渗透脱水传质研究及参数优化

以失水率(WLR)和固形物增加率(SGR)为实验指标,采用二次回归正交旋转设计,选取葡萄糖溶液浓度(10%～40%)、氯化钠溶液浓度(2%～5%)、温度(35～65℃)、切片厚度(3～7mm)和渗透时间(60～150min)为影响因素,研究这5因素对莴笋渗透脱水指标的影响。使用SPSS软件拟合出了指标的回归方程,并利用方差分析研究了各因素对指标的影响程度。结果表明:除氯化钠溶液浓度外,其他4因素对失水率有极显著影响,而5种因素对固形物增加率有极显著作用。由Matlab软件优化的莴笋渗透脱水回归方程各参数为:葡萄糖浓度32.5%,氯化钠浓度2%,温度35℃,厚度5mm,渗透时间139min。     

热带亚热带果蔬渗透脱水研究进展

从渗透脱水的影响因素、渗透脱水对热带亚热带果蔬的影响以及渗透脱水传质动力学三个方面综述了果蔬渗透脱水的研究进展,其中重点介绍了渗透脱水的影响因素,同时对果蔬渗透脱水技术的局限性及其应用前景进行了探讨。     

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。     

蘑菇渗透脱水规律的研究

通过多因素正交试验，得出影响蘑菇渗透脱水因素的主次顺序及因素间交互作用的关系；应用均匀试验，建立了蘑菇渗透脱水的回归数学模型，其理论值与实测值具有很好的一致性；利用回归模型，建立了不同条件下的渗透脱水规律预测表。     

超声场强化提取茶籽油动力学模型的研究

通过分析常规浸提过程中的传质机制及超声场对分子扩散传质的影响,在Fick第一定律的基础上研究了超声强化提取茶籽油的动力学模型,并与常规浸提动力学模型进行了比较。在不同的提取条件下对上述模型进行验证,结果表明:所建立的动力学模型与实验数据相吻合,可较好地模拟茶籽油的提取过程。     

超声波强化紫薯渗透脱水工艺

分别以蔗糖质量分数、渗透温度、渗透时间和超声波功率为单因素,研究其对紫薯超声波渗透脱水的脱水率和固形物增加率的影响。以各因素为自变量,以脱水率和固形物增加率为因变量,对紫薯渗透脱水进行响应面工艺研究,得出最优工艺参数。结果表明：影响脱水率和固形物增加率的主次顺序均为渗透时间＞渗透温度＞糖液质量分数＞超声波功率;响应面优化最优工艺参数为糖液质量分数56.29%、渗透液温度65℃、渗透时间2.46h、超声波功率142.33W。结合实际操作,响应面优化的最优工艺调整为糖液质量分数56%、渗透液温度65℃、渗透时间2.5h、超声波功率140W,经验证,此条件下脱水率为40.79%,固形物增加率为8.33%。     

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。     

蘑菇渗透脱水规律的研究

对蘑菇片在糖溶液中的脱水规律进行初步的试验研究。通过多因素正交试验，得出影响蘑菇渗透脱水因素的主次顺序及因素间交互作用的关系；通过应用均匀试验，建立了蘑菇渗透脱水的回归数学模型，其理论值与实测值具有很好的一致性；利用回归模型，建立了不同条件下的渗透脱水规律预测表。     

真空、脉冲真空和常压下蓝莓渗透脱水的研究

研究了真空渗透脱水、脉冲真空渗透脱水和常压渗透脱水下蓝莓水分含量和水分活度的变化规律，结果表明：真空渗透脱水时，蓝莓的水分含量和水分活度降低得最快。真空渗透脱水、脉冲真空渗透脱水、常压下渗透脱水蓝莓的有效水分扩散率分别为1.6777×10^-9、1.3629×10^-9、0.5679×10^-9m^2/s。真空渗透脱水、脉冲真空渗透脱水、常压下渗透脱水的有效固性物扩散率分别为9.1705×10^-10、6.3919×10^-10、5.1007×10^-10m^2/s。     

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.     

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.     

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.     

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.     

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.     

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.     

Recent Development in Osmotic Dehydration of Fruit and Vegetables: A Review

Osmotic dehydration of fruits and vegetables is achieved by placing the solid/semi solid, whole or in pieces, in a hypertonic solution (sugar and/or salt) with a simultaneous counter diffusion of solutes from the osmotic solution into the tissues. Osmotic dehydration is recommended as a processing method to obtain better quality of food products. Partial dehydration allows structural, nutritional, sensory, and other functional properties of the raw material to be modified. However, the food industry uptake of osmotic dehydration of foods has not been extensive as expected due to the poor understanding of the counter current flow phenomena associated with it. However, these flows are in a dynamic equilibrium with each other and significantly influence the final product in terms of preservation, nutrition, and organoleptic properties. The demand of healthy, natural, nutritious, and tasty processed food products continuously increases, not only for finished products, but also for ingredient to be included in complex foods such as ice cream, cereals, dairy, confectionaries, and bakery products.     

Mass Transfer Modeling and Shrinkage Consideration during Osmotic Dehydration of Fruits and Vegetables

During osmotic dehydration of fruits and vegetables, as water and/or other substances are removed from the material, shrinkage follows depending on the extent of net mass loss. Mass transfer is usually predicted through modeling. However, common models developed for osmotic dehydration of fruits and vegetables make assumptions that often deviate far from reality, including large heterogeneity, variability and complexity in properties of fruits and vegetables. This generates some skepticism about such models and minimizes their potential industrial reliability. This paper reviews osmotic dehydration of fruits and vegetables through a basic approach, provides a critical view on modeling and points out the factors that affect shrinkage and mass transfer based on an extensive evaluation of pertinent literature.     

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.