Influence of osmotic dehydration and freezing on the volatile profile of kiwi fruit

The effect of osmotic dehydration on the volatile fraction of kiwi fruit was studied, as well as the effect of freezing and frozen storage. Osmotic treatments were carried out in sucrose solutions until the kiwi fruit reached 30°Brix, at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD), by using 45 and 65°Brix sucrose. Volatile compounds of fresh, dehydrated and frozen-stored (at −18 °C for 1 month) samples were obtained by simultaneous distillation-extraction, and analyzed by GC-MS. Osmotic dehydration provoked formation of esters and a decrease in aldehydes and alcohols, depending on the dehydration treatment applied, which is similar to what occurs during kiwi ripening. A severe reduction of all volatile compounds occurred after one month in frozen storage, which smoothes the changes induced by osmotic treatments. Only small differences between dehydrated and non-pretreated frozen/thawed samples could be recognized.     

Effect of Power Ultrasound and Pulsed Vacuum Treatments on the Dehydration Kinetics,Distribution, and Status of Water in Osmotically Dehydrated Strawberry: a Combined NMR and DSC Study

The effect of power ultrasound and pulsed vacuum (PV) treatments on the dehydration kinetics and the status of water during osmotic dehydration of strawberries was investigated. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to determine the spatial distribution and status of water within the cellular and intercellular spaces. Differential scanning calorimetry (DSC) was used to determine the freezing point depression and the amount of frozen water. Osmotic treatment was performed by immersing the samples in 25 and 50 % (w/w) sucrose solutions at 40 °C for 3 h. Water loss and solid gain of strawberry samples were measured and the data were fitted by Peleg’s model. The Peleg’s model fitted the experimental water loss and solid gain kinetics data well (R ²?>?0.98). At a given sucrose concentration, the highest water loss and the highest decrease in firmness occurred while using ultrasound treatment, while the highest solid gain and the highest firmness values were achieved by pulsed vacuum treatment. LF-NMR signals were able to quantify the effect of water-osmotic solute exchange on the cell compartments (vacuole, cytoplasm plus intercellular space, and cell wall). The LF-NMR data showed that the relative space occupied by the vacuole decreased and the relative space occupied by the cytoplasm and intercellular space were increased due to these osmotic treatments. MRI results indicated that a bright “water strip” appeared in the periphery of all the osmotically dehydrated samples. DSC results showed that the decrease in water content and the increase in the osmotic solutes depressed the initial freezing point and the freezable water content in osmotically dehydrated strawberry.     

Effects of processing on kiwi fruit dynamic rheological behaviour and tissue structure

The effects of blanching and osmotic dehydration on the small deformation rheological properties and structure of kiwi fruit were determined. Kiwi fruit tissue behaved as an elastic solid with storage moduli (G′) dominating the viscoelastic response (G′′/G′∼0.2). Both storage (G′) and loss (G′′)moduli were frequency independent and a clear linear viscoelastic range was evident. In general, G′ and G′′ decreased upon blanching and osmotic dehydration due to tissue damage. Structural changes caused by blanching included swelling of the cell walls and increases in the extent of cell–cell separation in the middle lamella. For atmospheric osmotic dehydration, high levels of solutes were observed within the cells which lead to a reduction of freezable water. For unripe tissue, G′ and G′′ increased with vacuum dehydration and it seemed that both cell wall integrity and cellular turgor were preserved to a greater extent than in ripe processed tissue. When calcium was added to the osmoticum during osmotic dehydration under vacuum, no differences in dynamic rheological behaviour or tissue structure were detected.     

Microwave vacuum drying of osmotically dehydrated mandarin cv. (Sai‐Namphaung)

Mandarin [mandarin cv. (Sai‐Namphaung)] was subjected to osmotic dehydration prior to microwave vacuum drying. Osmotic solutions were varied using different ratios of sucrose to glycerol (9:1, 7:3 and 5:5 w/w). Because of the decreased moisture content and solid gain during osmotic dehydration, dielectric properties of mandarin were changed significantly (P ≤ 0.05). The osmotically dehydrated mandarin was then dried further using microwave vacuum drying at 4.8 and 6.4 W g^?1. Among thin layer models, page model was the best to describe the drying of osmotically dehydrated mandarin. An increase in the microwave power could increase drying rate without significant effect on hardness of dried samples. Nonetheless, the hardness was significantly (P ≤ 0.05) reduced by an increase in the glycerol ratio in the osmotic solution. The increase in microwave power and glycerol ratio significantly (P ≤ 0.05) decreased β‐carotene content and thereby affected colour of the dried mandarin.     

Physiology of pre-cut mango. I. ACC and ACC oxidase activity of slices subjected to osmotic dehydration

Physiologically mature mangoes were ripened for 6 days at 24°C and 98% relative humidity. Slices from these fruits were osmotically dehydrated by immersion in sucrose 65°Brix at 30°C and 211 mbar vacuum during 30 min. Slices not subjected to osmotic dehydration (NOD) and slices with osmotic dehydration (OD) were stored at 24, 13 or 5°C. The respiration rate of both slice types was affected by the storage temperature. 1-Aminocyclopropane-1-carboxylic acid (ACC) synthesis indicated activity of ACC synthase in both slices as well as in the whole fruit. ACC oxidase activity was greater in OD slices as compared to NOD and that was associated to better membrane stability. OD favored compaction of external layer in slices. No ethylene was detected in slices; however, the tissues did not lose their ability to synthesize ethylene. Results suggest that OD under vacuum may be beneficial as a pre-treatment of mango slices for longer shelf life under refrigeration.     

Volatile profile of mango (Mangifera indica L.), as affected by osmotic dehydration

The effect of osmotic dehydration on the volatile fraction of mango fruit was studied. Osmotic treatments were carried out at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD). Sucrose at 35, 45, 55 and 65 °Brix was used as osmotic solution until reaching 20 or 30 °Brix in the liquid phase of dehydrated mango. Volatile compounds of fresh and dehydrated samples were obtained by simultaneous distillation–extraction, and analyzed by GC–MS. In general, osmotic dehydration provoked changes in the concentration of analyzed compounds to different extents, depending on process conditions. The use of highly concentrated osmotic solutions, and the high level of sample osmodehydration, induced losses of volatiles with respect to the fresh samples. On the other hand, more heavily diluted solutions and shorter treatment times (lower osmodehydration level) could give rise to the enhancement of volatile production. In these cases, sample mass loss was reduced during treatment since sugar gain was promoted against water loss.     

Osmotic dehydration of apple: Influence of sugar and water activity on tissue structure,rheological properties and water mobility

Osmotic dehydration of apple tissue (Malus pumila, Granny Smith cultivar) to water activity (a_w) 0.97 or 0.94 with maltose or maltose syrup solutions was studied and compared with previous results using glucose or trehalose as humectants. Structure (optical and transmission electronic microscopy observations), rheological properties (small scale dynamic oscillatory and creep/recovery measurements and large scale compression force-deformation testing), and water mobility (¹H NMR spectra) of parenchymatous apple tissue were significantly affected by osmotic treatments. Osmotically dehydrated apples became soft and extensible and lost crispness and hardness, while the behavior of the moduli G′ and G″ indicated weaker gels after osmosis. Compression properties of the tissues abruptly changed after osmotic dehydration to a_w 0.97, while reduction to a_w 0.94 led to a compression response more similar to that of untreated apples. Compression behavior and state and distribution of water in apple tissues were influenced by the osmotic agent employed and the a_w level, while in general mechanical spectra and creep analysis were not able for distinguishing physical differences between osmotic treatments assayed.     

INFLUENCE OF OPERATING CONDITIONS ON SENSORY QUALITY OF MINIMALLY PROCESSED OSMOTICALLY DEHYDRATED GUAVA

Abstract The influence of solution temperature (T), process time (t) and pressure regimen (P) on the sensory quality of minimally processed, osmotically dehydrated guava was analyzed. The study encompassed these values of each independent variable: T-30, 40 and 50C; t-60, 120 and 180 min, and P-atmospheric pressure, pulsed vacuum (5 min under vacuum, then atmospheric pressure) and continuous vacuum. The product was sensorially evaluated for color, flavor and firmness. Results were processed by means of the Design Expert version 5 software. Temperature, time and pressure regimen were shown to significantly influence the product's flavor. No effect of the factors on the fruit's color and firmness could be demonstrated. At the cellular level the tissues of guava treated at 40C for 60 min under pulsed vacuum are not significantly altered.     

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。     

Viscoelastic characterization of solid foods from creep compliance data: application to potato tissues

 Two software systems were developed to simplify acquisition and analysis of data describing creep behavior of viscoelastic solid foods and to determine the magnitude of instantaneous elastic compliance, viscoelastic compliances and viscosity associated with Newtonian flow. The first of these systems was used to store information on the experiment, to collect the data generated during the experiment, to present these in real time and to create files containing the experimental data for subsequent analysis. The second system was used to fit data to discrete Kelvin-Voigt models with four, six or eight constants. The systems were tested in the calculation of rheological properties of fresh and cooked potato tissues. A six-element Burgers model containing two discrete Voigt units proved the most suitable for defining tissue creep behavior, suggesting that different structural components could be related to each unit. The instantaneous elastic modulus could be associated with internal cell pressure. Gelatinization of starch and viscoelastic units appeared to reflect the viscoelastic properties of pectic substances and hemicelluloses, respectively. Received: 5 March 1998     

Changes in optical and mechanical properties during osmodehydrofreezing of kiwi fruit

The influence of osmotic dehydration and freezing–thawing on optical (colour and translucency) and mechanical properties of kiwi slices were analysed. Osmotic treatments were carried out in sucrose solutions up till the soluble solids in kiwi fruit reached 30 °Brix, both at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD). Analyses were carried out on fresh and dehydrated samples before and after frozen storage (at −18 °C for 1 and 30 days). Reflexion spectra (400–700 nm) were measured to obtain the Kubelka–Munk coefficients and CIE-L*a*b* colour co-ordinates. Mechanical properties were analysed through the compression test. A transparency gain was observed in PVOD treated samples and in frozen–thawed samples, which implied a reduction in product clarity and chrome. Colour hue did not change notably, due to either osmotic treatments or freezing. Samples treated with 45 °Brix osmotic solution at atmospheric pressure were the best preserved in mechanical properties after freezing–thawing.     

Influence of Modified Atmosphere Packaging and Osmotic Dehydration on the Quality Maintenance of Minimally Processed Guavas

ABSTRACT: The quality of minimally processed guavas ( Psidium guajava L.), osmotically dehydrated and packed under passive modified atmosphere, was evaluated during 24 d of storage at 5 °C. Modified atmosphere packaging (MAP) in polyethylene terephthalate (PET) containers had a strong influence on color preservation and weight loss of the guavas. Significant changes in the texture were found due to osmotic dehydration, but the color of the fresh fruit remained unchanged. Osmotically dehydrated guavas stored in MAP showed good microbial conditions during storage. The combination of storage temperature, modified atmosphere packaging, and the osmotic dehydration process maintained the quality of the guavas during 24 d of storage.     

Original article: Effect of sucrose and glycerol mixtures in the osmotic solution on characteristics of osmotically dehydrated mandarin cv. (Sai‐Namphaung)

This study investigated the effects of a series of osmotic solutions consisting of sucrose and glycerol on the quality of osmotically dehydrated mandarin, namely mandarin cv. (Sai‐Namphaung). Mandarin samples were peeled and osmotically dehydrated at 55 °C with agitation at 3.5776 × 10^?1g in five osmotic solutions containing various mixtures of 60% sucrose and 60% glycerol (9:1, 8:2, 7:3, 6:4 and 5:5 w/w, respectively). The osmotically dehydrated mandarin was further dried using hot‐air drying at 70 °C for 360 min. Increasing the glycerol ratio in the mixtures significantly (P ≤ 0.05) increased water loss and solid gain during osmotic dehydration, and significantly (P ≤ 0.05) affected kinetic rate constants during drying. An increase in the glycerol ratio in the mixtures caused a significant decrease in the quality factors of hardness, moisture content, water activity and reducing sugar. However, the increase resulted in an increase in the darkness of the dried mandarin, compared with increasing the sucrose ratio in the mixtures (P ≤ 0.05). The increase had an insignificant (P > 0.05) effect on vitamin C content.     

Osmotic Dehydration and Vacuum Impregnation on Physicochemical Properties of Chilean Papaya (Carica candamarcensis)

ABSTRACT: The effect of osmotic dehydration (OD) at atmospheric pressure and vacuum impregnation (VI) treatments on some physiochemical parameters of papaya (aw, pH, color, firmness, and microstructure) was analyzed. Osmotic treatments were carried out on papaya with 55°Brix and 65°Brix sucrose solutions at 30 °C. VI with 65°Brix osmotic solution was the most effective in reducing aw due to the highest sucrose gain during osmotic treatment. Color differences were associated to loss of clarity in line with transparency gain. Scanning electron microscopy observations show that osmotic dehydration caused shape changes and size reduction of papaya cells; also differences in microstructural features were observed between OD-treated and VI-treated samples. Moreover, the largest firmness observed in VI samples compared with OD treatments was associated with the thickness of the middle lamella between cells, which was greater in VI than OD treatments. Improvement in texture and palatability of papaya was obtained with VI rather than OD treatment compared with fresh papaya.     

CREEP BEHAVIOUR OF TOMATO PERICARP TISSUE AS INFLUENCED BY AMBIENT TEMPERATURE RIPENING AND CHILLED STORAGE

The influence of normal ripening and chilling stress on viscoelastic properties of tomato pericarp tissue were investigated by measuring creep behaviour of tissue from fruit stored at 22C (nonchilled) or 5C (chilled) for 28 days, or at 5C for 16 days prior to transfer to 22C for an additional 12 days (prechilled). Creep compliance of tissue from all treatments subjected to a constant shear stress of 150 Pa for 5 min was best represented by a 6-element Burgers model containing two discrete Voigt-Kelvin units characterizing fast and slow rate viscoelastic properties. The magnitude of instantaneous elastic, viscoelastic and steady-state viscous compliances each increased steadily and contributed to the overall softening of nonchilled and prechilled tissues during ripening, but remained unchanged during chilling of tomato fruit. Increased fluidity of ripening tissues occurred at the expense of elasticity, consistent with a decrease in molecular weight-size distribution of structural elements contributing to respective viscoelastic properties. The physico-mechanical changes in prechilled tissue preceded those in nonchilled tissue by several days, and occurred at a faster rate. The 6-element Burgers model defining the creep behaviour of tomato pericarp tissue was interpreted with respect to general plant cell wall structure and biochemical changes known to occur during ripening of tomato fruits. Multiple mechanisms of softening were thereby consolidated into a single physico-mechanical model.     

Structural Impact of Osmotically Pretreated Freeze-Dried Strawberries 0n Their Mechanical Properties

The paper investigates the impact of osmotic dehydration on the mechanical properties (i.e., structural changes and shrinkage) of freeze-dried strawberries. In the research, Senga Sengana strawberries were osmotically dehydrated in sucrose, glucose solution, and starch syrup and subjected to freeze-drying. The osmotic dehydration process strengthened the fruit structure by increasing their cell wall thickness. Osmotic pre-treatment limited the shrinkage of the strawberries by about 50%, while the compression force required for 25% deformation of the dried material was almost 2–963 times greater in comparison to the fruit not subjected to osmotic dehydration, dependent on the type of osmotic solution used.     

Relationships between rheological properties, texture and structure of apple (Granny Smith var.) affected by blanching and/or osmotic dehydration

The objective of this work was to evaluate and correlate rheological properties (small-scale dynamic oscillatory and creep/recovery measurements and large-scale compression force-deformation testing), texture (sensory evaluation by trained panel) and structure (optical and transmission electronic microscopy observations) of apples osmotically dehydrated to water activity (a _w) 0.97 with glucose, with or without previous blanching. All apple samples showed a solid behavior (G′?>?G″) dominating the viscoelastic response, but both dynamic moduli were reduced due to processing. The instantaneous elastic compliance (J ₀) and the retarded compliances (J ₁ and J ₂) increased for treated tissues and the steady-state viscosity (η _N) was approximately 15% to 29% of the value of fresh apple. In general, compression parameters decreased for all treated tissues. Changes in structural features were mainly evidenced in heated samples. Partial least squares regression analysis regression models revealed that texture could be well predicted by rheological properties (compression and creep parameters). Juiciness, crispness and sensory hardness were negatively correlated to J ₀, J ₁ and J ₂, and η _N was negatively correlated to sensory fracturability. Some mechanical parameters (fracturability, hardness 2, area 2, modulus of deformability and cohesiveness) were positively related to sensory fracturability, crispness and sensory hardness; and juiciness was negatively correlated to hardness. Compression and creep parameters showed ability to evidence structure differences (rupture of membranes, swelling of cells and degradation of cell walls) and to explain texture of treated apples.     

Rheological properties of ice cream mixes and frozen ice creams containing fat and fat replacers

Ice cream mixes and frozen ice creams at milk fat levels of 12%, 8%, 6%, 6% plus a protein-based fat replacer, and 6% plus a carbohydrate-based fat replacer were evaluated for viscoelastic properties by dynamic testing with sinusoidal oscillatory tests at various frequencies. The storage modulus (G'), loss modulus (G"), and tan delta (G"/G') were calculated for all the treatments to determine changes in the viscous and elastic properties of the mixes and frozen ice creams due to fat content. In ice cream mixes, G' and G" exhibited a strong frequency dependence. The G" was higher than G' throughout the frequency range (1 to 8 Hz) examined, without any crossover, except for the 12% mix. Elastic properties of the ice cream mixes decreased as fat content decreased. Tan delta values indicated that fat replacers did not enhance the elastic properties of the ice cream mixes. In all frozen ice creams, G' and G" again showed a frequency dependence throughout the range tested (0.5 to 10 Hz). The amount of fat in ice creams and the degree of fat destabilization affected the elasticity in the frozen product. Even though the ice creams did not have significant elastic properties, when compared as a group the samples with higher fat content had higher elastic properties. The addition of protein-based and carbohydrate-based fat replacers did not enhance the elastic properties of the ice creams but did increase the viscous properties.     

常用微胶囊壁材的分子结构及流变学特性研究

本文研究了五种壁材分子结构及其流变学特性。以喷雾干燥制备微胶囊的五种常用壁材变性淀粉、阿拉伯胶、明胶、大豆分离蛋白和羧甲基纤维素为研究对象,采用凝胶渗透色谱法(GPC)测定壁材的分子量分布;傅里叶变换红外光谱法(FT-IR)分析不同壁材的特征基团和蛋白类壁材的二级结构;旋转流变仪研究壁材的表观黏度、动态模量和蠕变柔量。研究结果表明:五种壁材溶液均呈现剪切稀化现象,随着温度的上升壁材溶液的表观黏度逐渐下降;壁材的弹性模量G'和黏性模量G'均随着振荡频率的增大而增大;相同时间下,壁材的蠕变柔量J(t)大小为:变性淀粉阿拉伯胶明胶羧甲基纤维素大豆分离蛋白;壁材分子量越大,表观黏度就越大;同一数量级分子量的壁材,分子量分布越宽,非牛顿"剪切稀化"现象越明显;分子结构越刚性,极性越大,表观黏度也越大。     

OSMOTIC DEHYDRATION OF STRAWBERRIES IN A BATCH RECIRCULATION SYSTEM

Physical and chemical characteristics of two cultivars of strawberries during osmotic dehydration in sucrose and glucose solutions were investigated. Temperature was found to have a significant effect on the water and sugars (glucose, fructose and sucrose) exchange between strawberry and the osmotic solution. Mass transfer was found not to be significantly different between cultivars. Glucose gain was found to be higher than sucrose for the strawberries osmotically dehydrated in glucose and sucrose solutions at the same mole fraction, respectively. Sugars other than the osmotic sugar were found to decrease in concentration during the osmotic process. The combination of 63% sucrose solution with 25C process temperature for 2 h was able to remove more than 40% of moisture and load less than 0.1% of sucrose in the strawberries.