Air Drying Behaviour of Fresh and Osmotically Dehydrated Onion Slices (Allium cepa) and Tomato Fruits (Lycopersicon esculentum)

Onion slices (0.5 cm thick) and tomato fruits, fresh and osmotically dehydrated in sugar (600 g/l), salt (300 g/l) or mixed salt and sugar (45/15, w/w) solutions, were air dried at 60°C and drying constants determined. The air drying occurred in two falling rate periods, characterised each by a drying constant. The drying rate and the moisture diffusivity of osmosed samples were higher than that of fresh samples. The overall drying behaviour of osmosed onion slices was not influenced by osmotic conditions (solution and time), while the drying behaviour of osmosed tomato samples depended on osmotic solution and pre-treatment time. 15 minutes and 20 hours of pre osmosis seemed more convenient before drying of onion slices and tomato respectively. In this respect, the structural modification of cells of tomato membrane during extended pre treatment seemed to explain the variation in the drying behaviour.     

Egg Yolk Antibody (Ig Y) Stability in Aqueous Solution with High Sugar Concentrations

Effect of sugars on the stabilization of hen egg yolk immunoglobulin (IgY) under various processing conditions was investigated. By adding 30–50% (w/v) sucrose or invert sugar to an IgY solution heat denaturation of the IgY antibody at 75–80°C was markedly suppressed. A high concentration of sugar was also effective to retain the IgY activity under acidic conditions of pH 3 or high pressure of 5,000 kg/cm² at 60°C. Addition of high concentrations of sucrose may be a simple means to stabilize IgY for processing and preservation.     

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.     

Development of cantaloupe (Cucumis melo) juice powders using spray drying technology

Cantaloupes are a good source of carotenoids and vitamin C. Cantaloupe fruit juice powder containing vitamin C and β-carotene can be produced by spray drying. The objective of this study was to develop cantaloupe fruit juice (CJ) powder and to evaluate its nutritional and physical properties. Fresh cantaloupe fruits purchased from a local store were diced and juiced. CJ with 10% maltodextrin (MD) added was spray dried at inlet temperatures of 170, 180 and/or 190 °C. Three spray dried cantaloupe powders, including CJ dried with MD at 170 °C (CJP1), CJ dried with MD at 180 °C (CJP2), CJ dried with MD at 190 °C (CJP3) were analyzed for moisture, water activity, vitamin C, β-carotene, dissolution, and microstructure. The actual production rate of the cantaloupe juice powders was lower than the estimated production rate. CJP1 had (p < 0.05) higher moisture content and water activity than CJP2, and CJP3. Vitamin C content (mg/100 g, dry solids) was significantly (p < 0.05) higher in CJP1 (136.36 ± 5.84) than CJP2 (91.85 ± 5.23) and CJP3 (78.30 ± 1.96). The powder produced at inlet temperatures 170 °C had higher β-carotene content (μg/g) than that produced at 180 and 190 °C.     

Effect of drying methods on osmotically dehydrated cashew apples

Matured ripe cashew apples were transversely cut into 10 mm, 15 mm and 20 mm slices and immersed in sugar solutions of 52°Brix, 60°Brix and 68°Brix, for 10 h. The osmotic temperature was maintained at 27 °C in a water bath. Osmosed samples were subsequently dried in either an air-oven (50 °C) or a vacuum-drier (50 °C), both for 6 h.The instantaneous moisture content (d.b) of osmosed cashew apples decreased with increasing immersion time and osmotic solution concentration, but also increased with increasing slice thickness. The water loss, solids gain and percentage weight reduction increased with increasing osmotic solution concentration and immersion time, but decreased with increasing slice thickness. Osmotically dried samples received high acceptability. Sample pre-osmosed in 60°Brix and 68°Brix solutions were significantly better (P>0.05) than those pre-osmosed in a 51°Brix solution. A significant difference (P>0.05) between the osmo-oven and osmo-vacuum dried cashew apples could not be ascertained (under the conditions of the investigation).     

Adsorption isotherm and heat of sorption of fresh- and osmo-oven dried plantain slices

Firm ripe plantain was transversely cut into 10-mm slices and osmotically pretreated in 52 °, 60 ° and 68 °B sucrose solutions, for 12 h at 25 °C. Fresh- and osmosed plantain slices were air-dried in a cross flow forced draught oven at 60 °C for 72 h. Adsorption isotherms of the products were determined at 20 °C and 40 °C, using a gravimetric-static method. Adsorption data were fitted into eight isotherm models. Isosteric heat of sorption was calculated using the Clausius-Clapeyron equation. Adsorption isotherms of fresh- and osmo-oven dried plantain slices followed type I (J-shaped) isotherms, characteristic of high sugar products. Inversion of 20 C and 40 C isotherms occurred between a_w 0.65 and 0.70. Among the models tested, the Guggenhein Anderson deBoer (GAB) gave the best fit. Isosteric heat of sorption increased with decreasing moisture contents. Negative isosteric heat of sorption occurred at high moisture content. Moreover, isosteric heat of sorption increased with increase in sucrose solution concentration during the osmotic dehydration prior to oven drying.     

Combined Effects of Drying Methods,Extract Concentration,and Film Thickness on Efficacy of Antimicrobial Chitosan Films

An idea of using a suitable drying method to minimize the loss of added antimicrobial agent and, at the same time, to modify the structure, and hence the release characteristics of chitosan films was proposed. Chitosan film‐forming solution was incorporated with galangal extract (0% and 1.5% w/w) and formed into films with the thickness of 15 and 30 μm via hot air drying (HD) (40 °C) and low‐pressure superheated steam drying (LPSSD) (70 °C, 10 kPa). The extract retention, release characteristics, and antimicrobial efficacy of the films were then assessed; fresh‐cut cantaloupe was used as the test food material, while Staphylococcus aureus was the test pathogenic microorganism. The retention and release of 1,8‐cineole, a major bioactive compound in the galangal extract, was monitored during 5‐d storage at 25 °C. The film swelling was also evaluated and their results used to interpret the release characteristics of 1,8‐cineole from the films to the cantaloupe. At the same thickness, the films prepared by HD had lower extract retention and higher degree of swelling, thus exhibiting faster extract release and lower antimicrobial efficacy than the films prepared by LPSSD. Within the same drying method, the increased film thickness led to higher extract retention and antimicrobial efficacy. The concentration of the extract in the cantaloupe matched well with the extract retention and release characteristics as well as the antimicrobial efficacy of the films.     

Microbial counts and invert sugars in juice extracts from stored tubers of Cyperus esculentus Linn. (earth almond)

The microbial populations and the levels of invert sugars in juice extracts from healthy tubers of Cyperus esculentus L. stored at 10, 20, 30 and 40 °C were determined. Bacterial counts increased with time and attained the peak on the 25th and 35th d at 40 and 30 °C respectively. Similar trends were obtained for the yeasts, but the peak counts were recorded on the 20th and 35th d at 40 and 30 °C respectively. At 10 and 20 °C, the counts, both for bacteria and yeasts increased throughout the 40-d period. Invert sugar levels increased throughout the investigation period at all the tested temperatures. Highest levels were recorded at about 30 and 40 °C while the lowest levels were obtained at 10 °C. Of the seven bacteria and five yeasts tested, only Saccharomyces rouxii, S. cerevisiae, Schizo-saccharomyces sp., Pseudomonas chlororaphis, P. fluorescens and Bacillus subtilis brought about significant hydrolysis of sucrose in vitro. Results on the microbial populations and levels of invert sugars in raw juice extracts suggest that yeasts could possibly play a greater role than bacteria in the hydrolysis of sucrose in vivo.     

Drying and Crystallization of Sucrose Solutions in Thin Films at Elevated Temperatures

ABSTRACT: Thin sucrose films were dried over 30-min periods during which sucrose crystal growth rates were monitored by videomicroscopy. Drying parameters and sucrose solution properties were varied to determine their effect on initial sucrose crystal growth rates. Growth rates increased by a factor of 4.5 as temperature increased from 40 to 70 °C. Varying initial sucrose concentration (70 to 80%) and drying air velocity (2 to 5 m/s) produced no change in crystal growth rates. Increases in film thickness from 150 to 450 μm and the presence of moisture in the drying air reduced growth rates by 33% at 70 °C, but had no effect at 50 °C. The addition of invert sugar (up to 5%) reduced growth rates by a factor of 2 to 3.     

Sorption Isotherms and Drying Rates of Jerusalem Artichoke (Helianthus tuberosus L.)

Moisture sorption properties and drying behavior of Jerusalem artichoke roots were investigated. Sorption isotherms of dehydrated and freeze-dried material, its water insoluble components, fructose, glucose and sucrose were determined at 10, 25 and/or 40°C. Adsorption-desorption isotherms indicated a combination of sorption by soluble sugars, in the crystalline, amorphous and aqueous solution state, and sorption by polymeric material such as cellulose, inulin and protein. In drying experiments conducted at 50, 65, 80, and 95°C, and also at 65°C and four air velocities and four bed depths, it was found that temperature and drier load conditions are of critical importance to drying behavior, drying time and finished product color. Increasing the air velocity from 2.0 to 4.2 m/set, at a temperature of 65°C and a bed depth of 10.5 cm, did not change the rate for drying 1 cm cubes.     

Effect of leavening agents and sugars on the formation of hydroxymethylfurfural in cookies during baking

The effects of recipe compositions in terms of leavening agent (ammonium and sodium bicarbonates) and sugars (sucrose and glucose), and baking conditions (temperature and time) on HMF formation in cookies were studied. Five recipes were prepared by varying the types of leavening agent and sugar. The cookies were baked at different temperatures (180, 200, 210 and 220 °C) for different time (10, 15, 20 and 25 min) to monitor physical and chemical changes in cookie composition in terms of water activity, pH, surface browning, sugar decomposition, and hydroxymethylfurfural (HMF) formation. Decreasing moisture to a level under a water activity of 0.4 appeared as the critical point in baking where the rate of HMF formation drastically increased after this point. After this stage, sucrose decomposed very rapidly if ammonium bicarbonate was used as the leavening agent at temperatures greater than 200 °C. Replacing ammonium bicarbonate with sodium bicarbonate maintained pH of cookies ranging between 9.0 and 10.0 during baking, which limited the decomposition of sucrose.     

Effects of calcium chloride and calcium lactate applications with osmotic pretreatment on physicochemical aspects and consumer acceptances of dried papaya

This study explored the effects of calcium chloride (CaCl₂) and calcium lactate (Ca‐L) pretreatments prior to osmotic dehydration on physicochemical characteristics and consumer acceptance of dried papaya. Three different calcium concentrations [0.5, 1.5 and 2.5% (w/v)] were applied to samples before they were soaked in a 30 °Brix sucrose solution and subsequently dried at 70 °C. The results showed that the dried samples treated with calcium exhibited significantly lower moisture content, water activity, apparent density and shrinkage, while volume was higher when compared to the control. Calcium applications did not obviously influence sugar content of samples and maintained the quality of dried papaya in terms of colour and textural characteristics. Calcium chloride at 2.5% (w/v) was found to particularly impart undesirable bitterness to the dried papaya. In contrast, using 2.5% (w/v) Ca‐L provided the best acceptance scores. Thus, the use of Ca‐L could be an alternative to CaCl₂ in the pretreatment of fruits prior to drying as it offers improved quality.     

Mass transfer kinetics during osmotic dehydration of bananas (Musa sapientum,shum.)

Osmotic dehydration is used widely to partially remove water from plant tissues by immersion in a hypertonic solution. In this work, the influence of temperature (25–55 °C), sugar concentration (30–60%) and salt concentration (0–10%) of the osmotic solution was investigated during osmotic dehydration of banana (Musa sapientum, shum.). Mass transfer kinetics were modelled according to Peleg’s equation. Kinetic parameters were evaluated using response surface methodology. Peleg’s equation showed to be suitable for modelling the water removal and solute uptake. Initial rate of water loss and water concentration at equilibrium were influenced by linear factors of the three independent variables. Initial rate of sucrose uptake and sucrose uptake at equilibrium were affected by all factors and interactions. Initial rate of salt uptake and salt concentration at equilibrium showed a positive correlation with temperature and NaCl concentration and a negative correlation with sucrose concentration.     

Osmotic-Convective Dehydrofreezing Process for Drying Kiwifruit

Osmotic and convective dehydrofreezing were studied to determine sugar concentration, ascorbic acid loss, and texture changes in dried and dehydrofrozen kiwifruit. Two concentrations of sucrose (60° and 72° Brix) were used as osmotic solutions after convective air drying. Time needed to reach desired moisture was reduced with combined drying compared with osmotic drying. Firmness was evaluated by the maximum force from a back extrusion test. A reduction in maximum force was observed after freezing, as compared with fresh and dried fruit. Addition of ascorbic and citric acid as antioxidants in the osmotic solution prevented browning, and significant loss of ascorbic acid during osmotic drying. Air drying at 30°C produced distinguishable color changes.     

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.     

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.     

Thin layer modeling of drying kinetics,rehydration kinetics and color changes of osmotic pre-treated pineapple (Ananas comosus) slices during drying: Development of a mechanistic model for mass transfer

This study aimed to develop an effective and safe drying protocol for pineapple fruits. The combination of different osmotic pre-treatments and drying temperatures were used to evolve a novel method that can reduce drying associated changes in pineapple fruits. The pre-treatment was accomplished by soaking fresh pineapple slices in four osmotic solutions (1% trehalose, 2% NaCl, 10% sucrose, and 10% fructose) for 30 min. A hot air convection dryer carried out the drying at 50, 55, and 60 °C temperatures maintaining a constant 30% relative humidity (RH). During the drying experiment, moisture content data were taken and transformed into moisture ratio (MR) and then fitted to the four thin layer models viz. Page, Logarithmic, Newton (Exponential model), and Henderson and Pabi's Model. The impact of pre-treatments and drying temperature on drying kinetics, mass transfer rate, moisture diffusion, rehydration capacity, and color changes of pineapple slices were observed. The drying process was affected by both osmotic pre-treatments and temperature. A satisfactory curve with good fitting as anticipated by the Page and Logarithmic models, with the Logarithmic model fitting best during the drying of pineapple slices. The ideal drying temperature integrated with pre-treatments was 55 °C at 30% RH based on maintaining the color and rehydration. The Page equation provided an excellent statistical fit to experimental rehydration data, with low mean percentage error values of 2.188–7.479%. The pre-treatment of dried pineapples, particularly with trehalose, improved structural retention as seen by increased rehydration capacity and lower color changes after reconstitution. The mechanistic model, which describes activation energy for the increase of moisture diffusion coefficient and mass transfer coefficient, and their correlation to drying conditions (temperature and time), showed a better fit for mass transfer and diffusion. Weibull's distribution model gave a better fit for the water loss model during drying at various temperatures. As a result, the combination of dipping in 1% trehalose solution and hot air drying at 55 °C appears to be a promising procedure for producing high-quality, nutritious dried pineapple products for consumers. This work will assist future researchers in understanding the influence of osmotic pre-treatments on plant foods and improve the existing literature.     

Effect of osmotic dehydration on the quality of air-dried Porphyra

Osmosis with a solution of NaCl and sucrose to depress the water activity (a_w) to 0.970 and the pH to 3.0 was assayed as a pretreatment to air-drying of red seaweeds (Porphyra columbina Montagne). Air-drying was performed at 30°C and 14% relative humidity. Process characteristics, color, flow pattern and rehydration ability of the milled product, were evaluated to determine the usefulness of osmosis. The a_w attained after 2 h of drying was similar for both osmosed and nonosmosed Porphyra and higher than monolayer water activity for both products. Consequently, no additional benefits concerning stability during storage were observed, after applying osmosis. Moreover, severe changes in color occurred. Powder flowability evaluated through the measurement of compressibility and cohesiveness decreased with pretreatment, which also determined a more plastic behavior. In summary, osmotic dehydration as a pretreatment for air-dried seaweeds did not seem to improve the final product quality.     

Evaluation of Factors Influencing Microwave Osmotic Dehydration of Apples Under Continuous Flow Medium Spray (MWODS) Conditions

Microwave osmotic dehydration under continuous flow medium spray (MWODS) conditions is an innovative concept with high potential for enhancing moisture loss as well as improving product quality. Quantification of mass transfer kinetics under different processing conditions is important for managing and optimizing the osmotic dehydration process. A response surface methodology was used for evaluating and quantifying the moisture loss and solids gain kinetics of apples during the MWODS process. Experiments were designed according to a central composite rotatable design with all independent variables included at five levels (sucrose concentration, 33.3–66.8°Brix; medium temperature, 33.3–66.8 °C; medium flow rate, 2,120–3,480 ml/min; and medium contact time, 5–55 min). The process responses were moisture loss (ML), solids gain (SG), and weight reduction (WR) and were related to process variables using second-order polynomial regression models. The lack of fit was not significant (p?>?0.05) for any of the developed models. For ML, SG, and WR, the medium contact time was the most significant factor during the MWODS process followed by medium temperature and sucrose concentration. The effect of medium flow rate was only significant with moisture loss and weight reduction. The quantity of ML, SG, or WR achieved over a 30 min treatment time was chosen as the drying rate. These rates were shown to be responsive to the osmotic treatments increasing with sucrose concentration, medium flow rate, and medium temperature.     

Effect of drying method on the sorption characteristics of model fruit powders

Pectin-sugar gels were dehydrated with four different drying methods: freeze, microwave, vacuum and conventional drying to a moisture content of about 5%. The effect of the drying method on the water sorption properties of dehydrated products was evaluated at 25 °C. Freeze-dried gel adsorbed more water vapour than microwave-dried gel, which had a higher sorption capacity than vacuum- and conventional-dried product. The sorption isotherms were in agreement with the reported shape for high sugar foodstuffs. Three different equations proposed in the literature (GAB, Oswin, Hasley) were used to fit the sorption data. The GAB equation gave the best fit to the experimental data. The porosity of the dehydrated products depended on the drying method, ranging between 0.2 and 0.5. Freeze- and vacuum-dried pectin developed the highest porosity, whereas the lowest porosity was obtained using conventional and microwave drying. Hunter colour parameters (L, a, b) also depended on the drying method. The colour of freeze- and vacuum-dried pectin was close to that of commercial pectin, while the colour of the conventional- and microwave-dried product changed significantly.