Optimisation of osmotic dehydration of carrot cubes in sucrose-salt solutions using response surface methodology

Osmotic dehydration of carrot cubes in ternary solution of water, sucrose and sodium chloride at different solution concentrations, temperatures and process durations were analysed for water loss and solute gain during osmotic dehydration. The osmotically pre-treated carrot cubes were further dehydrated in a cabinet dryer at 65 °C and were then rehydrated in water at ambient temperature of water for 10–12 h and were analysed for rehydration ratio, shrinkage and overall acceptability after rehydration. The process was optimised for maximum water loss, rehydration ratio and overall acceptability of the rehydrated product, and for minimum solute gain and shrinkage of rehydrated product by response surface methodology. The optimum conditions of various process parameters are 50°B+10% w/v aqueous sodium chloride concentration, 46.5 °C solution temperature and 180 min process duration.     

OPTIMIZATION OF OSMOTIC DEHYDRATION PROCESS OF CARROT CUBES IN SUCROSE SOLUTION

ABSTRACT

For optimization of the osmotic dehydration process of carrot cubes in sucrose solution by response surface methodology (RSM), the experiments were conducted according to face‐centered central composite design. The independent process variables for the osmotic dehydration process were osmotic solution concentrations (45–55°Brix), temperature (35–55C) and process durations (120–240 min). Statistical analysis of results showed that all the process variables had a significant effect on all the responses at 5% level of significance (P < 0.05). The osmotic dehydration process was optimized by RSM for maximum water loss, rehydration ratio, retention of color, sensory score and minimum solute gain. The optimum process conditions were 52.5°Brix sucrose syrup concentration, 49C osmotic solution temperature and 150‐min process duration.

PRACTICAL APPLICATIONS

The process of osmotic dehydration can be used for the preparation of shelf‐stable products for the purpose of use during off‐season. The quality of preosmosed carrots is much superior to the product dehydrated with the convectional method of convective dehydration. The osmotically dehydrated carrots can be used for cooking as vegetables after rehydration or can be added directly into soups, stews or casseroles before cooking. If the product is blanched before osmotic dehydration, the process can be used successfully for the preparation of carrot candy.     

Kinetics of water absorption and soluble‐solid loss of hot‐air‐dried carrots during rehydration

Cubes of carrots dried at 60, 70, 80 and 90 °C were rehydrated at 20 and 95 °C. Kinetics of water gain and soluble‐solid loss were monitored and described by Peleg model. Dry matter holding capacity, water absorption capacity and rehydration ability were derived to assess the rehydration process. It was found that leaching flow was higher for the samples dried at higher temperatures. Rehydration ability and dry matter holding capacity of the samples rehydrated at 95 °C were higher than those observed for the samples soaked at 20 °C. Swelling of carrots during rehydration neither depended on temperature of drying nor on the temperature of the water. The results indicate that the use of low drying temperatures is suitable for preserving the quality attributes of carrots after rehydration.     

Centrifugal osmotic dehydration and rehydration of carrot tissue pre-treated by pulsed electric field

This paper studies the centrifugal osmotic dehydration (OD), rehydration and texture of carrot tissue treated by pulsed electric field (PEF). The influence of centrifugal acceleration (0-5430g), salt addition (NaCl/sucrose solutions 0/65, 7/44 and 15/50% w/w), and temperature (20-40 °C) on the OD kinetics was investigated in the presence and absence of PEF (E=0.60 kV/cm, treatment duration t_PEF=0.05 s). The centrifugal OD of samples untreated and treated by PEF was compared with OD under stirring (250 tr/min).Centrifugal force, PEF and salt addition increase the amount of water removed during OD. However, the centrifugal force decreases the intake of solids by the product.The application of PEF enhances both water loss (WL) and solid gain (SG) during OD (under stirring or centrifugation), increases the rehydration capacity of carrot tissue, but somewhat decreases the firmness of rehydrated product.The combination of centrifugal field with PEF and salt addition can be advantageous for reducing the OD duration. The textural study shows that the product obtained with OD is less affected by thermal treatment than the directly dried product.     

Rehydration properties of dried plant tissues

Apples, carrots and potatoes cut in cubes were dried by convection and then subjected to rehydration in water at room temperature. Mass and volume changes were followed during rehydration. A minimal displacement gauge was used to record changes of height of individual cubes during wetting. Porosity of the dried material was calculated and its changes during rehydration were observed. Comparing volume increase with mass gain during rehydration it was found that the mechanism of water imbibing is strongly influenced by porosity and chemical composition of the dried material. Dried apple was very porous, hence its mass gain was much faster than the volume increase. On the other hand, gelatinised starch in dried potato strongly absorbed water and the volume increase outpaced the mass gain. Recording changes of height of the dried cubes upon rehydration evidenced phase changes and injury incurred to the tissue structure by dehydration. In apple a collapse of structure was observed, while potato cubes swelled from the very beginning of the wetting process. In carrot instantaneous changes of height of the cube were observed, which could be due to relaxation of shrinkage stresses and displacements of injured tissue structures.     

Osmotic dehydration kinetics of carrot cubes in sodium chloride solution

Osmotic dehydration kinetics of carrot cubes in sodium chloride solution having concentrations 5%, 10% and 15% (w/v), solution temperature 35, 45 and 55 °C, sample to solution ratio (STSR) 1:4, 1:5 and 1:6 were studied up to 240 min duration. During the experimentation, effect of solution temperature and process duration was significant and that of solution concentration and STSR were non-significant on water loss. Among the different models applied (Penetration model, Magee Model, and Azuara model), Azuara model best fitted to the experimental data for water loss and solute gain during osmotic dehydration. Effective diffusivities of water and solute were calculated by using the analytical solution of Fick's unsteady state law of diffusion by iterative technique with a computer program. For the above conditions, the effective diffusivity of water was found to be in the range between 2.6323 × 10⁻⁹ and 6.2397 × 10⁻⁹ m²/s and that of solute between 3.1522 × 10⁻⁹ and 4.6400 × 10⁻⁹ m²/s.     

Membrane Packaging System to Permit Safe Hydration of Freeze-Dried Contents with Impure Water

We tested the feasibility of using polymer membranes for a self-hydrating packaging system to reconstitute freeze-dried foods using nonpurified water. Several commercial membranes were screened according to (1) hydration rate, (2) water permeability, (3) passage of microorganisms, (4) salt rejection, and (5) strength. The most promising membranes were used for developing and testing prototype packaging systems. A feasible self-contained rehydration system was a nylon-6 polyamide membrane that rehydrated the freeze-dried food within 30 min while passage of microorganisms was prevented. The temperature was 37°C, and the food contained 0.5g/5g of a low molecular weight solute (salt). Such self-contained membrane rehydration systems must be designed to accommodate expected environmental conditions such as temperature, relative humidity, and nature of the product.     

Response surface optimisation of osmotic dehydration of Chinese ginger (Zingiber officinale Roscoe) slices

Response surface methodology (RSM) of Box–Behnken design with 27 experimental runs and the desirability function method were used in the osmotic dehydration process of Chinese ginger (Zingiber officinale Roscoe) slices in ternary solution of water, sucrose and sodium chloride for maximising water loss (WL), rehydration ratio (RR) and total phenolic content (TPC) and minimising solute gain (SG) and hunter colour change (HCC) of dehydrated product. The results indicated that the optimum operating conditions were found to be process duration of 102 min, solution temperature of 30 °C, solution concentration of 50 Brix sucrose + 7.31% sodium chloride and solution to food ratio of 8:1 (w/w). Under this condition, the WL, SG and TPC were 58.8% (wb), 12.56% (wb) and 1.46% (db), while its RR and HCC were 1.59 and 6.55, respectively. The immersion time was the most significant variable for WL, HCC, SG and RR, and for TPC it was temperature (P < 0.05).     

Influence of Drying Temperature and Rehydration on Selected Textural Properties of Carrots

Cubes of carrots dried at 60, 70, 80, and 90°C were rehydrated up to 180 min at 20°C and up to 10 min at 95°C. Kinetics of cutting strength were determined for the samples soaked at 95°C. Compression stress relaxation behavior of the samples was studied on carrots rehydrated at 20 and 95°C. Kinetics of cutting strength were satisfactorily described by means of a first-order kinetic model. The compression stress relaxation of carrots was analyzed using five element Maxwell and empirical Peleg models. Both of the models were found to be appropriate for characterizing viscoelastic properties of dried and rehydrated carrot cubes. The results indicated that the use of low drying temperatures was suitable for preserving the quality attributes of carrots after rehydration, and drying air temperature of 60°C was chosen as the most appropriate for hot air processing of carrots.     

INFLUENCE OF PLATE TEMPERATURE AND MODE OF REHYDRATION ON TEXTURAL PARAMETERS OF PRECOOKED FREEZE-DRIED BEEF

The effects of various plate temperatures and rehydration procedures in texture of precooked freeze-dried beef, were evaluated. Frozen precooked commercial beef was freeze-dried at 20, 40, 60 and 80C during 24 h. The rehydration procedure involved two main variables: distilled water at room-temperature and at 80C, for 30 min. The texture profile analysis was performed with a TA-XT2 Texture Analyzer (SMS) for freeze-dried rehydrated samples and compared to frozen precooked beef. The results showed that with a same drying period, the 60C plate temperature and rehydrated in distilled water at room-temperature resulted in a better product texture, in regards to texture parameters hardness and chewiness.     

Optimisation of osmotic dehydration process of carrot cubes in mixtures of sucrose and sodium chloride solutions

In the optimisation of the osmotic dehydration process of the carrot cubes in mixtures of sucrose and sodium chloride by response surface methodology, using face-centred central composite design (CCF), it was shown that the independent process variables for osmotic dehydration process were osmotic solution concentrations (5–15% w/v sodium chloride in 50 °Brix sucrose syrup), temperature (35–55 °C) and process duration (120–240 min). Statistical analysis of results showed that the linear terms of all the process variables have a significant effect on all the responses. The optimum osmotic dehydration process conditions for maximum water loss, minimum solute gain, maximum retention of colour, and sensory score were: 50 °Brix + 15% w/v sodium chloride solution, 54.8 °C solution temperature and 120 min process duration.     

PRODUCTION OF A LOW-CHOLESTEROL SHRIMP USING SUPERCRITICAL EXTRACTION

A low‐cholesterol shrimp was produced using supercritical extraction. The processing sequence included freeze drying, cholesterol extraction and rehydration. The shrimp was freeze dried, kept under vacuum until an experimental central composite rotatory design was applied using Response Surface Analysis for the supercritical extraction process. Three variables at five levels each were tested during the experiment (pressure, volume and temperature). After the extraction procedure, various rehydration and cooking conditions were applied to obtain a processed product with characteristics similar to those of the natural shrimp. Two sensory analyses were performed: one which compared the attributes of fresh shrimp with those of the freeze‐dried and rehydrated products, and another one which compared the acceptability between fresh shrimp and low‐cholesterol shrimp after freeze drying, supercritical extraction and rehydration. Under the conditions of 310 bar, 1875 L of carbon dioxide and 37C, it was possible to obtain a low‐cholesterol shrimp with acceptable organoleptic properties.     

REHYDRATION OF FREEZE-DRIED STRAWBERRIES AT VARYING TEMPERATURES

Strawberries (var. Seascape), cut in halves or 5‐mm slices, were freeze‐dried at a heating plate temperature of 55C for 28 h. Freeze‐dried products were then rehydrated at 0, 20, 40 and 80C in distilled water. The progression of the rehydration coefficient (RC) was followed as a function of time (up to 25 min). Less than 2 min were necessary to fully rehydrate the slices and less than 5 min for half strawberries. The results showed that halved and sliced freeze‐dried strawberries had higher RCs when rehydrated at a temperature near 0C. A simple diffusive‐type equation was used to represent water uptake during rehydration. Effective diffusion coefficients were modeled as a function of temperature using an Arrhenius‐type relationship.     

辣椒渗透脱水处理及渗后热风干燥特性及品质分析

以脱水率、固形物获取率、脱水率与固形物获取率比值、有效水分扩散系数、活化能、VC保留率、辣度、复水比、复原率和感官评价为考察指标,通过渗透脱水实验、渗后热风干燥实验和复水实验,考察了辣椒的渗透脱水特性、渗后热风干燥特性、复水特性和品质。结果表明:随着渗透温度的升高或渗透液中食盐含量的增加,辣椒的脱水率和固形物获取率增大。对渗透后的辣椒样品进行热风干燥处理发现,热风温度是影响热风干燥的最主要因素,其次是风速。辣椒样品的有效水分扩散系数随着温度的升高而增大,在风速为1.8 m/s的条件下,直接热风干燥辣椒样品和渗后热风干燥辣椒样品的活化能分别为(53.25±1.08)k J/mol和(44.42±0.88)k J/mol。渗后热风干燥样品的有效水分扩散系数、VC保留率、辣度、复水比和复原率均高于直接热风干燥样品,渗后热风干燥样品的复水特性和品质更好。     

A RESPONSE SURFACE METHODOLOGY APPROACH to OPTIMIZE POTATO DEHYDRATION PROCESS

A process for the production of high quality dehydrated potato cubes by high temperature fluidized bed (HTFB) initial drying followed by tunnel drying was optimized by response surface methodology. Drying temperature (T), exposure time in HTFB drier (t) and concentration of biopolymers (C) as pretreatment were determined as the most important factors affecting rehydration ratio, puffing, nonenzymatic browning and water holding capacity in the finished product. Optimum conditions for 0.95 cm potato cubes were: T = 145°C; t = 10 min; C = 1.2% and blanching time (b) = 4.5 min. Values predicted by the surface response model for rehydration ratio, bulk density, nonenzymatic browning and expressible fluid at the optimum were 5.75, 0.156, 0.20 and 4.8%, respectively. These values were experimentally varified and very close agreement between experimental and predicted values were obtained.     

SORPTION ISOTHERM BEHAVIOR OF OSMOCONVECTIVELY DEHYDRATED CARROT CUBES

Carrot cubes, osmotically pretreated with aqueous sodium chloride (10%, w/v), sucrose syrup (55°Brix), and mixture of sucrose and sodium chloride (50°Brix + 10%, w/v), were convectively dehydrated at 65C temperature up to final moisture content of 4–5% (wet basis). To study their equilibrium moisture content (EMC) behavior, the dehydrated carrot cubes were stored at temperature ranging from 10 to 50C and relative humidity ranging from 15–95% using static desiccator technique. Five isotherm equations, viz, Chung–Pfost, modified Henderson, modified Halsey, modified Oswin and modified exponential were applied to examine the data. Among the applied models, modified Oswin model was best fit for control (untreated) and salt‐treated samples, modified Hesley model for sucrose‐treated samples and two‐term exponential model for mixture of sucrose–salt treatment over the entire range of relative humidity and temperature. The EMC values of cubes osmotically pretreated with sodium chloride solution were highest among all pretreatments, and were lowest for control (unosmosed) samples.     

Effect of osmotic pretreatment on equilibrium moisture content of dehydrated carrot cubes

The equilibrium moisture contents were determined for carrot cubes osmotically pretreated in salt, sucrose and salt plus sucrose combined solution using static method at 10, 25, 40 and 50 °C over a range of relative humidities from 14% to 95%. Six isotherm equations were applied for analysing the experimental data. Modified exponential equation, is the best equation for predicting the equilibrium moisture contents (EMC) of the dehydrated carrot cubes preosmosed in salt and sucrose plus salt solution, whereas modified Hasley equation is suitable for dehydrated carrot cubes preosmosed in sucrose solution over the relative humidity range of 14–95%. The EMC of carrot cubes osmotically pretreated with salt was highest among all pretreatments, and was lowest for un‐osmosed samples.     

毛肚涨发工艺优化及其水分分布和组织结构变化研究

为更安全有效地使盐渍毛肚复水涨发,本实验研究了碳酸钠涨发毛肚的工艺条件。采用单因素和响应面试验,对碳酸钠浓度、碳酸钠处理时间、温度进行优化。以增重率和破碎力为响应值,确定碳酸钠涨发毛肚的最优工艺条件。结果表明,毛肚的最优工艺条件为碳酸钠浓度1.03%(w/v),碳酸钠处理时间2.3 h,温度43℃,此时毛肚的增重率达185.25%±3.61%,破碎力为2333.31±99.12 g,脆度高,感官评价良好。碳酸钠处理后毛肚不易流动水和自由水含量明显增加,肌纤维断裂、肌细胞膨润饱满。本研究表明该碳酸钠涨发盐渍毛肚工艺可靠,增重率高,嫩化效果好。     

Structural and physical properties of dried Anaheim chilli peppers modified by low‐temperature blanching

The effect of low‐temperature blanching and drying processes on the ultrastructural and physical properties of Anaheim chilli pepper was studied and optimum conditions to provide a final product with maximum firmness were determined. Lots of Anaheim pepper were blanched in water for 4 min at 48, 55, 65, 75 and 82 °C and maintained for hold times of 35, 45, 60, 75 and 85 min, blanched again for 4 min at 96 °C and dehydrated at 53, 60, 70, 80 and 87 °C. After treatment the samples were rehydrated in water at 30 °C. Rehydration ratio, texture and structural changes were evaluated. Optimisation used a second‐order rotatable central composite design. Texture and rehydration ratio were affected by blanching temperature and the interaction of blanching temperature with hold time (p ≤ 0.05); drying temperature did not show a significant effect. The best results, ie those which gave greatest firmness, were obtained by blanching at 64 °C for 4 min, holding for 55 min after blanching, followed by a second blanching at 96 °C for 4 min and then drying at 70 °C. Evaluation of the rehydrated dried pepper by microscopy showed that low‐temperature blanching close to the optimum conditions provided a protective effect in maintaining cell wall integrity. The results of processing increased firmness in the rehydrated product by a factor of 1.97. Copyright © 2003 Society of Chemical Industry     

Mass transfer kinetics during osmotic dehydration of pomegranate arils

The mass transfer kinetics during osmotic dehydration of pomegranate arils in osmotic solution of sucrose was studied to increase palatability and shelf life of arils. The freezing of the whole pomegranate at -18 °C was carried out prior to osmotic dehydration to increase the permeability of the outer cellular layer of the arils. The osmotic solution concentrations used were 40, 50, 60°Bx, osmotic solution temperatures were 35, 45, 55 °C. The fruit to solution ratio was kept 1:4 (w/w) during all the experiments and the process duration varied from 0 to 240 min. Azuara model and Peleg model were the best fitted as compared to other models for water loss and solute gain of pomegranate arils, respectively. Generalized Exponential Model had an excellent fit for water loss ratio and solute gain ratio of pomegranate arils. Effective moisture diffusivity of water as well as solute was estimated using the analytical solution of Fick's law of diffusion. For above conditions of osmotic dehydration, average effective diffusivity of water loss and solute gain varied from 2.718 × 10(-10) to 5.124 × 10(-10) m(2)/s and 1.471 × 10(-10) to 5.147 × 10(-10) m(2)/s, respectively. The final product was successfully utilized in some nutritional formulations such as ice cream and bakery products.