Carrot Cubes Research Articles

Air drying characteristics and moisture diffusivity of carrots

The effects of air temperature on drying kinetics of carrot cubes were investigated. Convective drying characteristics of carrot cubes in a spout-fluidized bed were evaluated through the effect of air temperature on drying kinetics. Drying was carried out at 60, 70, 80 and 90 °C and the falling drying rate data were used to calculate the effective diffusion coefficients from the Fick's equation. Four mathematical models available in the literature were fitted to the experimental data. The Two-term model is given better prediction than the Henderson and Pabis, Page and Lewis model and satisfactorily described drying characteristics of carrot cubes. Two different models were applied to describe moisture diffusivity in carrots. Both consider the changes in temperature and moisture content of carrots during drying as well as account for or neglect the material shrinkage which was the parameter diversifying the models. It was confirmed that shrinkage should be accounted for to attain reliable values of effective moisture diffusivity in carrots. It was observed that if shrinkage phenomena are not taken into consideration during modeling of drying kinetics, then the effective moisture diffusivity in carrots is underestimated at the initial phase of drying and is overestimated at the final drying phase.

AIR IMPINGEMENT DRYING CHARACTERISTICS AND QUALITY OF CARROT CUBES

ABSTRACT The effects of air temperature (40, 50 and 60C), air velocity (3.0, 8.0 and 13.0 m/s) and air relative humidity (10, 20 and 40%) on air impingement drying characteristics of carrot cubes and the quality of dried carrots were investigated. The drying experiments were carried out according to orthogonal design method on the air impingement dryer. Results indicated that drying time of carrot cubes was more affected by drying air temperature, followed by air relative humidity and air velocity. The moisture effective diffusivity calculated from the second Fick's law of diffusion ranged from 0.265 × 10−9to 1.052 × 10−9 m2/s. The activation energy determined from the slope of the Arrhenius plot, ln(Deff) versus 1/(T + 273.15), was 20.17 kJ/mol. The color values L (white/dark), a (red/green) and b (yellow/blue) of the samples decreased from 50.02 to 32.71, 32.49 to 14.34 and 35.52 to 16.38 separately when the drying temperature increased from 40 to 60C. Rehydration experiments demonstrated that the rehydration ratio of dried carrot cubes was significantly affected by drying air temperature and air relative humidity. The surface microstructures of dried carrot cubes were observed using a scanning electron microscope, which showed that the outer layers of the samples dried at 60C drying temperature and 10% air relative humidity had more consolidated rigid and denser structure than the samples dried at 40C drying temperature and 40% air relative humidity.PRACTICAL APPLICATIONSAir impingement drying is used for food and agricultural product processing. But, it is a complicated process. Many factors such as drying temperature, air velocity and relative humidity can influence its drying characteristics and quality. Carrot is a typical vegetable, which is sensitive to microbial spoilage and deterioration reactions. Using drying technology can prolong its shelf life. Investigating air impingement drying characteristics and quality of carrots can help to understand its drying process and the effect of drying parameters on drying quality. This research was done to provide enough information to build a commercial impingement drying system.

Influence of the Applied Acoustic Energy on the Drying of Carrots and Lemon Peel

The application of power ultrasound could constitute a way of improving traditional convective drying systems. The different effects produced by the application of power ultrasound may influence the drying rate without provoking any significant increase in product temperature. Due to the fact that the effect of power ultrasound is product dependent, the aim of this work was to address the influence of the applied acoustic energy on the convective drying of carrot and lemon peel. Convective drying kinetics of carrot cubes (side 8.5 mm) and lemon peel slabs (thickness 7 mm) were carried out at 40°C and 1 m/s by applying different levels of acoustic power density: 0, 4, 8, 12, 16, 21, 25, 29, 33, and 37 (kW/m3). The application of power ultrasound during drying was carried out using an airborne ultrasonic transducer (21.7 kHz). Drying kinetics were described considering a diffusion model. In both products, the application of power ultrasound improved the effective moisture diffusivity (De ). The improvement was linearly proportional to the applied acoustic power density. In the case of lemon peel, the effects of power ultrasound were found over all the range tested (0–37 kW/m3), whereas in the case of carrot, it was necessary to apply an acoustic power density of over 8–12 kW/m3 to be able to observe the influence. The more intense effect of acoustic energy in lemon peel drying may be explained by the fact that lemon peel is a more porous product than carrot.

Value addition to spent osmotic sugar solution (SOS) by enzymatic conversion to fructooligosaccharides (FOS), a low calorie prebiotic

Abstract Value addition of spent osmotic sugar solution (SOS) obtained after the osmotic dehydration of carrot cubes using 60 °Bx sucrose solution has been studied. Two sets of experiments, one with the use of fresh carrots in every cycle of osmotic dehydration (3 h) and in the other set, carrots of previous cycle were reused in successive cycles, were carried out. The SOS obtained in each cycle was concentrated to 60 °Bx and used in successive cycles. FOS was produced from SOS (with or without concentration) by transfructosylation reaction of fructosyl transferase enzyme produced by Aspergillus oryzae MTCC 5154 under submerged fermentation condition. An FOS yield of 50.63 ± 0.94 to 57.86 ± 0.18% was obtained in both cases, which is comparable with the literature reports. FOS produced from SOS gets enriched with leached out bioactive components of fruits and vegetables used. The β-carotene concentration was in the range of 1300.9 ± 25.1 to 2800 ± 68.3 µg/100 ml of FOS. The colour of the FOS produced was golden brown and was much more appealing than FOS produced from sucrose. Industrial relevance The implementation of osmotic treatment of fruits and vegetables using concentrated sugar solution presents a critical factor due to the management of spent osmotic solutions. Disposal of spent osmotic solution has severe economical, environmental and technological implications. The possibilities of reuse of SOS have been suggested. The present investigation offers a better alternative for the use of SOS for developing a technologically viable process for the production of FOS. The resulting FOS is a highly valued low calorie, non-cariogenic prebiotic with high market demand in neutraceutical food sector.

Osmotic dehydration kinetics of carrot cubes in sodium chloride solution

SummaryOsmotic 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.

Combined effects of heat, nisin and acidification on the inactivation of Clostridium sporogenes spores in carrot-alginate particles: From kinetics to process validation

Combined effects of mild temperatures, acidification and nisin on the thermal resistance of Clostridium sporogenes ATCC 11437 spores were assessed. Inoculated carrot-alginate particles were used as a solid-food model for the validation of the spore inactivation during the flow of a solid–liquid food system through the holding tube of an aseptic processing unit. Inactivation kinetics was studied in a water bath with the spores inoculated into carrot-alginate particles and in Sorensen's phosphate buffer. For temperatures of 70–90 °C, D-values in the buffer were 24.9–5.7 min, much lower than those evaluated for the particles (115.1–22.2 min). Statistical analyses showed significant synergistic effects of temperature and pH on spore inactivation for both media. Acidification reduced the heat resistance of the spores by reducing the D-values. Nisin was not significantly effective at the lower concentrations (up to 750 IU/g). The combination of 90 °C, pH: 4.5 and 500 IU/g nisin resulted in a ten-fold decrease of the D-value for spores inoculated in the particles (from 111.1 to 10.6 min). Microbial validation tests were conducted using a pilot-scale aseptic processing unit with a mixture of carrot cubes (10%) and carrier liquid of 2%-carboxymethylcellulose solution (90%). Spore-inoculated carrot-alginate particles (initial counts of 106 CFU/g, obtained after come-up-time pre-heat) with pH 3.5 and 2000 IU/g nisin were processed at 90 °C in the aseptic processing unit. Microbial analysis showed no spore survivors in the particles after passing through the holding tube (5.2–6.0 min of residence time). The proposed combination of these hurdles significantly enhanced the spore inactivation rate ( D 90=1.17 min) as compared to that for thermal treatment only ( D 90=19.6 min).

Heat and mass transfer during drying of a bed of shrinking particles – Simulation for carrot cubes dried in a spout-fluidized-bed drier

The purpose of the present study was to develop a model to describe the heat and mass transfer during the drying of carrot cubes in a spout-fluidized-bed drier. The model took into account the non-homogeneous shrinkage of the material. The Arbitrary Lagrange–Eulerian (ALE) formulation was applied to enter the problem with moving boundaries. Three phases of drying were distinguished according to the behavior of changes in percent local error of estimation: an initial phase of warming up the material – characterized by a low level of error of moisture content prediction, a second phase – characterized by an increase in the error of moisture content prediction and a phase of decreasing error. A simple test of the sensitivity of the model to the changes in heat transfer coefficient was performed in order to improve the ability of the model to predict the changes in moisture content and temperature of dried carrots. The predicted changes in both the moisture content and the temperature of carrot cubes during drying in a spout-fluidized-bed drier indicate that the model can be successfully applied to describe moisture content, temperature and deformation of dried particles in cases when the very high accuracy of moisture content and temperature prediction is not a crucial element of investigation of the drying process.

Optimization of Osmotic Dehydration Process of Carrot Cubes in Sodium Chloride Solution

For optimization of osmotic dehydration process of carrot cubes in sodium chloride solution by response surface methodology, the experiments were conducted according to Face-Centered Central Composite Design (CCF). The independent process variables for osmotic dehydration process were osmotic solution concentrations (5 -15% w/v sodium chloride), temperature (30 -50°C) and process durations (90 -150 minutes). The osmotic dehydration process was optimized for maximum water loss, minimum solute gain, maximum retention of colour and sensory score. The optimum conditions were 7.9 % sodium chloride concentration; 30°C osmotic solution temperature and 150 minutes process duration.

Drying of a Low Porosity Product (Carrot) as Affected by Power Ultrasound

The main aim of this work was to assess the influence of power ultrasound on mass transfer process during convective drying of a low porosity product submitted to different acoustic energy levels. Drying kinetics of carrot cubes (side 8.5 mm) were carried out at 40 °C and 1 m/s applying different electric power levels to the ultrasonic transducer: 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90 W. Drying kinetics were modelled considering the diffusion theory. From the results, a significant (p<0.05) influence of power ultrasound application on drying kinetics of carrot cubes was found. Drying rate increased as the electric power applied got higher. The influence was only observed above an acoustic energy threshold, which corresponded to an electric power applied to the transducer of 20-30 W. From this threshold, a linear relationship was found between the average effective moisture diffusivity or the mass transfer coefficient and the electric power applied to the transducer.

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

SummaryThe 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.

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 APPLICATIONSThe 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.

Drying curve modelling of blanched carrot cubes under natural convection condition

Carrot cubes were submitted to combined treatments of blanching and drying. Blanching was alternatively performed 3 min in boiling 5% brine solution, 3 min in boiling water or 6 min in boiling water. It was observed that the applied pre-treatments influence on the kinetics of drying. The mathematical model describing the course of drying curve of single blanched carrot cubes (not touching each other) under natural convection condition was formulated on the basis of the general theory of heat and mass transfer laws. The course of the drying curve was described in two ways: (i) using the linear model of the first drying period (without shrinkage) and then using the model of second drying period; and (ii) applying the model of first drying period taking into account shrinkage and followed by the model of second drying period. The second drying period was described in both cases by the same model which approximated the shape of dried particle to the cube. It turns out from the verification that the values of relative error (RE) were not higher than: 1% for linear model, 20% for model with shrinkage, 40% for model of cube drying. The correlation between the data obtained from mathematical models and empirical data was high (the lowest correlation coefficient amounted to 0.96). Proposed mathematical model can be accepted. The results obtained from the experiments and from mathematical modelling suggest that drying of carrot cubes occurs in the first and the second drying period.

Drying Behavior of Carrots Dried in a Spout–Fluidized Bed Dryer

The effect of water blanching treatment and the inlet air temperature on drying kinetics as well as the quality attributes of carrot cubes dried in a spout–fluidized bed dryer at 60, 70, 80, and 90°C were analyzed. The material shrinkage and the rehydration potential were calculated to assess the changes in quality of dried carrots. It was found that the value of the air velocity during the drying of carrot cubes in a spout–fluidized bed dryer should be related to the moisture content of the carrot particles. A high value of air velocity at the beginning of the drying cycle and a lower value for the later stages were also required. The linear equation was correlated to the data of shrinkage of raw and blanched carrots. Blanching significantly influenced the coefficients in the shrinkage model derived for drying of carrot cubes in a spout–fluidized bed dryer, while drying temperature did not influence the shrinkage of carrot particles. The intensity of heat and mass transfer during spout–fluidized drying of carrot cubes was dependent on the drying temperature. A correlation was developed to calculate the values of effective moisture diffusivity of dried carrot cubes as a function of the moisture content and temperature of the material. It was observed that for any given time of rehydration, both the moisture content and the rehydration ratio calculated for samples dried at 60°C were higher than for samples dried at temperatures of 60, 70, 80, and 90°C.

APPLICATION OF RESPONSE SURFACE METHODOLOGY FOR THE OSMOTIC DEHYDRATION OF CARROTS

ABSTRACT Osmotic dehydrations of carrot cubes in sodium chloride salt solutions at different solution concentrations, temperatures and process durations were analyzed for water loss and solute gain. The osmotically pretreated carrot cubes were further dehydrated in a cabinet dryer at 65C and were then rehydrated in water at ambient temperature for 8–10 h and analyzed for rehydration ratio, color and overall acceptability of the rehydrated product. The process was optimized for maximum water loss, rehydration ratio and overall acceptability of rehydrated product, and for minimum solute gain and shrinkage of rehydrated product by response surface methodology. The optimum conditions of various process parameters were 11% salt concentration, 30C osmotic solution temperature and process duration of 120 min.

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 Air Temperature on Convective Drying Assisted by High Power Ultrasound

Drying kinetics of carrot cubes were carried out at 1 m/s air velocity at different air drying temperatures (30, 40, 50, 60 and 70±0.1 °C) (AIR experiments), and also at the same experimental conditions but applying high power ultrasound (US experiments). Two kind of diffusion models were used to simulate the drying kinetics, according to external resistance to mass transfer being considered (ER model) or neglected (NER model) for solving the diffusion equation. Diffusion ER model was solved using a finite difference method. Drying rate increased as air temperature was higher. Ultrasound also increased drying rate at the different temperatures, but the improvement on drying rate decreased at high temperatures, and almost disappeared at 70 °C. Effective moisture diffusivities only showed an Arrhenius type relationship with temperature for AIR experiments. The NER diffusion model was not accurate to simulate the drying kinetics at any experimental conditions tested. However, diffusion ER model provided a high closeness between experimental and calculated drying data (VAR>99.80). Through the parameters identified of the ER diffusion model, effective moisture diffusivity and mass transfer coefficient, the influence of the power ultrasound application on internal and external resistance to mass transfer was shown to be significant (p<0.05).

A mathematical model for low-pressure superheated steam drying of a biomaterial

Low-pressure superheated steam drying (LPSSD) has recently received much attention as an alternative drying technique for heat-sensitive biomaterials. Although there are a number of works that report studies of this drying technique experimentally, there are a very limited number of works that report attempts to model this drying process. The aim of the present study was therefore to propose the use of a simple three-dimensional liquid diffusion based model to predict the evolutions of the moisture content and temperature of a product undergoing LPSSD. The effect of the product shrinkage was also included directly in the model and the effect of this inclusion on the predictability of the model is shown. The model was found to be able to predict the heat and mass transfer behavior as well as the change of a selected chemical quality, i.e., β-carotene, of a model biomaterial viz., carrot cube reasonably well over some range of moisture content if accurate values of the heat transfer coefficient were used.

Instrumental Textural Characteristics of Restructured Carrot Cubes

Studies were carried out on the instrumental textural evaluation of restructured carrot cubes. The experiment was conducted by incorporating different levels of alginate, glucono delta lactone (GDL), and calcium salt to the carrot pulp. Investigations showed that as pulp level increased from 0 to 90%, there was a corresponding decrease in failure stress, failure strain, and deformability modulus. Instrumental textural profile analysis (TPA) parameters viz. hardness, springiness, gumminess, cohesiveness, chewiness, and resilience also showed a similar trend. Effect of formulation variables, i.e., alginate, GDL, and calcium salt on hardness (response variable) were evaluated by the application of response surface methodology. All the three ingredients showed a significant (P < 0.05) influence on hardness of carrot gel. Heat treatment of restructured carrot samples resulted in an increased hardness, cohesiveness, gumminess, and chewiness while springiness, cohesiveness, and resilience decreased. The data indicated that the shrinkage during thermal treatment may be responsible for the change in textural attributes. The authors concluded that a thermally stable restructured product with appreciable textural integrity can be obtained from carrot pulp.

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.

Ultrasonic drying of foodstuff in a fluidized bed: Parametric study

The application of high power ultrasound for dehydration of porous materials may be very effective in processes in which heat-sensitive materials such as foodstuffs have to be treated. In fact, high-intensity ultrasonic vibrations are capable of increasing heat and mass transfer processes in materials. The application of ultrasonic energy can be made alone or in combination with other kind of energy such as hot-air. In this case, ultrasound helps in reducing temperature or treatment time. The aim of this work is to study the effect of air flow rate, ultrasonic power and mass loading on hot-air drying assisted by a new power ultrasonic system. The drying chamber is an aluminium vibrating cylinder, which is able to create a high intensity ultrasonic field in the gas medium. To that purpose the chamber is driven at its centre by a power ultrasonic vibrator at 21.8 kHz. Drying kinetics of carrot cubes and lemon peel cylinders were carried out at 40 °C for different air velocities, with and without ultrasound. The results show that the effect of ultrasound on drying rate is affected by air flow rate, ultrasonic power and mass loading. In fact, at high air velocities the acoustic field inside the chamber is disturbed and the effect of ultrasound on drying kinetics diminishes.