Microwave heat treatment of leek: drying kinetic and effective moisture diffusivity

The effect of microwave drying technique on moisture ratio, drying time and effective moisture diffusivity of white and green parts of leek ( Allium porrum ) were investigated. By increasing the sample amount (100–300 g) at constant microwave output power of 180 W, the drying time increased from 52 to 130 min and increased from 55 to 135 min for white and green parts of leek, respectively. Effective moisture diffusivity values for white and green parts of leek ranged from 0.618 × 10⁻¹⁰ to 2.128 × 10⁻¹⁰ m².s⁻¹ and 0.256 × 10⁻¹⁰ to 0.611 × 10⁻¹⁰ m² s⁻¹, respectively. Among the models proposed, Midilli et al. model gave a better fit for all drying conditions applied. The activation energy for microwave drying of white and green parts of leek was calculated using an exponential expression based on Arrhenius equation; found as 0.9530 and 1.2045 W g⁻¹, respectively. The dependence of drying rate constant on effective moisture diffusivity gave a linear relationship.     

DRYING KINETICS OF RED PEPPER

Desorption isotherms of unblanched and blanched red peppers were experimentally obtained at 30C. The desorption data were exploited to estimate equilibrium moisture contents of the peppers at drying temperatures other than 30C by using a semi-empirical method. Red pepper samples were dried in a tunnel-type drier with an air velocity of 2 m/s at 50C, 60C, 70C, and 80C. The blanched samples dried faster than the unblanched ones. The drying behavior of unblanched and blanched samples was characterized by falling rate period, and constant and falling rate drying periods, respectively. The interphase mass and heat transfer coefficients of the blanched sample during the constant rate period were not affected by temperature and estimated to be 1.94*10⁻³ kg mol/s. m² and 57.3 W/m². K, respectively. Effective moisture diffusivity was estimated between 6.83*10⁻¹⁰−17.4*10⁻¹⁰ m²/s for the unblanched sample and 11.4*10⁻¹⁰−31.0*10⁻¹⁰ m²/s for the blanched sample within the given temperature range. Effect of temperature on the diffusivity was described by an Arrhenius-type equation with an activation energy of 28.4 kJ/mol for the unblanched pepper and 33.3 kJ/mol for the blanched pepper.     

Convective hot air drying of blanched yam slices

In this study, a laboratory convective hot air dryer was used for the thin layer drying of blanched yam slices and experimental moisture ratio was compared with Newton, Logarithmic, Henderson and Pabis, modified Henderson and Pabis, approximation of diffusion, modified page 1, two-term exponential, Verma et al. and Wang and Singh models. Among all the models, the approximation of diffusion model was found to satisfactorily describe the kinetics of air-drying of blanched yam slices. The increase in air temperature significantly reduced the drying time with no constant rate period but drying occurs in falling rate period. The effective diffusivity values varied between 7.62 × 10⁻⁸ to 9.06 × 10⁻⁸ m² s⁻¹ and increased with increase in temperature. An Arrhenius relation with an activation energy value of 8.831 kJ mol⁻¹ showed the effect of temperature on moisture diffusivity.     

Osmotic Dehydration of Tomato in Sucrose Solutions: Fick's Law Classical Modeling

ABSTRACT:  Osmotic dehydration of tomato was modeled by the classical Fick's law including shrinkage, convective resistance at the interface and the presence of water bulk flow. Tomato slices having 8 mm thickness were osmotically dehydrated in sucrose solutions at 50, 60, and 70 °Brix and at 35, 45, and 55 °C. Other experiments were done in a 70 °Brix sucrose solution at 35 °C with tomato slices of 4, 6, and 8 mm thickness and at different motion levels (velocities 0, 0.053, and 0.107 m/s). Tomato weight, water content, and °Brix of the products were measured as a function of processing time (20, 40, 80, 160, and 320 min). Results showed that temperature, concentration, thickness, and solution movement significantly influenced water loss and sucrose gain during the osmotic dehydration of tomato. The model predicted the modifications of soluble solid content and water content as a function of time in close agreement with the experimental data. Experimental Sherwood number correlations for sucrose and water were determined as Sh _s = 1.3 Re ^0.5 Sc _s^0.15 and Sh _w = 0.11 Re ^0.5 Sc _w^0.5, respectively. The effective diffusion coefficients of water (4.97 10⁻¹¹– 2.10 10⁻¹⁰ m²/s) and sucrose (3.18 10⁻¹¹– 1.69 10⁻¹⁰ m²/s) depended only on temperature through an Arrhenius-type relationship.     

APPLICATION OF CORRELATION BETWEEN BIOT AND DINCER NUMBERS FOR DETERMINING MOISTURE TRANSFER PARAMETERS DURING THE AIR DRYING OF COROBA SLICES

The moisture mass transfer parameters characterizing the air drying of coroba slices were determined using the correlation between Biot and Dincet numbers. The air drying was carried out at temperatures of 71, 82 and 93C and velocities of 0.82, 1.00 and 1.18 m/s. Experimental moisture content data for coroba slices were collected. The drying coefficient and lag factor were calculated from the experimental data and were incorporated into the correlation. The moisture diffusion coefficient, Biot number and mass transfer coefficient ranged between 1.147  ×  10 ^{− 12} –3.740  ×  10 ^{− 12}  m²/s, 0.097–0.114 and 0.903  ×  10 ^{− 4} –1.729  ×  10 ^{− 4}  m/s, respectively. The predicted dimensionless moisture content profiles showed adequate agreement with the experimental observations, with the mean relative error between 0.98 and 4.61%.

PRACTICAL APPLICATION

As drying is an energy-intensive operation, it has become the prime concern of the researchers to optimize process conditions that lead to energy savings. Moisture transfer parameters are important transport properties needed for accurate modeling in food drying applications. Therefore, accurate determination of these parameters for the drying operation is essential. There is a large amount of studies available in the literature to determine and calculate these parameters for the products subjected to drying. But limited studies have been carried out to determine these parameters using the drying process parameters in terms of lag factor and drying coefficient as first introduced by Dincer and Dost.     

The increase of CO2 permeability of paper packaging with increasing hydration

CO₂ transport through hydrated paper was studied using gas chromatography to measure CO₂ permeability (P) and diffusivity (D). With increasing water content from 0 to 0.8 g water/g paper, P and D increased from 3.47 to 9.03 × 10⁻⁶ m³ m⁻² s⁻¹ bar⁻¹ and from 1.35 to 3.51 × 10⁻⁵ m² s⁻¹, respectively. This resulted from structural changes in the cellulose network as reported in the literature; water sorption isotherms were used to explain these changes using BET theory.     

Alginate- and gellan-based edible films for probiotic coatings on fresh-cut fruits

ABSTRACT:  Alginate- (2% w/v) or gellan-based (0.5%) edible films, containing glycerol (0.6% to 2.0%), N-acetylcysteine (1%), and/or ascorbic acid (1%) and citric acid (1%), were formulated and used to coat fresh-cut apple and papaya cylinders. Water vapor permeability (WVP) was significantly higher ( P < 0.05) in alginate films (0.30 to 0.31 × 10⁻⁹g m/Pa s m²) than in the gellan ones (0.26 to 0.27 × 10⁻⁹g m/Pa s m²). Addition of 0.025% (w/v) sunflower oil decreased WVP of gellan films (0.20 to 0.22 × 10⁻⁹ g m/Pa s m²). Water solubility of gellan and alginate films at 25 °C (0.47 to 0.59 and 0.74 to 0.79, respectively) and their swelling ratios (2.3 to 2.6 and 1.6 to 2.0, respectively) indicate their potential for coating high moisture fresh-cut fruits. Fresh-cut apple and papaya cylinders were successfully coated with 2% (w/v) alginate or gellan film-forming solutions containing viable bifidobacteria. WVP in alginate (6.31 and 5.52 × 10⁻⁹g m/Pa s m²) or gellan (3.65 and 4.89 × 10⁻⁹ g m/Pa s m²) probiotic coatings of papaya and apple, respectively, were higher than in the corresponding cast films. The gellan coatings and films exhibited better water vapor properties in comparison with the alginate coatings. Values > 10⁶ CFU/g B. lactis Bb -12 were maintained for 10 d during refrigerated storage of fresh-cut fruits, demonstrating the feasibility of alginate- and gellan-based edible coatings to carry and support viable probiotics on fresh-cut fruit.     

Drying of carrot slices using infrared radiation

Carrot slices were dried from initial moisture content of 8.52 kg water kg⁻¹ dry matter to 0.11 kg water kg⁻¹ dry matter by infrared dryer. Experiments were conducted using three levels of infrared power (300, 400 and 500 W) and at air velocities (1.0, 1.5 and 2.0 m s⁻¹). The effects of process variables on the drying kinetics of carrot, drying time, specific energy consumption and quality parameters of dried carrot (shrinkage, rehydration ratio and colour) were investigated. The drying time at infrared power of 300, 400 and 500 W was 252 and 277 min, 205 and 236 min, and 145 and 155 min at air velocities of 1.0 and 2.0 m s⁻¹, respectively. The drying rate increased with increasing infrared power. The specific energy consumption values varied between 12.22 and 14.58 MJ kg⁻¹-evaporated water for all the drying conditions. Shrinkage, rehydration ratio and colour parameters were found to be affected by process variables.     

Inverse Method to Estimate Kinetic Degradation Parameters of Grape Anthocyanins in Wheat Flour Under Simultaneously Changing Temperature and Moisture

ABSTRACT:  Thermal and moisture effects on grape anthocyanin degradation were investigated using solid media to simulate processing at temperatures above 100 °C. Grape pomace (anthocyanin source) mixed with wheat pastry flour (1: 3, w/w dry basis) was used in both isothermal and nonisothermal experiments by heating the same mixture at 43% (db) initial moisture in steel cells in an oil bath at 80, 105, and 145 °C. To determine the effect of moisture on anthocyanin degradation, the grape pomace–wheat flour mixture was heated isothermally at 80 °C at constant moisture contents of 10%, 20%, and 43% (db). Anthocyanin degradation followed a pseudo first-order reaction with moisture. Anthocyanins degraded more rapidly with increasing temperature and moisture. The effects of temperature and moisture on the rate constant were modeled according to the Arrhenius and an exponential relationship, respectively. The nonisothermal reaction rate constant and activation energy (mean ± standard error) were k _{80 °C, 43% (db) moisture} = 2.81 × 10⁻⁴± 1.1 × 10⁻⁶ s⁻¹ and Δ E  = 75273 ± 197 J/g mol, respectively. The moisture parameter for the exponential model was 4.28 (dry basis moisture content)⁻¹. One possible application of this study is as a tool to predict the loss of anthocyanins in nutraceutical products containing grape pomace. For example, if the process temperature history and moisture history in an extruded snack fortified with grape pomace is known, the percentage anthocyanin loss can be predicted.     

A mathematical model to describe the change in moisture distribution in maize starch during hydrothermal treatment

Instantaneous Controlled Pressure Drop, ' Détente Instantanée Contrôlée ' (DIC) was performed on standard maize starch at residual moisture content (∼12%). Changes in moisture distribution were observed during the treatment and modelled through a phenomenological model based on gravimetric data. The model proposes an exponential variation in the moisture content with processing time at various pressures. The predicted data were found to be in good agreement with experimental data. The values of water activity coefficient ( γ ) obtained from the model decrease, when processing pressure increases; 5.86, 3.71 and 3.36 (dry basis)⁻¹ for 1, 2 and 3 bar, respectively. The mass transfer coefficient decreases, when the pressure increases. Its value ranged from 5.89 × 10⁻⁵ m s⁻¹ for 1 bar down to 0.92 × 10⁻⁵ m s⁻¹ for 2 bar and 0.77 × 10⁻⁵ m s⁻¹ for 3 bar. This coefficient is not only controlled by a simple resistance to the mass transfer, but also by gelatinisation phenomenon that progresses when temperature increases.     

Whey Protein Film Composition Effects on Potassium Sorbate and Natamycin Diffusion

ABSTRACT: To assess the ability of whey protein films to act as antimicrobial carriers, the effect of film composition on preservative diffusion was investigated. Preservative diffusion coefficients were measured at 24°C in whey protein isolate (WPI) films with different WPI-glycerol plasticizer ratios (1:1 to 15:1), beeswax (BW) content, 0% to 40% w/w dry solids, and preservative addition of 0.3% (w/w) natamycin or 1.6% (w/w dry solids) potassium sorbate. Diffusion coefficients for potassium sorbate and natamycin were in the ranges 1.09 × 10⁻¹¹ to 13.0 × 10⁻¹¹ m²/s and 6.16 × 10⁻¹⁴ to 37.8 × 10⁻¹⁴ m²/s, respectively, and significantly decreased as the WPI-glycerol ratio increased. No significant difference in sorbate diffusion was seen with the addition of BW.     

Desulfiting Dried Apricots by Hydrogen Peroxide

ABSTRACT: Removal of sulfites from excessively sulfited dried apricots using hydrogen peroxide (H₂O₂) was studied. Dried apricots were dipped into 0.5, 1.0, and 1.5% H₂O₂ solutions at 20 °C and 40 °C for various times. At 60 °C, apricots were also treated with 1% H₂O₂ solution. Removal of sulfites by H₂O₂ followed a 1st-order kinetic model. At 20 °C to 60 °C and 1% H₂O₂ concentration, the E_a value was 22.46 kJ mol⁻¹. H₂O₂ treatment caused lighter, more yellow, and less red dried apricots. Critical factors for H₂O₂ application are choosing the appropriate H₂O₂ concentration, temperature, and exposure time and without bleaching the natural color of dried apricots.     

Drying Kinetics of Curcuma longa Rhizomes

ABSTRACT: Modeling drying kinetics is very useful for optimization purposes. Hot air drying kinetics were carried out in monolayer at different temperatures (60°C, 70°C, 80°C, 90°C, and 100°C) and for different sample types (peeled and unpeeled rhizomes of different sizes). Mathematical models based on Fick's law were used to describe water removal, considering different boundary conditions and geometries. Effective moisture diffusivities identified from modeling presented an Arrhenius-type relationship. An additional mass transfer resistance was identified as due mainly to the peridermis layer (peridermial resistance). The accuracy of the model assuming peridermial resistance only in the radial direction and solved using the finite differences method was illustrated, and the mass transfer coefficient was identified (k = 9.7 × 10^-5 kg water/m²/s). Keywords: Curcuma longa , drying, modeling, peridermial resistance     

CHANGES IN SIZE OF GAS CELLS IN DOUGH AND BREAD DURING BREADMAKING AND CALCULATION OF CRITICAL SIZE OF GAS CELLS THAT EXPAND

Microscopic observation showed that a group of small air cells entrained during the early stage of mixing is the original cause of cell structure of bread. At the beginning of fermentation, about 3 × 10⁸/m² gas cells with diameters between 3 × 10⁻⁶ and 8 × 10⁻⁴ m were entrained in the dough. The distribution curve of cell size was approximately normal on a logarithmic scale. During fermentation and proofing, a great portion of carbon dioxide was released into cells larger than about 10⁻⁴ m in diameter that was equivalent to a few percentages of total number of gas cells. After baking, gas cells smaller than 10⁻⁴ m in diameter were not observed and the total number of cells in baked bread reduced to about 10⁶/m² with diameters between 10⁻⁴ and about 5 × 10⁻³ m. The critical cell size to expand generally agreed with the calculated value using an equation, rc'= 3s/E (re': critical radius to expand, s: surface tension, E: elasticity), and cited value of s and E.     

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.     

BULK THERMAL CONDUCTIVITY AND DIFFUSIVITY OF SOYBEAN

Bulk thermal conductivity of soybean, determined by the transient heat flow method, exhibited positive linear correlation with moisture content. The bulk thermal conductivity values increased from 0.1157 to 0.1756 W/m-K in the moisture range of 8.1 to 25% d.b. Further, thermal diffusivity of soybean, computed from the values of thermal conductivity, specific heat and bulk density showed linear increase from 2.94 × 10⁻⁴ to 3.07 × 10⁻⁴ m²/h in the specified range of 8.1 to 25% d.b. moisture content.     

THIXOTROPY OF ORANGE CONCENTRATE AND QUINCE PUREE

Orange juice with pulp and pectins is thixotropic at soluble solids concentrations of 55 and 60 Brix in the range of temperatures from 0 to 20C and shear rate from 7.2 to 57.6 s⁻¹. Quince purée is thixotropic at soluble solids concentrations of 12.3 to 28 °Brix in the range of temperatures between 0 to 20C and shear rate from 7.2 to 57.6 s⁻¹. The thixotropic behaviour of orange juice and quince purée increases with increasing concentration and decreasing temperature and they can be described by the kinetic model proposed by Figoni and Shoemaker (1983):

The thixotropic structure of orange juice was destroyed by applying a shear rate of 57.6 s⁻¹ for 5 min, and for quince purée for 10 min. Quince purée shows a greater thixotropic character than orange juice, because it has a higher content of fiber, pulp and pectins and also because it shows a microscopic structure consisting of long particles and heterogeneous fibers.     

Effective water diffusivity in deep-fat fried restructured potato product

Water diffusivity was determined for a restructured potato product undergoing deep-fat frying. Pre-fried product gel-strength, expressed by its deformability modulus, varied from 37 to 127 kPa and markedly affected the effective diffusion coefficients, ranging from 3.31 to 1.58 × 10⁻⁹ m² s⁻¹, respectively. Pre- and post-fried effective water diffusivity decreased with higher deformability modulus. Frying time reduced the effective water diffusivity only when the initial deformability modulus was higher than 52 and 79 kPa for 1 and 5 min, respectively. Oil uptake criterion was found to increase with the effective water diffusivity for frying durations of 1 and 5 min.     

Moisture Diffusivity in Tylose Gel (Karlsruhe Test Material)

ABSTRACT: Tylose gel (the Karlsruhe test substance) is a meat analog commonly used for studying heat transfer during freezing and thawing operations. It has thermal properties similar to lean beef, which are well defined in literature; however, moisture diffusivities for Tylose gel are not available in the literature. In this article, the mass transfer properties of Tylose were investigated. This included determining a moisture isotherm for Tylose and measuring effective moisture diffusivity as a function of temperature using 2 different methods: a drying method and a concentration-distance method. The moisture isotherm was fit best using the Guggenheim-Anderson-de Boer (GAB) equation. The resulting moisture diffusivities were fit to an Arrhenius model for temperature dependence from 2.5 °C to 12 °C. The moisture diffusivities measured for Tylose ranged from 4.00 × 10^-11 to 9.75 × 10^-11 m²/ s, depending on temperature. The drying method resulted in moisture diffusivities that were found to have higher dependence on temperature than when the concentration-distance method was used. The concentration-distance method gave much more variation among measurements.     

Moisture diffusivities for bran and endosperm during soaking of long-grain brown rice

A three-dimensional transmission line matrix (TLM) model, using axisymmetric elements, was developed for describing moisture diffusion during the soaking of long-grain brown rice. On the basis of this model, moisture diffusivities for bran and endosperm were calculated as a function of temperature. Endosperm diffusivities of 0.92, 1.08 and 1.26X10^-10 m² s^-1 and bran diffusivities of 0.11, 0.18 and 0.37x10^-10 m² s^-1 were found, both at 30, 40 and 50°C respectively. The activation energies for moisture diffusion were calculated to be 13.08 and 49.85 kJ mol^-1 for endosperm and bran respectively.