Drying kinetics of grape seeds

Drying of grape seeds representing waste products from white wine processing (Riesling), red wine processing (Cab Franc), and juice processing (Concord) was studied at 40, 50, and 60 °C and constant air velocity of 1.5 m/s. Equilibrium moisture content had a significant effect on the normalized drying curve and was determined for each grape seed at each drying temperature. Effective moisture diffusivity ranged between 1.57 and 3.96 × 10⁻¹⁰ m²/s for Riesling seeds, 2.93–5.91 × 10⁻¹⁰ m²/s for Concord seeds, and 3.89–8.03 × 10⁻¹⁰ m²/s for Cab Franc seeds. The temperature dependence of the effective diffusivity followed an Arrhenius relationship, and the activation energies were 40.14 kJ/mol for Riesling seeds, 30.45 kJ/mol for Concord seeds, and 31.47 kJ/mol for Cab Franc seeds. Three thin-layer models were used to predict the drying curves: Page model, Lewis model, and the Henderson–Pabis model. All three models were found to produce accurate predictions compared to the mass average moisture loss for each grape seed variety (percent error less than 10%), and the Lewis model was shown to be an excellent model for predicting all three grape seed varieties (percent error less than 5%).     

Moisture diffusivity and shrinkage of broad beans during bulk drying in an inert medium fluidized bed dryer assisted by dielectric heating

Drying behavior of broad beans (Vicia faba) was studied in a pilot scaled fluidized bed dryer with inert particles assisted by dielectric heating. The effective diffusion coefficient of moisture transfer was determined by Fickian method at four different air drying temperatures of 35, 45, 55 and 65 °C. Correlations for moisture diffusivity as a function of moisture content and temperature of the drying medium were developed. The values of moisture diffusivity were obtained within the range of 1.27 × 10^?9–6.48 × 10^?9 m²/s and the activation energies for FBD and FBD + DE were found to be 27.71 and 17.10 kJ/mol, respectively. The shrinkage behavior of the broad beans was also investigated by considering the volume ratio of (V/V_O) to be function of moisture content alone and fitting a polynomial of the third order. The dielectric heating power was also found to be effective on the rate of drying.     

The drying kinetics of kale (Brassica oleracea) in a convective hot air dryer

The effect of air temperature and sample thickness on the drying kinetics of kale was investigated using a convective air dryer at a fixed airflow rate of 1 m/s and drying air temperatures of 30, 40, 50 and 60 °C. The sliced kale leaves were dried in wire trays in 10, 20, 40 and 50 mm thick layers. The drying rate increased with drying air temperature but decreased with layer thickness. The effective diffusivity for 10 mm thick layers was found to increase with the drying air temperature and ranged between 14.9 and 55.9 × 10⁻¹⁰ m²/s. The effect of temperature on diffusivity could be expressed by an Arrhenius type relationship with a high R² of 0.9989. The activation energy of kale was found to be 36.115 kJ/mol. When four drying models were developed using the experimental data the Modified Page model was found to be marginally better than the other models in estimating the drying curve over the experimental temperature range.     

Modeling sulfur dioxide uptake in dent corn during steeping

A mathematical model is employed to describe sulfur dioxide (SO₂) diffusion and reaction during steeping of dent corn. Experiments are performed to measure change of SO₂ content of grain during process. A computer-aided nonlinear optimization technique is used to estimate the effective diffusion coefficients and rate constants in the temperature range 25–55 °C. The effective diffusion coefficient for SO₂ varied between 2.27×10⁻¹¹ and 6.24×10⁻¹¹ m²/s and had an Arrhenius activation energy of 24.3 kJ/mol. The reaction rate of SO₂ in dent corn followed first-order kinetics, with rate constants in the range of 0.80×10⁻⁶–5.38×10⁻⁶ s⁻¹ and activation energy of 49.16 kJ/mol.     

Time–temperature study of the kinetics of migration of DPBD from plastics into chocolate,chocolate spread and margarine

Migration of low molecular weight substances into foodstuffs is a subject of increasing interest and an important aspect of food packaging because of the possible hazardous effects on human health.The migration of a model substance (diphenylbutadiene) from low-density polyethylene (LDPE) was studied in foodstuffs with high fat contents: chocolate, chocolate spread and margarines (containing 61% and 80% fat).A simplifying mathematical model based on Fick’s diffusion equation for mass transport processes from plastics was used to derive effective diffusion coefficients which take also kinetic effects in the foods into account and to determine partition coefficients between plastic and food. With this model migration levels obtainable under other storage conditions can be predicted. The effective diffusion coefficients for both margarines stored at 5 °C (3.0–4.2 × 10⁻¹⁰ cm² s⁻¹) and at 25 °C (3.7–5.1 × 10⁻⁹ cm²  s⁻¹) were similar to each other, lower than for chocolate spread stored at 5 °C (9.1 × 10⁻¹⁰ cm² s⁻¹) and higher than the diffusion coefficient for chocolate stored at 25 °C (2.9 × 10⁻¹⁰ cm² s⁻¹). Good agreement was found between the experimental and the estimated data, allowing validation of this model for predicting diffusion processes in foodstuffs with high fat contents.     

Controlling moisture transport in a cereal porous product by modification of structural or formulation parameters

Equilibrium and dynamic water sorption properties of sponge cakes with varying porosity (86–52%) and fat content (0–0.30 g/g d.b.) were determined using a water vapour sorption microbalance. Contrary to porosity, addition of fat decreased equilibrium moisture contents. The effective moisture diffusivity (D_eff) was identified from a numerical solution of Fick’s second law, taking into account an external mass transfer coefficient and the swelling of the solid matrix. D_eff increased from 1.61 to 8.67 × 10⁻¹⁰ m²/s with moisture content, reached a threshold at moisture content 0.15 g/g d.b. and then decreased until water saturation. D_eff decreased from 8.67 to 2.97 × 10⁻¹⁰ m²/s with decreasing porosity. This effect was attributed to a change of water diffusion mechanism, from predominant vapour to liquid. D_eff decreased from 8.67 to 2.12 × 10⁻¹⁰ m²/s with increasing fat content. Addition of fat had an effect on the water diffusion in two ways, decreasing porosity (sagging of the foam) and increasing tortuosity.     

Moisture diffusivity coefficient estimation in solid food by inversion of a numerical model

Knowledge of moisture diffusivity coefficients of water in food is a very important physical parameter for design, modelling and simulation of different food plants and related processes such as baking, drying and ripening. Unfortunately specific moisture diffusivity values are not easily found in literature, particularly for processed foods. The aim of this study was to develop a method, based on the inversion of finite element models, to estimate the moisture diffusivity in different solid food products. An example on salami, biscuit and flat bread is shown. The research work was divided in three phases: experimental determination of the moisture concentration versus time in various food products stored in water saturated atmosphere; development of a numerical model of water transfer inside the food product for the numerical determination of moisture content versus time and parameter estimation of moisture diffusivity, by minimizing the distance between numerical model and experimental results using the Levenberg–Marquardt algorithm.The estimated moisture diffusivity coefficients resemble those reported in literature for almost similar products (3.857E − 12, 6.804E − 11 and 1.792E − 12 m²/s for salami, biscuits and flat bread respectively). The obtained values were then used for solving direct models, in unsteady conditions, showing a good agreement with experimental data.The method may be used on different food materials and it is possible to hypothesize an integrated automatic instrument, useful both for laboratory and industrial purposes.     

Modelling of red abalone (Haliotis rufescens) slices drying process: Effect of osmotic dehydration under high pressure as a pretreatment

Simultaneous application of osmotic dehydration and high pressure as a pretreatment to drying process on red abalone (Haliotis rufescens) slices was studied. During drying process the process time was reduced by increasing temperature from 40 to 60 °C along with the application of different pretreatments: high pressure (350 and 550 MPa), pressure time (5 and 10 min), and osmotic solution (10 and 15% NaCl). Effective moisture diffusivity was determined and varied from 4.35 to 9.95 × 10^− 9 m²/s, for both control and pretreated samples (R² ≥ 0.97). The Weibull, Logarithmic and Midilli–Kucuk models were applied to drying experimental data, where Midilli–Kucuk model was found to be the best fitting model. Furthermore, all drying curves were normalized and then modelled by the same three above models showing a R² ≥ 0.96. As to energy consumption and efficiency values for drying processes were found to be in the range of 777–1815 kJ/kg and 8.22–19.20%, respectively. Thus, knowledge on moisture transfer kinetics, energy consumption and data normalization, is needed to manage and control efficiently drying process under different pretreatment conditions.Industrial relevanceThis article deals with the mass transfer modelling and energy consumption during simultaneous high hydrostatic pressure treatment and osmotic dehydration as a pretreatment to drying process of abalone slices. Water and salt transfer during this combined process was satisfactorily simulated with the Midilli–Kucuk model. Results indicated that application of this combined innovative technology improved abalone slices dehydration rates compared to atmospheric pressure operation resulting in a dried abalone with intermediate moisture content ready to be used as input material of further processes. Furthermore, the different energetic features were determined in order to realize the importance of the changes that can influence to alter process time.     

Mass transfer characteristics during convective,microwave and combined microwave–convective drying of lemon slices

BACKGROUND: The investigation of drying kinetics and mass transfer phenomena is important for selecting optimum operating conditions, and obtaining a high quality dried product. Two analytical models, conventional solution of the diffusion equation and the Dincer and Dost model, were used to investigate mass transfer characteristics during combined microwave‐convective drying of lemon slices. Air temperatures of 50, 55 and 60 °C, and specific microwave powers of 0.97 and 2.04 W g^?1 were the process variables. RESULTS: Kinetics curves for drying indicated one constant rate period followed by one falling rate period in convective and microwave drying methods, and only one falling rate period with the exception of a very short accelerating period at the beginning of microwave‐convective treatments. Applying the conventional method, the effective moisture diffusivity varied from 2.4 × 10^?11 to 1.2 × 10^?9 m² s^?1. The Biot number, the moisture transfer coefficient, and the moisture diffusivity, respectively in the ranges of 0.2 to 3.0 (indicating simultaneous internal and external mass transfer control), 3.7 × 10^?8 to 4.3 × 10^?6 m s^?1, and 2.2 × 10^?10 to 4.2 × 10^?9 m² s^?1 were also determined using the Dincer and Dost model. CONCLUSIONS: The higher degree of prediction accuracy was achieved by using the Dincer and Dost model for all treatments. Therefore, this model could be applied as an effective tool for predicting mass transfer characteristics during the drying of lemon slices. © 2012 Society of Chemical Industry     

Modeling of rice hydration using finite elements

Great effort has been devoted towards developing models that describe cooking processes. A difficulty towards developing such models arises from the fact that during cooking, the physical properties and quite often sample geometry are time dependent. In this work a finite element model describing cooking of rice and water uptake using a Fickian diffusion model was developed, assuming axisymmetric conditions. Effective diffusivity was considered a function of moisture content. The numerical model compared favorably with experimental results. The value of the effective water diffusivity was estimated to be in the order of 7 × 10⁻¹⁰ m²/s, by minimizing the error between experimental and numerically predicted results.The effect of grain size on the cooking was also investigated using the model. Cooking time, i.e. the time to reach about 70% moisture content (wet basis), appeared to be a strong function of the initial size distribution.     

Effects of pulsed vacuum osmotic dehydration (PVOD) on drying kinetics of figs (Ficus carica L)

Drying kinetics of non-pretreated (fresh) and pretreated Sarılop (Ficus carica L.) variety figs were compared. In experiments, figs were performed as a whole (unsliced and unpeeled). Pretreatment was pulsed vacuum osmotic dehydration (PVOD). Osmotic dehydration was performed in sucrose solution at 50 °Brix and 50 °C with a solution/fruit mass ratio of 4/1. Vacuum impregnation in osmotic dehydration was applied at 130 mbar for 15 min then the osmotic treatment continued at atmospheric pressure for 165 min, therefore the total pretreatment period lasted for 180 min (15 min (130 mbar) + 165 min (P_atm)). Pretreated and non-pretreated figs were dried at 55, 65 and 75 °C in a convective oven. Results showed that increasing of drying temperature shortened the drying time for both non-pretreated and pretreated figs. Drying period of pre-treated figs lasted shorter than non-pretreated figs, thus PVOD shortened the drying period. Non-pretreated (fresh) figs had greater shrinkage than the pretreated figs. Effective moisture diffusivity (D_eff) values of pretreated figs are greater than the non-pretreated figs during the drying at all three temperatures. D_eff increased with drying temperature for both pretreated and non-pretreated figs. D_eff values of non-pretreated and pretreated figs ranged 2.75·10^− 10–5.69·10^− 10 m²/s and 3.57·10^− 10–10.25·10^− 10 m²/s, respectively. Activation energy (E_a) of non-pretreated and pretreated figs were obtained 34.68 (kJ/mol) and 50.27 (kJ/mol), respectively. Also, sensory evaluation of color, flavor, odor, texture and overall acceptability of the samples was made.Industrial relevanceThe use of PVOD technique is relevant for food industry. So that, PVOD treatment shortened the drying period of figs. Thus, this result can cause the economic advantage as reducing the further costs for drying process. Additionally, results of sensory evaluation show that there was no significant difference (p > 0.05) between the pretreated and traditional dried figs except for flavor. Sensory properties of pretreated figs may be improved by changing conditions of pretreatment.     

Effects of Osmotic Dewatering and Oven Drying on β-Carotene Content of Sliced Light Yellow-Fleshed Sweet Potato (Ipomea batatas L.)

The effects of pre-treatment in osmotic salt solution followed by oven-drying on the moisture removal, and β-carotene content of yellow-fleshed sweet potato were investigated. Potato rings of 3 cm diameter and thicknesses of 2 mm, 3 mm and 4 mm were soaked in NaCI solutions of 10, 15, 20, 25 and 30% w/v, for varying time of 20, 40, 60, 80 and 100 minutes. The pre-treated slices were then oven-dried in a convective oven at 60 °C. Moisture diffusivity was determined by the method of slopes, while β-carotene was measured by UV/VIS- spectrophotometer. Moisture diffusivity values during drying were between 3.648 × 10^− 7 m²/s and 1.459 × 10^− 6 m²/s, while losses in β- carotene ranged from 47 to 86%. The amount of water removed by pre-treatment with NaCl solution decreased significantly as the concentration and the time soaking increased, however, the water out flow was found to increase significantly with increase in thickness of the samples, where the 4 mm size had the highest (1.535 g H₂O/g sample) and 2 mm the least (1.434 g H₂O/g sample) Osmotic pre-treatment in salt solution had no effect on β-carotene, but subsequent oven-drying however degraded the β-carotene.     

Acid and moisture uptake in steamed and boiled sweet potatoes and associated structural changes during in vitro gastric digestion

Orange-fleshed sweet potatoes are a good source of phytochemicals. For these nutrients to be absorbed, they must be released from the food matrix as a result of physical and chemical breakdown. A key factor in food breakdown is gastric acid diffusion into the matrix, and its influence on structural changes. Cooking treatment may influence mass transport properties and structural changes of foods during digestion. The objective of this study was to determine the acid and moisture uptake into sweet potatoes and its influence on macro- and micro-structures during in vitro gastric digestion as a result of varying cooking treatments. Sweet potatoes were cut into cubes and cooked (boiled or steamed) for different times. In vitro oral and gastric digestions were simulated in a shaking water bath at 37 °C. Acidity, moisture content, and solid loss were measured after 9 digestion times (15 to 240 min). Hardness of individual cubes and microstructure (light microscopy) were completed before and after digestion. Effective diffusivity of acid and moisture into the cubes was estimated using MATLAB. Cooking method, cooking severity, and digestion time significantly influenced moisture uptake (p < 0.0001). Acid uptake was significantly influenced by digestion time (p < 0.0001). The change of softening after digestion was influenced by cooking method and severity (p < 0.05). Effective diffusivity of acid ranged from 0.03 × 10^− 10 (mild steamed) to 11.40 × 10^− 10 m²/s (severely boiled). Percent texture decrease after digestion from the initial hardness ranged from 16% (severely steamed) to 34% (mild boiled). Textural changes were related to cell wall breakdown and starch degradation. In general, mass transport properties and macro- and microstructural changes were influenced by cooking treatment and gastric digestion. The link between food cooking and behavior during digestion is crucial in determining optimal food processing and cooking methods for specific food functional properties.     

Influence of relative humidity on carbon dioxide sorption in wheat gluten films

The influence of relative humidity (RH) on carbon dioxide sorption at 10⁵ Pa in wheat gluten films (WGF) was investigated in the range of 0–96% RH at 25 °C. The amount of water sorbed by these protein based films reached up to 60% of the dry weight at 96% RH. Carbon dioxide sorption increased with water content, ranging from 2.8 × 10⁻⁴ to 1.9 × 10⁻² mol Pa⁻¹ m⁻³ respectively at 0% and 96% RH. This behavior was tentatively explained on the grounds that sorbed water enhanced carbon dioxide accessibility to protein active sorption sites. The dependence of both the solubility and the diffusivity coefficients of CO₂ and O₂ on WGF water content explains the very good permselectivity of these films observed at high RH values (22 at 93% RH and 25 °C).     

Combined effect of γ-irradiation and osmotic pretreatment on mass transfer during dehydration

The combined effect of γ-irradiation (3.0–9.0 kGy) and osmotic pretreatment (10 and 50°B) on dehydration kinetics was studied. The exposure to irradiation pretreatment resulted in an increase in cell wall permeabilization, leading to softening of tissue, which in turn resulted in faster dehydration. The effective diffusion coefficient of water in case of potato during dehydration, considering Fickian diffusion, increased from 2.38 × 10⁻⁹ to 4.14 × 10⁻⁹ m²/s at 9.0 kGy, whereas the osmotic pretreatment resulted in lower dehydration rates due to infusion of solute from osmotic solution, which resulted in lower mass transfer rates. Even though the effective diffusion coefficients decreased from 2.38 × 10⁻⁹ to 1.55 × 10⁻⁹ m²/s (up to 50°B), the osmotic pretreatment improves nutritional, sensorial and functional properties of food without changing its integrity, apart from partial removal of water present in food. The combining of γ-irradiation treatment with osmotic pretreatment resulted in increased mass transfer rates during air dehydration, offering a feasible solution for satisfactorily enhancing the mass transfer rates.     

Migration of α-tocopherol from LDPE films to corn oil and its effect on the oxidative stability

The migration of α-tocopherol (α-T) from low density polyethylene (LDPE) films, added with 20 (film A) and 40 mg g^?1 (film B) to corn oil for 12 weeks at 5, 20 and 30 °C was determined. A LDPE film added with no α-T was used as control (film C). Diffusion coefficient (D) values for the film A system were 1.4 × 10^?11, 7.1 × 10^?11 and 30.3 × 10^?11 cm² s^?1 at 5, 20 and 30 °C, respectively. Meanwhile, D values for the film B system were 1.3 × 10^?11, 9.6 × 10^?11 and 51.1 × 10^?11 cm² s^?1 at the same temperatures. The activation energy (E_a) for the diffusion of α-T was 126.5 (film A) and 105.9 kJ mol^?1 (film B). The effect of the migration of α-T on the oxidative stability of corn oil was evaluated by monitoring hexanal content by solid phase micro-extraction (SPME) and gas chromatography. The hexanal content in the oil showed that both films added with α-T resulted suitable to maintain the oxidative stability of the oil for about 16 weeks at 30 °C, compared to 12 weeks for the oil in contact with the film C.     

Monitoring nisin desorption from a multi-layer polyethylene-based film coated with nisin loaded HPMC film and diffusion in agarose gel by an immunoassay (ELISA) method and a numerical modeling

Polyethylene-based films coated with nisin loaded HPMC films were put in contact with food simulants, i.e. agarose gels with 5 or 30% (w/w) fat. Nisin desorption from the multi-layer films and diffusion in agarose gels were monitored by ELISA (Enzyme Linked ImmunoSorbent Assay). The data obtained after 2 or 6 days of contact between antimicrobial films and agarose gels were employed to determine nisin mass transfer by numerical modeling following Fick's second law. The values were in the range from 0.87 × 10^? 3 m s^? 1 to 4.30 × 10^? 3 m s^? 1 and 6.5 × 10^? 11 m² s^? 1 to 3.3 × 10^? 10 m² s^? 1, for nisin apparent desorption and diffusion coefficients, respectively. The diffusion process was governed by interactions between food matrix simulant and nisin. Moreover, it was observed that the polymer in the coating did not modify plastic film initial mechanical resistance and water vapor permeability.Industrial relevanceThis paper concerns active packaging, considered as a new approach to preserve food shelf life. Active packaging is a real gain for plastic and Food industrials. The paper deals with coating as a manner to activate packaging. The impact of coating on film properties is investigated.Also, predictive models are proposed to determine antimicrobial agent desorption and diffusion during some storage conditions.     

Water vapor transport properties during staling of bread crumb and crust as affected by heating rate

In order to develop a mathematical model to simulate mass transfer occurring between the crumb and the crust during bread staling, water vapor sorption properties, i.e., moisture diffusivity, WVP and sorption of bread crumb and crust were investigated at 15 °C. Two types of bread baked with two heating rates (7.39 °C/min and 6.32 °C/min) were considered. Sorption and desorption isotherms were determined using Dynamic Vapor Sorption (DVS) and FF and GAB models were applied in the range of 0–0.95 a_w, to fit isotherm curves. Diffusivity was determined from sorption isotherms by using Fick's law and WVP was measured by two methods (gravimetric and from sorption data). Results exhibited maximum values of D_eff in the range of 0.1 and 0.14 g/g d.b. moisture contents. They varied between 0.88 × 10^? 10 and 0.92 × 10^? 10 m²/s for the crust and between 2.24 × 10^? 10 and 2.64 × 10^? 10 m²/s for the crumb, baked respectively at 220 °C and 240 °C. Results of WVP showed that the crust baked at 240 °C was significantly more permeable than the crust baked at 220 °C. This fact was attributed to the difference in porosity and the molecular structure due to heating effects. Also, the presence of steam in the oven atmosphere enhanced the development of higher porosity in the crust, leading to different structures and properties. Moreover, SEM images showed that starch granules were intact and less swelled in the upper crust when baking at 240 °C, resulting in higher WVP.     

The protective effect of monosodium glutamate on survival of Lactobacillus rhamnosus GG and Lactobacillus rhamnosus E-97800 (E800) strains during spray-drying and storage in trehalose-containing powders

The use of trehalose as a means of preserving Lactobacillus rhamnosus GG (LGG) and L. rhamnosus E-97800 (E800) during spray-drying and the effects of incorporated monosodium glutamate (MSG) in the carrier medium on the survival rates during drying and storage were examined. E800 was more resistant to heat than LGG in 20%, w/w, trehalose; the d-values at 65 °C were 14 s and 5.1 s, respectively. An air outlet temperature of 65–70 °C was taken as optimal for the drying process, as the resultant moisture levels in trehalose containing these bacteria were 4.1% (w/w) and 3.79% (w/w) with corresponding viable counts of 3.65 × 10⁸ cfu mL^?1 and 1.80 × 10⁹ cfu mL^?1, respectively. The presence of MSG increased the final viable counts of LGG and E800 to 3.05 × 10⁹ cfu mL^?1 and 1.30 × 10⁹ cfu mL^?1, respectively. Survival of LGG and E800 remained constant at a minimum level of ～10⁸ cfu mL^?1 during storage at 25 °C in trehalose–MSG medium.     

Determination of trace tin in foods by single-sweep polarography

A new method for the determination of trace tin in a solution of oxalic acid–methylene blue by single-sweep polarography is developed. The mechanism for the polarographic waves and the conditions for determining tin are discussed in this report. The peak height is directly proportional to the concentration of tin (IV) over the range 2.0×10⁻⁸–1.0×10⁻⁶ g ml⁻¹. The detection limit and the recovery of the method are 1.0×10⁻⁸ g ml⁻¹ and 93–98%, respectively. The method was successfully employed for the determination of tin in juices of canned fruits.