جستجوی مقالات مرتبط با کلیدواژه « diffusion coefficient » در نشریات گروه « صنایع غذایی »

Drying foods, such as freezing methods and hot air, are not ideal and reduces the nutritional value and is also expensive and is used only for high value food. In this research, drying with supercritical fluid of carbon dioxide was investigated to remove moisture from the figs. In the drying process with supercritical fluid, the structure of food products is maintained during drying. The design of the experiment was carried out in a factorial arrangement using Design Expert software and analysis variance table to determine the effect of three pressure parameters, temperature, and time to measure the removal rate of moisture. The calculated factorial model was meaningful and able to select the best drying parameters. In optimum conditions, the highest yield (78.109%) with the desirability of 0.992 at 20 MPa, 60 °C and 120 minutes duration. The results showed that the drying of figs during the whole drying period is carried out at the downstream stage, which indicates that the drying of these materials, the internal moisture control, controls the rate of drying and mass transfer. In this study, by solving the second Fick's law and in the range of pressure and temperature tested, with the assumption of the spherical of the fig using the Crank equation, the amount of moisture diffusion coefficient between 4.51× 10-10 and 0.18 × 10 -10 m2/s were obtained. The fig's drying rate was also calculated. Increasing temperature and pressure caused to increase the drying rate.

Heat treatment of potato tissue involves chemical, physical and structural changes. The magnitude of these changes will depend on the extent of thermal processing in terms of time and temperature. Blanching is a heating process that used to inactivate enzymes, de-aeration and modification of texture, preserving color, flavor and nutritional value of fruits and vegetables prior to freezing, canning, drying and frying. Temperature and time of blanching is largely determined by the amount of reducing sugars and textural characteristics of the species. In the previous studies performed on the changes of reducing sugars content in potatoes during blanching, some researchers found evidence that besides the mass transfer to the bath there exists an internal generation of reducing sugars, probably due to an enzymatic hydrolysis of starch. Therefore when predicting the concentration of reducing sugars changes, both mechanisms should be considered. Considering that no study has been done on the effect of internal generation of reducing sugars on their effective diffusivity during blanching and so far there is no comprehensive study on the kinetic of texture changes during blanching of potato at different temperatures and also direct relationship of reducing sugars with Maillard reaction and acrylamide formation in potato, therefore the aims of this study are: 1) determination of effective diffusivity of reducing sugars with and without consideration of them generation and 2) investigation of kinetic of texture changes during blanching of potato strips at the temperature range of 50-90 ºC and modeling of these phenomena.
Potatoes (variety Agria, ~23 g/100g (dry basis)) was the raw material used in this study. Potatoes stored in a dark room at 20 ºC for 2 weeks were washed and peeled. Then, were striped into dimensions of 0.8×0.8×8 cm using an electric striping machine (Halldeh, model RG-100). Raw potato strips were rinsed immediately after cutting for 1 min in distilled water to eliminate the starch material adhering to the surface prior to blanching. Then, blanching was accomplished by immersing the potato strips in hot distilled water (ratio of mass of potato to water of 1:20) at 50, 60, 70, 80 and 90 ºC. To investigate the kinetic of generation of reducing sugars, strips packaged in duplex in the polyethylene (HDPE with 10 micron thickness) film were immersed in hot distilled water to blanching at the temperatures. Samples were withdrawn after 5, 10, 15, 20, 40, 60, 80, 100 and 120 minutes to measure the reducing sugars content and texture firmness. All experiments were done in triplicate. Maximum stress caused by penetrating of the probe (diameter of 2 mm) into strip texture was the texture evaluation index. To describe the mass transfer (extraction of reducing sugar) during blanching, a three dimensional numerical model based on finite difference method of solving Fick's Second Law has been developed in MATLAB software. The first order kinetic with production rate limiting effect was used to describe the potato strips texture changes during blanching. All experiments were done in triplicate as factorial based on completely randomized design. Data analysis and plotting of figures were performed in SAS and Excel software respectively.
The results showed that increasing of blanching temperature increase the reducing sugars effective diffusion coefficient significantly (P

Polyethylene terphthalate (PET) is one of the plastics that are widely used for packaging of foods, especially, beverages and edible oils. In this study, the migration of di (2- ethylhexyl) adipate (DEHA), which is convenient plasticizer in PET, from PET bottles into the lemon juice stimulant was investigated. According to EC directives, specific migration limit (SML) for DEHA is 18 µg/L. In present work, air associate liquid-liquid micro-extraction (AALLM) was offered as extraction method to the DEHA and the effect of some important parameters such as type of extraction solvent, extraction solvent volume, salt amount was optimized. According to EC regulations, 3% acetic acid (w/v) was chosen as simulant. The samples were stored at 5, 25, and 40°C for three months and analyzed at 10,30,60,90 by gas chromatography. The diffusion coefficients of DEHA from PET bottle were calculated by using Fick’s second law. The migration of DEHA was increased with increasing of storage temperature and storage time. After 90 days, level of migrated DEHA were below and above of SML in 25˚C and 40˚C, respectively. The diffusion coefficients (D) determined for DEHA were 0.109, 0.12, and 0.092 ×10-9 cm2/s at 5, 25, and 40˚C, respectively. Storage of lemon juice packaged in PET bottle can potentially cause risk by DEHA migration in warm climate. However, it seems there are not high risks in moderate climate and the storage of it in refrigerator can reduce risks of DEHA migration into lemon juice.

Polyethylene terphthalate (PET) is one of the materials that are widely used for packaging of beverages and edible oils. In this study, the migration of di(2- ethylhexyl) phthalate (DEHP), dimethyl phthalate (DMP), diethyl phthalate (DEP), di-iso-butylphthalate (DIBP) and di-n-butylphthalate (DBP) from PET bottles into the lemon juice was investigated.
Material and According to European Commission regulations, 3% acetic acid (w/v) was chosen as simulant. The acetic acid samples were stored at 5, 25, and 40°C for three months and analyzed periodically by gas chromatography.
It was concluded that the storage temperature and time had a large effect on the migration of phthalet ester. The concentrations of migrating substance were more than its specific migration limit. The release kinetics of phthalet ester from PET bottle was described using Fick’s second law of diffusion coefficient, and crank model. The diffusion coefficients (D) determined for DEHP have most migration than other, were 0.084, 0.109, and 0.159 ×10-9 cm2/s at 5, 25, and 40°C, respectively. The diffusion coefficients (D) determined for DBP have most migration than other, were 0.084, 0.105, and 0.138 ×10-9 cm2/s at 5, 25, and 40°C, respectively. The diffusion coefficients (D) determined for DIBP have most migration than other, were 0.084, 0.177, and 0.125 ×10-9 cm2/s at 25, and 40°C, respectively. The temperature dependence of D, Arrhenius equation giving values of activation energy (Ea) for DIBP, DBP and DEHP are 2.82, 2.06 and 1.302 J mol-1 respectively.

Flavor release from food during consumption in the mouth plays an important role in flavor perception and influenced by the food matrix. Since, food matrix changes biochemically and physically during eating, therefore, food flavor microencapsulation results in controlled release at specific situations. On the other hand, stability and availability of flavors are affected by food processing and storage. To control the flavor release at specific condition during consumption or stability and availability during food processing and storage; it is essential to encapsulate flavor components before use in food complex. Encapsulation is the term for a collection of technique that used as delivery of active and bioactive parts. This novel technology enables isolated of gases, liquid droplets, or solid particles in the core of microscopic vesicular system with porous or non porous semi permeable shell that release occurs in response to the specific situations. Controling release of active compound depends on microcapsule characteristics such as pore size, mechanical stability of the colloidal shell, shell thickness and shell permeability; molecular size and solubility of active parts in the shell and properties of the release media including shear force, temperature, pH, ionic strength, etc. This paper presents the formation and characterization of novel diacetyl encapsulated alginate-whey protein concentrate (AL-WPC) microcapsules. Diacetyl release was investigated at simulated mouth condition in different ratios of artificial saliva (0, 1:4 and 1:8) and three various oral shear rates (0, 50 and 100 s-1) and the diffusion coefficient was estimated using Fick’s law. The main aim of this work was to develop a prediction model to study the flavor release from microcapsules. Materials and Methodes: Aiming to show the applicability of our agent-based model platforms, the release of 2,3-butanedione (diacetyl) from alginate-whey protein concentrate (AL-WPC) microcapsules was used as a case study to validate our simulation model based on NetLogo platforms. For this purpose, our previous work on evaluation of diacetyl encapsulated alginate-whey protein microspheres release kinetics and mechanism at simulated mouth conditions was used (Zandi, M., Mohebbi, M., Varidi, M., Ramezanian, N., 2014). In previous our work, encapsulated diacetyl release was measured at three oral shear rates (0, 50 and100 s-1) and various ratios of saliva to microcapsule (0, 1:4 and 1:8) simulating mouth conditions. Then, experimental release data were fitted using different kinetic models. It was found that release from these microcapsules followed a classical Fickian diffusion. We use release data for calculating release rate. For model validating, diffusion equation was fitted to the experimental data, and diffusion coefficient was obtained for diacetyl release at various mouth conditions. To this purpose, the following model was obtained by solving unsteady diffusion equation in spherical coordinate: (M(t))/M_0 =100-exp⁡(-(3×D×(R+b))/(R^2×b)×t) (1) where M (t) and M0 are the diacetyl release at time t and 0 respectively, R is a microcapsules radius (m), t is time, D is the diffusion coefficient and b is the shell thickness (m). We also use diffusion coefficient to calculate permeability for each specific condition by equation (2): P=(D×K)/b (2) Where P is the permeability coefficient, D is the diffusion coefficient and K is the partition coefficient. Finally, the model and experimental data were analyzed using Matlab software (R2007).

In our study, AL-WPC microcapsule was fabricated by emulsification/internal gelation method, and diacetyl was loaded into microcapsule. Most of microspheres had a completely spherical shape with smooth surface, and range in size from 20-150 μm. The diacetyl encapsulated microsphere had a porous and smooth shell with some holes that caused the quicker diacetyl release initially. The mean hydrodynamic diameter 112.8 ± 0.9 μm (mean value ± SD for n= 2) was measured via particle size analyzer (DLS). the high efficiency of 79.34% was obtained for diacetyl encapsulated AL-WPC microcapsule. About 20% of diacetyl was loosed because of the solubility and volatility of the diacetyl molecule (diacetyl is a low molecular weight and water soluble component)..

It was showed that the shear rate of release media had a significant (p<0.05) effect on the release of diacetyl from AL-WPC microspheres, but saliva ratio had not any significant effect. The diacetyl release data fit well to developed model with R2 values greater than 0.95

The purpose of this research was to study the effect of thin layer drying conditions (temperature at three levels of 60,70, and 80 oC, air velocity at two levels of 1/5 and 2/5 m/s, and four pretreatments including potassium carbonate and Paksan drying oil, olive oil, hot water without pretreatment (control)) on cabinet drying process of grape and color of obtained raisin. Six mathematical models were fitted on drying data and the best one was selected according to coefficient of determination (R2), Root Mean Square Error (RMSE) and coefficient of relative average deviation (P). The results showed that temperature, air velocity and pretreatment have significant effects on drying rate and color of raisin. Among these models, two term and page models showed more ability to evaluating and describing drying behavior of grape. Diffusion coefficient values were between 4/6274×10-10 to 8/6541×10-10 m/s2 and activation energy obtained 13470/83 J/mol. The best values of lightness and redness were related to dried raisin at 60 oC and the maximum value of yellowness was related to dried raisin at 70o C. Drying air velocity just significantly affected the redness. Increasing drying air velocity decreased the redness. It was also found out that potassium carbonate and Paksan drying oil pretreatment caused the best raisin color.

In this research, drying of green bell peppers by hot air dryer at temperatures, 60, 70 and 80°c kinetic drying parameters were investigated. The results showed that the temperature 80°c has highest rate of drying and lowest time. Also increasing the temperature caused increasing the shrinkage and most shrinkages were observed in 80 centigrade. rehydration rate decrease when temperature increase and the highest rehydration rate observed in 60 centigrade due to the decreasing of destroying capillary tube. the result showed that increasing temperature increasing moisture dispersion and activation energy value was 34.577kj/mol. Modeling based on 11 standard mathematical models was fitted to the experimental data. And criteria for evaluating models Determination of Coefficient (R3), Root Mean Square Error (RMSE), Chi-square(X2), and Mean Bias Error (MBE) were analyzed. Survey results showed that the Approximation of diffusion Model for the drying at temperature of 60 and 80 and Verma. et al model at temperature of 70 stages of drying peppers make a better assessment. So this model to predict changes in humidity and high quality product with hot air dryer for drying green bell peppers was diagnosed.

The effects of air temperature (40، 50، 60 and 70 oC)، air velocity (1 and 2m/s) and bed depth [1 (monolayer)، 3 and 5cm)] on drying time، drying rate and quality indicators of Pistachio-nuts such as peroxide value and free fatty acids was determined in an experimental air cross flow drier and optimum conditions for pistachio-nuts drying was obtained. Also effective diffusion coefficient (Deff(and activation energy were determined by using Ficks second law (between 40 to 70oC) and Arrhenius model، respectively.