جستجوی مقالات مرتبط با کلیدواژه « خشک کن انجمادی » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

In recent years, much consideration has been paid to use of essential oils and aromatic plants with anti-oxidant and antimicrobial properties in the food and pharmaceutical industries because of increasing in consumers’ tendency in using foods without Chemical preservative. However, the essential oils are volatile compounds, sensitive towards heat and insoluble in water, which limits their application. Therefore, this study aimed to investigate the capability of encapsulation technique as a suitable method for protecting essential oil against environmental conditions and assessing the colloidal properties of nanocapsules. For this purpose, identification of active compounds of Citrus Limon L. essential oil was performed using Gas Chromatography (GC). Then, Oil-in-water emulsion with a ratio of 1: 4 Essential oils: coatings with chitosan and modified starch with different ratios (0.5: 9.5, 1: 9 and 1.5: 8.5 % w/v) using freeze drying method was prepared by sonication. The effect of different wall concentrations on the physical and chemical properties of emulsion and nanocapsules were measured. The results showed that increasing in chitosan concentration resulted in higher stability and viscosity of nano-emulsion prepared with 1.5: 8.5% chitosan: Modified starch. Nano-emulsion which coated with higher concentration of chitosan showed smaller droplets and more uniform size distribution than the other treatments. The study of nano-capsule properties determined a significant difference (P≤0.05) based on the different ratios of wall materials on moisture content, encapsulation efficiency and particle size. The morphology of the nanocapsules confirmed that the capsules with higher encapsulation efficiency had smooth surfaces, without gaps and with the least porosity.

Freeze drying is one of the best methods for the removal of water in temperature sensitive agricultural products. In the present study was investigated the process of drying the Fijou fruit in a freeze dryer under the influence of different pretreatments and were calculated the moisture diffusion coefficients (mass transfer coefficient) by using of Dincer and Dost models and Fick’s model, drying rate constant, convective mass transfer coefficient, specific energy consumption and specific moisture extraction ratio. Various pre-treatments applied to the samples are ascorbic acid (with 1% concentration and 1, 2 and 3 min), microwave (with 90 W for 10 min, 180 W for 5 min and 360 W for 2.5 min), blanching with hot water and steam (with 1, 2 and 3 min), potassium carbonate (with 2.5% concentration and 1, 2 and 3 min), osmotic (with 45% sucrose concentration and 10, 20 and 30 min), and ultrasound (with 10, 20 and 30 min). The highest drying rate constant and convective mass coefficient were obtained in microwave pre-treatment to 0.0073 (s-1) and 2.900×10-5 (m2/s), respectively. The range of moisture diffusion coefficients was variable in Fick’s model from 0.7404×10-8 to 1.3996×10-8 (m2/s) and for Dincer and Dost model from 4.5318×10-7 to 9.2149×10-7 (m2/s). The highest and lowest specific energy requirements were 47.23 and 23.61 kWh/kg in osmotic and microwave pre-treatment, respectively. Also the highest and lowest specific moisture extraction ratio were 0.0423 and 0.0212 kg/kWh in microwave and osmotic pre-treatment, respectively.

Recently, there has been much attention to use of natural pigments as food colorants and healing components. Red beetroot is rich in betalain pigments. In this research, the effect of different solvents (water, water: ethanol: citric acid ratios (60: 40: 0) and (60: 38.5 :1.5)v/v and ascorbic acid concentration (in two levels of 0 and 0.05%)w/v on the extraction efficiency were studied. Betalains were extracted from red beetroot and encapsulated with different encapsulating agents including: maltodextrin (MD) with extract (ER) (20g: 100ml), gum arabic (GA) with extract (20g: 100ml) and maltodextrin+ gum arabic with(ER) (10g: 10g: 100ml) w/v (as encapsulating agents) and then were dried using the freeze dryer. Effect coating agents were studied on the betalain stability. The results showed that various solvents have different effects on the extraction efficiency. Pure water and ethanol: citric acid as solvent, showed the highest (68%) and lowest (7.6%) extraction efficiency, respectively . Ascorbic acid increased the stability of all betalain samples, but it had greatest impact on water extracts and water - ethanol (p<0.05). Effect of different encapsulating agents were studied on the betalain stability. Encapsulated betalains with gum arabic and maltodextrin showed more recovery efficiency than the non- encapsulated betalain sample (as control).

In this work, with a simple freeze dryer has been reported drying curve of roses. Powdered dry ice which has -78.5 ºC sublimation temperature, has been used for freezing cycles and vacuum oven as freeze drying chamber. During the process, the pressure of chamber has been kept below the triple point of water (< 0.01 atm). Primary and secondary stages of drying for two samples of roses in drying curve have been specified. The results show in constant drying condition, sample weight affects the drying curve and in constant chamber pressure, increasing of temperature decreases the drying time.

In recent years, freeze drying has found many applications in various industries. In this study, a dynamic model is developed to describe bonded moisture removing in freeze drying by mass and energy balance. Primary and secondary drying are distinguished. Three different geometrical shapes (slab, cylinder, sphere) of wet solid take into consideration in this mathematical modeling. Each of them subjected to three different thermal boundary conditions: constant temperature, constant heat flux and convection heat flux. Based on secondary stage of drying analysis, the percentage of bonded moisture desorbed in primary drying stage has been calculated analytically for all status. Results of computation show that for all of thermal boundary conditions, the percentage of desorbed bonded moisture in spherical sample is higher than cylindrical and removed bonded moisture percent in cylindrical sample is higher than slab.