Medeni Maskan

Kinetics of colour change of kiwifruits during hot air and microwave drying

Abstract The kinetics of colour changes of kiwifruits, due to drying by hot air, microwave (MW) and hot air–MW finish drying, were studied. Kinetic parameters for the colour change were determined using Hunter L-, a-, b-values, chroma, Hue, total colour difference and browning index (BI) values. The drying process changed all three colour parameters (L, a, b), causing a colour shift towards the darker region. Parameters L and b decreased and a-value increased during drying. The Hunter parameters were more influenced by MW drying. Zero- and first-order kinetic models were applied to describe colour change. Both models were found to describe the L- and b-data adequately. However, a-values and ΔE followed zero-order and whole data of hot air–MW drying followed first-order kinetics.

Microwave/air and microwave finish drying of banana

Abstract Banana samples ( 4.3±0.177, 7.4±0.251 and 14±0.492 mm thick) were dried using the following drying regimes; convection (60°C at 1.45 m/s); microwave (350, 490 and 700 W power) and convection followed by microwave (at 350 W, 4.3 mm thick sample) finish drying. The drying of banana slices took place in the falling rate drying period with convection drying taking the longest time. Higher drying rates were observed with the higher power level. Microwave finish drying reduced the convection drying time by about 64.3%. A physical model was employed to fit the experimental data and gave good fit for all experimental runs except microwave finish data. Microwave finish dried banana was lighter in colour and had the highest rehydration value.

Drying, shrinkage and rehydration characteristics of kiwifruits during hot air and microwave drying

Abstract Hot air, microwave and hot air-microwave drying characteristics of kiwifruits (5.03±0.236 mm thick) were investigated. Drying rates, shrinkage and rehydration capacities of these drying regimes were compared. The drying took place in the falling rate drying period regardless of the drying method. Drying with microwave energy or assisting hot air drying with microwave energy resulted in increased drying rates and substantial shortening of the drying time. Shrinkage of kiwifruits during microwave drying was greater than hot air drying. Less shrinkage was observed at hot air-microwave drying. Microwave dried kiwifruit slices exhibited lower rehydration capacity and faster water absorption rate than the other drying methods studied.

Hot air and sun drying of grape leather (pestil)

Abstract Pestil, a well known fruit leather in Turkey, was prepared from boiled grape juice and starch mixture by using traditional technique. Drying of pestil was carried out by hot air drying and sun drying. The factors investigated in hot air drying were air temperature (55, 65 and 75 °C), sample thickness (S1=0.71, S2=1.53, S3=2.20 and S 4 =2.86 mm ) and air velocity (V1=0.86, V2=1.27 and V 3 =1.82 m / s ). The effects of drying time, temperature and slab thickness on moisture content of pestil during drying were significant (P 0.05). Depending on sample thickness and air temperature, the drying time ranged between 50–140 min to achieve the commercial moisture content of pestil ( 0.12 kg H 2 O / kg DS ) in air drying. Whereas, sun drying took 180–1500 min. Almost all samples dried in the falling rate period, except S2, S3, S4 of sun drying and S4 at 55 °C. The latter had a short (negligible) constant rate period. Effective moisture diffusivity values were estimated from Ficks diffusion model. These values were between 3.00–37.6×10 −11 m 2 / s for hot air drying and 1.93–9.16×10 −11 m 2 / s for sun drying. Activation energy value of water diffusion was calculated using an Arrhenius-type equation. The estimated values were 21.7, 16.5, 12.0 and 10.3 kJ/mol for S1, S2, S3 and S4, respectively.

Sorption isotherms and drying characteristics of mulberry (Morus alba)

Abstract Drying characteristics of Mulberry (M. alba) including sorption isotherms and drying kinetics were investigated. Adsorption and desorption isotherms at 10, 20 and 30 °C and isosteric heats of sorption were determined. At higher water activities, as the temperature was increased, a crossing of the isotherm curves was detected. Some hysteresis effect decreasing with higher temperature was observed. Mulberry was dried in a pilot plant tray drier with a constant air velocity of 1.2 m s −1 at 60, 70 and 80 °C. Only falling rate drying periods (three falling rate periods) were observed in the mulberry drying experiments. The diffusivity values changed from 2.32 × 10 −10 to 2.76 × 10 −9 m 2 s −1 within the given temperature range. Effect of temperature on the diffusivity was expressed by an Arrhenius relation with an activation energy value of 21.2 kJ mol −1 .

Effect of sugar on the rheological properties of sunflower oil-water emulsions.

Abstract The rheological properties of sunflower oil–water emulsions were studied at constant oil (79%), with varying sugar concentrations (0.0–8.0%) and different temperatures (25–65°C). Sugar improved the emulsion stability. The empirical power law fitted the apparent viscosity-rotational speed data. All emulsions exhibited pseudoplastic behaviour. An average flow behaviour index of 0.49±0.03 was proposed as power law index for all emulsions. The consistency index was influenced by the sugar content and temperature. This dependency was described by an exponential equation. The effect of temperature on consistency of emulsions followed an Arrhenius type equation. Depending on the sugar content, the activation energy values varied from 31077 to 10716 kJ/kg mol.

Effect of extrusion cooking on functional properties and in vitro starch digestibility of barley-based extrudates from fruit and vegetable by-products.

Barley flour and barley flour-pomace (tomato, grape) blends were extruded through a co-rotating twin-screw extruder. The aim of the present study was to investigate the effects of die temperature, screw speed, and pomace level on water absorption index (WAI), water solubility index (WSI), degree of starch gelatinization, and in vitro starch digestibility using a response surface methodology. The selected extrudate samples were examined further using differential scanning calorimetry (DSC) and polarized light microscopy, respectively. The WAI of barley-pomace extrudates was affected by increasing pomace level. Temperature had significant effect on all types of extrudate but screw speed had significant linear effect only on barley and barley-grape pomace extrudates on degree of starch gelatinization. Although no gelatinization peak was detected, an endotherm was observed on all selected extrudates. In general, extrusion cooking significantly increased in vitro starch digestibility of extrudates. However, increasing level of both tomato and grape pomace led to reduction in starch digestibility.

Fatty acid oxidation of pistachio nuts stored under various atmospheric conditions and different temperatures

The fatty acid composition and stability of whole-split pistachio nuts were investigated at ambient conditions and under air and 98% CO2 at monolayer moisture content and different storage temperatures. High stability was determined under CO2 storage particularly at 10°C. It was revealed that, from the Arrhenius model, storage under CO2 was more temperature sensitive. A 18·24–72·05 reduction for linolenic and 2·15–20·16% for linoleic acid were observed depending on storage conditions. Rate constants of fatty acid oxidation at three temperatures and ambient conditions and Ea for various storage systems were estimated. Peroxide value and free fatty acid of pistachio nuts were also determined as indicators of product storage stability. Least product oxidation and hydrolysis occurred at or near the monolayer moisture content and under CO2 storage.© 1998 SCI.

Effect of concentration and drying processes on color change of grape juice and leather (pestil)

Abstract The Hunter color parameters (L,a,b) of grape juice during boiling, cooking and of pestil samples (1.53 mm) during drying were investigated. It was found that most of the color changes occurred during grape juice boiling. However, during hot air or sun drying only the Hunter a-value changed. The reaction associated with color change followed zero-order reaction kinetics. The temperature dependence of the reaction rate constant was described by an Arrhenius-type equation.

WATER ADSORPTION AND DRYING CHARACTERISTICS OF OKRA Hibiscus Esculentus L

ABSTRACT Moisture adsorption characteristics of okra were evaluated at 10, 20, 30° C. Isotherms were found to be of type III. Monolayer moisture contents were evaluated with GAB model. Drying was carried out at 60, 70, 80° C and drying data were analysed to obtain diffusivity values from the period of first felling drying rate. Effective diffusivity increased with increasing temperature. Calculated values of the effective diffusivity showed an Arrhenius type temperature dependence.