Mahir Turhan

Application of Peleg model to study water absorption in chickpea during soaking

Application of the Peleg model was investigated for predicting water absorption by five winter- and five spring-planted chickpea genotypes during soaking between temperature (T ) of 20 and 100 C. The Peleg model can predict kinetics of the chickpea soaking till equilibrium using short-term data at the given conditions. Its specific form for infinite time may also be used to estimate equilibrium moisture content (Me )a tT P 40 C. Spring and winter chickpeas showed no significant difference ðP < 0:05Þ in the Peleg rate constant (K1) and Peleg capacity constant (K2) within and between the groups at all temperatures except for K1 at T < 40 C. The discrepancy for K1 was attributed to characteristic water permeabilities of spring and winter chickpeas which were prominent at T < 40 C. The Peleg constant K1 decreased from 17:1 � 10 � 3 to 0:95 � 10 � 3 h% � 1 for the spring chickpeas, and from 22:2 � 10 � 3 to 1:02 � 10 � 3 h% � 1 for the winter chickpeas with increasing temperature from 20 to 100 C. An Arrhenius plot for K1 exhibited a slope change around 55 C corresponding to approximate gelatinization temperature of the chickpea samples. The Peleg constant K2 for the samples linearly increased from 7:26 � 10 � 3 to 9:48 � 10 � 3 % � 1 with increasing temperature from 20 to 100

Air-drying behavior of Dwarf Cavendish and Gros Michel banana slices

Air-drying behavior of untreated, and sodium bisulphite and ascorbic/citric acid treated Dwarf Cavendish and Gros Michel banana slices was investigated between 40 and 70 °C. Pretreatments and increasing temperature decreased the browning, and the color change in the untreated samples was acceptable. Pretreatments and temperature did not affect the shrinkage. Cavendish samples shrank more than Michel samples at the same conditions. The drying happened in two falling rate periods. Variety of the samples did not affect the drying behavior. Effect of the heat transfer on the drying compared to the mass transfer was assumed negligible due to modified Lewis number estimated greater than 60. The drying was evaluated using the diffusion equation for an infinite slab for a Fourier number greater than 0.1. In all conditions the equation fitted the process well. The effective moisture diffusivity (D) increased with increasing temperature between 40 and 70 °C in the untreated samples. It increased between 40 and 60 °C, and decreased at 70 °C in the pretreated samples probably due to case hardening and starch gelatinization above 60 °C. It was estimated to be of the order of 10−11 and 10−10 m2/s. The effect of temperature on D was evaluated using the Arrhenius equation. Activation energy (Ea) did not change with the variety. It was higher for the untreated samples than for the pretreated samples during the first falling drying period (I. FRP), and almost the same during the second falling drying period (II. FRP) for all samples. Value of Ea increased with transition from the I. FRP to the II. FRP. The surface moisture transfer coefficient exhibited the same behavior as did D. It was estimated to be of the order of 10−7 and 10−6 m/s. The whole process was controlled by the internal moisture transfer as deduced from the good fit of the diffusion equation and a Biot number greater than 10.

Analysis of chickpea soaking by simultaneous water transfer and water-starch reaction

Abstract The soaking process of five spring and five winter chickpea genotypes were investigated in water between 20°C and 100°C. Samples did not differ in initial water content (IWC), water absorption capacity (WAC), swelling capacity (SC), and seed coat thickness in terms of the growing season. While WAC decreased with increasing temperature, SC was not affected by temperature. The process was considered to be a simultaneous unsteady-state water diffusion and first order irreversible water–starch reaction phenomenon. The seed coat effectively controlled the water absorption up to 60% (d.b.) water content in all samples. The spring and winter samples showed no significant difference in the diffusivity (Deff) and true reaction rate constant (k) within the given temperature range except for Deff below 30°C. Spring samples had greater Deff values than winter samples below 30°C possibly due to more permeable seed coat structures of the former. The magnitude of Deff and k were between 10−10 and 10 −9 m 2 s −1 and 10−6 and 10 −4 s −1 , respectively, within the given temperature range. They increased with increasing temperature and the effect of temperature was evaluated through an Arrhenius type equation. Two distinct activation energies were observed below and above 55°C for both Deff and k. It was 48 and 18 kJ mol−1 for Deff and 23 and 41 kJ mol−1 for k below and above 55°C, respectively. The trend of the activation energies suggested that diffusion was more effective on the process than the reaction below 55°C and vice versa above 55°C, and significant textural changes start to take place in chickpea around 55°C. The internal effectiveness factor (η) increased from 0.61 to 0.74 with temperature from 20°C to 100°C. Its trend corroborated the above conclusion on the relative effects of the diffusion and reaction on the soaking process below and above 55°C. The birefringence of samples indicated that the gelatinization of chickpea starch starts around 55°C, which may explain why the activation energies of Deff and k changed around 55°C.

Kinetics of in situ and in vitro gelatinization of hard and soft wheat starches during cooking in water

Abstract Kinetics of in situ and in vitro gelatinization of hard ( T. durum ) and soft T. aestivum wheat starches were investigated during cooking in water at 60°C, 70°C, 80°C, 90°C, and 100°C. At the given temperatures, the gelatinization process ceased before 100% completion at a final degree of gelatinization (FDG) for all starches. At the same temperature, the FDG was higher for the in vitro gelatinization than the in situ gelatinization for both hard and soft wheat starches. It was higher for the soft wheat starch than the hard wheat starch for both in situ and in vitro processes. Effect of temperature on the FDG was assessed through a Clausius–Clapeyron type equation. Starch gelatinization followed first-order reaction kinetics for both in situ and in vitro processes. The reaction rate constant ( k r ) was higher for the in vitro gelatinization than the in situ gelatinization for both starches. It was higher for the soft wheat starch than the hard wheat starch for both processes. The k r values were in the order of 10 −5 to 10 −4 s −1 for the in situ gelatinizations and 10 −4 to 10 −3 s −1 for the in vitro gelatinizations. The rate of the gelatinization reaction increased with increasing temperature and the effect of temperature on k r was evaluated using an Arrhenius type equation. In vitro gelatinizations had an average activation energy ( E a ) of 76 kJ/mol between 60°C and 100°C. In situ gelatinizations had an average E a of 137 below 75°C, and 79 kJ/mol above 75°C. Assuming the in vitro gelatinizations were effectively controlled by the reaction of starch with water between 60°C and 100°C, the in situ gelatinizations were effectively controlled by water transfer below 75°C and reaction of starch with water above 75°C.

Abrupt changes in the rates of processes occurring during hydrothermal treatment of whole starchy foods around the gelatinization temperature-a review of the literature

Abstract The rate of processes such as water transfer, gelatinization, loss of soluble solids, volumetric expansion etc. occurring during hydrothermal treatment of whole starchy foods exhibits one common behavior: The plots of the rate constant specific to the given process versus temperature give a break-point temperature ( T bre ) around the gelatinization temperature ( T gel ). Some workers connected this phenomenon to starch gelatinization. The review of the pertinent works exhibited that the T bre values are in the ranges of the gelatinization temperatures given in the literature. These ranges are large enough that the observed T bre values could readily be within or close to them. The break-point phenomenon may potentially be a non-invasive simple method for determining the T gel in whole starchy foods, e.g. in situ T gel . This potential must be tested on different types of starchy foods by comparing the T bre with measured T gel of the same sample.

Estimation of liquid diffusivities of biosolutes by using diaphragm cell method with defined pore characteristics

Confidence of the diaphragm cell method with a diaphragm having defined pore characteristics was investigated for liquid diffusivity determination of some biosolutes. Diffusivities of NaCl, KCl, glucose, L-Tryptophan, lysozyme, and BSA were estimated. Satisfactory agreements were observed between estimated diffusivities and those in the literature.

Application of unreacted-core model to in situ gelatinization of chickpea starch

Unreacted-core model for reaction-controlled systems was tested on modeling of starch gelatinization in whole chickpea (in situ) during cooking. Experiments were conducted in deionized water at 50, 60, 70, 80, 90, and 100 °C. The process was followed through images of the flat sides of the chickpea cotyledons. During cooking between 60 and 100 °C, a white core in the original color of the cotyledons and a surrounding opaque yellow zone were observed on the cotyledons. According to birefringence studies starch granules in the yellow zone were gelatinized, and in the white core they remained ungelatinized. The formation of the yellow color was connected to the gelatinization in the peripheral zone. During cooking at 50 °C the color change was not observed because of working below the gelatinization temperature of chickpea starch. The area of the gelatinized zone increased at the expense of the area of the ungelatinized core with the progress of the cooking. The unreacted-core model fitted the process very well, and the estimated gelatinization times were in good agreement with the experimental gelatinization times. The kinetic data for the gelatinization reaction estimated after verifying the unreacted-core model were in agreement with the literature. These findings indicated that the in situ gelatinization of chickpea starch can be modeled using the unreacted-core model, and the process is effectively gelatinization-controlled under the given conditions.

Water vapor adsorption of ready-to-cook wheat

Abstract Water vapor adsorption of bulgur and hedik samples made from Triticum durum (Gediz 75) and Triticum aestivum (Panda) wheat were investigated. Experiments were conducted at 5, 15, 20, 30, and 40 °C for bulgur and at 20 °C for hedik samples between relative humidity (RH) of 11% and 100%. Bulgur samples became moldy before attaining equilibrium above 5 °C and 81% RH between 4 and 28 d depending on temperature (T). Hedik samples did not become apparently moldy and always had smaller equilibrium moisture content (X) than their bulgur counterparts at 20 °C and same RH. Type of wheat governed adsorption of the products. Bulgur and hedik of Gediz wheat always exhibited higher water adsorption capacity than bulgur and hedik of Panda wheat, respectively. The Guggenheim–Anderson–Boer model fitted all samples very well under the given conditions. The monolayer moisture content (Xm) was 9.7% and 9.6% (d.b.) for bulgur and hedik of Gediz wheat, and 7.5% and 6.5% (d.b.) for bulgur and hedik of Panda wheat, respectively. The heat of adsorption ( Q ) of bulgur samples was not affected by temperature and decreased with increasing X. Gediz bulgur had higher Q values than Panda bulgur up to the capillary condensation region. The average Q was obtained as 75, 50, and 45 kJ/mol for Gediz bulgur, and 73, 49, and 45 kJ/mol Panda bulgur for the monolayer, multilayer, and capillary adsorption regions, respectively.

DRYING OF GELATINIZED WHOLE WHEAT

Whole grains of gelatinized durum and soft wheat were dried by forced and natural convection at 40, 60, 80, and 100°C. Magnetic resonance images taken periodically during drying indicated that Ficks diffusion is not applicable to describe the moisture transfer during drying of the gelatinized wheat grains. A simple mathematical model based on overall moisture balance fitted the experimental data very well. The drying took place in the falling rate period, which was approximated by two regions – first and second falling rate periods (FFRP and SFRP). The internal drying coefficient linearly increased with increasing drying temperature, and was almost an order of magnitude (from 104 to 105 s-1) higher during FFRP than SFRP. The soft wheat dried faster than the durum wheat. The effect of forced convection was more pronounced during FFRP than SFRP.

Kinetics of κ-Casein/Immobilized Chymosin Hydrolysis

Abstract True kinetics of κ-casein hydrolysis with chymosin immobilized in Ca-alginate was investigated in pure κ-casein and reconstituted milk solutions at 7, 22, and 37°C. The true Michaelis-Menten constant (KM,T) was estimated to be 0.263, 0.154, and 0.133 μmol ml−1 at 7, 22, and 37°C in the milk solution, respectively. It was estimated to be 0.031 μmol ml−1 on average in the κ-casein solution within the given temperature range. The true reaction rate constant (k3,T) was estimated to be 14.7, 21.6, and 46.5 s−1 in the milk solution and 43.7, 75.2, and 146.4 s−1 in the κ-casein solution at 7, 22, and 37°C, respectively. The effect of temperature on k3,T was expressed by the Arrhenius equation. The activation energy (Ea) was estimated to be 6,610 × 10−6 cal μmol−1 in the milk solution and 6,993 × 10−6 cal μmol−1 in the κ-casein solution.