Sevim Kaya

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.

The effect of salep content on the rheological characteristics of a typical ice-cream mix

Salep is a natural stabilizing agent used widely in Turkish-type ice cream. The traditional concentration of salep added to these ice creams is about 0.78%. The effect of salep concentration on the rheological characteristics of a representative ice cream, prepared from whole cows’ milk and sugar, was studied together with a water–salep–sugar mix using a Brookfield viscometer. The temperature-dependency of the apparent viscosities of the samples with different salep concentrations was determined. The empirical power law model was observed to fit the apparent viscosity–rotational speed data (r2: 0.954–0.999). The power-law index values (n) of milk–salep–sugar and water–salep–sugar mixes were in the range of 0.95–0.77 and 0.99–0.85, respectively. This is an indication that milk–salep–sugar mix is non-Newtonian at all concentrations and temperatures studied. A gradual increase in salep concentration was found to alter the rheological characteristics of water–salep–sugar mix from Newtonian to non-Newtonian. Salep concentration was more effective on viscosity change than temperature.

Microwave drying effects on properties of whey protein isolate edible films

Whey protein isolate (WPI) edible films were dried using microwave drying or at room conditions. The drying time of the films required 5 min in microwave oven and 18 h at room conditions. Water vapor permeability (WVP), mechanical properties, gloss and haze of WPI based edible films were determined. Water vapor transmission rate (WVTR) increased with increasing temperature, but the results showed that WVP did not show a similar trend. Microwave drying and drying at room conditions gave similar results for the WVP. Application of microwave increased the elongation and tensile strength values.

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.

Effect of salt on hardness and whiteness of Gaziantep cheese during short-term brining

Changes in hardness and color of Gaziantep cheese with respect to salt concentration in brine (5%, 10%, 15%, 20% and 25%) were monitored using a Texture Analyzer and Hunter Lab Color-index. Hardness of cheese samples in 20% and 25% salt solutions was significantly different from the others (P<0.05). Mean hardness values of the samples brined in 5%, 10%, 15%, 20% and 25% salt solutions were 3.31, 8.19, 11.89, 44.60 and 52.45 N at 13 days, respectively. Weakening in structure was observed in the cheese stored in 5% and 10% salt solutions as a result of absorbing water from brine. Whiteness of the cheese samples was affected with changing the salt concentration in brine while L-value decreased with increasing salt concentration.

Effects of heat treatment and fat reduction on the rheological and functional properties of Gaziantep cheese

Abstract Gaziantep cheeses with different fat contents (50.4%, 33.4%, and 13.5% w/w) were made and the curds of these were dipped into hot whey at three different temperatures (75°C, 85°C and 95°C) in accordance with the traditional techniques. Cheeses, the curds of which were not dipped into hot whey, were prepared as controls. Cheese samples were analyzed with respect to viscoelastic parameters, meltability and hardness. Reduction in the fat content resulted in significant (P 35°C. The temperature at which G′=G″, i.e. tan δ equals 1.0, is called as crossover temperature. The crossover temperature was accepted as melting temperature (Tm) and there was a good correlation between Tm and meltability measured with Arnott test for control cheeses. Reduction of the fat content increased the Tm values and decreased meltability. In contrast, increasing the curd dipping temperatures resulted in lowering of both meltability and Tm due to possible structural changes upon heating.

Water vapor permeability of pestil (a fruit leather) made from boiled grape juice with starch

Pestil, a well known fruit leather in Turkey, was prepared by drying boiled grape juice and starch mixture. The water vapor permeability (WVP) properties of pestil were determined at three different temperatures (15, 25 and 37 °C) and different relative humidity (RH) values. It was found that there was significant difference within WVP values in the studied range of RH (p<0.05). Effect of temperature on WVP values increased with RH. WVPs of pestil were compared with other fruit leathers.

Effects of Fat Reduction and Curd Dipping Temperature on Viscoelasticity, Texture and Appearance of Gaziantep Cheese

The effects of varying fat content (from 13.5 to 50.4% w/w) and curd dipping temperatures (75, 85 and 95°C) on changes in viscoelastic properties, texture and appearance of Gaziantep cheese were examined. Viscoelastic properties of cheeses were studied using creep and recovery tests. Creep measurements showed that fat reduction from 50.4% (w/w) to 13.5% (w/w) decreased viscoelasticity while dipping into hot whey increased that of low-fat cheeses. Textural characteristics (hardness, gumminess, cohesiveness, springiness) were determined by texture profile analysis (TPA). Hardness, gumminess, cohesiveness and springiness values increased with decreasing fat content (P < 0.05). The application of curd dipping also increased hardness, gumminess, cohesiveness and springiness. Textural parameters were correlated with each others, except cohesiveness. Fat in dry matter correlated only with hardness and springiness, however curd dipping process correlated with all TPA parameters considered in this study. Colour of the cheese samples was affected by fat content as L value and b value decreased with decreasing fat content (P < 0.05). The decrease in curd dipping temperature increased the L value (P < 0.05) and decreased the b value.

The effect of salt concentration on rancidity in Gaziantep cheese

Gaziantep cheese is a non-fermented and enzyme clotted type cheese. The changes in oxidative and hydrolytic rancidity in the cheese were analysed during its storage. Storage conditions were selected as 4, 10 and 20°C and 90, 170, 200 and 230 g kg−1 salt solutions by considering the traditional storage conditions. Oxidative rancidity increased with increasing temperature and NaCl concentration in the brine. Hydrolytic rancidity increased with increasing temperature and decreasing salt content of the cheese. The extent of oxidative rancidity was found to be higher than hydrolytic rancidity. The results of this study showed that the storage temperature should not be higher than 10°C and brine concentration must be higher than 90 g kg−1 and lower than 230 g kg−1 to minimize lipid oxidation. Gaziantep cheese was organoleptically examined after 2 months of storage at 20°C and in 90, 170 and 230 g kg−1 salt solutions, and it was found that even at a peroxide value around 1 meq kg−1, acceptable levels of changes in flavour were observed. Sensory analysis results showed that textural properties of Gaziantep cheese changed with salt concentration of the brine. © 1999 Society of Chemical Industry

Evaluation of sorption properties of Turkish tarhana powder

Moisture adsorption isotherms of commercial tarhana powder, a popular Turkish food used in soup making, were determined at 10 °C, 20 °C and 30 °C. Gravimetric static method was applied at 0.08-0.92 water activity range. The data was fitted to Guggenheim-Anderson-de-Boer (GAB), Oswin, Henderson and Brunauer-Emmett-Teller (BET) equations. Mean relative deviation (%E) was used to compare the goodness of fit. The BET was found the best equation for the range of water activity 0.08-0.58. The GAB equation was found adequate and gave similar result with the Oswin equation at 10 °C and 20 °C, while the Oswin equation was better for characterizing the adsorption behavior of tarhana sample for the whole range of temperature and water activity studied.