The effect of wheat boiling time, bulgur particle size, drying time and temperature on some physical properties of hot air dried Tarkhineh

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1 Scientific Journal of Pure and Applied Sciences (2) 2(4) ISSN Contents lists available at Sjournals Journal homepage: The effect of wheat boiling time, bulgur particle size, drying time and temperature on some physical properties of hot air dried Tarkhineh A. Ghaitaranpour*, F. Tabatabaie Yazdi, B. Alizadeh Behbahani, A. Mortazavi, M. Mohebbi Food Science and Technology, Faculty of Agriculture, Ferdowsi university of Mashhad, Mashhad, Iran. * Corresponding author; A. Ghaitaranpour; Food Science and Technology, Faculty of Agriculture, Ferdowsi university of Mashhad, Mashhad, Iran. Original article A R T I C L E I N F O A B S T R A C T Article history: Received 6 March 2 Accepted 25 March 2 Available online 28 April 2 Keywords: Tarkhineh Drying Mathematical modeling color Tarkineh is one of the traditional products of western part of Iran. This work was carried out to study drying behavior of Tarkineh. The effect of wheat boiling time (. and.5 hours), drying temperature (, 8 and 9 C), drying time (from to 9 minutes) and bulgur particle size (fine,, coarse) on drying behavior of Tarkineh were analyzed. Different mathematical models were applied to evaluate the behavior of Tarkineh during hot air drying and color changes of Tarkineh during hot air drying was assumed using image processing. At the beginning of the drying process, the L* decreased rapidly and b* increasing quickly, but both were relatively stable afterward. a* slightly decreased initially but then depending on the type of sample increased or remain constant. When bulgur particle size increases, generally, the amount of L* increase but a* and b* decrease. The results indicated that At C, the logarithmic model can present better predictions for the moisture transfer than other models for ultra cooked samples but for raw and cooked samples, the two-term model were appropriate. At 8 and 9 C, the two-term model was the best descriptive for ultra cooked samples but for raw and cooked samples, the model were appropriate. Mentioned variables had major effect on the drying behavior of Tarkhineh. For increasing the production rate and improving the color of Tarkineh, boiling of wheat for one hour and drying at 8 C is recommended. 75

2 2 Sjournals. All rights reserved.. Introduction In western part of Iran (Kermanshah, Ilam, Lorestan, and Kurdistan Provinces), a traditional soup is made with dried tarkhineh. Tarkhineh is a traditional fermented food that generally prepared with wheat grout, doogh(churned sour milk) and turnip. The mixture is kneaded with vegetables, salt, leaven and spices and then fermented with doogh bacteria and yeast (Tajabadi et al., 2, Padshah, 957; tabatabaei-yazdi et al., 22). It fermented for -6 days. After fermentation the mixture is sun dried, Tarkhineh could be stored for -2 years under dry and cold storage conditions. It consumed as soup by cooking in water. Tarkhineh-like food consumed in other countries such as Iraq, Turkey and Egypt (bahnasawy et al., 24; Ekinci et al., 25; Hayata et al., 22; Karadozlu, 28). Tarhana has an acidic and sour taste. Flavor and aroma of tarkhineh depends on many factors including the quality of materials, the microbial properties and the drying conditions. Tarkhineh is a good source of minerals, organic acids and free amino acids which make it healthy for children, the elderly and medical patients. In addition, it is a good source of vitamins such as thiamine, riboflavin and vitamin B2 (Ibanoglu et al, 995, Tabatabaei-Yazdi et al, 22). Until now, most of Research has focused on tarkhine s nutritional properties and microbiological characteristics. Drying process is an important step in production of tarkhineh, because drying condition has a significant effect on its color and cost of production. Drying behavior of tarhana dough (Tarkhineh-like food) was studied by changing temperature (6 8 C) and sample thickness ( 6 mm). The result shows that cooking process accelerated the drying process. An increase in D eff values was observed at increased sample thickness for both normal and cooked dough (Ibanoglu et al., 22). Thin layer drying characteristics of parboiled wheat were studied for a temperature range of 4 6 C, using semi-theoretical and empirical models. Results show that total drying occurred in falling rate period. The effective diffusivity varied from.28 - to m 2 /s over the temperature range. The activation energy of for moisture diffusion during drying was found to be 7. kj/g mol K. The thin layer drying characteristics of parboiled wheat was best fitted with the Two-term model (Mohapatra et al., 25). In a study, thin layer drying of wheat (tajan) was modeled at temperatures of 5, 45, 5, 6 and C. Results of this study show that Henderson and pabis, Logarithmic, and Modified Henderson and pabis models have good agreement with the experimental data obtained (Rafiee et al., 25). The influence of two different rice cultivars with different flour particle size in batter characteristics and in sponge and layer cake formulas were analyzed. The result indicates that crust and crumb color parameters may be affected by flour particle size, for example in coarser particle size, make the flour color darker (Hera et al., 22).. Final stage of Tarkhineh production is drying. In this study, the influence of wheat boiling time (, and.5 hours), drying temperature (, 8 and 9 C), drying time (from to 9 minutes) and bulgur Particle Size (fine,, coarse) on drying behavior of Tarkineh were analyzed. 2. Materials and methods 2.. Production of Tarkhineh The ingredients used in Tarkhineh preparation (bulgur, doogh, yeast, turnip, salt and leaven) were purchased from local markets in Mashhad, Iran. The doogh used was made from cow s milk. Yeast was baker s yeast in active dry form. Three different wheat bulgur particle sizes, fine, and coarser, were supplied. Ingredients ratio of Tarkhineh is presented in table (). Turnip was grated and blended with doogh, salt and leaven. Then wheat grout added to this mixture. They were kneaded in a bowl to formed Tarkhineh dough. At the beginning of preparation, Tarkhineh samples were separated in to three parts. Sample () was made from raw wheat bulgur; the second sample (2) was made from cooked wheat bulgur (boiled about 6 min) and the third sample () was made from ultra boiled wheat (boiled about 2 min) bulgur. It was kneaded daily to facilitate fermentation. All samples were placed in a bag and then put them in a jar. The bulgur particle size was measured using sieves with different mesh numbers (4, 6 and 5). 76

3 Table Tarkhineh ingredient formula. Tarkhineh type 2 leaven Salt Ingredient(gr) Turnip Doogh Wheat Final moisture content of tarkhineh(%) Tray drying About 6 gr of each sample was spread into plate to mm thickness. The samples were dried at, 8, and 9 C. A laboratory scale hot air dryer (Soroush Medical Company) contain trays with dimensions 5 cm was employed for the present study. In this drier, air temperature could be varied within the range of 6-9 C and air velocity is constant at.5m/s. 2.. Mathematical modeling For drying model selection, the experimental data of the samples for each drying conditions was fitted to the well known thin layer drying models proposed in the literature for drying which are given in Table (2). The coefficients of the drying models were estimated from the experimental data using the nonlinear regression analysis (MATLAB R2a). The best of fit was determined using three parameters: higher values for coefficient of determination (R 2 ), sum square errors (SSE) and root mean square error (RMSE). The moisture ratio (MR) of tarkhineh during drying was calculated using the equation (). Table 2 Empirical drying equations. No. Name of equation Equation Newton f(x) = exp(-kt) 2 Page f(x) = exp(-kt n ) Henderson and pabis f(x) = a exp(-kt) 4 Logarithmic f(x) = a exp(-kt)+c 5 f(x) = a exp(-kt)+bexp(-gt) 6 exponential f(x) = a exp(-kt)+exp(-mt) 7 Approximation of diffusion f(x) = a exp(-kt)+(-a) exp(-kbt) 8 f(x) = a exp(-kt n )+bt 9 Verma et al f(x) = a exp(-kt)+(-a) exp(-gt) Wang and Singh f(x) = +at+bt 2 Equation (): MR= (X t -X e )/(X -X e ) Where X t, X, and X e are moisture content at any time, initial and equilibrium moisture content (kg water/kg dry matter), respectively. The value of M e is negligible, thus It was assumed zero (Abbasi et al., 2) Color tarkhineh pictures were taken using a digital camera (model kanon, pawershot A52). The digital images were saved in JPEG format (Figure ). The analysis of tarkhineh s surface color for obtaining the color parameters (L*a*b*) was performed using Analyze option in image J software (Shahidi et al., 22) Statistical analysis Analysis of variance were computed using SPSS 6 software and The experimental groups were then separated statistically using Duncan s multiple range tests (p<.5). 77

4 2 4 5 Fig.. Steps of image processing to estimate L*a*b*of tarkhineh with Image J software. : Original image, 2: after removal of background, : Parameter L*, 4: Parameter a*, 5: Parameter b*.. Results and discussion.. The effect of wheat boiling time, bulgur Particle Size, and drying temperature on drying time The obtained results (Table ) showed that as drying temperature increase, drying time of all tarkhineh samples was significantly decreased (Fig. ). This is because Moisture absorption ability drier s air increases with increasing temperature (Gazar et al., 29; Gholami et al., 29). Maximum influence of increasing temperature on the drying rate was observed in raw samples. The raw sample drying time decreases at least 5% when drying temperature increases from to 8 C, while maximum decreasing in drying time was 2% when temperature increases from 8 to 9 C in raw tarkhineh samples. But in cooked samples, the opposite state of raw samples, were occur (maximum decreasing in drying time was 9.4% when temperature increases from to 8 C in boiled tarkhineh samples but when drying temperature increases from 8 to 9 C, drying time decreases at least 9%). In addition results show that increasing the particle size of bulgur can reduce drying time significantly. Increase in drying temperature and bulgur Particle Size has positive interactions on drying time. Higher drying rate was observed in tarkhineh slices when increasing in bulgur Particle Size and drying temperature occur simultaneously. Table Drying time of tarkhineh samples. Drying temperature ( C) Sample characteristics Wheat boiling time (h) Bulgur Particle Size Drying time (min) 9± 69±7 69±7 9±7 48±5 5± ±5 45±5 6±2 45±2 45±22. 5±2 ±2.5 29±9. ± Influence of wheat boiling time, bulgur Particle Size, and drying temperature on color change of tarkhineh during drying 78

5 At the beginning of the drying process, in all samples L* value decreased rapidly but then reached a relatively stable amount. After a rapid increase in parameter b* in the early hours of drying it was almost constant. Relative stability L* and b* followed by rapid changes in the early hours of drying could be due to Millard reaction (Kahyaoglu et al., 2; Ibanoglu and Maskan, 22). In addition this could be due to this fact that doogh volume /bulgur volume ratio is high at the beginning of drying so White color of doogh is the dominant but during the drying process doogh volume reduces and bulgur s yellow color is more visible. Since the dehydration rate is higher at the beginning of the drying process and a large amount of water evaporated from the surface of the product therefore, a rapid increase in the b* (yellow/ blue indicators) and a rapid decrease in the L* (black/white indicators) can be observed but after this Period, L* and b* remains constant. a* parameter, in initial decreased slightly but after that, depending on the type of tarkhineh sample, may be increase or remain constant (Figure 2), When bulgur particle size increases, the amount of L* increase but a* and b* decrease, generally (Table 4). -5 a* time(h) b* time(h) Fig. 2. L, a, b. Influence of wheat boiling time on color change of Tarkhineh color grading during drying at 9 C. Fig.. The effect of drying time and temperature on the relative humidity of Tarkhineh. Wheat boiling time (h) As the drying temperature Increased from 8 to 9 C, L* decreased, but a* and b* increased. Drying temperature has a main effect on the color of the product. The rate of non-enzymatic browning reactions increases with increasing temperature. With the increase in temperature from to 8 C, L* increased but a* and b* factors decreased. This was in contrast with the results obtained by the other researchers (Kahyaoglu et al., 2; Hera et al., 22). This difference could be due to the longer duration of drying at C and the existence of doogh in the tarkhineh dough, As a result, the conditions will be better for browning reactions (Kahyaoglu et al, 79

6 2). Wheat boiling has a significant effect on a* and b* parameters but L* parameter did not change significantly. As a result of boiling, b* decreased but a* were not systematically changed. a* value with increasing boiling time initially decreased and then increased. Modeling: The low values of (SSE) and (RMSE) and high values of Adjusted R-square indicated that the two term model for raw and boiled samples and Logarithmic model for ultra boiled samples, could illustrate the drying curve of tarkhineh at temperature of C. At 8 and 9 C for ultra boiled samples two term model and for other samples, model is appropriate (Table 5). 4. Conclusion This study indicates that as a result of the boiling of wheat and starch gelatinization, drying rate of tarkhineh increases. If drying process performed at 8 ºC, tarkhineh has a lighter color. So in order to reduce production time and improve the color, wheat boiling for an hour and drying at 8 ºC is recommended. Acknowledgement The authors are thankful to Research's Deputy of Ferdowsi University of Mashhad for providing the cost of this project. The authors are also grateful to Ms. Banoo mirany for her helps. Table 4 Different values of color parameters of tarkhineh samples after the drying process. Drying Sample characteristics temperatur L* a* e ( wheat boiling Bulgur Particle C) time (h) Size ±4-6.8± ±5-9.95± ± ± ± ± ±4-2.94± ±.9 -.4± ±4-2.82± ± ± ± - 2.± ±4-2.2± ±4-5.24± ± ± ±4-2.64± ± ± ±4-2.8±.9 b* 22.9 ± ± ± ± ± ± ± 7.9 ± ± ± ± ± ± 2.72 ± ±.5 8

7 Table 5 Statistical results obtained from the best selected models and values of the drying constant and coefficients of the best model. Sample characteristics Constant and coefficients of the model Drying wheat Bulgur temperature ( boiling Particle Model a b c g k C) time (h) Size n SSE Adjusted R-square RMSE Logarithmic

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