Thin-layer Drying Characteristics and Modeling of Two Varieties Green Malt

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1 Aug. 010, Volume 4, No.4 (Serial No.9) Journal of Agricultural Science and Technology, ISSN , USA Thin-layer Drying Characteristics and Modeling of Two Varieties Green Malt N. Aghajani 1, M. Kashiri and M. Kashaninejad 1 1. Department of Food Science & Technology, Gorgan University of Agricultural Sciences and Natural Resources, Beheshti Ave., Gorgan , Iran. Department of Food Science & Technology, University of Khazar, Mahmoud Abad , Iran Received: November 30, 009 / Accepted: February 4, 010 / Published: August 15, 010. Abstract: Malting process includes steeping, germination and kilning of cereal grains in controlled conditions. The Kilning process is the most expensive stage of malting industry. In the present study, drying behavior of green malt of two different barley varieties (Sahra and Dasht) were evaluated at air temperatures ranging from 40 to 85, at constant air velocity of 6 m/s. The main objective of this research was to select the best drying equations, in order to use them for the calculation of drying time and energy consumption. For that the experimental data was fitted to five thin layer drying equations (Lewis, Henderson and Pabis, Page, Modified page and Two-term). The coefficients of the equations were compared by three statistical parameters as residual sum of squares, standard error of estimate and mean relative deviation. The effect of temperature on the coefficients of the five selected equations was evaluated by linear regression. The results show that The Page model was found to be most suitable in describing the drying characteristics of green barley malt because of that has the lowest statistical parameters. The color of green barley malt was determined after drying using a spectro-colorimeter (Hunter Lab) in terms of Hunter L, a, and b values. Color measurement indicated that the ΔE index increased with an increase in drying air temperature. Key words: Thin-layer drying equation, green barley malt, Hunter Lab, air temperature. 1. Introduction Drying is the most common food preservation method used in practice [1-3] and drying (kilning) of green malt with aim of arrest modification and render malt stable for storage, ensure survival of enzymes for mashing and introduce desirable flavour and colour characteristics and eliminate undesirable flavors have been done [4]. Rocha et al. (199) found that temperature is the main factor in controlling the drying rate and color of basil and mint. It was observed that as drying temperature increased, basil developed brown colour [5]. The moisture content of green malt is about 4%- Corresponding author: N. Aghajani, M.Sc., research fields: food engineering and technology. N.Aghajani386@gmail.com, Narjes_Aghajani@yahoo.com. 48% and usually an air temperature ranging from 30 to 85 or a constant temperature of air may be used to kilning of green malt. High energy cost and the all year round nature of the malting process have led to number of developments in energy conservation. However, the effectiveness of those depends greatly on a theoretical knowledge of the drying process. But a little information about simulation of green malt drying is available. The development of a deep bed drying simulation model is a valuable tool for optimization of design and prediction of performance of the drying system for germinated barley (malt kilning). Thin layer drying models are required for simulation of deep bed drying of germinated barley, hereafter referred to as malt. Simulation models provide an opportunity for the assessment of the energy conservation and saving

2 Thin-layer Drying Characteristics and Modeling of Two Varieties Green Malt 71 alternative without full scale experiment [6]. For that the main objective of this research was to select the best drying equations, in order to use them for the calculation of drying time and energy consumption.. Materials and Methods.1 Preparation of Green Malt In this study two most important varieties of barley for malting in Iran, Sahra and Dasht, were used. These varieties obtained from Seed and Plant breeding Institute of Jahad-Agricultural Organization, Gonbad, Iran. The samples were manually cleaned to remove foreign matter, dust, dirt, broken and immature grains. To produce malt, cleaned barley varieties were steeped to raise the water content from 9-11% to around 45% at 17. This process takes about 48 hours. The moist grains were then allowed to germinate at 17 for 6-7 days, then the green malt is ready for kilning.. Experimental Apparatus Drying experiments were performed at the Department of Food Science and Technology of Gorgan University of Agricultural Sciences and Natural Resources. An electric thermal blast dryer (Type WB-OB7-45, Memert, German) was used for drying germinated barley, which could be regulated to any desired drying air temperature between 30 and 00 with high accuracy. A balance with an accuracy of g was used to measure the weight of the samples. The air velocity in the tubes just before the trays was 6 m/s..3 Experiments Experiments were performed at air temperatures of 40, 55, 70, and 85. At least three repetitions were done for each drying temperatures. For the drying experiments the trays were loaded with 00 g green malt to have similar airflow resistance. During the drying process, the weight of the samples was measured by taking the trays out of the dryer. The shorter time intervals for weighing have been chosen at the beginning of each test than at the end. For instance the time interval was 15 min at first 5 hours of drying and 30 min at the end. All the tests were continued to reach to a constant weight of the samples. After drying, the final Moisture content (M) of the samples was measured using the oven method (105, 4 h). The final dry matter mass of a sample was used to derive the temporal course of M during the drying experiment: Wt DM M t = (1) DM in which M t is the moisture content in decimal during the drying process at time t, W t is the weight of the sample in kg at time t and DM is the dry matter weight in kg. As a check, also the initial M of the fresh sample was measured before each drying test..4 Color Measurement The color of malts was determined after drying after every temperature using Lab Scan 6000 spectro-colorimeter (Hunter Associates Laboratory Inc., VA, USA). The color was measured in terms of Hunter L, a, and b values. Hunter L represents the lightness or darkness of the object and it is measured on a scale of 0 to 100. L value of 100 represents white and L of 0 represents black. Hunter a represents redness or greenness. A positive value of Hunter a is assigned for red, zero for gray and negative for green. Hunter b represents yellowness or blueness. A positive value of Hunter b is assigned for yellow and a negative value is assigned for blue. The samples size of 5 g was used for color measurements. For each sample, five replicates of the color test were performed. Since color is a combined effect of all three coordinates (L, a, and b) it should be viewed as a combined index. To evaluate the effect of different drying temperature on the overall combined color of dried green malt, the index ΔE as given by following equation was calculated by taking the color of undried green malt as the base value. Δ E = ( ΔL) + ( Δa) + ( Δb) () Where L, a, and b are the color coordinates of the

3 7 Thin-layer Drying Characteristics and Modeling of Two Varieties Green Malt sample and L base, a base, and b base are the color coordinates of the undried sample..5 Drying Equations For calculating M e at each air temperature, the specified sample placed in dryer and kilning were continued to reach to a constant weight. Then M e was calculated from previous equation. The moisture ratio (MR) of the green malt during the drying experiments was calculated using the following equation: M t M e MR = (3) M M 0 In which M t is moisture content (dry basis) at time t, M e is equilibrium moisture content and M 0 is initial moisture content. A list of drying equations was made based on the literature (Table 1). All equations are monotonic decreasing equations, which is the property of drying, except the Wang and Singh, and Midilli and Kucuk equations. The Wang and Singh equation as well as Midilli and Kucuk equation are rejected because these equations may lead to an increase of MR at long term. The remaining equations were arranged in the order of complexity. The complexity was defined based on number of coefficients, number of terms, and power of time. For instance the Lewis equation, which is the simplest among the equations, has one coefficient, one term and the power of time is one. The equation of two terms has four coefficients and the power of t is one. Finally we can conclude that there are five different equations for fitting to the data (Table 1). 3. Data Analysis The moisture content data obtained at different drying air temperatures were converted to the MR. Then the selected MR equations for each drying experiment was determined. Linear regression procedure was used to estimate the parameters associated with the five drying models from the experimental data at 5% significant level using Matlab e software. Functional relationship between the estimated parameters associated with the models and the drying temperature were also determined using linear regression procedure to estimate the coefficients for these relationships. The fitting steps for both variety of green malt were as follows: (a) A linear regression program in Matlab was used to fit the equations to the experimental data to find the equation and the error parameters residual sum of square (RSS), standard error of estimation (SEE) and mean relative deviation (MRD). SEE= RSS= m i= 1 m i= 1 ( ) MR MR d. f. ( ) MR i= 1 (4) MR (5) m 1 MR MR MRD = (6) m MR Where MR is moisture Ratio (dimensionless) and d.f. is degree of freedom. (b) The best equation was selected based on values of the statistical parameter and simplicity (less parameter). (c) The parameters in the equations were fitted as a function of temperature. The color data of products was analyzed with Matlab software at 5% significant level and Duncan experiment. 4. Results and Discussion 4.1 Experimental Results Fig. 1 presents the drying curves of the Dasht and Sahra green malts, which were dried at the same air temperature (40 ). They showed almost a similar behavior. Drying curves determined that drying of green malts of two varieties occurs in the falling rate period. To describe this phenomenon, the drying rate was calculated at different times and temperatures and plotted against moisture content (d.b.%) as shown in

4 Thin-layer Drying Characteristics and Modeling of Two Varieties Green Malt 73 Table 1 Some of mathematical equations given by various authors for the drying curves and grouping of the equation based on the mathematical similarity. No. Model name Equation Coefficients Reference 1 Lewis MR=exp (-kt) 1 [7] Henderson and pabis MR=a exp (-kt) [8] 3 Page MR=exp (-kt n ) [9] 4 Modified page MR=exp (-kt) n [10-11] 5 Two-term MR=a exp (-k 1 t) + b exp (-k t) 4 [1], [1] 0 Wang and Singh MR=1+ at +bt Rejected [13] 0 Midilli and Kucuk MR=a exp (-kt n )+ bt Rejected [] Fig. 1 Moisture ratio changes of Sahra and Dasht green malts at 40. Fig.. Initially the drying rate was higher because of initially water for evaporation comes from regions near the surface. As drying progressed the drying rate decreased with decrease of moisture content, as the water to be evaporated comes from parenchyma cells within the structure and must be transported to the surface. The falling rate region is indicative of an increased resistance to both heat and mass transfer through the inner cells. 4. Selection of the Best Equation All the data series were fitted to the remaining five equations. The average values of the RSS, SEE and the MRD for all equations at different temperature are shown in Fig. 3A for Sahra and in Fig. 3B for Dasht green malts. The lower value of RSS, SEE or MRD shows a higher accuracy of the fitting. In Fig. 3A and 3B Lewis and Henderson and pabis models have high values of RSS, SEE and MRD. Although the Page, Modified page and Two-term were very similar among (A) (B) Fig. Effect of temperature on drying rate of Sahra and Dasht green malt (respectively from A to B). the selected equations, the Page equation was selected as the appropriate equation for this research because the levels of the Page equation were very similar, but the Page equation is simpler with two parameters while two-term equation has four parameters. The lower numbers of parameters is preferable to find a relationship between the parameter values and the drying conditions. Also the Page equation is simpler than the Modified page.

5 74 Thin-layer Drying Characteristics and Modeling of Two Varieties Green Malt (A) Dasht green malts using all data series. The results are given in Eq. (7) for Sahra (S) and Eq. (8) for Dasht green malts (D), T represents the temperature in n = ( 6.10 T ) + (0.0099T ) (7) n S + D = ( T ) + (0.043T ) (8) Several expressions were applied for the relation of k and temperature. The exponential and polynomial equations were chosen to find the best fit for the k values as a function of temperature (T in ) for Sahra and Dasht green malts respectively. Finally the following equations [Eqs. (9) and (10)] were found for drying of those. ( T ) k S = exp (9) k D = (8.10 T ) (0.0078T ) (10) The complete equation become therefore for leaves Eq. (11) and for chopped plants Eq. (1). (B) Fig. 3 The average level of RSS, SEE and MRD of all data series for different drying equations for Sahra and Dasht green malt (respectively from A to B). Table Page model parameters in different drying temperature. Variety Temperature ( ) k N Sahra Dasht The experimental data were fitted to the Page equation to find the k and n values simultaneously at each temperature. The Page model coefficients (k and n) for each drying temperature run were calculated (Table ). For the n value at different temperatures a polynomial equation was fitted for Sahra as well as (A) (B) Fig. 4 Observed and predicted moisture ratios of sahra and dasht malt at different drying air temprature (respectively from A to B).

6 Thin-layer Drying Characteristics and Modeling of Two Varieties Green Malt 75 Table 3 Color of dried green malt measured using the hunter lab spectrocolorimeter. Temperature Color Variety ( ) L a b ΔE c b Sahra ab a b b Dasht ab a * Letters a and b indicate that means with the same letter are not significantly different at 5% level of significance. MR S = ( 0.019T ) ( 6.10 T ) ( ) exp( (0.0106exp ) + T t ) (11) MR = exp( (8.10 T ) (0.0078T ) D ( T ) + (0.043T ) ) t ) (1) Some of the experimental MR values as a function of time are presented in Fig. 4A for Sahra and in Fig. 4B for Dasht green malt together with the predicted values using the above given exponential equations. We can see that these equations are good enough to estimate the M at different drying time for our purpose of calculating energy and drying time. 4.3 Effect of Drying Air Temperature on Color of Malt Table 3 shows the color data in terms of Hunter L., a and b values of dried green malt at four drying air temperatures. It was observed from the data that value of a increased as drying air temperature was increased and value of L decreased when drying air temperature was increased but the value of b was approximately constant as drying air temperature increased. Visually, the sample became darker at higher drying air temperatures. The color index ΔE was calculated by taking L, a and b values of undried green malt as the base values. Also the results showed that differences in ΔE values for dried green malt at different temperatures were significant (P<0.05). It was found that greenness decreased with an increase in drying air temperature. 5. Conclusions As the drying behavior of the Sahra and Dasht green malts was similar, the same drying model can be used for both varieties. Among the drying equations, which were evaluated in this research, the Page, Modified page and Two-term equations showed the similar fit. The difference between the Page equation and the Two-term equation is small. The Page equation is simpler than Modified page and that has two variables, which makes it easier to find the dependency of the parameters with temperature. Therefore, the Page equation is selected as a relevant equation for drying of green malt. Relevant equations as well as n and k values were found as function of temperature for Sahra and Dasht green malts. Equations show small difference with experiments. The equations can be used at temperatures They are suitable to estimate the moisture content during drying in order to calculate energy consumption, drying time and cost estimations. They are also usable in dryer design. Color measurement indicated that greenness decreased and samples became darker with an increase in drying air temperature. Acknowledgments These investigations were partly supported by the Gorgan University of Agricultural Sciences and Natural Resources. The authors are thankful for providing facilities to conduct this research. References [1] O. Yaldýz, C. Ertekýn, Thin layer solar drying of some vegetables, Drying Technology 19 (001) [] A. Midilli, H. Kucuk, Z. Yapar, A new model for single-layer drying, Drying Technology 0 (00) [3] S. Janjai, P. Tung, Performance of a solar dryer using hot air from roof-integrated solar collectors for drying herbs and spices, Renewable Energy 30 (005) [4] C.W. Bamforth, Food Fermentation and Micro-organisms, Blackwell Publishing, 005. [5] T. Rocha, A. Lebert, C.M. Audouin, Effect of Drying Conditions and of Blanching on Drying Kinetics of Mint (Mentha spicata Huds.) and Basil (Ocimum basilicum),

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