Studies on microwave energy absorption of fresh green bell pepper (Capsicum)

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1 June, 015 AgricEngInt: CIGR Journal Oen access at htt:// Vol. 17, No. 105 Studies on microwave energy absortion of fresh green bell (Casicum) Ahmad Kouchakzadeh *, Aref Safari (Deartment of Biosystem Engineering, Ilam University, Ilam, Iran) Abstract: Electromagnetic wave of extremely high frequency caused non-uniform absortion in foodstuffs. To measure the ability of fresh green bell in absorbing microwave energy, the water as the medium absortion radiation was used and by determining the water temerature and then calculating its absorbed microwave energy, the microwave energy absorbed by the fresh green bell s were acquired. The results showed that absorb energy is roortional to the square of irradiated owers. Keywords: microwave, energy absortion, green bell Citation: Kouchakzadeh, A., and A. Safari Studies on microwave energy absortion of fresh green bell (Casicum). AgricEngInt: CIGR Journal, 17(): Introduction1 The microwaves are the art of electromagnetic waves with the frequency about GHz and wavelength of m (Jones et al., 00). They are reflected by metals, effluence by material such as lastic, glass, aer and ceramic, and absorbed by material with biolar molecules such as foodstuffs. Highly secific in heating effect in foods are the characteristic of microwave energy (Buffler, 1993). As the water molecules are biolar and revolve in the quickly altering electromagnetic field (billion times a second), heat is develoed in the foodstuff because of discord between the water molecules. Because the waves can enetrate directly into the material, heating is volumetric (from inside out) and sulies raid and constant heating in every art of roduct. The fast absortion of energy by water molecules causes raid evaoration that imroves drying, which succeeds in most convective drying techniques. The most widely commercially used frequency is.450 GHz Received date: Acceted date: *Corresonding author: Ahmad Kouchakzadeh, Deartment of Biosystem Engineering, Ilam University, Ilam, Iran. Phone: Fax: akouchakzadeh@mail.ilam.ac.ir. (Kouchakzadeh and Shafeei, 010). In microwave heating, the ower absorbed at a location x inside a food is related to the electric field, E, at that location by the Equation 1 (Metaxas, 1983): 1 ( x) E ωε ε (1) where (x) is ower, W; ω is angular frequency, rad/s; ε, ε are the dielectric constant and dielectric loss factor of the material, and E is the electric filed, V/m. In microwave oven, E is roortionate of oven s magnetron length like an antenna in the waveguide and current excitation, I; thus, the total ower absorbed by the load can be written as Equation (Collin, 007): total I () Some factors that may affect the microwave heating rocess are mostly included as foodstuff geometry, thermal, hysical and dielectric roerties, and arameters such as frequency, temerature, ower alied and radiation eriod. The dielectric constant and dielectric loss factor describe the behavior of a material under the electromagnetic field. The dielectric constant is a relative measurement of olarization that occurs when a material is laced in an electric field. The

2 106 March, 015 AgricEngInt: CIGR Journal Oen access at htt:// Vol. 17, No. dielectric loss factor is a measure of a material s ability to convert electrical energy to heat. The extent of these roerties is significant in microwave absortion that resulting heating (Kouchakzadeh, 013). These roerties are resonsible for water, salt, fat, carbohydrate and rotein levels. The dielectric roerties for a wide range of food and agriculture commodities have been recorded; the dielectric roerties of foods are temerature deendent (Nelson, 008; Jones et al., 00), studies must be conducted over the wide range of temeratures exerienced by the roduct during thermal rocessing if dielectric heating behavior is to be recisely redicted. Sun et al. (1994) develoed equations for a series of foods as a function of temerature, moisture and ash content u to 70 C. Uan et al. (004) studied the dielectric conduct of mashed otatoes at temerature from 0 C to 10 C n microwave and RF range. Tulasidas et al. (1995) researched about dielectric roerties of graes and sugar solution. Dielectric roerties of four ale cultivars were also measured about codling moth control studies (Sun et al., 1994). The research has been reorted for dry agricultural commodities, such as alfalfa seeds (Yang et al., 003), walnuts (Wang et al., 007), legumes (Wang et al., 010), istachio nuts (Kouchakzadeh, 013), and some fruits and vegetables (Sagar et al., 010). Prediction of absortion microwave energy for heat treatments as they relate to the dielectric roerties of a foodstuff has been fully known. However, it is ractically difficult to acquire the microwave energy absorbed by foods based on theoretical calculation. There are some methods for directly measuring a foodstuff temerature to get the absorbed microwave energy. Many methods have been reorted. For examle, the temerature of a microwave-irradiated samle can be evaluated by inserting a measuring device into the hot food shortly after turning off microwave ower. The measuring aaratus maybe fail in execution when contacted with some heated materials that were sensitive to microwave absortion and fast reached high temerature. The temerature measurement was limited to some oints, so that the mean values could not show the accurately temerature of the bulk, articularly for merged foodstuffs. Thus, it is imortant to get a simly faceable method to check it out the characteristic of foodstuffs in microwave absortion to redict the heating conduct of foods when heated by microwave irradiation. Ma et al. (009) used an easy method to determine the ability of microwave energy absortion by using water as the medium matter to circuitously reflect microwave of the tested materials. The consequences showed that it is not roer to use the rate of surface heating to infer the microwave absortion conduct. Housova and Hoke (00) studied about microwave cavity (oven) volume and food density. They showed that the ability of microwave absortion in dense foodstuffs decreased in oven with the smaller volume caacity. Hossan et al. (010) examined the effects of microwave irradiation in different length of the cylindrical foodstuff. They found that the temerature within the body is very sensitive to cylinder length and time. Zhang and Datta (003) tested about ower absortion in single and comlex foods that are radiated in a microwave field. They showed that some trends in ower absortion as influenced by the dimensions and dielectric roerties so foods with small loss factor may not absorb less ower if their size is enough large, while high loss foods usually absorb more ower at small sizes. In this aer, a method for measuring absorbed microwave energy in green bell (Casicum) has been introduced, in which water, because of its resonsiveness to microwave energy, was used as the medium material to absorb circuitously reflected microwave radiation of the tested s. The method would be suitable for use as a simle alternate method to the other foods as well. Peer has high moisture content that increase bacterial activity in them so make to be readily subjected to decline and ost-harvest losses. One of the best ways of remove the bacterial activity in because of their high moisture content

3 June, 015 Studies on microwave energy absortion of fresh green bell (Casicum) Vol. 17, No. 107 is by drying to a safe moisture level that will not ermit bacterial activity to reserve the erishable and extend the shelf-life beyond few weeks when they are in seasons (Tunde-Akintunde et al., 005). Microwave irradiation is an addition in the drying techniques, relative to convective air drying, vacuum and freeze-drying in industry. Materials and methods.1 Exerimental rocedure As shown in Figure 1, the tests device consisted of a microwave oven.45 GHz (CH-3071, 900 W LG Electronics, Korea), a Pyrex beaker for containing water, and a glass an to have within for tests. The temeratures of water were measured by a digital thermometer (TM-917 Lutron, Taiwan) with thermocoule (tye K) as the robe with the accuracy of 0.1 C when the oven was switched off. Figure 1 Schematic of microwave oven tests device. Samle rearation The green bell s got from a field in Iran, Ilam rovince during harvesting season in Setember 013. The samles were first washed and then were ut in lastic bags, and laced in a refrigerator before conducting exeriments. The initial moisture content of samles were determined by oven drying at temerature of 105 C for 4 h according to a standard method ASABE (006). About 50 g of grind s were laced in an oven, its final weight was taken, and the difference in weight was taken as water loss and exressed as grams water er grams dry matter. The initial moisture content for s was 93% (wb)..3 The tests In initially tests, 100 g of distillated water in Pyrex beaker was weighing on a laboratory-weighing latform (Model AB04, Mettler-Toledo AG, Switzerland) with readability of 0.01 g and was taking in microwave oven for the 0, 5, 30 and 35 s microwave heating time at 180, 360, 540, 70 and 900 W ower irradiation. The water temerature was measured before and after radiation. The energy absorbed by the water is calculated by Equation 3 as follow: w m C ΔT (3) w w where w is the absorbed energy, J; m w is the water mass, kg; C w is the secific heat of water, 4184 J/kg C; ΔT is the temerature rising T T ), C. ( final initial The deendence between the microwave ower alied in water heating and the increase of temerature can be described by the Equation 4 (Ma et al., 009): t Δ T k (4) m w C w where is the microwave ower used for heating, W; t is the time of heating, s; and k is the utilization efficiency of the outut microwave energy.

4 108 March, 015 AgricEngInt: CIGR Journal Oen access at htt:// Vol. 17, No. In finally tests, green bell s were weighed and added in microwave oven, so that both of 100 g water and quantity of 30, 40 and 50 g grind were irradiated as similar as time and ower in initially tests. The water temerature was measured before and after radiation. Each test was reeated three times and the results were averaged. In order to discussion; indicate as the absorbed microwave energy in the cavity for heating the and the water medium, J; and 1 as the absorbed microwave energy in the cavity for heating only the water, J; then the following Equation 5 and Equation 6 can be derived: 1 m C Δ T kt (5) w w w 1 + (6) = w + = mwcwδt J; ΔT 1 is the temerature rising in initial tests, C; ΔT is the temerature rising in finally tests, C. By equalizing Equation 3 and Equation 4 the required equilibrium condition is written as following Equation 7: kt mwcwδt (7) So by finding utilization efficiency of the outut microwave energy, k; from Equation in initial tests and measuring temerature rising of water in final tests, ΔT ; the energy absorbed by were determined. 3 Results and discussion It can be seen from Table 1 that the utilization efficiency of the outut microwave energy rises from 0.38 to 0.6 and in all microwave owers the efficiency is ascending by irradiation times. This suggests that radiation with lower microwave ower and longer times where is the absorbed microwave energy by, have more efficient for heating. Table 1 the microwave irradiation test results P, W T, s ΔT 1, C k +30g ΔT, C +40g +50g +30g +40g, J/g +50g average standard deviation

5 June, 015 AgricEngInt: CIGR Journal Oen access at htt:// Vol. 17, No. 109 time. Figure shows the variation of absorbed energy vs. As shown in Figure the elevation in microwave ower caused increase rogressive ratio in absorbed heats by s at each times. Figure The averages of absorbed microwave energy in green bell vs. time The exerimental data were resented as lot of absorbed energy vs. microwave ower as shown in Figure 3. Figure 3 The variation of absorbed energy vs. microwave ower

June, 015 AgricEngInt: CIGR Journal Oen access at htt://www.cigrjournal.org Vol. 17, No.

6 June, 015 AgricEngInt: CIGR Journal Oen access at htt:// Vol. 17, No. 110 The quadratic regression s equations were fitted to data (using Statgrahics Centurion XVI software) as following Equation 8, Equation 9, Equation 10 and Equation 11: (Irradiation time 0s, R = 0.94) (8) (Irradiation time 5s, R = 0.94) (9) (Irradiation time 30s, R = 0.93) (10) (Irradiation time 35s, R = 0.9) (11) where is the absorbed microwave energy by er unit mass, J/g. As can be observed in general from data and fitted curves, at all times the absortion energy as the nd degree functions with high correlation coefficients were identified. This showed consistence with Equation 1. Figure 4 shows the olynomial regression exression for absorbed microwave energy as function of time and ower that were determined as following Equation 1: t (R = 0.96) (1) Figure 4 Absorbed microwave energy vs. time and ower 4 Conclusions It is not roer to use the rate of surface temerature to infer the microwave absortion behavior by foods; according to method resented, the absortion can be calculated directly. By using water as the medium material to absorb microwave irradiation, the quantities of absortion energy by were measured. The results showed that energy absorb has quadratic roortionate to irradiated owers. References ASABE Standard for measurement of moisture in grin and seed. Agricultural Engineers Yearbook. P:564. Buffler, C. R Microwave cooking and rocessing. Van Nostrand Reinhold.

7 June, 015 Studies on microwave energy absortion of fresh green bell (Casicum) Vol. 17, No. 111 Collin, R. E Foundations for microwave engineering. John Wiley & Sons. Hossan, M. R., D. Byun, and P. Dutta Analysis of microwave heating for cylindrical shaed objects. International Journal of Heat and Mass Transfer, 53(3): Housova, J., and K. Hoke. 00. Microwave heating the influence of oven and load arameters on the ower absorbed in the heated load. Czech journal of food sciences, 0(3): Jones, D. A., T. P. Lelyveld, S. D. Mavrofidis, S. W. Kingman, and N. J. Miles. 00. Microwave heating alications in environmental engineering a review. Resources, conservation and recycling, 34(): Kouchakzadeh, A., and S. Shafeei Modeling of microwave-convective drying of istachios. Energy Conversion and Management, 51(10): Kouchakzadeh, A Microwave Penetration Deth in Bulk Pistachios. Int. J. Emerg. Sci, 3(3): Ma, S. J., X. W. Zhou, X. J. Su, W. Mo, J. L. Yang, and P. Liu A new ractical method to determine the microwave energy absortion ability of materials. Minerals Engineering, (13): Metaxas, A. A., and R. J. Meredith Industrial microwave heating (No. 4). IET. Nelson, S. O Dielectric roerties of agricultural roducts and some alications. Research in Agricultural Engineering, 54(): Sagar, V. R., and P. S. Kumar Recent advances in drying and dehydration of fruits and vegetables: a review. Journal of food science and technology, 47(1): Sun, E., A. Datta, and S. Lobo Comosition-based rediction of dielectric roerties of foods. The Journal of microwave ower and electromagnetic energy: a ublication of the International Microwave Power Institute, 30(4): Tulasidas, T. N., G. S. V. Raghavan, F. Van de Voort, and R. Girard Dielectric roerties of graes and sugar solutions at.45 GHz. Journal of microwave ower and electromagnetic energy, 30(): Tunde-Akintunde, T. Y., T. J. Afolabi, and B. O. Akintunde Influence of drying methods on drying of bell- (Casicum annuum). Journal of Food Engineering, 68(4): Uan, D. G., M. Cheng, Y. Wang, and J. Tang Dielectric roerties of mashed otatoes relevant to microwave and radio frequency asteurization and sterilization rocesses. Journal of Food Science, 69(1): FEP30-FEP37. Wang, S., M. Monzon, J. A. Johnson, E. J. Mitcham, and J. Tang Industrial-scale radio frequency treatments for insect control in walnuts: I: Heating uniformity and energy efficiency. Postharvest Biology and Technology, 45(): Wang, S., G. Tiwari, S. Jiao, J. A. Johnson, and J. Tang Develoing ostharvest disinfestation treatments for legumes using radio frequency energy. Biosystems engineering, 105(3): Yang, J., Y. Zhao, and J. H. Wells Comuter simulation of caacitive radio frequency (RF) dielectric heating on vegetable srout seeds. Journal of food rocess engineering, 6(3): Zhang, H., and A. K. Datta Microwave ower absortion in single-and multile-item foods. Food and bioroducts rocessing, 81(3):

The extreme case of the anisothermal calorimeter when there is no heat exchange is the adiabatic calorimeter.

The extreme case of the anisothermal calorimeter when there is no heat exchange is the adiabatic calorimeter. .4. Determination of the enthaly of solution of anhydrous and hydrous sodium acetate by anisothermal calorimeter, and the enthaly of melting of ice by isothermal heat flow calorimeter Theoretical background