Osmotic drying is a process of partial removal of water by submersing fruits in sucrose solution. The goal of this paper is to examine kinetic features of osmotic drying of apricot halves in sucrose solution. For osmotic drying of apricot halves in a thick immovable layer, a planned experiment was conducted. Experimental results were used to create an empirical model of osmotic drying kinetics which expresses the influence of analyzed experiment factors on water loss (WL). The experiment factors were temperature of osmotic solution, varied at two levels, 35 °C and 60 °C, and sucrose concentration varied at two levels, 50 °Bx and 65 °Bx. Using regression analysis of experimental data for water loss (WL) at statistical probability of 99 %, parameters of empirical model and correlation coefficient were calculated for the proposed mathematical model. Experimental results were approximated using the derived equation. Conformance of experimental results with the empirical model was evaluated using correlation coefficient (R). Correlation coefficient calculated for the proposed model was high, R = 0.976. It indicates fi ne agreement between experimental and model values for water loss

Ivan Pavkov

Ljiljana Babić

Milivoj Radojčin

Mirko Babić

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253Agriculturae Conspectus Scientifi cus | Vol. 74 (2009) No. 3 (253-257)ORIGINAL SCIENTIFIC PAPERSummaryOsmotic drying is a process of partial removal of water by submersing fruits in sucrose solution. Th e goal of this paper is to examine kinetic features of osmotic drying of apricot halves in sucrose solution. For osmotic drying of apricot halves in a thick immovable layer, a planned experiment was conducted. Experimental results were used to create an empirical model of osmotic drying kinetics which expresses the infl uence of analyzed experiment factors on water loss (WL). Th e experiment factors were temperature of osmotic solution, varied at two levels, 35 oC and 60 oC, and sucrose concentration varied at two levels, 50 oBx and 65 oBx. Using regression analysis of experimental data for water loss (WL) at statistical probability of 99 %, parameters of empirical model and correlation coeffi  cient were calculated for the proposed mathematical model. Experimental results were approximated using the derived equation. Conformance of experimental results with the empirical model was evaluated using correlation coeffi  cient (R). Correlation coeffi  cient calculated for the proposed model was high, R = 0.976. It indicates fi ne agreement between experimental and model values for water loss.Key wordsosmotic drying, kinetics, mathematical model, apricotOsmotic Drying of Apricot (Prunus armeniaca) in Sucrose Solution Ivan PAVKOV ( )Ljiljana BABIĆMirko BABIĆMilivoj RADOJČINFaculty of Agriculture, Department of Agricultural Engineering, Trg Dositeja Obradovića 8, Novi Sad, Serbia e-mail: ivan@polj.ns.ac.yuReceived: November 5, 2008 | Accepted: March 18, 2009ACKNOWLEDGEMENTS This research was funded by the Ministry of Science of the Republic of Serbia, through Project no. 20065 entitled “Quality of Dried Fruit Production” within the program of technological development from 01. 04. 2008.Agric. conspec. sci. Vol. 74 (2009) No. 3254 Ivan PAVKOV, Ljiljana BABIĆ, Mirko BABIĆ, Milivoj RADOJČINIntroductionFor its biochemical structure, apricot (Prunus armeniaca) is considered a fruit very suitable for drying. It features high content of provitamin A, vitamin C as well as a complex of other vitamins which are benefi cial to human organism. Th e complex of mineral matter in apricot fruits - especially high contents of potassium, phosphorus, magnesium and iron - improves blood count, blood circulation and regulates blood pressure in humans (Đurić, 2003).Conventional drying technologies featuring convective drying as the sole technological drying operation, yield dried apricots of unsatisfactory quality. Using combined drying tech-nology with osmotic drying as one of the fundamental tech-nological operations, rectifi es this problem (Babić and Babić, 2003; Babić et al., 2003; Babić et al., 2004a; Riva et al., 2005).Osmotic drying by submersion in concentrated solutions is used for partial removal of water from plant tissue. Th e concentration gradient of water infl uences extraction of water from the tissue, while conditioning penetration of osmotic solution into the tissue. Extraction of water from the tissue is much more intensive than the penetration of osmotic solute into the tissue. Velocity of diff usion of water molecules from biological materials depends on a number of factors such as: temperature and concentration of osmotic solution, solute properties, dimension and geometric shape of submersed material, mass ratio between material and osmotic solution, velocity of solution fl ow, material preprocessing and other factors (Rastogi et al., 2002; Rahimzade and Hesari, 2007; Pavkov, 2007). In recent years, numerous empirical models have been developed, of which the Biswal model stands out as the most frequently used. Biswal equation allows simple calculation of water loss and dry matter gain, WL/SG. Th e results can be used for optimization of the process of osmotic drying (Shi and Le Maguer, 2002; Jokić et al., 2007):5,0tkWL W      (1)5,0tkSG S      (2)where kw and ks are coeffi  cients of total mass transfer for water, i.e. osmotic solute; WL/SG is net water loss, i.e. dry matter gain (g), while t denotes drying time (min).Th e models derived do not explicitly express the infl u-ence of relevant factors on osmotic drying kinetics. For each combination of factors, values of coeffi  cient functions kw and ks need to be calculated. Th is paper presents calculation of water loss (WL) parameters of empirical model, based on ex-perimental data for osmotic drying of apricot halves in thick immovable layer. Th e proposed model explicitly expresses infl uence of examined factors on water loss during osmotic drying of apricot halves. Materials and method In the experiment, fresh apricot halves (Prunus armeni-aca) of the cultivar “Novosadska rodna” were used as mate-rial. Th e picked apricots were at the stage of full technological maturity (3.4 pH). Th e basic physical properties of the fresh fruits were: average mass of whole fruit 47.5 g and dimen-sions: acp = 47.18 mm, bcp = 45.54 mm and ccp =41.08 mm.Th e preprocessing of fresh apricots included washing, halving, stoning and sulfurization. Dry sulfurization was per-formed using sulfur-dioxide (SO2), in a sulfurization chamber. Apricot halves were exposed to SO2 for the duration of four hours. Two grams of technical powdered sulfur were used per one kilogram of fresh apricot halves. Th e prepared sam-ples, four kilograms, were set in osmotic dryer. Aft er osmotic drying the samples were moved to convective dryer where were further dried until they reached equilibrium moisture.For osmotic solution, sucrose in the form of crystal sugar was used as solute, while distilled water was used as the sol-vent. Th e experiment was conducted in a semi-industrial type osmotic dryer, maximum capacity of 0.032 m3 solution (Figure 1). Th e principle of operation of this dryer is based on circulation of osmotic solution through a drying chamber with fruit sample and a heat exchanger. Previous examinations on the process of osmotic drying of fruit tissue and infl uential parameters, accentuate that the temperature and concentration of osmotic solution are the two parameters with utmost impact on the velocity of mass transfer during osmotic drying (Babić et al, 2004a; Babić et al, 2004b; Riva et al, 2005). Based on this fi nding, the exper-iment was performed as a two-factor experiment. Th e tem-perature of osmotic solution was varied at two levels, 35 oC and 60 oC, while the sucrose concentration levels were 50 oBx and 65 oBx. Duration of osmotic drying was two hours. Mass ratio between osmotic solution and a sample of apricot halves was 12:1. Velocity of circulation of osmotic solution through material layer changed only slightly during the experiment due to variable solution viscosity and layer porosity. Eff ects of osmotic drying were monitored by taking sam-ples from the dryer during specifi c time intervals (0, 30, 60, 90, 120 min). Th e samples were washed in order to eliminate solution remnants and then carefully wiped off  with an ab-sorbing cloth. Dry matter was determined by drying at 80 0C for the period of 24 hours. Water loss (WL) was determined by measuring mass diff erence before and aft er the drying. Water loss was calculated as the ratio between net water loss from the fresh sample and the initial mass of the sample:100(%)00WMMWL i     (3)where M0 is mass of the fresh sample (g), Mi is mass of the sample aft er osmotic dehydration (g), W0 is the total mass of the fresh sample (g).According to the goal of this examination, an empirical model of water loss kinetics was proposed and used for re-gression analysis. Th e model is based on the Biswal equation that was extended by the infl uence of the analyzed experi-ment factors (Pavkov et al, 2006):Agric. conspec. sci. Vol. 74 (2009) No. 3255Osmotic Drying of Apricot (Prunus armeniaca) in Sucrose Solution321nonrnw CCttkWL    (4)where WL is water loss [%];  is duration of osmosis [min];. Co, Cr are chosen and referential sucrose concentrations [oBx]; t, tr are chosen and referential temperatures of solution; kw is mass transfer coeffi  cient for water [%/min], and n1, n2, n3 are equation exponents.In model (4) the infl uence of solution temperature and con-centration is expressed as a non-dimensional value, namely, as the ratio between the selected factor level and some refer-ential value (Babić, 1995). Referential values of concentration and temperature of osmotic solution are:tr = 100 oC;Cr = 82.87 oBx maximal concentration at t = 100 oC ac-cording to A. Herzfeld (Šušić, 1980).Also, the measurement was performed using digital re-fractometer with the measurement range of 0-85 oBx, 0.1oBx (model Atago, Japan).For each selected factor-level combination, three itera-tions were made. In total, twelve experimental units of os-motic drying of apricot halves were performed. Statistical analysis of experimental results was run on Statistica 7.1 (StatSoft  Inc., 2003).Results and discussionChanges of moisture content increased with the rise of temperature and concentration of osmotic solution (Figure 2). Th e most signifi cant changes in water loss took place within the fi rst 90 minutes of the process. Water loss maxi-mum was reached at 65 oBx concentration of sucrose and 60oC temperature. Th e infl uence of osmotic solution temperature can be ex-plained by the fact that higher temperatures cause changes in cell membrane structure. Th e membrane becomes more permeable to water molecules which diff use through apricot tissue towards boundary surface, while the tissue lowers its resistance to liquid diff usion. At the same time, increased temperature lowers viscosity of osmotic solution which, in turn, lowers resistance to transition of liquid molecules from the boundary surface of apricot halves into osmotic solution. In addition, changing permeability of cell membrane inten-sifi es diff usion of solute molecules into intercellular space.Higher concentrations mean higher concentration gra-dients of water and solute molecules, between the bound-ary surface of apricot halves and osmotic solution. It is well known that intensity of water molecules’ transition from the boundary surface to osmotic solution depends on the area of active surface of interchange, velocity fi eld of solution and, fi -nally, concentration gradient of this component. Furthermore, concentration gradient of solute between apricot halves and         7578818487900 20 40 60 80 100 120 140Time  [min]Moisture [%]65 [oBx], 60 [oC]50 [oBx], 60 [oC]65 [oBx], 35 [oC]50 [oBx], 35 [oC]Figure 1. Semi-industrial type osmotic dryer (Babić et al. 2004c); OS – drying chamber, P – lid, CP – circulation pump, Z – sealing, CR – piping, KR – heat exchanger housing, TK – T-flange piece, UC – U-flanged pipe, TM – Mercury thermometer, K – basket, EG – electric heater, S1,– tap, EP – expansion vessel, PK – front chamber , ZK – aft chamber,  direction of solution circulationFigure 2. Moisture content of apricot halves as a function of time at different temperatures and concentration of sucrose during osmotic dryingAgric. conspec. sci. Vol. 74 (2009) No. 3256 Ivan PAVKOV, Ljiljana BABIĆ, Mirko BABIĆ, Milivoj RADOJČINosmotic solution causes diff usion of solute into apricot tissue. Th e solute does not penetrate the cell but remains within the intercellular space, thus increasing the active surface of mass interchange between apricot tissue and osmotic solution. Using regression analysis of experimental data for water loss (WL) at statistical probability of 99 %, coeffi  cients and correlation coeffi  cient were calculated for the proposed math-ematical model (4) (Table 1). Correlation coeffi  cient calculated for the proposed model was high, R = 0.976. It indicates fi ne agreement between ex-perimental and model values for water loss. Based on statis-tical signifi cance of coeffi  cients (p–level) it is evident that all function coeffi  cients are signifi cant. Th e fi nal form of em-pirical model is:528,0789,0613,087,82100761,0 CtWL  (5)Th e empirical model (5) is applicable within the range of temperature from 35 oC to 60 oC, solution concentration from 50 oBx to 65 oC and immersion time 120 minutes. Figure 2 shows curves of the moisture content as a function of time for the examined combinations of temperature and concentration of osmotic solution. Th e graphic presentation (Figure 3) con-fi rms good agreement between the model and experimental water loss curves for apricot halves during osmotic drying.Monitoring of changes in concentration of osmotic solu-tion during the process of osmotic drying at the 12:1 mass ratio between solution and plant tissue, revealed that the solu-tion concentration changes only slightly. Fig. 4 shows average measurement results for variation of sucrose concentration in osmotic solution at 60 oC during 120 min.ConclusionsTh e model derived (5) yields good approximation of the experimental results of water loss kinetics of apricots in su-crose solutions. Th e model directly correlates water loss kinet-ics with temperature and concentration of osmotic solution. In its fi nal form, the model is applicable within the range of temperature from 35 oC to 60 oC, solution concentration from 50 oBx to 65 oC and immersion time 120 minutes.At the 12:1 mass ratio between the solution and apricot halves, the solution is mildly diluted. Signifi cant changes occur within the fi rst 90 minutes of the process. During that period the highest water loss occurs at the 65 % sucrose con-centration and 60 oC temperature. Th e increase of total sugars causes change of organoleptic properties of osmotically dried apricot halves, i.e. it causes increased content of sucrose. Th is occurrence contributes to clogging of pores in apricot tissue, and also hinders the process of convective drying. Considering this, medium concentrated sucrose solutions and higher so-lution temperatures should be adopted in order to prevent undesirable enzyme reactions in apricot tissue.ReferencesBabić L., Babić M., (2000). Drying and Storing, Faculty of Agriculture, Novi Sad,.Babić Lj., Babić M., Pavkov I., (2003). Combined Osmotic and Convective Drying of Apricot, PTEP - Journal on Processing and Energy in Agriculture, Novi Sad, 7:1-2, pp 1-3Coefficient Result Standard deviation t-value p-level kw 0.7616 0.1457 5.22515 0.000003 n1 0.6135 0.0403 15.1966 0.000000 n2 0.7899 0.0654 12.0695 0.000000 n3 0.5283 0.1243 4.2503 0.000082 01234567890 20 40 60 80 100 120 140Time  [min]WL [%]35oC; 50oBx35oC 65oBx60oC, 50oBx60oC; 65oBxmodelSucrose concentration :62.9048.50 010203040506070800 20 40 60 80 100 120 140Time  [min]Solution concentration  [o Bx]Co =65 [oBx]Co =50 [oBx];Table 1. Results of regression analysis for statistical probability V = 99 %Figure 3. Water loss as a function of time at different temperatures and concentrations of sucrose during osmotic drying of apricot halves, experimental and model curveFigure 4. Average variation of sucrose concentration in osmotic solutions at 60 oC within a 120 min intervalAgric. conspec. sci. Vol. 74 (2009) No. 3257Osmotic Drying of Apricot (Prunus armeniaca) in Sucrose SolutionBabić Lj., Babić M., Pavkov I., (2004a). Apricot Osmotic Drying in Dependence upon Solution’s Temperature and Concentration, PTEP -Journal on Processing and Energy in Agriculture, Novi Sad, 8:1-2, pp 1-3.Babić Lj., Babić, M., Pavkov I., (2004b). Aff ected Factors on Apricot Halves Moisture Content Changes During Osmotic Dehydration, Contemporary Agricultural Engineering, Novi Sad, 30:3-4, pp 117-126Babić M., (1995). Study of the Impact of the Wheat Grain Basic Physical Properties Onto the Characteristics of the Air Flow Th rough the Poured Layer, Th esis, Faculty of tehnical Sciences, Novi SadBabić M., Babić Lj., Pavkov I., (2004c). Mass and Energy Balance of Apricot Drying, Contemporary Agricultural Engineering, Novi Sad, 30:3-4, pp 127-133Đurić B., (2003). Apricot growing, Faculty of Agriculture, Novi Sad Jokić A., Prodanić B., Gyura J., Zavargo Z., Lević Lj. (2007). Kinetics of Osmotic Dehydration of Carrots In Sucrose Solutions, PTEP -Journal on Processing and Energy in Agriculture, Novi Sad, 11:1-2, pp 42-43Rastogi N., K., Raghavaro K., S., Niranjan K., Knorr D., (2002). Recent Developments in Osmotic Dehydration Methods to Enhance Mass transfer, Food Science and Technology 13, pp 48-59Riva M., Campolongo S., Avitabile Alexa, Maestrelli Andrea, Danila Torreggian (2005). Structure–property relationships in osmo-air-dehydrated apricot cubes, Food Research International 38, pp 533–542Rahimzade, K., M., Hesari J., (2007). Osmotic dehydration kinetics of apricot using sucrose solution, Journal of Food Engineering 78, pp 1355–1360Pavkov I., Babić Lj., Babić M., (2006). Mathematical Modeling of the Osmotic Drying Kinetic of Fruit Tissue, PTEP -Journal on Processing and Energy in Agriculture, Novi Sad, 10:3-4, pp 67-70.Pavkov I., (2007). Kinetic of the Osmotic Drying Apricot, M.Sc. Th esis, Faculty of Agriculture, Novi Sad Šušić S., ed. (1980) Priručnik za industriju šećera, II deo [Handbook for Sugar Industry, Part II ]. Poslovna zajednica industrije šećera Jugoslavije, Beograd.Handbook for sugar industry, Second Book (1980). Business Communyti, Yugoslavia, Belgrade, Shi J., Le Maguer M.,: Osmotic Dehidration of Foods (2002). Mass Transfer and Modeling Aspects, Food Reviwes International, 18:4, pp. 305-335StatSoft  Inc (2006). Statistica for Windows (data analysis soft ware system), version 7.1acs74_44

English

Osmotic Drying of Apricot (Prunus armeniaca) in Sucrose Solution

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253Agriculturae Conspectus Scientifi cus | Vol. 74 (2009) No. 3 (253-257)ORIGINAL SCIENTIFIC PAPERSummaryOsmotic drying is a process of partial removal of water by submersing fruits in sucrose solution. Th e goal of this paper is to examine kinetic features of osmotic drying of apricot halves in sucrose solution. For osmotic drying of apricot halves in a thick immovable layer, a planned experiment was conducted. Experimental results were used to create an empirical model of osmotic drying kinetics which expresses the infl uence of analyzed experiment factors on water loss (WL). Th e experiment factors were temperature of osmotic solution, varied at two levels, 35 oC and 60 oC, and sucrose concentration varied at two levels, 50 oBx and 65 oBx. Using regression analysis of experimental data for water loss (WL) at statistical probability of 99 %, parameters of empirical model and correlation coeffi  cient were calculated for the proposed mathematical model. Experimental results were approximated using the derived equation. Conformance of experimental results with the empirical model was evaluated using correlation coeffi  cient (R). Correlation coeffi  cient calculated for the proposed model was high, R = 0.976. It indicates fi ne agreement between experimental and model values for water loss.Key wordsosmotic drying, kinetics, mathematical model, apricotOsmotic Drying of Apricot (Prunus armeniaca) in Sucrose Solution Ivan PAVKOV ( )Ljiljana BABIĆMirko BABIĆMilivoj RADOJČINFaculty of Agriculture, Department of Agricultural Engineering, Trg Dositeja Obradovića 8, Novi Sad, Serbia e-mail: ivan@polj.ns.ac.yuReceived: November 5, 2008 | Accepted: March 18, 2009ACKNOWLEDGEMENTS This research was funded by the Ministry of Science of the Republic of Serbia, through Project no. 20065 entitled “Quality of Dried Fruit Production” within the program of technological development from 01. 04. 2008.Agric. conspec. sci. Vol. 74 (2009) No. 3254 Ivan PAVKOV, Ljiljana BABIĆ, Mirko BABIĆ, Milivoj RADOJČINIntroductionFor its biochemical structure, apricot (Prunus armeniaca) is considered a fruit very suitable for drying. It features high content of provitamin A, vitamin C as well as a complex of other vitamins which are benefi cial to human organism. Th e complex of mineral matter in apricot fruits - especially high contents of potassium, phosphorus, magnesium and iron - improves blood count, blood circulation and regulates blood pressure in humans (Đurić, 2003).Conventional drying technologies featuring convective drying as the sole technological drying operation, yield dried apricots of unsatisfactory quality. Using combined drying tech-nology with osmotic drying as one of the fundamental tech-nological operations, rectifi es this problem (Babić and Babić, 2003; Babić et al., 2003; Babić et al., 2004a; Riva et al., 2005).Osmotic drying by submersion in concentrated solutions is used for partial removal of water from plant tissue. Th e concentration gradient of water infl uences extraction of water from the tissue, while conditioning penetration of osmotic solution into the tissue. Extraction of water from the tissue is much more intensive than the penetration of osmotic solute into the tissue. Velocity of diff usion of water molecules from biological materials depends on a number of factors such as: temperature and concentration of osmotic solution, solute properties, dimension and geometric shape of submersed material, mass ratio between material and osmotic solution, velocity of solution fl ow, material preprocessing and other factors (Rastogi et al., 2002; Rahimzade and Hesari, 2007; Pavkov, 2007). In recent years, numerous empirical models have been developed, of which the Biswal model stands out as the most frequently used. Biswal equation allows simple calculation of water loss and dry matter gain, WL/SG. Th e results can be used for optimization of the process of osmotic drying (Shi and Le Maguer, 2002; Jokić et al., 2007):5,0tkWL W       (1)5,0tkSG S       (2)where kw and ks are coeffi  cients of total mass transfer for water, i.e. osmotic solute; WL/SG is net water loss, i.e. dry matter gain (g), while t denotes drying time (min).Th e models derived do not explicitly express the infl u-ence of relevant factors on osmotic drying kinetics. For each combination of factors, values of coeffi  cient functions kw and ks need to be calculated. Th is paper presents calculation of water loss (WL) parameters of empirical model, based on ex-perimental data for osmotic drying of apricot halves in thick immovable layer. Th e proposed model explicitly expresses infl uence of examined factors on water loss during osmotic drying of apricot halves. Materials and method In the experiment, fresh apricot halves (Prunus armeni-aca) of the cultivar “Novosadska rodna” were used as mate-rial. Th e picked apricots were at the stage of full technological maturity (3.4 pH). Th e basic physical properties of the fresh fruits were: average mass of whole fruit 47.5 g and dimen-sions: acp = 47.18 mm, bcp = 45.54 mm and ccp =41.08 mm.Th e preprocessing of fresh apricots included washing, halving, stoning and sulfurization. Dry sulfurization was per-formed using sulfur-dioxide (SO2), in a sulfurization chamber. Apricot halves were exposed to SO2 for the duration of four hours. Two grams of technical powdered sulfur were used per one kilogram of fresh apricot halves. Th e prepared sam-ples, four kilograms, were set in osmotic dryer. Aft er osmotic drying the samples were moved to convective dryer where were further dried until they reached equilibrium moisture.For osmotic solution, sucrose in the form of crystal sugar was used as solute, while distilled water was used as the sol-vent. Th e experiment was conducted in a semi-industrial type osmotic dryer, maximum capacity of 0.032 m3 solution (Figure 1). Th e principle of operation of this dryer is based on circulation of osmotic solution through a drying chamber with fruit sample and a heat exchanger. Previous examinations on the process of osmotic drying of fruit tissue and infl uential parameters, accentuate that the temperature and concentration of osmotic solution are the two parameters with utmost impact on the velocity of mass transfer during osmotic drying (Babić et al, 2004a; Babić et al, 2004b; Riva et al, 2005). Based on this fi nding, the exper-iment was performed as a two-factor experiment. Th e tem-perature of osmotic solution was varied at two levels, 35 oC and 60 oC, while the sucrose concentration levels were 50 oBx and 65 oBx. Duration of osmotic drying was two hours. Mass ratio between osmotic solution and a sample of apricot halves was 12:1. Velocity of circulation of osmotic solution through material layer changed only slightly during the experiment due to variable solution viscosity and layer porosity. Eff ects of osmotic drying were monitored by taking sam-ples from the dryer during specifi c time intervals (0, 30, 60, 90, 120 min). Th e samples were washed in order to eliminate solution remnants and then carefully wiped off  with an ab-sorbing cloth. Dry matter was determined by drying at 80 0C for the period of 24 hours. Water loss (WL) was determined by measuring mass diff erence before and aft er the drying. Water loss was calculated as the ratio between net water loss from the fresh sample and the initial mass of the sample:100(%)00  WMMWL i     (3)where M0 is mass of the fresh sample (g), Mi is mass of the sample aft er osmotic dehydration (g), W0 is the total mass of the fresh sample (g).According to the goal of this examination, an empirical model of water loss kinetics was proposed and used for re-gression analysis. Th e model is based on the Biswal equation that was extended by the infl uence of the analyzed experi-ment factors (Pavkov et al, 2006):Agric. conspec. sci. Vol. 74 (2009) No. 3255Osmotic Drying of Apricot (Prunus armeniaca) in Sucrose Solution321nonrnw CCttkWL ¸¸¹·¨¨©§¸¸¹·¨¨©§ W    (4)where WL is water loss [%];  is duration of osmosis [min];. Co, Cr are chosen and referential sucrose concentrations [oBx]; t, tr are chosen and referential temperatures of solution; kw is mass transfer coeffi  cient for water [%/min], and n1, n2, n3 are equation exponents.In model (4) the infl uence of solution temperature and con-centration is expressed as a non-dimensional value, namely, as the ratio between the selected factor level and some refer-ential value (Babić, 1995). Referential values of concentration and temperature of osmotic solution are:tr = 100 oC;Cr = 82.87 oBx maximal concentration at t = 100 oC ac-cording to A. Herzfeld (Šušić, 1980).Also, the measurement was performed using digital re-fractometer with the measurement range of 0-85 oBx, 0.1oBx (model Atago, Japan).For each selected factor-level combination, three itera-tions were made. In total, twelve experimental units of os-motic drying of apricot halves were performed. Statistical analysis of experimental results was run on Statistica 7.1 (StatSoft  Inc., 2003).Results and discussionChanges of moisture content increased with the rise of temperature and concentration of osmotic solution (Figure 2). Th e most signifi cant changes in water loss took place within the fi rst 90 minutes of the process. Water loss maxi-mum was reached at 65 oBx concentration of sucrose and 60oC temperature. Th e infl uence of osmotic solution temperature can be ex-plained by the fact that higher temperatures cause changes in cell membrane structure. Th e membrane becomes more permeable to water molecules which diff use through apricot tissue towards boundary surface, while the tissue lowers its resistance to liquid diff usion. At the same time, increased temperature lowers viscosity of osmotic solution which, in turn, lowers resistance to transition of liquid molecules from the boundary surface of apricot halves into osmotic solution. In addition, changing permeability of cell membrane inten-sifi es diff usion of solute molecules into intercellular space.Higher concentrations mean higher concentration gra-dients of water and solute molecules, between the bound-ary surface of apricot halves and osmotic solution. It is well known that intensity of water molecules’ transition from the boundary surface to osmotic solution depends on the area of active surface of interchange, velocity fi eld of solution and, fi -nally, concentration gradient of this component. Furthermore, concentration gradient of solute between apricot halves and          WZ7578818487900 20 40 60 80 100 120 140Time  W [min]Moisture Z[%]65 [oBx], 60 [oC]50 [oBx], 60 [oC]65 [oBx], 35 [oC]50 [oBx], 35 [oC]Figure 1. Semi-industrial type osmotic dryer (Babić et al. 2004c); OS – drying chamber, P – lid, CP – circulation pump, Z – sealing, CR – piping, KR – heat exchanger housing, TK – T-flange piece, UC – U-flanged pipe, TM – Mercury thermometer, K – basket, EG – electric heater, S1,– tap, EP – expansion vessel, PK – front chamber , ZK – aft chamber,  direction of solution circulationFigure 2. Moisture content of apricot halves as a function of time at different temperatures and concentration of sucrose during osmotic dryingAgric. conspec. sci. Vol. 74 (2009) No. 3256 Ivan PAVKOV, Ljiljana BABIĆ, Mirko BABIĆ, Milivoj RADOJČINosmotic solution causes diff usion of solute into apricot tissue. Th e solute does not penetrate the cell but remains within the intercellular space, thus increasing the active surface of mass interchange between apricot tissue and osmotic solution. Using regression analysis of experimental data for water loss (WL) at statistical probability of 99 %, coeffi  cients and correlation coeffi  cient were calculated for the proposed math-ematical model (4) (Table 1). Correlation coeffi  cient calculated for the proposed model was high, R = 0.976. It indicates fi ne agreement between ex-perimental and model values for water loss. Based on statis-tical signifi cance of coeffi  cients (p–level) it is evident that all function coeffi  cients are signifi cant. Th e fi nal form of em-pirical model is:528,0789,0613,087,82100761,0 ¹¸·©¨§¹¸·©¨§ CtWL W  (5)Th e empirical model (5) is applicable within the range of temperature from 35 oC to 60 oC, solution concentration from 50 oBx to 65 oC and immersion time 120 minutes. Figure 2 shows curves of the moisture content as a function of time for the examined combinations of temperature and concentration of osmotic solution. Th e graphic presentation (Figure 3) con-fi rms good agreement between the model and experimental water loss curves for apricot halves during osmotic drying.Monitoring of changes in concentration of osmotic solu-tion during the process of osmotic drying at the 12:1 mass ratio between solution and plant tissue, revealed that the solu-tion concentration changes only slightly. Fig. 4 shows average measurement results for variation of sucrose concentration in osmotic solution at 60 oC during 120 min.ConclusionsTh e model derived (5) yields good approximation of the experimental results of water loss kinetics of apricots in su-crose solutions. Th e model directly correlates water loss kinet-ics with temperature and concentration of osmotic solution. In its fi nal form, the model is applicable within the range of temperature from 35 oC to 60 oC, solution concentration from 50 oBx to 65 oC and immersion time 120 minutes.At the 12:1 mass ratio between the solution and apricot halves, the solution is mildly diluted. Signifi cant changes occur within the fi rst 90 minutes of the process. During that period the highest water loss occurs at the 65 % sucrose con-centration and 60 oC temperature. Th e increase of total sugars causes change of organoleptic properties of osmotically dried apricot halves, i.e. it causes increased content of sucrose. Th is occurrence contributes to clogging of pores in apricot tissue, and also hinders the process of convective drying. Considering this, medium concentrated sucrose solutions and higher so-lution temperatures should be adopted in order to prevent undesirable enzyme reactions in apricot tissue.ReferencesBabić L., Babić M., (2000). Drying and Storing, Faculty of Agriculture, Novi Sad,.Babić Lj., Babić M., Pavkov I., (2003). Combined Osmotic and Convective Drying of Apricot, PTEP - Journal on Processing and Energy in Agriculture, Novi Sad, 7:1-2, pp 1-3Coefficient Result Standard deviation t-value p-level kw 0.7616 0.1457 5.22515 0.000003 n1 0.6135 0.0403 15.1966 0.000000 n2 0.7899 0.0654 12.0695 0.000000 n3 0.5283 0.1243 4.2503 0.000082 01234567890 20 40 60 80 100 120 140Time W [min]WL [%]35oC; 50oBx35oC 65oBx60oC, 50oBx60oC; 65oBxmodelWWSucrose concentration :62.9048.50 010203040506070800 20 40 60 80 100 120 140Time W  [min]Solution concentration  [o Bx]Co =65 [oBx]Co =50 [oBx];Table 1. Results of regression analysis for statistical probability V = 99 %Figure 3. Water loss as a function of time at different temperatures and concentrations of sucrose during osmotic drying of apricot halves, experimental and model curveFigure 4. Average variation of sucrose concentration in osmotic solutions at 60 oC within a 120 min intervalAgric. conspec. sci. Vol. 74 (2009) No. 3257Osmotic Drying of Apricot (Prunus armeniaca) in Sucrose SolutionBabić Lj., Babić M., Pavkov I., (2004a). Apricot Osmotic Drying in Dependence upon Solution’s Temperature and Concentration, PTEP -Journal on Processing and Energy in Agriculture, Novi Sad, 8:1-2, pp 1-3.Babić Lj., Babić, M., Pavkov I., (2004b). Aff ected Factors on Apricot Halves Moisture Content Changes During Osmotic Dehydration, Contemporary Agricultural Engineering, Novi Sad, 30:3-4, pp 117-126Babić M., (1995). Study of the Impact of the Wheat Grain Basic Physical Properties Onto the Characteristics of the Air Flow Th rough the Poured Layer, Th esis, Faculty of tehnical Sciences, Novi SadBabić M., Babić Lj., Pavkov I., (2004c). Mass and Energy Balance of Apricot Drying, Contemporary Agricultural Engineering, Novi Sad, 30:3-4, pp 127-133Đurić B., (2003). Apricot growing, Faculty of Agriculture, Novi Sad Jokić A., Prodanić B., Gyura J., Zavargo Z., Lević Lj. (2007). Kinetics of Osmotic Dehydration of Carrots In Sucrose Solutions, PTEP -Journal on Processing and Energy in Agriculture, Novi Sad, 11:1-2, pp 42-43Rastogi N., K., Raghavaro K., S., Niranjan K., Knorr D., (2002). Recent Developments in Osmotic Dehydration Methods to Enhance Mass transfer, Food Science and Technology 13, pp 48-59Riva M., Campolongo S., Avitabile Alexa, Maestrelli Andrea, Danila Torreggian (2005). Structure–property relationships in osmo-air-dehydrated apricot cubes, Food Research International 38, pp 533–542Rahimzade, K., M., Hesari J., (2007). Osmotic dehydration kinetics of apricot using sucrose solution, Journal of Food Engineering 78, pp 1355–1360Pavkov I., Babić Lj., Babić M., (2006). Mathematical Modeling of the Osmotic Drying Kinetic of Fruit Tissue, PTEP -Journal on Processing and Energy in Agriculture, Novi Sad, 10:3-4, pp 67-70.Pavkov I., (2007). Kinetic of the Osmotic Drying Apricot, M.Sc. Th esis, Faculty of Agriculture, Novi Sad Šušić S., ed. (1980) Priručnik za industriju šećera, II deo [Handbook for Sugar Industry, Part II ]. Poslovna zajednica industrije šećera Jugoslavije, Beograd.Handbook for sugar industry, Second Book (1980). Business Communyti, Yugoslavia, Belgrade, Shi J., Le Maguer M.,: Osmotic Dehidration of Foods (2002). Mass Transfer and Modeling Aspects, Food Reviwes International, 18:4, pp. 305-335StatSoft  Inc (2006). Statistica for Windows (data analysis soft ware system), version 7.1acs74_44

Osmotic Drying of Apricot (Prunus armeniaca) in Sucrose Solution

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