INFLUENCE OF OSMOTIC TREATMENT IN THE DRYING OF SULTANINA GRAPES (Vitis vinifera L.)

Transcription

1 386 Bulgarian Journal of Agriultural Siene, 15 (No 5) 2009, Agriultural Aademy INFLUENCE OF OSMOTIC TREATMENT IN THE DRYING OF SULTANINA GRAPES (Vitis vinifera L.) N. PENOV 1, V. ROYTCHEV 2 and CH. CHRISTOV 1 1 University of Food Tehnologies, BG Plovdiv, Bulgaria 2 Agriultural University, BG Plovdiv, Bulgaria Abstrat PENOV, N., V. ROYTCHEV and Ch. CHRISTOV, Influene of osmoti treatment in the drying of Sultanina grapes (Vitis vinifera L.). Bulg. J. Agri. Si., 15: The possibility for onvetion drying of grapes from the seedless ultivar Sultanina by applying a preliary osmoti treatment, and the proess kinetis has been investigated. By means of a omplete fatorial experiment of the type 2 2 regression models of the veloity oeffiient of sugar solution onentration gradient in the osmoti treatment and a veloity oeffiient model for the drying proess in onvetion drying of the treated grapes have been derived. The influene of sugar solution onentration and its temperature on the kinetis of the studied proesses has been detered. A taste evaluation of the different variants has been arried out. The dendrogram showing taste evaluation ranks for dried raisins is divided into two major lusters. Appropriate parameters for grapes treatment have been suggested. Key words: osmoti treatment of grapes, seedless vine ultivar Sultanina, onentration and temperature of sugar solution, kinetis Introdution Due to their exellent taste harateristis dried grapes are a popular and valuable produt, whih ontains onentrated and easily-absorbed sugars, organi aids, vitas, erals and other substanes essential for the human body. Drying is a basi proedure, often applied in the tehnologial proessing of various produts of the food and biotehnologial industries (Burih and Berky, 1978; Sharma, 1983; Christov et al., 2002, Dithev et al., 2006). Being a heat and mass exhange proess, it depends both on the parameters of the drying agent temperature, veloity and relative air humidity, and on the ultivar and properties of the material physial and hemial properties; speifi drier loading; produt shape and size, type of the preliary treatment and so on (Penov et al., 2002). The great signifiane of the seedless ultivar Sultanina for raisin prodution worldwide is undeniable (Logotetis, 1971; Deer and Whiting, 1989). Detering the influene of individual parameters as well as their interations is of great importane for the orret performane of the drying proess in different vine ultivars. The urrent investigation aims at optimizing the drying proess of Sultanina grapes by applying a preliary osmoti treatment with a imum energy onsumption, whih allows the develop-

2 Influene of Osmoti Treatment in the Drying of Sultanina Grapes (Vitis vinifera L.) 387 ment of a finished produt with ertain qualitative and taste indies. Materials and Methods Grapes from the seedless ultivar Sultanina, whih is haraterized by medium-sized berries ( mm) and average berry weight 3.36g, were used. The seeds are rudimentary and not detetable during onsumption. The strutural omposition of grape inludes: stalks 2.39%; berries 97.61%; millerandage berries 0.63%; mehanial berry analysis berry skins 7.39%, mesoarp (flesh) 90.22%; physial and hemial omposition dry matter refration perentage 23.3%, dry matter weight perentage 27.29%, total aid ontent g/dm 3. The grapes were freed from the stalks and bruised berries, immersed in 1 % solution of sodium biarbonate with a temperature of 95 î Ñ for 1 ute, and then treated with a 0.01 % solution of sulphurous aid for 15. Having been prepared in this way the grapes were immersed in a sugar solution (solution : produt ratio 3:1) with onentration and temperature values varying aording to the design matrix of the experiment as shown in Tables 1 and 2. Following this treatment the material was dried at a temperature of 65 0 C and drying agent veloity 1 m/s in a laboratory onvetion hamber drier. The physial and hemial analyses were performed aording to methods inluded in the Bulgarian State Standard (BSS): dry matter refration and weight perentages BSS ; total aid ontent - BSS In order to study the kinetis of osmoti treatment of grapes the funtions S =f(τ) and S-S =f(τ) (1) have been onstruted, Where: S is the dry matter ontent of the sugar solution, %. From equation (1) by means of graphial differentiation the urves, depiting the veloity of the sugar syrup onentration hange have been derived: S S d = f ( S S ) (2) By linear approximation of the urve, depiting the veloity of the sugar syrup onentration hange, it is possible to write the equation: Table 1 Variation levels and names of the independent variables in osmoti drying Independent variables, z j, Upper level, Lower level, Plan entre, Variation interval, z u j (x u i ) z l i (x l i ) z o j (х o j ) Dz j Sugar solution onentration, z 1, %, (x 1 ) Sugar solution temperature, z 2, î Ñ, (x 2 ) Table 2 Plan of the experiment in a natural form NFE 2 2 Variant Z 1, (S, %) Z 2, (t, î Ñ) S - sugar solution onentration, %

3 388 N. Penov, V. Roythev and Ch. Christov d ( S S ) = K ( S S ) s (3) where: K s is the veloity oeffiient of the sugar syrup onentration gradient, -1. By integrating equation (3) within the limits of onentration and time hange, the following expression is derived: S S ln = Ksτ Smax S This expression ould be written as: S = S ( K ) ( ) s τ S S e (4) + max (5) In order to study the kinetis of onvetion drying the urve of the drying proess - U =f(τ) has been plotted, from whih the urve of drying veloity- du = f(u ), and ln( U U ) = f ( τ ) p has been derived, Where: U water ontent, %; τ - drying time, (Kolarov, 1990). The veloity oeffiient of drying has been detered using the equation of the drying proess urve: du = K ( U Where: U p U p equilibrium water ontent, %; U ) urrent water ontent, %; K veloity oeffiient of drying, -1. (6) A omplete fatorial experiment of the type 2 2 was applied with three repliations in eah point of the experiment. The influene of independent variables was detered by means of the response surfae method (Bojanov and Vuhkov, 1973; Lambrev, 1994). The taste evaluation was arried out using the rank- ing method. A total of seven tasters partiipated. Eah of these experts ranked the dried grape samples in desending order. In order to evaluate the obtained rankings the funtion of Eulidian distane between two objets (Everitt 1979, Murphy et al., 1986, Romesburg 1990) was applied: R(X, Y)=(Σ(X I -Y I ) 2 ) 0.5 =1,n (7) The statistial program SYSTATâ6.0, SPSS In.Ó1996 SPSS In. was used for plotting the response surfae and the luster analysis dendrogram. Results and Disussion The analysis of the kinetis of osmoti treatment of grapes is onneted with the funtion S =f(τ), whih allows the maintenane of onstant osmoti solution onentration throughout the proess. The urves of sugar solution onentration gradient - S S τ = f ln Smax S are presented in Figure 1, while in Table 3 their veloity oeffiients (Ê s ) for the different variants of the experimental plan are shown. The values of the deteration oeffiients (R 2 ) vary from to and they are adequate for the orresponding degrees of freedom. The analysis of the urves of sugar solution onentration gradient reveals that the proess of osmoti dehydration of Sultanina grapes is most intensive at high values of sugar solution onentration (Figure 2). The following regression model for the veloity oeffiient of sugar solution onentration gradient has been obtained: K s.10 3 = S S.t, -1 (8) This model desribes the relation between the dependent variable (veloity oeffiient of sugar solution onentration gradient) and the independent vari-

4 Influene of Osmoti Treatment in the Drying of Sultanina Grapes (Vitis vinifera L.) 389 Fig. 1. Curves of sugar solution onentration gradient Fig. 2. Student s distribution values of the regression model oeffiients for the veloity oeffiient of sugar solution onentration gradient (K s, -1 ) Table 3 Veloity oeffiient of the sugar syrup onentration gradient Coeffiients Variants K s, R Fig. 3. Response surfae of the regression model of the veloity oeffiient of sugar solution onentration gradient (K s, -1 ) ables (sugar solution onentration and temperature). The deteration oeffiient of the regression equation R 2 = is high, Standard Error of Est. is , and MAE is , whih means that the model desribes the proess adequately at the orresponding degrees of freedom. Sugar syrup onentration exerts the greatest influene on osmoti treatment of grapes, followed by inter-fatorial interation between independent variables. The temperature of the syrup in the studied interval does not have a signifiant influene. In Figure 3 the response surfae of the obtained regression model is presented. The response surfae is slightly saddle-shaped. The highest value of sugar solution onentration gradient K s = is observed in osmoti treatment with sugar solution onentration 82% at a temperature of 75 î Ñ (Variant ¹4), while the lowest K s = is reported at sugar solution onentration 62% and a temperature of 75 î Ñ (Variant ¹3). The ombination of high onentration and temperature of the sugar solution provides more favorable onditions for the development of osmoti-diffusion proesses. No signifiant variation of the sugar solution onentration gradient K s = is observed in the intervals t= o C and S=62 68%. Of great importane in dried grapes prodution is not only the osmoti treatment of the material but also the influene of this treatment on the following drying proess in a onvetion hamber drier, or the drying

5 390 N. Penov, V. Roythev and Ch. Christov kinetis of osmotially treated raisins. The data on the influene of sugar syrup onentration and temperature in osmoti treatment on the veloity oeffiient of onvetion drying helps to selet a drying regime with imal duration. The urves of onvetion drying of the osmotially treated grapes U =f(τ) and the urves of orrelation ln ( U U p ) = f ( τ ) are presented in Figure 4a and 4b. the drying agent. This period lasts for about 20, during whih 10-15% of the expendable water ontent is eliated. The duration of onvetion drying varies from 3.5 tî 8.5 hours depending on the osmoti treatment of the material. As a result the following regression model for the veloity oeffiient of onvetion drying of osmotially treated raisins has been obtained: A B Fig. 4. A - Curves of drying of osmotially treated grapes U =f(τ); B - Curves of orrelation of osmotially treated grapes Table 4 Veloity oeffiients (Ê ) in onvetion drying of osmotially treated Sultanina raisins Coeffiients Variants ¹1 ¹2 ¹3 ¹4 ¹5 K, R The veloity oeffiients (Ê ) in onvetion drying of osmotially treated Sultanina raisins for the different variants of the experimental plan are shown in Table 4. The values of their deteration oeffiients (R 2 ) vary from tî and are adequate for the orresponding degrees of freedom. A period of onstant drying veloity is absent in all variants. The proess takes plae at a onstant dereasing of drying veloity sine the initial humidity annot reah the ritial value. At the beginning of the proess a relatively short period is observed in whih the temperature of the produt reahes the temperature of K.10-3 = t S.t, -1 (9) Sugar solution temperature in osmoti treatment of grapes and inter-fatorial interation between independent variables exert the strongest influene on onvetion drying of osmotially treated grapes from the studied ultivar, whereas the influene of sugar solution onentration proves to be insignifiant (Figure 5). The presented response surfae of the regression model is of a linear type (Figure 6). The shortest dry-

6 Influene of Osmoti Treatment in the Drying of Sultanina Grapes (Vitis vinifera L.) 391 Fig. 5. Student s distribution values of the regression model oeffiient for the veloity oeffiient of onvetion drying of osmotially treated raisins Fig. 6. Response surfae of the regression model for the veloity oeffiient of onvetion drying (K, -1 ) of osmotially treated raisins Table 5 Taste evaluation of osmotially treated and onvetion dried Sultanina raisins Variants ¹ 1 ¹ 2 ¹ 3 ¹ 4 ¹ 5 Σa ij Q R Dj Dj ΣD j 2 = 450; ai j= 21 aj Std.Err. Mean Fig. 7. Diagram of taste evaluation ranks of osmotially treatedand onvetion-dried Sultanina raisins Fig. 8. Dendrogram of the results from luster analysis of the taste evaluations of osmotially treated and onvetion-dried Sultanina raisins

7 392 N. Penov, V. Roythev and Ch. Christov ing duration is reported at sugar solution onentration 82% and a temperature of 75 0 C (K ñ = ), while the longest drying duration is observed at sugar solution onentration 82% and a temperature of 55 î Ñ (K = ). The influene of sugar solution onentration in osmoti treatment of grapes on the following drying of the material in a onvetion hamber drier is not signifiant. The taste evaluations of osmotially treated and onvetion-dried Sultanina raisins aording to the ranking method are presented in Table 5, when the number of the degrees of freedom is k 1 =4 and the rate of signifiane α=0.01; W=0.918; χ 2 =25.71 and χ ò2 =7.78. After omparing χ 2 >χ ò 2 it ould be stated that the tasters have reahed a onsensus of opinion. The diagram of taste evaluation ranks of Sultanina dried grapes belongs to the growing linear funtion type and it ould be divided into two major groups: 1 st group - variants ¹ 5 and 4; 2 nd group variants ¹ 1, 3 and 2 (Figure 7). This onlusion is also supported by the luster analysis dendrogram, whih implies that the variants in the 1 st group of the preliary osmoti treatment of Sultanina grapes are the most suitable for drying (Figure 8). Conlusions - In the drying proess of grapes from the seedless ultivar Sultanina by applying a preliary treatment in osmoti solutions, sugar solution onentration exerts a stronger influene on the osmoti-diffusion proess than its temperature does. The highest value of the veloity oeffiient of sugar solution onentration gradient - K s =0, is observed at onentration 82% and a temperature of 75 î Ñ, while the lowest value of K s = is reported at sugar solution onentration 62% and a temperature of 75 î Ñ. - Depending on the osmoti treatment of grapes, the duration of onvetion drying varies from 3.5 to 8.5 hours, sugar solution temperature having the strongest influene on it. It is best to perform the preliary treatment of Sultanina grapes for raisin prodution at sugar solution onentration 72% and a temperature of 65 î Ñ for a period of 3 hours. Referenes Reeived June, 24, 2009; aepted for printing September, 2, Bojanov, B. and I. Vuhkov, Statistial methods for modelling and optimizing multi-fatorial objets. State Publishing Company Tehnology, Sofia, 530 pp. (Bg). Burih, Î. and F. Berky, Drying of Fruits and Vegetables. Mosow, 279 pp. (Ru). Christov, Ch., N. Penov and S. Dithev, Kinetis investigation on a low temperature heat pump drying method. Siene Congress 2002, University of Tehnologies- Sofia, Reports Colletion, Vol. II: Deer, T. W. W. and J. R. Whiting, Evaluation of Sultana grapevine seletions for table grape prodution. Australian Journal of Experimental Agriulture, 29: Dithev, S., Ch.Christov, N. Penov and V. Roihev, Kinetis investigation on a ombined (osmoti and low temperature heat pump) method of grape dróing. 3 rd Central European Congress on Food, May 2006, Sofia, Bulgaria, Reports Colletion (Ð46), pp Everitt, B. S., Unresolved problems in luster analysis. Biometris, 35: Kolarov, Ê., Proesses and devies in the food industry. Plovdiv, Ch. G. Danov Publishing Company, 322 pp. (Bg). Lambrev, À., Bases of the Engineering Experiment in the Investigation of Mahines and Devies for the Food Industry. Plovdiv, Ch. G. Danov, 211 pp. (Bg). Logotetis, V., Raisin prodution from Sultanina grapes (White seedless), Vitiulture Issues, Sofia, pp Murphy, J. P., T. S. Cox and D. M. Rodgers, Cluster analysis of red winter wheat ultivars based upon oeffiients of parentage. Crop. Si., 26: Penov, N., D. Ludneva, D. Braikov and V. Roythev, Investigation on the influene of osmoti treatment in the drying of seedless vine ultivars-i. International Siene Congress Stara Zagora 2002, 6-7 June Vol 2. Agriultural Sienes. Hortiulture and Stok-Breeding, pp Romesburg, Ch., Cluster analysis for researhers. Robert E. Krieger Publishing Company, 334 pp. Sharma, R. Ch., Investigation on osmoti drying of fruits and vegetables. Dissertation, University of Food Tehnologies, Plovdiv, 279 pp. (Bg).