- Email: [email protected]
Shrinkage of osmotically dehydrated sardine sheets at changing moisture contents
Journal of Food Engineering 65 (2004) 333–339 www.elsevier.com/locate/jfoodeng
Shrinkage of osmotically dehydrated sardine sheets at changing moisture contents Otoniel Corzo a
a,*
, Nelson Bracho
b
Department of Food Technology, Universidad de Oriente, Guatamare, Venezuela b Department of Statistic, Universidad de Oriente, Guatamare, Venezuela
Received 26 April 2003; received in revised form 1 December 2003; accepted 19 January 2004
Abstract The objective of this work was to determine the relationship between moisture content and shrinkage factor of osmotically dehydrated sardine sheets. Dehydration was performed according to a 5 · 5 · 7 factorial design where the temperature, concentration and dehydration time were 30, 32, 34, 36 and 38 C, 15%, 18%, 21%, 24%, and 27% NaCl, and 20, 40, 60, 120, 180 and 240 min, respectively. The shrinkage factor in each sardine sheet was calculated according to the Viberg et al. [J. Food Eng. 35 (1998) 135] equation. Linear simple regression was used to fit the database to the model of the shrinkage factor as a function of moisture content. The models as fitted explained the 82.54–95.71% of the variability in the shrinkage factor as a function of moisture content and, the 90–99% of the variability in the shrinkage factor as a function of dimensionless moisture content at the 95% confidence level. 2004 Elsevier Ltd. All rights reserved. Keywords: Shrinkage; Sardine sheet; Osmotic dehydration
1. Introduction There is a family of operations which involve the interaction between a water containing foodstuff and water in the surrounding medium at the prevailing temperature, such as drying, osmotic dehydration, storing and packaging. Osmotic dehydration is generally used as an upstream step for the dehydration of food before they are subjected to further processing such as freezing (Ponting, 1973), freeze drying (Hawkes & Flink, 1978), vacuum drying (Dixon & Jen, 1977), and air drying (Nanjundaswamy, Radhakrishnaiah, Balachandran, Saroja, & Murthy, 1978). Osmotic dehydration is a viable process for the partial removal of water in which cellular material are placed in a concentrated solution of soluble solute. A driving force for water removal is set up because of a difference in osmotic pressure between the food and its surrounding solution. The complex cellular structure of food acts as a semi-per*
Corresponding author. Address: Department of Food Technology, Universidad de Oriente, Amador Hdez cc Guilarte y Colina, Porlamar 3111, Venezuela. Tel.: +58-295-2631230; fax: +58-295-2656545. E-mail addresses: [email protected] (O. Corzo), [email protected]. edu.ve (N. Bracho). 0260-8774/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2004.01.030
meable membrane. Since the membrane responsible for osmotic transport is not perfectly selective, other solutes present in the cells can also be leached into the osmotic solution (Dixon & Jen, 1977; Giangiacomo, Torreggiani, & Abbo, 1987; Lerici, Pinnavaia, Dalla Rosa, & Bartolucci, 1985). Final product characteristics and mass transfer kinetics are largely affected by uptake of solute from the solution. Representative heat and mass transfer equations have been outlined. When these equations are used, there is need to account for the change in porosity and the overall shrinkage of the samples as they lose moisture. Shrinkage studies have been performed on air or freeze drying, but information concerning osmotic drying is rarely reported. The importance of the shrinkage is twofold: firstly it affects texture and other quality factors and secondly its knowledge is needed for mass transfer modeling. Kilpatrick, Lowe, and Van Arsdel (1975) studied volume shrinkage of potatoes and other vegetables as drying proceeds. Charm (1978) reported on volumetric contraction of meat and potatoes. Lozano, Rotstein, and Urbicain (1980) reported shrinkage and porosity of apple tissue at different moisture contents. Lozano, Rotstein, and Urbicain (1983) modeled the water loss based on a bulk shrinkage coefficient to obtain a
334
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
predictive equation based on composition of the foodstuff. Volume changes are dependent of several factors as geometry, drying method and experimental conditions. Physical properties such as bulk density and porosity change due to the shrinkage. In osmotic dehydration of fruits the shrinkage depends on water loss and solute gain in the food (Viberg, Freuler, Gekas, & Sjoholm, 1998). Mathematical expressions have been developed for the one or the two transfers of mass that happen, that allow determination of the shrinkage factor in dehydrated fruits (Gabas, Menegalli, & TelisRomero, 1999; Gabas, Telis-Romero, & Menegalli, 2001; Lozano et al., 1980; Moreira, Figuereido, & Sereno, 2000; Moreira & Sereno, 2001; Ochoa, Kessel, Piron, Marquez, & De Michels, 2002a, 2002b; Sjoholm & Gekas, 1995; Viberg et al., 1998) and in vegetables (Suzuki, Kubota, Hasegawa, & Hosaka, 1976); however, there has been relatively little work on shrinkage of fish (Balaba & Pigott, 1986). The objective of this work was to determine the relationship between moisture content and shrinkage factor of osmotically dehydrated sardine sheets.
2. Materials and methods 2.1. Sample preparation The fresh sardines (Sardinella aurita) were all acquired from same capture zone of Margarita Island, Venezuela, from fishermen who caught them within 1 h before selling them. Sardines were 15–20 cm long and weighted 30–35 g/fish. Sardines were manually filleted with stainless steel knives, and then the fillets were cut into sheets from the muscle nearest to head, thus only obtaining 2 sheets per each fillet. After samples had been collected, their dimensions were measured by means of a micrometer. Sheets had an average length of 20.1 ± 0.5 mm (N ¼ 525), average width of 15.0 ± 0.6 mm, and average thickness of 6.4 ± 0.9 mm. 2.2. Osmotic dehydration Seven groups of 3 sheets each were randomly selected. Weight and moisture content were measured for each sheet. A basket with three-marked compartment was used in which to place the sheets of each group to avoid interference between them. The seven groups were immersed simultaneously into an osmotic solution of a given concentration and temperature. One group was removed at time intervals of 20 min during the first hour, at 30 min intervals during the second hour and hourly during the 2 remaining hours. After the removal from brine, the dehydrated sheets of each group were drained for 5 min, blotted with absorbent paper to remove the excess solution, and the weight and moisture
content were measured individually. Each experimental treatment was performed in duplicate. All reported results are based on average values of six replicates. Each treatment condition was performed according to a 5 · 5 · 7 factorial design where the temperature, concentration and dehydration time were 30, 32, 34, 36 and 38 C, 15%, 18%, 21%, 24%, and 27% NaCl, and 20, 40, 60, 120, 180 and 240 min, respectively. The osmotic solutions were prepared by mixing commercial grade salt with the proper amount of distilled water. The brine to sample ratio was always higher than 20:1 to avoid significant dilution of the medium by water removal, which would lead to local reduction of the osmotic driving force during the process. The concentration of the brine was monitored throughout each experiment. Experiments were performed with the same constant magnetic agitation for each experiment. The concentration of the brine (%NaCl) was adjusted initially and thereafter monitored throughout each run by the Mohr method (AOAC, 1990). The moisture content of fresh and treated sardine sheets was determined by drying under vacuum (0.1 mmHg) at 60 C until constant weight (AOAC, 1990). With the obtained values of the initial weight and the final weight, the shrinkage factor was calculated for each sardine sheet at the different dehydration times for each combination of concentration and temperature of brine, according to the Viberg et al. (1998) equation: S ¼ 1 ðm0 mt Þ=m0 ¼ 1 Dm=m0
ð1Þ
where mt is the mass at a dehydration time t and m0 is the initial mass. Since this method is based on the assumption of nearly constant density throughout the process, this limitation was considered in this work. The volume of each untreated and dehydrated sheets for each experimental condition (low concentration and low temperature, high concentration and high temperature) were measured with a pycnometer and then their densities were calculated from their weights. ANOVA shows that the initial density and the dehydrated sheets density were not significantly different (p > 0:05) in the range of studied conditions. This can be explained because Del Valle and Nickerson (1967) demonstrated that the volume of a salted fish is only related to its water content and unsalted dry matter concentration. In addition, Deumier, Mens, Heriard-Dubreuil, and Collingnan (1997) considered that the salt specific volume is negligible in order to describe a system for continuous determination of mass transfer during brining operation of herring. 2.3. Statistical analysis Statistical evaluation of the results was performed using a 5 · 5 · 7 split (on time) factorial design (five concentrations, five temperatures, and seven time
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
intervals). Data were subjected to analysis of variance (ANOVA) and multiple comparison tests were performed using a least significant difference (LSD), suitable for factorial designs, at the 95% of confidence level. Linear simple regression (Montgomery & Peck, 1982) was used to fit database to the model of the variation of shrinkage factor as a function of moisture content, for each combination of concentration and temperature of brine. All the analysis was carried out using the statistical software, Statgraphics 5.0 (Statistical Graphics Corp., Rockville, MD, USA).
335
1
0.98
S 0.96
0.94
3. Results and discussion 3.1. Effect of the conditions of the dehydration
0.92
ANOVA shows significant differences (p < 0:05) in the shrinkage factor caused by concentration and temperature of brine, dehydration time, and the interactions of these factors. Multiple comparison of means using LSD shows that the shrinkage factor diminishes when concentration, temperature and time were increased. In Fig. 1 it is observed that the shrinkage factor diminishes when increasing the time for the concentrations of 21% and 24% NaCl respectively. These results agree with reports that the weight loss from any material depends upon factors such as temperature and concentration of the osmotic solution and dehydration time (RaoultWack, 1994; Torreggiani, 1993). 3.2. Modeling shrinkage factor Fig. 2 shows the change in shrinkage factor of sardine sheets, as a result of osmotic dehydration at 30 C, using 0.95
Temperature 30 32 34 36 38
0.93
s 0.91 0.89 0.87 0.85 20
40
60
90 120 180 240
Time (min)
(a) 0.96
Temperature 30 32 34 36 38
0.93 0.9
s 0.87 0.84 0.81 0.78
(b)
20
40
60
90 120 180 240
Time (min)
Fig. 1. Multiple comparison of means for shrinkage factor of osmotically dehydrated sardine sheets in brine of (a) 21% NaCl, (b) 24% NaCl, at different temperatures of brine.
1.3
1.4
1.5
1.6
1.7
1.8
X (d.b) Fig. 2. Shrinkage factor (S) of sardine sheets as a function of moisture content, as a result of osmotic dehydration at 30 C: () 21% NaCl; (+) 24% NaCl; (·) 27% NaCl.
21%, 24% and 27% NaCl. The shrinkage factor is plotted as a function of moisture content X (dry basis). A uniform behavior is observed, which is essentially independent of each set of experimental conditions. This behavior suggests a simple linear relation between moisture content and shrinkage factor. It appears desirable to be able to predict shrinkage factor of a foodstuff without having to measure the property itself. Relation between moisture content of sheets and shrinkage factor. For each combination of concentration and temperature, simple linear regression was used to fit the values of the shrinkage factor (S) to a model as a function of the moisture content (X ). The model as fitted corresponds to: S ¼ A þ BX
ð2Þ
where X is the moisture content in dry basis and, A and B are the constant parameters. The model as fitted explained 82.54–95.71% of the variability in the shrinkage factor at the 95% confidence level, and the standard errors of the estimate are low (Table 1). With these models the shrinkage factors of sardine sheets can be calculated when they are osmotically dehydrated in brines of 15–24% NaCl at temperatures of 30–38 C for dehydration times of 20–240 min. This relationship is similar for dried pork meat in a convective dryer with air at 25 C (Clemente, Bon, Carcel, Garcia-Pascual, & Mulet, 2001), and osmotically dehydrated apple in 50% and 60% sucrose solutions at 5 and 20 C (Moreira & Sereno, 2001). At a constant temperature, the parameter B increases and A decreases with increasing brine concentration. At a constant brine concentration, equilibrium water content decreased and
336
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
Table 1 Linear regression analysis for shrinkage factor as a function of the moisture content (Eq. (2)) Concentration (% NaCl)
15 15 15 15 15 18 18 18 18 18 21 21 21 21 21 24 24 24 24 24 27 27 27 27 27 a
Temperature (C)
30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38
Parameters Aa
Ba
0.7202 0.7295 0.7987 0.7705 0.7324 0.6287 0.5662 0.6285 0.4036 0.5466 0.5290 0.5614 0.4487 0.3829 0.5956 0.5413 0.6000 0.5733 0.4245 0.5798 0.7094 0.5282 0.6351 0.4875 0.4684
0.1561 0.1391 0.0870 0.1006 0.1060 0.1985 0.2334 0.1800 0.3537 0.2498 0.2584 0.1959 0.2682 0.3531 0.2538 0.2287 0.1989 0.2314 0.3122 0.2221 0.1421 0.2724 0.1800 0.2584 0.2991
R2
Standard error
0.8763 0.8704 0.8535 0.8629 0.9061 0.8419 0.8254 0.8773 0.9147 0.9611 0.8931 0.9246 0.9326 0.9278 0.9459 0.8794 0.8929 0.9365 0.8729 0.8582 0.9254 0.8827 0.8086 0.9420 0.9571
0.0075 0.0074 0.0114 0.0085 0.0108 0.0125 0.0142 0.0144 0.0143 0.0105 0.0179 0.0157 0.0151 0.0157 0.0122 0.0195 0.0178 0.0159 0.0209 0.0229 0.0122 0.0192 0.0261 0.0140 0.0121
Indicates significant effect at a ¼ 0:001.
equilibrium salt content increased with the increasing temperature. Relation between dimensionless moisture content and shrinkage factor. Another factor at our disposal was initial moisture content of the sardine sheets used in the trials. Therefore, we investigated the possibility that the initial moisture content (X0 ) of sheets could influence the shrinkage factor. ANOVA shows that the initial moisture constant is a significantly covariable (p < 0:05) in the variation of shrinkage factor. Dimensionless volume change (V =V0 ) as a function of the dimensionless moisture content (X =X0 ) was studied. Amongst others were studied those of Suzuki et al. (1976), Lozano et al. (1980, 1983), Ratti (1994) and Ochoa et al. (2002b), who, starting from specific experimental data for different foods, have fitted expressions to them. The model by Suzuki et al. (1976) has represented the phenomena with a straight line. In turn, Lozano et al. (1983) modified that model for any food products for the cases where two linear fits are needed: one for high moistures and another for low (X < 0:15). Lozano et al. (1983) and Ochoa et al. (2002b) represented the phenomena with only one equation, obtained by nonlinear regression of experimental data. Ratti (1994) has indicated that for some foodstuff the V =V0 vs. X =X0 function is linear in the whole range of water content. Ochoa et al. (2002b) proposed a linear model for whole sour cherry. There are no models for osmotically dehydrated foods.
Analyzing the results of this work, the nonlinear models did not represent appropriately the experimental values of shrinkage factor for osmotically dehydrated sardine sheets. Simple linear regression was used to fit the values of the shrinkage factor (S) to a model as a function of the dimensionless moisture content (X =X0 ). The model as fitted corresponds to: S ¼ C þ DðX =X0 Þ
ð3Þ
where X is the moisture content (dry basis), X0 is the initial moisture content (dry basis) and, C and D are the constant parameters (Table 2). The model as fitted explained 90–99% of the variability in the shrinkage factor at the 95% confidence level (Table 3). We observed that the R2 are higher and the standard errors of the estimate are lower for this model compared with these parameters for the model when initial moisture content is not taken into account (Table 2). Relation between shrinkage in volume and volume of water lost. Kilpatrick et al. (1975) showed that the shrinkage in volume for some dried vegetables was very near to the volume of water lost. Suzuki et al. (1976) showed that the shrinkage in volume equals the volume of water lost by evaporation in the uniform drying stage of root vegetables. Clemente et al. (2001) found that the decrease in the volume of pork meat was bigger than the volume of water lost during drying with air at 25 C.
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
337
Table 2 Linear regression analysis for shrinkage factor as a function of the dimensionless moisture content (Eq. (3)) Concentration (% NaCl)
15 15 15 15 15 18 18 18 18 18 21 21 21 21 21 24 24 24 24 24 27 27 27 27 27 a
Temperature (C)
30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38
Parameters Ca
Da
0.3871 0.3934 0.5712 0.4940 0.4154 0.1903 0.1150 0.1657 )0.2529 0.1118 0.0273 0.0655 )0.1231 )0.2556 0.3152 0.0434 0.2343 0.1060 )0.1733 0.1071 0.4070 0.0642 0.2665 )0.0317 )0.0171
0.6689 0.5911 0.4102 0.4923 0.5721 0.0115 0.0546 0.0575 1.2266 0.0649 1.0120 0.9536 1.1579 1.3054 0.6577 0.9724 0.0127 0.0701 1.1754 0.7914 0.4018 0.9014 0.7548 1.0171 1.0107
R2
Standard error
0.8842 0.8571 0.8448 0.8300 0.8967 0.8427 0.8005 0.9006 0.9115 0.9667 0.9336 0.9410 0.9047 0.9190 0.9502 0.8950 0.9091 0.9648 0.8764 0.9062 0.9418 0.9072 0.8844 0.9310 0.9476
0.0073 0.0078 0.0116 0.0949 0.0111 0.0121 0.0152 0.0129 0.0145 0.0098 0.0142 0.0139 0.0280 0.0176 0.0128 0.0181 0.0181 0.0163 0.0206 0.0195 0.0109 0.0171 0.0202 0.0151 0.0139
Indicates significant effect at a ¼ 0:001.
Table 3 Linear regression analysis for the volume shrinkage as a function of the volume of the loss water (Eq. (8)) Concentration (% NaCl)
Temperature (C)
E parameter
p-value
R2
15 15 15 15 15 18 18 18 18 18 21 21 21 21 21 24 24 24 24 24 27 27 27 27 27
30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38
0.3921 0.4749 0.3434 0.3674 0.4204 0.4412 0.6267 0.4047 0.5050 0.5438 0.4242 0.4457 0.5512 0.5341 0.5120 0.5251 0.3290 0.3549 0.5676 0.5300 0.4507 0.4542 0.4707 0.6225 0.5776
<0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
0.9453 0.9835 0.9674 0.9633 0.9778 0.9870 0.9846 0.9707 0.9797 0.9907 0.9840 0.9822 0.9876 0.9818 0.9802 0.9819 0.9911 0.9851 0.9837 0.9818 0.9743 0.9853 0.9836 0.9912 0.9849
p-value <0.001 indicates significant effect at a ¼ 0:001.
338
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
There is no relation for osmotically dehydrated fish. For that purpose the shrinkage in volume (V0 V ) of sardine sheets and the volume of water lost (Vw ) were computed according to: S¼
V V0
ð4Þ
V0 V ¼ V0 SV0 ¼ V0 ð1 SÞ ¼ Vs
ð5Þ
mw0 mwt ¼ m0 xw0 mt xwt ¼ mlost
ð6Þ
qw mlost
water
¼ Vw
water
ð7Þ
Simple linear regression without an intercept was used to fit the values of the volume shrinkage (Vs ) to a model as a function of the volume of water lost (Vw ). The model as fitted corresponds to: Vs ¼ EVw
ð8Þ
where E is the constant parameter (Table 3). The models as fitted explained 82.54–95.71% of the variability in the shrinkage in volume at the 95% confidence level (Table 3). The shrinkage in volume can be predicted as a function of the volume of water lost. As can be observed, the slope (E value) is lower than 1.0. This indicates that the shrinkage in volume is lower than the volume of water lost. Further studies are necessary to determine the changes in volume.
4. Conclusions Linear relationships between the shrinkage factor and moisture content and between shrinkage in volume and the volume of water lost have been found for osmotically dehydrated sardine sheets in brines of 15–24% NaCl at temperatures of 30–38 C for dehydration times of 20–240 min. The shrinkage in volume is lower than the volume of water lost during the osmotic dehydration under the restricted conditions of our experiment. To consider only the water content was not sufficient to explain the changes in volume observed for osmotically dehydrated sardine sheets.
References AOAC (1990). Official methods of analysis (15th ed.). Washington, DC, USA: Association of Official Analytical Chemists. Balaba, B., & Pigott, G. M. (1986). Shrinkage of fish muscle during drying. Journal of Food Science, 51(12), 510–511. Charm, S. E. (1978). The fundamentals of food engineering (3rd ed.). Westport: AVI Publishing Co Inc. Clemente, G., Bon, J., Carcel, J. A., Garcia-Pascual, P., & Mulet, A. (2001). Meat shrinkage during drying. In J. Welti-Chanes, G. V. Barbosa-Canovas, & J. M. Aguilera (Eds.), Proceedings of the eighth international congress on engineering and food (vol. II, pp. 1225–1229). Lancaster: Technomic Publication.
Del Valle, F. R., & Nickerson, J. T. R. (1967). Studies on salting and drying fish. I. Equilibrium considerations in salting. Journal of Food Science, 32, 173–179. Deumier, F., Mens, F., Heriard-Dubreuil, B., & Collingnan, A. (1997). Control of immersion process: a novel system for monitoring mass transfer tested with herring brining. Journal of Food Engineering, 32, 293–311. Dixon, G. M., & Jen, J. J. (1977). Changes of sugar and acid in osmovac dried apple slices. Journal of Food Science, 42, 1126– 1131. Gabas, A. L., Menegalli, F. C., & Telis-Romero, J. (1999). Effect of chemical pretreatment on the physical properties of dehydrated grapes. Drying Technology, 17(6), 1215–1226. Gabas, A. L., Telis-Romero, J., & Menegalli, F. C. (2001). Determination of concentration dependent effective moisture diffusivity of plums based on shrinkage kinetics. In J. Welti-Chanes, G. V. Barbosa-Canovas, & J. M. Aguilera (Eds.), Proceedings of the eighth international congress on engineering and food (vol. II, pp. 1086–1090). Lancaster: Technomic Publication. Giangiacomo, R., Torreggiani, D., & Abbo, E. (1987). Osmotic dehydration of fruit. Part I: Sugar exchange between fruit and extracting syrup. Journal of Food Processing Preservation, 11, 183– 195. Hawkes, J., & Flink, J. M. (1978). Osmotic concentration of fruit slices prior to freeze dehydration. International Journal of Food Science and Technology, 2, 265–284. Kilpatrick, P. W., Lowe, E., & Van Arsdel, W. B. (1975). Tunnel dehydrators for fruits and vegetables. Advances in Food Research, 50, 313–372. Lerici, C. L., Pinnavaia, G., Dalla Rosa, M., & Bartolucci, L. (1985). Osmotic dehydration of fruit: influence of osmotic agents on drying behavior and product quality. Journal of Food Science, 50, 1217– 1219. Lozano, J. E., Rotstein, E., & Urbicain, M. J. (1980). Total porosity and open porosity in the drying of fruits. Journal of Food Science, 45, 1403–1407. Lozano, J. E., Rotstein, E., & Urbicain, M. J. (1983). Shrinkage, porosity and bulk density of foodstuffs at changing moisture contents. Journal of Food Science, 48, 1497–1502. Montgomery, D., & Peck, E. (1982). Introduction to linear regression analysis. New York: John Wiley and Sons. Moreira, R., Figuereido, A. M., & Sereno, A. M. (2000). Shrinkage of apple disks during drying by warm air-convection and freeze drying. Drying Technology, 18(1–2), 279–294. Moreira, R., & Sereno, A. M. (2001). Volume shrinkage of apple cylinders during osmotic dehydration. In J. Welti-Chanes, G. V. Barbosa-Canovas, & J. M. Aguilera (Eds.), Proceedings of the eighth international congress on engineering and food (vol. II, pp. 1351–1355). Lancaster: Technomic Publication. Nanjundaswamy, A. M., Radhakrishnaiah, S. G, Balachandran, C., Saroja, S., & Murthy, R. B. S. (1978). Studies of development of new categories of dehydrated product from indigenous fruits. Indian Food Packaging., 22, 91–93. Ochoa, M. A., Kessel, A. G., Piron, B. N., Marquez, C. A., & De Michels, J. (2002a). Shrinkage during convective drying of whole rose hip (Rosa Rubiginosa L.) fruits. Lebensmittel-Wissenschaft und-Technolgie, 35, 400–406. Ochoa, M. A., Kesseler, A. G., Pirone, B. N., Marquez, C. A., & De Michelis, J. (2002b). A volume and areas shrinkage during dehydration of whole sour cherry fruits (prunus cerasus). Drying Technology, 20, 147–156. Ponting, I. D. (1973). Osmotic dehydration of fruits––recent modifications and applications. Processing Biochemistry, 8, 18–20. Raoult-Wack, A. L. (1994). Advances in osmotic dehydration. Trends in Food Science and Technology, 5, 255–260. Ratti, C. (1994). Shrinkage during drying of foodstuffs. Journal of Food Engineering, 25, 91–105.
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339 Sjoholm, I., & Gekas, V. (1995). Apple shrinkage upon drying. Journal of Food Engineering, 25, 123–130. Suzuki, K., Kubota, K., Hasegawa, T., & Hosaka, H. (1976). Shrinkage in dehydration of root vegetables. Journal of Food Science, 41, 1189–1193.
339
Torreggiani, D. (1993). Osmotic dehydration in fruits and vegetables processing. Food Research International, 26, 59–68. Viberg, U., Freuler, S., Gekas, V., & Sjoholm, I. (1998). Osmotic pretreatment of strawberries and shrinkage effects. Journal of Food Engineering, 35, 135–145.
Shrinkage of osmotically dehydrated sardine sheets at changing moisture contents Otoniel Corzo a
a,*
, Nelson Bracho
b
Department of Food Technology, Universidad de Oriente, Guatamare, Venezuela b Department of Statistic, Universidad de Oriente, Guatamare, Venezuela
Received 26 April 2003; received in revised form 1 December 2003; accepted 19 January 2004
Abstract The objective of this work was to determine the relationship between moisture content and shrinkage factor of osmotically dehydrated sardine sheets. Dehydration was performed according to a 5 · 5 · 7 factorial design where the temperature, concentration and dehydration time were 30, 32, 34, 36 and 38 C, 15%, 18%, 21%, 24%, and 27% NaCl, and 20, 40, 60, 120, 180 and 240 min, respectively. The shrinkage factor in each sardine sheet was calculated according to the Viberg et al. [J. Food Eng. 35 (1998) 135] equation. Linear simple regression was used to fit the database to the model of the shrinkage factor as a function of moisture content. The models as fitted explained the 82.54–95.71% of the variability in the shrinkage factor as a function of moisture content and, the 90–99% of the variability in the shrinkage factor as a function of dimensionless moisture content at the 95% confidence level. 2004 Elsevier Ltd. All rights reserved. Keywords: Shrinkage; Sardine sheet; Osmotic dehydration
1. Introduction There is a family of operations which involve the interaction between a water containing foodstuff and water in the surrounding medium at the prevailing temperature, such as drying, osmotic dehydration, storing and packaging. Osmotic dehydration is generally used as an upstream step for the dehydration of food before they are subjected to further processing such as freezing (Ponting, 1973), freeze drying (Hawkes & Flink, 1978), vacuum drying (Dixon & Jen, 1977), and air drying (Nanjundaswamy, Radhakrishnaiah, Balachandran, Saroja, & Murthy, 1978). Osmotic dehydration is a viable process for the partial removal of water in which cellular material are placed in a concentrated solution of soluble solute. A driving force for water removal is set up because of a difference in osmotic pressure between the food and its surrounding solution. The complex cellular structure of food acts as a semi-per*
Corresponding author. Address: Department of Food Technology, Universidad de Oriente, Amador Hdez cc Guilarte y Colina, Porlamar 3111, Venezuela. Tel.: +58-295-2631230; fax: +58-295-2656545. E-mail addresses: [email protected] (O. Corzo), [email protected]. edu.ve (N. Bracho). 0260-8774/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2004.01.030
meable membrane. Since the membrane responsible for osmotic transport is not perfectly selective, other solutes present in the cells can also be leached into the osmotic solution (Dixon & Jen, 1977; Giangiacomo, Torreggiani, & Abbo, 1987; Lerici, Pinnavaia, Dalla Rosa, & Bartolucci, 1985). Final product characteristics and mass transfer kinetics are largely affected by uptake of solute from the solution. Representative heat and mass transfer equations have been outlined. When these equations are used, there is need to account for the change in porosity and the overall shrinkage of the samples as they lose moisture. Shrinkage studies have been performed on air or freeze drying, but information concerning osmotic drying is rarely reported. The importance of the shrinkage is twofold: firstly it affects texture and other quality factors and secondly its knowledge is needed for mass transfer modeling. Kilpatrick, Lowe, and Van Arsdel (1975) studied volume shrinkage of potatoes and other vegetables as drying proceeds. Charm (1978) reported on volumetric contraction of meat and potatoes. Lozano, Rotstein, and Urbicain (1980) reported shrinkage and porosity of apple tissue at different moisture contents. Lozano, Rotstein, and Urbicain (1983) modeled the water loss based on a bulk shrinkage coefficient to obtain a
334
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
predictive equation based on composition of the foodstuff. Volume changes are dependent of several factors as geometry, drying method and experimental conditions. Physical properties such as bulk density and porosity change due to the shrinkage. In osmotic dehydration of fruits the shrinkage depends on water loss and solute gain in the food (Viberg, Freuler, Gekas, & Sjoholm, 1998). Mathematical expressions have been developed for the one or the two transfers of mass that happen, that allow determination of the shrinkage factor in dehydrated fruits (Gabas, Menegalli, & TelisRomero, 1999; Gabas, Telis-Romero, & Menegalli, 2001; Lozano et al., 1980; Moreira, Figuereido, & Sereno, 2000; Moreira & Sereno, 2001; Ochoa, Kessel, Piron, Marquez, & De Michels, 2002a, 2002b; Sjoholm & Gekas, 1995; Viberg et al., 1998) and in vegetables (Suzuki, Kubota, Hasegawa, & Hosaka, 1976); however, there has been relatively little work on shrinkage of fish (Balaba & Pigott, 1986). The objective of this work was to determine the relationship between moisture content and shrinkage factor of osmotically dehydrated sardine sheets.
2. Materials and methods 2.1. Sample preparation The fresh sardines (Sardinella aurita) were all acquired from same capture zone of Margarita Island, Venezuela, from fishermen who caught them within 1 h before selling them. Sardines were 15–20 cm long and weighted 30–35 g/fish. Sardines were manually filleted with stainless steel knives, and then the fillets were cut into sheets from the muscle nearest to head, thus only obtaining 2 sheets per each fillet. After samples had been collected, their dimensions were measured by means of a micrometer. Sheets had an average length of 20.1 ± 0.5 mm (N ¼ 525), average width of 15.0 ± 0.6 mm, and average thickness of 6.4 ± 0.9 mm. 2.2. Osmotic dehydration Seven groups of 3 sheets each were randomly selected. Weight and moisture content were measured for each sheet. A basket with three-marked compartment was used in which to place the sheets of each group to avoid interference between them. The seven groups were immersed simultaneously into an osmotic solution of a given concentration and temperature. One group was removed at time intervals of 20 min during the first hour, at 30 min intervals during the second hour and hourly during the 2 remaining hours. After the removal from brine, the dehydrated sheets of each group were drained for 5 min, blotted with absorbent paper to remove the excess solution, and the weight and moisture
content were measured individually. Each experimental treatment was performed in duplicate. All reported results are based on average values of six replicates. Each treatment condition was performed according to a 5 · 5 · 7 factorial design where the temperature, concentration and dehydration time were 30, 32, 34, 36 and 38 C, 15%, 18%, 21%, 24%, and 27% NaCl, and 20, 40, 60, 120, 180 and 240 min, respectively. The osmotic solutions were prepared by mixing commercial grade salt with the proper amount of distilled water. The brine to sample ratio was always higher than 20:1 to avoid significant dilution of the medium by water removal, which would lead to local reduction of the osmotic driving force during the process. The concentration of the brine was monitored throughout each experiment. Experiments were performed with the same constant magnetic agitation for each experiment. The concentration of the brine (%NaCl) was adjusted initially and thereafter monitored throughout each run by the Mohr method (AOAC, 1990). The moisture content of fresh and treated sardine sheets was determined by drying under vacuum (0.1 mmHg) at 60 C until constant weight (AOAC, 1990). With the obtained values of the initial weight and the final weight, the shrinkage factor was calculated for each sardine sheet at the different dehydration times for each combination of concentration and temperature of brine, according to the Viberg et al. (1998) equation: S ¼ 1 ðm0 mt Þ=m0 ¼ 1 Dm=m0
ð1Þ
where mt is the mass at a dehydration time t and m0 is the initial mass. Since this method is based on the assumption of nearly constant density throughout the process, this limitation was considered in this work. The volume of each untreated and dehydrated sheets for each experimental condition (low concentration and low temperature, high concentration and high temperature) were measured with a pycnometer and then their densities were calculated from their weights. ANOVA shows that the initial density and the dehydrated sheets density were not significantly different (p > 0:05) in the range of studied conditions. This can be explained because Del Valle and Nickerson (1967) demonstrated that the volume of a salted fish is only related to its water content and unsalted dry matter concentration. In addition, Deumier, Mens, Heriard-Dubreuil, and Collingnan (1997) considered that the salt specific volume is negligible in order to describe a system for continuous determination of mass transfer during brining operation of herring. 2.3. Statistical analysis Statistical evaluation of the results was performed using a 5 · 5 · 7 split (on time) factorial design (five concentrations, five temperatures, and seven time
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
intervals). Data were subjected to analysis of variance (ANOVA) and multiple comparison tests were performed using a least significant difference (LSD), suitable for factorial designs, at the 95% of confidence level. Linear simple regression (Montgomery & Peck, 1982) was used to fit database to the model of the variation of shrinkage factor as a function of moisture content, for each combination of concentration and temperature of brine. All the analysis was carried out using the statistical software, Statgraphics 5.0 (Statistical Graphics Corp., Rockville, MD, USA).
335
1
0.98
S 0.96
0.94
3. Results and discussion 3.1. Effect of the conditions of the dehydration
0.92
ANOVA shows significant differences (p < 0:05) in the shrinkage factor caused by concentration and temperature of brine, dehydration time, and the interactions of these factors. Multiple comparison of means using LSD shows that the shrinkage factor diminishes when concentration, temperature and time were increased. In Fig. 1 it is observed that the shrinkage factor diminishes when increasing the time for the concentrations of 21% and 24% NaCl respectively. These results agree with reports that the weight loss from any material depends upon factors such as temperature and concentration of the osmotic solution and dehydration time (RaoultWack, 1994; Torreggiani, 1993). 3.2. Modeling shrinkage factor Fig. 2 shows the change in shrinkage factor of sardine sheets, as a result of osmotic dehydration at 30 C, using 0.95
Temperature 30 32 34 36 38
0.93
s 0.91 0.89 0.87 0.85 20
40
60
90 120 180 240
Time (min)
(a) 0.96
Temperature 30 32 34 36 38
0.93 0.9
s 0.87 0.84 0.81 0.78
(b)
20
40
60
90 120 180 240
Time (min)
Fig. 1. Multiple comparison of means for shrinkage factor of osmotically dehydrated sardine sheets in brine of (a) 21% NaCl, (b) 24% NaCl, at different temperatures of brine.
1.3
1.4
1.5
1.6
1.7
1.8
X (d.b) Fig. 2. Shrinkage factor (S) of sardine sheets as a function of moisture content, as a result of osmotic dehydration at 30 C: () 21% NaCl; (+) 24% NaCl; (·) 27% NaCl.
21%, 24% and 27% NaCl. The shrinkage factor is plotted as a function of moisture content X (dry basis). A uniform behavior is observed, which is essentially independent of each set of experimental conditions. This behavior suggests a simple linear relation between moisture content and shrinkage factor. It appears desirable to be able to predict shrinkage factor of a foodstuff without having to measure the property itself. Relation between moisture content of sheets and shrinkage factor. For each combination of concentration and temperature, simple linear regression was used to fit the values of the shrinkage factor (S) to a model as a function of the moisture content (X ). The model as fitted corresponds to: S ¼ A þ BX
ð2Þ
where X is the moisture content in dry basis and, A and B are the constant parameters. The model as fitted explained 82.54–95.71% of the variability in the shrinkage factor at the 95% confidence level, and the standard errors of the estimate are low (Table 1). With these models the shrinkage factors of sardine sheets can be calculated when they are osmotically dehydrated in brines of 15–24% NaCl at temperatures of 30–38 C for dehydration times of 20–240 min. This relationship is similar for dried pork meat in a convective dryer with air at 25 C (Clemente, Bon, Carcel, Garcia-Pascual, & Mulet, 2001), and osmotically dehydrated apple in 50% and 60% sucrose solutions at 5 and 20 C (Moreira & Sereno, 2001). At a constant temperature, the parameter B increases and A decreases with increasing brine concentration. At a constant brine concentration, equilibrium water content decreased and
336
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
Table 1 Linear regression analysis for shrinkage factor as a function of the moisture content (Eq. (2)) Concentration (% NaCl)
15 15 15 15 15 18 18 18 18 18 21 21 21 21 21 24 24 24 24 24 27 27 27 27 27 a
Temperature (C)
30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38
Parameters Aa
Ba
0.7202 0.7295 0.7987 0.7705 0.7324 0.6287 0.5662 0.6285 0.4036 0.5466 0.5290 0.5614 0.4487 0.3829 0.5956 0.5413 0.6000 0.5733 0.4245 0.5798 0.7094 0.5282 0.6351 0.4875 0.4684
0.1561 0.1391 0.0870 0.1006 0.1060 0.1985 0.2334 0.1800 0.3537 0.2498 0.2584 0.1959 0.2682 0.3531 0.2538 0.2287 0.1989 0.2314 0.3122 0.2221 0.1421 0.2724 0.1800 0.2584 0.2991
R2
Standard error
0.8763 0.8704 0.8535 0.8629 0.9061 0.8419 0.8254 0.8773 0.9147 0.9611 0.8931 0.9246 0.9326 0.9278 0.9459 0.8794 0.8929 0.9365 0.8729 0.8582 0.9254 0.8827 0.8086 0.9420 0.9571
0.0075 0.0074 0.0114 0.0085 0.0108 0.0125 0.0142 0.0144 0.0143 0.0105 0.0179 0.0157 0.0151 0.0157 0.0122 0.0195 0.0178 0.0159 0.0209 0.0229 0.0122 0.0192 0.0261 0.0140 0.0121
Indicates significant effect at a ¼ 0:001.
equilibrium salt content increased with the increasing temperature. Relation between dimensionless moisture content and shrinkage factor. Another factor at our disposal was initial moisture content of the sardine sheets used in the trials. Therefore, we investigated the possibility that the initial moisture content (X0 ) of sheets could influence the shrinkage factor. ANOVA shows that the initial moisture constant is a significantly covariable (p < 0:05) in the variation of shrinkage factor. Dimensionless volume change (V =V0 ) as a function of the dimensionless moisture content (X =X0 ) was studied. Amongst others were studied those of Suzuki et al. (1976), Lozano et al. (1980, 1983), Ratti (1994) and Ochoa et al. (2002b), who, starting from specific experimental data for different foods, have fitted expressions to them. The model by Suzuki et al. (1976) has represented the phenomena with a straight line. In turn, Lozano et al. (1983) modified that model for any food products for the cases where two linear fits are needed: one for high moistures and another for low (X < 0:15). Lozano et al. (1983) and Ochoa et al. (2002b) represented the phenomena with only one equation, obtained by nonlinear regression of experimental data. Ratti (1994) has indicated that for some foodstuff the V =V0 vs. X =X0 function is linear in the whole range of water content. Ochoa et al. (2002b) proposed a linear model for whole sour cherry. There are no models for osmotically dehydrated foods.
Analyzing the results of this work, the nonlinear models did not represent appropriately the experimental values of shrinkage factor for osmotically dehydrated sardine sheets. Simple linear regression was used to fit the values of the shrinkage factor (S) to a model as a function of the dimensionless moisture content (X =X0 ). The model as fitted corresponds to: S ¼ C þ DðX =X0 Þ
ð3Þ
where X is the moisture content (dry basis), X0 is the initial moisture content (dry basis) and, C and D are the constant parameters (Table 2). The model as fitted explained 90–99% of the variability in the shrinkage factor at the 95% confidence level (Table 3). We observed that the R2 are higher and the standard errors of the estimate are lower for this model compared with these parameters for the model when initial moisture content is not taken into account (Table 2). Relation between shrinkage in volume and volume of water lost. Kilpatrick et al. (1975) showed that the shrinkage in volume for some dried vegetables was very near to the volume of water lost. Suzuki et al. (1976) showed that the shrinkage in volume equals the volume of water lost by evaporation in the uniform drying stage of root vegetables. Clemente et al. (2001) found that the decrease in the volume of pork meat was bigger than the volume of water lost during drying with air at 25 C.
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
337
Table 2 Linear regression analysis for shrinkage factor as a function of the dimensionless moisture content (Eq. (3)) Concentration (% NaCl)
15 15 15 15 15 18 18 18 18 18 21 21 21 21 21 24 24 24 24 24 27 27 27 27 27 a
Temperature (C)
30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38
Parameters Ca
Da
0.3871 0.3934 0.5712 0.4940 0.4154 0.1903 0.1150 0.1657 )0.2529 0.1118 0.0273 0.0655 )0.1231 )0.2556 0.3152 0.0434 0.2343 0.1060 )0.1733 0.1071 0.4070 0.0642 0.2665 )0.0317 )0.0171
0.6689 0.5911 0.4102 0.4923 0.5721 0.0115 0.0546 0.0575 1.2266 0.0649 1.0120 0.9536 1.1579 1.3054 0.6577 0.9724 0.0127 0.0701 1.1754 0.7914 0.4018 0.9014 0.7548 1.0171 1.0107
R2
Standard error
0.8842 0.8571 0.8448 0.8300 0.8967 0.8427 0.8005 0.9006 0.9115 0.9667 0.9336 0.9410 0.9047 0.9190 0.9502 0.8950 0.9091 0.9648 0.8764 0.9062 0.9418 0.9072 0.8844 0.9310 0.9476
0.0073 0.0078 0.0116 0.0949 0.0111 0.0121 0.0152 0.0129 0.0145 0.0098 0.0142 0.0139 0.0280 0.0176 0.0128 0.0181 0.0181 0.0163 0.0206 0.0195 0.0109 0.0171 0.0202 0.0151 0.0139
Indicates significant effect at a ¼ 0:001.
Table 3 Linear regression analysis for the volume shrinkage as a function of the volume of the loss water (Eq. (8)) Concentration (% NaCl)
Temperature (C)
E parameter
p-value
R2
15 15 15 15 15 18 18 18 18 18 21 21 21 21 21 24 24 24 24 24 27 27 27 27 27
30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38 30 32 34 36 38
0.3921 0.4749 0.3434 0.3674 0.4204 0.4412 0.6267 0.4047 0.5050 0.5438 0.4242 0.4457 0.5512 0.5341 0.5120 0.5251 0.3290 0.3549 0.5676 0.5300 0.4507 0.4542 0.4707 0.6225 0.5776
<0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
0.9453 0.9835 0.9674 0.9633 0.9778 0.9870 0.9846 0.9707 0.9797 0.9907 0.9840 0.9822 0.9876 0.9818 0.9802 0.9819 0.9911 0.9851 0.9837 0.9818 0.9743 0.9853 0.9836 0.9912 0.9849
p-value <0.001 indicates significant effect at a ¼ 0:001.
338
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339
There is no relation for osmotically dehydrated fish. For that purpose the shrinkage in volume (V0 V ) of sardine sheets and the volume of water lost (Vw ) were computed according to: S¼
V V0
ð4Þ
V0 V ¼ V0 SV0 ¼ V0 ð1 SÞ ¼ Vs
ð5Þ
mw0 mwt ¼ m0 xw0 mt xwt ¼ mlost
ð6Þ
qw mlost
water
¼ Vw
water
ð7Þ
Simple linear regression without an intercept was used to fit the values of the volume shrinkage (Vs ) to a model as a function of the volume of water lost (Vw ). The model as fitted corresponds to: Vs ¼ EVw
ð8Þ
where E is the constant parameter (Table 3). The models as fitted explained 82.54–95.71% of the variability in the shrinkage in volume at the 95% confidence level (Table 3). The shrinkage in volume can be predicted as a function of the volume of water lost. As can be observed, the slope (E value) is lower than 1.0. This indicates that the shrinkage in volume is lower than the volume of water lost. Further studies are necessary to determine the changes in volume.
4. Conclusions Linear relationships between the shrinkage factor and moisture content and between shrinkage in volume and the volume of water lost have been found for osmotically dehydrated sardine sheets in brines of 15–24% NaCl at temperatures of 30–38 C for dehydration times of 20–240 min. The shrinkage in volume is lower than the volume of water lost during the osmotic dehydration under the restricted conditions of our experiment. To consider only the water content was not sufficient to explain the changes in volume observed for osmotically dehydrated sardine sheets.
References AOAC (1990). Official methods of analysis (15th ed.). Washington, DC, USA: Association of Official Analytical Chemists. Balaba, B., & Pigott, G. M. (1986). Shrinkage of fish muscle during drying. Journal of Food Science, 51(12), 510–511. Charm, S. E. (1978). The fundamentals of food engineering (3rd ed.). Westport: AVI Publishing Co Inc. Clemente, G., Bon, J., Carcel, J. A., Garcia-Pascual, P., & Mulet, A. (2001). Meat shrinkage during drying. In J. Welti-Chanes, G. V. Barbosa-Canovas, & J. M. Aguilera (Eds.), Proceedings of the eighth international congress on engineering and food (vol. II, pp. 1225–1229). Lancaster: Technomic Publication.
Del Valle, F. R., & Nickerson, J. T. R. (1967). Studies on salting and drying fish. I. Equilibrium considerations in salting. Journal of Food Science, 32, 173–179. Deumier, F., Mens, F., Heriard-Dubreuil, B., & Collingnan, A. (1997). Control of immersion process: a novel system for monitoring mass transfer tested with herring brining. Journal of Food Engineering, 32, 293–311. Dixon, G. M., & Jen, J. J. (1977). Changes of sugar and acid in osmovac dried apple slices. Journal of Food Science, 42, 1126– 1131. Gabas, A. L., Menegalli, F. C., & Telis-Romero, J. (1999). Effect of chemical pretreatment on the physical properties of dehydrated grapes. Drying Technology, 17(6), 1215–1226. Gabas, A. L., Telis-Romero, J., & Menegalli, F. C. (2001). Determination of concentration dependent effective moisture diffusivity of plums based on shrinkage kinetics. In J. Welti-Chanes, G. V. Barbosa-Canovas, & J. M. Aguilera (Eds.), Proceedings of the eighth international congress on engineering and food (vol. II, pp. 1086–1090). Lancaster: Technomic Publication. Giangiacomo, R., Torreggiani, D., & Abbo, E. (1987). Osmotic dehydration of fruit. Part I: Sugar exchange between fruit and extracting syrup. Journal of Food Processing Preservation, 11, 183– 195. Hawkes, J., & Flink, J. M. (1978). Osmotic concentration of fruit slices prior to freeze dehydration. International Journal of Food Science and Technology, 2, 265–284. Kilpatrick, P. W., Lowe, E., & Van Arsdel, W. B. (1975). Tunnel dehydrators for fruits and vegetables. Advances in Food Research, 50, 313–372. Lerici, C. L., Pinnavaia, G., Dalla Rosa, M., & Bartolucci, L. (1985). Osmotic dehydration of fruit: influence of osmotic agents on drying behavior and product quality. Journal of Food Science, 50, 1217– 1219. Lozano, J. E., Rotstein, E., & Urbicain, M. J. (1980). Total porosity and open porosity in the drying of fruits. Journal of Food Science, 45, 1403–1407. Lozano, J. E., Rotstein, E., & Urbicain, M. J. (1983). Shrinkage, porosity and bulk density of foodstuffs at changing moisture contents. Journal of Food Science, 48, 1497–1502. Montgomery, D., & Peck, E. (1982). Introduction to linear regression analysis. New York: John Wiley and Sons. Moreira, R., Figuereido, A. M., & Sereno, A. M. (2000). Shrinkage of apple disks during drying by warm air-convection and freeze drying. Drying Technology, 18(1–2), 279–294. Moreira, R., & Sereno, A. M. (2001). Volume shrinkage of apple cylinders during osmotic dehydration. In J. Welti-Chanes, G. V. Barbosa-Canovas, & J. M. Aguilera (Eds.), Proceedings of the eighth international congress on engineering and food (vol. II, pp. 1351–1355). Lancaster: Technomic Publication. Nanjundaswamy, A. M., Radhakrishnaiah, S. G, Balachandran, C., Saroja, S., & Murthy, R. B. S. (1978). Studies of development of new categories of dehydrated product from indigenous fruits. Indian Food Packaging., 22, 91–93. Ochoa, M. A., Kessel, A. G., Piron, B. N., Marquez, C. A., & De Michels, J. (2002a). Shrinkage during convective drying of whole rose hip (Rosa Rubiginosa L.) fruits. Lebensmittel-Wissenschaft und-Technolgie, 35, 400–406. Ochoa, M. A., Kesseler, A. G., Pirone, B. N., Marquez, C. A., & De Michelis, J. (2002b). A volume and areas shrinkage during dehydration of whole sour cherry fruits (prunus cerasus). Drying Technology, 20, 147–156. Ponting, I. D. (1973). Osmotic dehydration of fruits––recent modifications and applications. Processing Biochemistry, 8, 18–20. Raoult-Wack, A. L. (1994). Advances in osmotic dehydration. Trends in Food Science and Technology, 5, 255–260. Ratti, C. (1994). Shrinkage during drying of foodstuffs. Journal of Food Engineering, 25, 91–105.
O. Corzo, N. Bracho / Journal of Food Engineering 65 (2004) 333–339 Sjoholm, I., & Gekas, V. (1995). Apple shrinkage upon drying. Journal of Food Engineering, 25, 123–130. Suzuki, K., Kubota, K., Hasegawa, T., & Hosaka, H. (1976). Shrinkage in dehydration of root vegetables. Journal of Food Science, 41, 1189–1193.
339
Torreggiani, D. (1993). Osmotic dehydration in fruits and vegetables processing. Food Research International, 26, 59–68. Viberg, U., Freuler, S., Gekas, V., & Sjoholm, I. (1998). Osmotic pretreatment of strawberries and shrinkage effects. Journal of Food Engineering, 35, 135–145.