H. W. Ockerman1 *, F. León Crespo2, H. Galan Solvedilla2,
A. Peralta Fernandez2, N. Ciudad Gonzalez2, B. Balderas
Zubeldia2, F. Cespedes Sanchez2, A. Martin Serrano2, and
M. C. Torres Munoz2
1The Ohio State University Department of Animal Sciences
2University of Córdoba, Spain
Dry salt penetration into muscle tissue is not a simple process with a constant diffusion coefficient. In contrast to expected results, the majority of the salt penetration occurs late in the salting process. This penetration rate could be due to the time for moisture to escape from the tissue to form the initial salt brine. Salt penetrates through capillary spaces, and at the same time salt can influence the tissue structure. It is important to monitor this process closely since a balance has to be maintained between minimum salt level for preservation and a maximum salt level for sensory purposes.
Spanish traditional jamón is manufactured by salting and then drying and aging of pork hams for an adequate length of time to produce flavor. This process usually ranges from six months to two years. The most appreciated products are those prepared from hams of Ibérico pigs, which are aged for at least 18 months.
Processing of this type of ham (jamón) starts at the salting step. In this traditional process, the green hams are buried in dry salt and kept in a cold room for a variable length of time, based on the weight of the ham (i.e., x days per kg of green weight, with x being a specific value for each processor, depending on their historical empirical results). Using this procedure, it is common to see a great deal of variability among the same type of hams processed by the same processor. The hams with higher green weight usually contain more salt than the hams with the lower green weight (Crespo et al., 1991). These results seem inappropriate since most of the final organoleptic characteristics in this product depend on the salt content and the additional desired requirement of getting the appropriate amount of salt into the final product.
The objective of this research is to establish a rational basis for the salting step of jamón, which includes the evaluation of the effective diffusion coefficient of salt during this processing step.
A recent reference attributes a unique diffusion coefficient for salt migration in ham processing that could be used to predict salt penetration during salting (Palmia, 1992). The model proposed has been tested against the results of experimental salt migration in jamón.
A total of 27 hams were salted in dry salt according to the traditional Spanish method. First, the hams were rubbed with salt and then buried in three to four layers of dry salt. They were then maintained in a cool room at 3 to 5°C. Three hams were taken from the salting room every day during the first five days, and then at 7, 9, and 11 days.
The salt penetration in hams was measured in cores of meat taken with a metallic hollow cylinder 3 cm in diameter, from the center of the lean meat part of the ham (under the coxal joint, close to the femur). These meat cylinders, with a mean length of 14 cm, were cut at regular depths of 2 cm, which resulted in seven equal sections. Each section was analyzed for moisture and salt content according to the procedure reported by Ockerman (1985).
The total amount of salt penetrating each cylinder at any time was evaluated as:
with:
M0 = total kilograms of salt that penetrate per square meter at the surface of the cylinder.
ci. = % (w/w) of salt in each "meat section" from 1 to 7.
The effective diffusion coefficient in each salting period was evaluated according to Crank (1957) from the total amount of salt penetrating per square meter at the evaluated zone:
with:
and with:
c0 = salt concentration at surface [263.4 kg/m3- taken from (Ockerman, 1991)]
D = Diffusion coefficient (m2/sec)
t = time (sec).
The results obtained in this study establish that salt penetration during the salting step is not a simple process with a constant diffusion coefficient.
The total amount of salt penetrating each day in jamón is presented in Figure 1. It is possible to see that that there is a complex penetration pattern and most of the salt penetrating the jamón tissue occurs at the end of the salting process. These are not the expected results since the differences in salt concentrations are much higher at the beginning of the salting process.
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| Figure 1. Total amount of salt penetrating in Spanish Jamón during salting. | Figure 2. Apparent diffussion coeficient (D) of salt in the Jamón salting step. |
To further clarify these results, the apparent D values were calculated and presented in Figure 2. It is possible to see that the D value changes during the salting step in a rather complex pattern.
The D values calculated from our results in the first day were lower than the normal effective diffusion coefficient found for fresh pork by Fox (1980) and were further reduced in the following days to very low values until the 11th day of salting. Then the effective coefficient of diffusion increased to values close to those found in the literature.
The low initial results might be due to the time required for the initial brine formation outside the ham tissue. Initial salt penetration in meat requires that water from the product escapes from the ham to create a brine solution. According to Saravacos (1994), in salting food products, complex mechanisms operate. In addition to the simple diffusion due to the differences in concentration, salt diffuses into meat tissues due to osmotic processes in the membranes, flowing through capillary spaces between fibers and hydrodynamic flow (Bruin and Luyben, 1980). It is also necessary to realize that salt can influence the tissue structure (Raoult Wack, 1994).
In fact, the existence of "speeding paths" into meat tissues would explain the relative high D value for salt in meat vs. the D value for salt in water (Saravacos, 1994). As salt diffuses into the tissues, there is an interaction with meat proteins that increases their WHC (Hamm, 1960). As proteins hydrate, there is a "closing" of the paths for salt penetration, and a very low D value is obtained until the salt concentration reaches 6 to 8%. When the salt content further increases as diffusion proceeds, proteins shrink and the paths again open, increasing the D value.
These results are very significant in ham processing since it suggests that most of the salt penetration during ham salting occurs at the end of the salting process. Therefore, it is necessary to maintain close control at the end of the salting step, to be able to obtain at least the minimum salt level required for processing, as well as to avoid too much salt in jamón.
Bruin, S. and Luyben, K. Ch. 1980. Drying of food materials: A review of recent developments. In: Advances in Drying. A. S. Mujumdar, Ed. Hemisphere, N.Y.
Crank, J., 1957. The Mathematics of Diffusion. Oxford University Press.Hamm, R. 1960. Advances in Food Research 10:414.
Fox, J. B. 1980. J. Food Sci. 45:1740—1744.
León Crespo, F., Penedo Padron, J. C., Bandeira Velloso, C., Galan Soldevilla, H., Barranco Sanchez, A., Ciudad Gonzalez, N., and Peralta Fernandez, A. 1991. Distribution of salt in Spanish ham during the post-salting period. Proc. 37th Int. Cong. Meat Sci. Technol., Kulmbach; Vol III; 892—895.
Ockerman, H. W. 1985. Quality Control of Post-Mortem Muscle Tissue. 13th Ed. Department of Animal Sciences, The Ohio State University, Columbus, Ohio.
Ockerman, H. W. 1991. Food Science Source Book. VanNostrand Reinhold, New York.
Palmia, F., Mazoyer, C., Diaferia, C., Baldini, P., and Porretta, A., 1992. Rev. Esp. Cienc. Tecnol. Aliment. 32(1):71—83.
Raoult Wack, A. L. 1994. Trends in Food Sci. Technol. 5(8):255—260.
Saravacos, G. D. 1994. Mass transfer properties of foods. In: Engineering Properties of Foods. Rao and Rizvi, Ed. M. Decker.
* Collaborative research with the University of Cordoba,
Cordoba, Spain.
1 For more information,
contact at: The Ohio State University 15 Animal Science, 2029 Fyffe Road, Columbus,
OH 43210, (614) 292-4317, Fax (614) 292-2929; email:ockerman.2@osu.edu