According to ‘‘codex standard for salted fish and dry salted fish‘‘, published by FAO, heavy salted fish contain not less than 12% saturated salt solution. The definition says that the fish should be from Gadidae family and have to be properly prepared before salting. Very important is to carefully bleed the fish then gutted, beheaded, and split or filleted fish. In the end filet should be washed before salting (Commission 1989). A centuries ago, this process was used to preserve food from postmortem spoilage and use for this phenomenon of osmosis and diffusion (Thorarinsdottir 2010);(Ismail 1992). However the transport of salt and water depends on very important factors (Andrés 2005). High concentration of salt in the environment (0.3–1 M) causes a decrease of water activity in fish filet thus the flow of water from the fish outside and an diffusion of salt into the muscle (Barat JM 2003); (Gallart-Jornet L. 2007a); (Kovácsné Oroszvári 2004). Then a large amount of salt in the muscle (~20%) causes protein aggregation and this leads to loss of water holding capacity (WHC) and the consequent loss of water (from 80% to 56%) and uptake the salt (salting-in) (Offer G. 1988); (Kristin Anna Thorarinsdottir 2011). Through the water loss the growth of microorganisms is limited and enzymes activity responsible for destroying the building components are inhibited, what prevents from spoilage of food (van Klaveren 1965), (Bjarnason 1986). On the other hand, too high salt concentration (>1M) may causes the ´´case-hardening´´. At low concentration of salt rate of the water in the myofibrillar is higher than in extracellular what leads to swelling of muscle when salt-in. The result is a reduction in diffusion caused by the closure of the channels on the surface (Ockerman H 2003). Nowadays, salting is a method used mostly to obtain a product with specific qualities, flavor and texture properties (Andrés 2005); (Boudhrioua 2009); (Esaiassen 2004). The heavy salted fish (bacalao) is very popular as a traditional food in the Southern Europe, in countries such as Portugal, Spain, Italy and Greece as well as in Latin America (Thorarinsdottir 2010) as well as in the Africa because of the possibility of storage without the use of the cooling method (Lauritzsen 2004). Due to consumer demand except heavy salted fish (~20% of salt) very popular is also light salted cod (~2% of salt) which takes less time to prepare and is a little cheaper (Thorarinsdottir 2010). There is special product evaluation system which tells us about quality grades of fish. Evaluated are: the appearance- color, blood stains in belly flaps or at the spinal column and gaping; and sensory evaluation after rehydration- taste of salt, curing and TMA taste, tender and moist of fish. There are two quality groups SPIG which is stricter in evaluation and PORT which allowed for slight defects in it do not decrease consumption quality (Kristín Anna Þórarinsdóttir 2010).
Pre- processing Very important on quality of raw fish is catching and handling methods. It is a stage in which the fish should be well bled out. Then follows beheading, filleting and splitting of fish. Very important is to prepare the raw material with caution because blood clots my cause more rapid oxidation and faster spoilage or bruises which reduces the quality (Sajid Maqsood 2011); (Richards 2002). What is more, filleting provide a better surface for mass transfer. Salt can penetrate into the muscle more carefully so salt uptake is much higher than in the gutted fish (Thorarinsdottir 2010). Salting Salting is composed of several methods: brine salting, pickle salting, and a pile of cured (dry) salting. Salting process has been changed since 1970, where the process one step (kench) was used, through the times where the pre-salting stages occur. In 1980 producers have been using pickle and in 1990 started to adapt brining,...