In January 2008, we completed a five year strategic institute program for improving the production of salted meat and fish. The program was focused on developing analytical methods to understand the characteristics of salt and water in muscle foods. The experimental work has mainly been carried out at Nofima Mat – Matforsk AS and SINTEF Fisheries and Aquaculture, with assistance from the University of Life Sciences and the Norwegian University of Science and Technology. We have built a considerable knowledge base in collaboration with well-known institutes in several European countries, including Denmark, France and Spain. Three Ph.D students have been educated in the program. The program has been funded by the Research Council of Norway.
Microstructure of salmon and pork
One of the key issues in the project has been to study the effect of salt on muscle proteins in dry cured ham and salted salmon, mostly examined by spectroscopic techniques, as for example Fourier transform infrared (FT-IR) and Raman microspectroscopy. Salmon, which has been filleted and salted before rigor mortis (pre rigor), has a very dense structure of muscle fibres. On the other hand, frozen and thawed muscles have a more open structure. Salt penetrates slowly in pre-rigor fish. If fish processors want to use pre-rigor salmon, the salting process needs to be altered. Salting and heating of pork changed microstructure and distribution of water. Meat has a more dense structure than fish and is therefore easier to measure.
NMR for sodium measurement
We have used techniques for low field NMR and MRI to control salting processes. NMR measures the content of sodium directly in salted muscle, and we have greatly improved the accuracy of the analysis. The examinations showed that areas high in fat hindered the uptake of salt, while the fish skin had little effect as a salt barrier. In addition, low field 1H NMR was used to study how water is bound to the muscle structure, and how the binding is affected by salting of salmon and cod fillets, for example by using different brine concentrations, stressed versus unstressed fish, and fish in pre- or post-rigor conditions.
X-rays of dry cured hams and clip fish
We have developed CT (X-rays) to a more precise method for analysing salt in muscle. CT is a rapid method for detailed and non-destructive measurement of salt in full scale samples of meat and fish. Salt is acting like a contrast medium in the muscle. New knowledge on CT was used to improve salting processes for dry cured ham (dry salting) and clip fish (brine salting, brine injection and dry salting). The accuracy of the salt analysis with CT is increasing much when the chemical content of the sample is known, and by combining two or three foton energies of the instrument. Under ideal conditions for dry cured ham, we obtained an analytical error of only ca. +/- 0.5 % salt. Therefore, CT is a useful tool for the control and steering of salting processes of fish and meat.
Future work
Results from the project have been disseminated through two seminars for the Norwegian industry and project partners, in addition to a two days international workshop in the fall 2007. This workshop clearly demonstrated that the new Norwegian research on salt in muscle foods is highly evaluated internationally. According to the view of the industry, salt in foods inevitably will be an important research issue in the future.
