Salting is a big deal

New doctoral dissertation shows that salting and heating of pork and fish are a big deal.

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Ulrike Böcker

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On 25 January 2008, Ulrike Böcker defended her doctoral thesis on the effects of two of the most common steps in the processing of food – salting and heating – as well as their use in combination with each other.

Altered salting process required

She has studied the effect of salt on muscle proteins from cured ham and salted salmon. Both the cell structure and the protein structure in the meat are altered during the processing. This has been studied with the aid of different spectroscopic methods. "In addition to the effects of salt, I have studied the significance of the differences between the raw materials to the results of the process. Different raw materials often have distinctly different effects," says Ulrike Böcker. This becomes particularly clear with fish that are filleted and salted prior to rigor mortis arising. Pre-rigor muscle often displays a really tight muscle fibre structure, whereas frozen and defrosted muscle displays a more open structure. The microstructure is important in terms of how much salt the muscle will take in. "The salt permeates more slowly in pre-rigor salmon. If fish producers wish to switch over to pre-rigor salmon, then the salting process must be changed," explains Böcker. The results from these experiments on fish have been discussed previously in the Norwegian periodical Norsk Fiskeoppdrett [Norwegian Aquaculture].

Reducing the salt content of food has been quite popular now that the focus on health is so strong. However, this is not without a price. "We need to salt the salmon in order to maintain its shelf life. However, the protein structures are altered by the salt and it is important to know what affects this. One danger of reducing the salting may be that the shelf life will be reduced," says the doctoral candidate.

Substantial, but not equal effects

"For the consumers to want to eat the meat is crucial. The industry needs background knowledge about heating and salting because these processes, along with the quality of the raw materials, affect the end product," says Ulrike Böcker. Her work on her doctoral thesis has tied the structure of the muscles together with the chemical properties of the meat.

The results show that heating had a clear effect. At the same time, substantial changes arose in the distribution of the water in the muscle. Salting also affected the muscle tissue of pork, however the effect was different from the effect derived from heating. The changes that arose during salting were more complex in salmon than in pork. "Meat from the simple muscles in pork has a more homogeneous structure than salmon meat, especially when it concerns fat. Pork thus is easier to measure," explains Böcker.

Began with sweets

Ulrike Böcker came to Norway as a Food Science and Biotechnology specialist from Universität Hohenheim in Stuttgart, Germany. There, she studied, among other things, chemical determinants of water content in sweets. "My interest in research was enhanced after a year as a guest student at the University of Massachusetts in the US and subsequent work at the Institute of Food, Nutrition and Human Health (IFNHH) at Massey University in New Zealand. Towards the end of my studies I found an interesting research fellow position at Matforsk’s Web site. I thought it would be exciting to learn a new language and become acquainted with a new country," says Böcker, who had never been to Norway before she came for an interview for the research fellow position. She now speaks and reads Norwegian fluently, but she concedes that she has not fully mastered writing in Norwegian yet.

From meat to yeast

"I would like to continue working as a researcher," says Böcker, who will continue in a post-doc position at Matforsk, initially slated to last for a year. She will be continuing to work with spectroscopic methods and multivariate data analysis, but the material that will be analysed will be completely different. It will now involve yeast. One of the methods that she has been using, FT-IR, is extremely applicable and much used in other areas of research, such as cancer research and research on plant cells.

Doctoral thesis

The research fellowship is a part of a 5-year project entitled "Production improvements of salted meat and fish – development of analytical methods for studies of salt and water characteristics in muscle foods" and financed by the Research Council of Norway. This is a collaborative project between SINTEF Fisheries and Aquaculture in Trondheim and Matforsk. The supervisors are Achim Kohler and Ragni Ofstad (Matforsk) and Bjørg Egelandsdal (Dept. of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences).

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