Opponents are Professor Dr. José Manuel Baviera Baviera, Professor, Food Technology Department, Polytechnic University of Valencia, Spain, and Dr. Hörður G. Kristinsson, Director, Matís ohf. The Dean of the Faculty of Food Science and Nutrition, Professor Inga Þórsdóttir, will conduct the ceremony, which takes place in the University Aula (Hátíðasalur) and commences at 14:00.

Salted cod has been produced in Iceland and other countries since the 16th century. In recent years, salting procedures have been altered to improve yield and stabilise quality of the salted products during storage. The production has changed from being a single-step process salting to a multistep procedure, starting with pre-salting methods like injection and/or brining. One of the key factors in quality criteria is the appearance of salted products, which can be negatively affected by yellow discolouration originating from oxidation of the fish muscle. In order to minimise the risk of quality defects, the interest in using antioxidants such as polyphosphates has been increasing. Presently, polyphosphates are not approved additives in salted cod products. Scientific information on the functionality and fate of added phosphate in salted cod products has been lacking.

The overall aim of this study was to obtain a deeper understanding on heavy salting of cod. Effects of salt concentration on mass transfer and changes in protein conformation during brining of cod muscle were investigated, as well as the antioxidative properties and degradation of added phosphates. Furthermore, the effects of potassium ferrocyanide (CN) as an anti-caking agent in salt on lipid oxidation of salted cod were evaluated. The influence of temperature on quality changes of salted cod during storage was also studied.

Salt concentration significantly affected salt and water diffusion during brining, resulting in differences in weight yields, kinetic parameters and salt diffusion coefficient. Conformational changes in proteins depended on salt concentration in the muscle liquid phase Z-(NaCl), which could be explained by salting-in effects at low salt concentrations (Z-(NaCl) < 6%) and salting-out effects (Z-(NaCl) > 6%). From the mass transfer results, it can be concluded that Z-(NaCl) = 15% was the critical concentration in separating hydration from dehydration regimes for brining of cod.

Lipid hydrolysis and lipid oxidation occurred simultaneously during salt curing of cod and were significantly accelerated by increasing CN levels. However, lipid oxidation was significantly retarded by adding phosphates to the brine. A yellow discolouration of salted cod was associated with increased levels of lipid oxidation derivatives. TBARS, b* value and For were the strongest indicator of lipid oxidation during salting and storage of salted cod. Furthermore, this study confirmed fluorescence intensity measurements as a promising technique for accessing tertiary lipid oxidation products. The results also showed that storing salted cod at temperatures below -1 °C is not recommended. Storage at -4 °C had a detrimental influence, resulting in darker colour and higher TVB-N values compared to the ordinary temperature used (2 °C).

The changes in quality and quantity of phosphate species were determined by ion chromatography (IC) and standard spectrophotometric method. Added tri- and pyrophosphates degraded in the cod muscle during salting and storage, leading to increase in orthophosphate content. Most added phosphates and a part of natural phosphates were washed out during the rehydration process of the cod muscle, leading to significant reduction in phosphate content compared to the raw material. However, the added phosphates species could still be identified even after rehydration. Lower values were obtained for the total phosphate content by the IC method than with the standard spectrophotometric method.

For further information please contact Sigurjón Arason at Matís.