Superchilling of Salmon: Changes due to Proteolytic Degradation

Abstract

Isolation and identification of peptides in muscle foods can help us to understand the complex reactions that occur during storage of food, and help us improve shelf life. This work is part of the project “Competitive Food Processing in Norway” (KMB project). The aim of this thesis is to investigate the changes that occur in the peptide fraction of muscle tissue extract during storage, so that the proteolytic changes that occur during storage can be better understood.

In this thesis changes in proteins and peptides during storage have been investigated in samples superchilled using air and liquid carbon dioxide (LIC) to two ice levels and chilling references. Measurements of drip loss, water content and liquid loss have been done for the chilled reference samples, while the measurements of the superchilled samples have been collected from previous work in the KMB project. The investigations of the proteins and peptides have been done by extracting water soluble proteins from muscle tissue, and isolate peptides by precipitation using ethanol. The proteins in the extracts have been quantified using Lowry’s method and they have been identified using gel filtration by fast protein liquid chromatography (FPLC) and mass spectrometry (MS).

In this thesis changes in proteins and peptides during storage have been investigated in samples superchilled using air and liquid carbon dioxide (LIC) to two ice levels and chilling references. Measurements of drip loss, water content and liquid loss have been done for the chilled reference samples, while the measurements of the superchilled samples have been collected from previous work in the KMB project. The investigations of the proteins and peptides have been done by extracting water soluble proteins from muscle tissue, and isolate peptides by precipitation using ethanol. The proteins in the extracts have been quantified using Lowry’s method and they have been identified using gel filtration by fast protein liquid chromatography (FPLC) and mass spectrometry (MS).

There were no significant differences in drip loss between the different chilling methods during storage. However, the significantly higher drip loss in samples superchilled by air indicate some formation of large ice crystals in the muscle compared to superchilling using liquid carbon dioxide. The liquid loss was significantly higher for samples superchilled using air before sixteen days of storage. After this there were no significant differences between the chilling methods.