Proteomic and microscopic approaches in understanding mechanisms of shell-loosening of shrimp (Pandalus borealis) induced by high pressure and protease.

Shell-loosening is of importance in facilitating shrimp peeling. In this study, enzyme and high pressure (HP) improved the shell-loosening at different degrees, which were observed as gaps by microscopy. The shell-loosening gap induced by an endoprotease with broad specificity (Endocut-03L, 53 µm) was much higher than that induced by HP at 100 MPa (HP100, 12 µm), followed by an endoprotease with high specificity (Tail21, 8 µm), and HP at 600 MPa (HP600, 5 µm). The degree of shell-loosening was found to be correlated to the extent of protein changes that were obtained by 2D gel electrophoresis. Shell-loosening due to HP100 and Endocut-03L was mainly caused by physical and enzymatic degradation of high molecular-weight proteins in shell and epidermis and subsequent loss of degradation products, disrupting the structure of muscle-shell connection. However, HP100 was less effective than Endocut-03L due to its stabilizing effect on the shell collagen, lowering its shell-loosening effect.

Antioxidative low molecular weight compounds in marinated herring (Clupea harengus) salt brine.

This study aimed at unravelling the antioxidative capacity of low molecular weight compounds (LMWC) (peptides, amino acids and phenolic acids) present in salt brines from the marinated herring production. Brines were fractionated into <10kDa fractions using dialysis and further into 94 fractions using size exclusion chromatography. All samples were analysed for protein, total phenolic content (TPC) and antioxidant activities. Protein-enriched samples were pooled (P1, P2 and P3) and analysed for phenolic acids, total amino acids and peptide/protein sequence using advanced mass spectrometry. All salt brines contain LMWC holding ABTS-radical scavenging activity, reducing power and iron chelating activity. Generally, a strong correlation between TPC and ABTS-radical scavenging was found. In contrast, reducing power and iron chelating activity seemed to be caused by peptides. Protein/peptide sequencing revealed 1kDa peptides with the presence of HDF-motif which could be responsible for some of the antioxidant capacity observed in marinated herring salt brine.