Comparison of odour-active compounds in raw Baltic herring with pH-shift produced protein isolate using gas chromatography olfactometry

Abstract

Baltic herring is used in a limited capacity for human consumption in Finland even though it has largest annual catch out of other fish species. There is a substantial amount of interest in improving the rate of consumption for humans instead of most of the catch being used as feed for animals or farmed fish. The aim of the study was to investigate the difference in important odour-active compounds between the raw Baltic herring and protein isolate produced by alkaline pH-shift process i.e., alkaline solubilisation and isoelectric precipitation. If there are desired changes in the odour of the fish after the pH-shift, the protein isolate produced with the method could have some utility in novel food products by reducing the impact of the odour to consumer perception. The pH-shift was used under alkaline conditions in this study. There were 28 odour-active compounds in the raw Baltic herring and 21 in the protein isolate that had nasal impact frequency values of 40 % or higher. There were 8 such compounds that had a modified frequency rating of 80 % or higher in the raw Baltic herring and 4 in the protein isolate. These compounds were 2,3-butanedione, 3-methylbutanal, 2,3-pentadione, hexanal, (Z)-4-heptenal, methional, 1-octen-3-ol and (E,Z)-2,6-nonadienal in the raw Baltic herring and in the protein isolate they were 2,3-pentadione, hexanal, (Z)-4-heptenal and 1-octen-3-ol. The pH-shift did have notable effect on the odour-active compounds, additional studies can be done with different pH-shift parameters to see what potential changes would occur in the odour-active compounds. Adding antioxidants during the process could prove to have interesting results because of lipid oxidation on the formation of odour-active compounds.