Volatile compounds responsible for the fishy off-flavour in beef with enhanced healthful fatty acids

There have been many attempts to increase n-3 fatty acids (FA) in beef due to their health benefits and their presence in ruminant animals. However, when polyunsaturated fatty acids are too abundant, oxidation can result in a shorter shelf life and negative flavours or off-flavours in cooked meat. The profile of health favourable FA (n-3, vaccenic and rumenic) in beef has been improved by feeding co-extruded flaxseed (flaxseed, peas, and alfalfa) before alfalfa-grass hay. However, this beef enriched with healthful FA resulted in tougher steaks with lower beef flavour and greater off-flavour intensity, presenting a fishy off-flavour to an extent that might be detectable by consumers. The aim of this study was to characterize the volatile compounds responsible for the fishy off-flavour found in beef with health enhanced FA profiles.
Twelve 2.5-cm steaks enriched with healthful FA presenting a fishy off-flavour according to trained panellists (Fishy), and 11 steaks from commercial cattle (Non-fishy) collected from the caudal end of the longissimus thoracis were frozen at -20 °C. Upon thawing at 4 °C for 24 h, steaks were cooked to a final internal temperature of 71 °C. Stir bar sorptive extraction (SBSE) coupled with thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) was used for identification and quantification of volatile flavour compounds in grilled beef samples. Partial least squares discriminant analysis (PLS-DA) based on volatile compounds was applied to classify steaks into presence or absence of fishy off-flavour (Fishy and Non-fishy, respectively).
The PLS-DAincluding only two factors identified two clusters: the first group included Fishy samples and the second cluster Non-fishy samples. Hence, a clear separation between Fishy and Non-fishy was observed based on the volatile compounds. 17 volatile compounds significantly (P < 0.05) contributed to the presence of fishy off-flavour. Compounds produced by autoxidation of linolenic acid, such as (E,E)-2,4-Heptadienal and heptanal, and 2-undecanone and pentadecane have been described as major contributors to fishy odour. To our knowledge, the other 10 compounds have not been independently related to fishy off-flavour, although they might have contributed to this off-flavour when their odour was mixed with others in a complex beef sample.
A variety of compounds appears to have contributed towards the fishy off-flavour found in beef with enhanced healthful FA. Fishy off-flavour is a complex sensory phenomenon, and further research to confirm the contribution of those volatile compounds not previously related to this off-flavour is warranted.