Oxidative stability of frozen mackerel batches ― A multivariate data analysis approach

Mackerel are usually caught in the autumn and often frozen either on board the fishing vessel or soon after landing. Due to the seasonality of the catching period, mackerel can be stored frozen for a long time period before entering the production chain. However, frozen storage of fatty fish such as mackerel can lead to a significant loss in fish quality primarily due to oxidation of the long chain omega-3 fatty acids. These quality changes results in significant loss for the fish processing industries and in fish with poor eating quality. In order to investigate batch-to-batch variation due to different catching methods and different freezing procedures 6 batches of frozen mackerel were obtained from the local producer of caned mackerel. Fish were processed as soon as possible after landing i.e. headed, gutted and individually frozen at the industry. However, one of the catch was abused and stored on ice for 8 days before entering the production line. Subsequently, samples from the catches were sent to our laboratory where they were stored frozen at -30 °C for a period of 12 months. At intervals of 6 weeks samples were taken and analysed for proximate analysis as well as for oxidative deterioration and texture changes. The aim was to investigate the correlation between the raw material history and the quality loss observed during frozen storage using relevant multivariate data analysis such as Principal Component Analysis (PCA) and Partial Least Square Analysis (PLS). Preliminary results showed that it was possible to differentiate between the different batches depending on their history and that some batches were more oxidised than others. Furthermore, based on the results from the data analysis, critical control points in the entire production chain will be identified and strategies to prevent quality loss proposed.