Report by the Analytical Methods Committee. Nitrogen factor for Nephrops norvegicus (scampi)

Abstract

The nitrogen factor (the percentage of nitrogen in the raw flesh) was determined on 70 samples of scampi taken on a total of nine fishing trips to two fishing grounds over a period of 16 months. A representative sample of the catch from each fishing trip was classified on board the fishing vessel for size, sex and shell condition. Selected samples were placed in plastic boxes, sealed and stored on ice until landing (the ice did not come into contact with the animals) when 500 g samples were sealed into plastic bags and blast frozen at −20 °C. The samples were stored at −20 °C until thawed in the laboratory prior to analysis. The objective was to produce a figure for the nitrogen content of the separated meat portion which represented the composition of the material ‘fresh from the sea’. Samples were analysed for fat, moisture, ash and nitrogen content by standardised procedures. It is known that changes in composition can take place during commercial handling and processing of the whole scampi and the figure obtained in this exercise would therefore represent a standard for comparison with the commercially processed material.

The nitrogen content was significantly higher and the moisture content significantly lower in hard-shelled scampi than those with thin or soft shells. However, taking into account the distribution of the shell type in the catches an overall figure of 2.90 is recommended for the nitrogen factor of scampi fresh from the sea.

In commercial fishing practice the heads of the scampi are removed on board the fishing vessel and discarded and the tail portions are packed in plastic fish boxes which are sealed and stored in ice. In parallel with the investigation carried out by the Analytical Methods Committee on the composition of scampi fresh from the sea, the Sea Fish Industry Authority carried out an exercise to determine the proximate composition of the tail meat during commercial processing. Samples were taken at all stages during the processing operation and these sample were analysed by the same laboratories as had analysed the samples of scampi fresh from the sea and working to the same QC standards. This work is reported in the Appendix.