Lipid content in herring (Clupea harengus L.)-influence of biological factors and comparison of different methods of analyses: solvent extraction, Fatmeter, NIR and NMR

The lipid content in herring from research vessel surveys and commercial landing was measured by chloroform/methanol/water extraction and correlated to Fatmeter-, NIR and NMR-measurements. A broad variation in lipid content was found within catches, and herring size and maturity status could not be used to sort herring according to lipid content. The results showed the Fatmeter, NIR and NMR to have different suitability and applicability. Fatmeter readings were influenced by gonad maturity in whole herring and could therefore only be used in a primary sorting of fillets. High correlation was found between NIR and solvent extraction, but the prediction results were influence by measuring point. Measurements performed by NIR and Fatmeter on meat side of fillets could not predict the lipid content in herring fillets. The average lipid content in a fillet or whole herring could be predicted from single NIR spectra if measurements were performed in the middle section of the sample. A high correlation was also found with the NMR measurements on mince. The NIR technique showed highest potentiality as a production line measurement for sorting whole herring or fillets into more homogenous batches, and thus allowing more optimal utilization of the resources.