Fish are highly perishable and it is important to have reliable spoilage assessment methods. Most effort has been devoted to chemical methods of characterizing freshness: assays of TVBN (total volatile basic nitrogen), TMA (trimethylamine), nucleotide derivatives using the H, K and K’ ratios and assay of fatty acids. Other methods include spectroscopic, microbiological, texture assessment, study of electrical properties and determination of biogenic amine composition. Atlantic salmon is rich in bioactive proteins, antioxidants, vitamins and omega-3 fatty acids, making it rich source of essential nutrients. However, it is highly susceptible to biochemical, physicochemical and microbial spoilage. The aim of the study was to use natural antioxidants in oregano and dill extracts in combination with modified atmosphere packagaing MAP (CO₂:N₂60:40) to retain the quality and delay lipid oxidation in Atlantic salmon (Salmo salar) during storage.

Extract treated samples and controls (both vacuum packed and in MAP) were stored under chilled conditions (4±1°C) for 0-16 days. Quality changes during storage were assessed in terms of drip loss, microbial growth, colour, pH, protein solubility and lipid oxidation. Primary and secondary lipid oxidation products were determined by means of peroxide value, conjugated dienes and TBARS. In parallel, volatile compounds were analysed using GC-MS, SIFT-MS and SESI-MS.

GC-MS indicated 29 recognizable VOCs present in the headspace of the salmon samples. SIFT-MS quantification was carried out for ammonia and the following VOCs: Ethanol, acetaldehyde, butyric acid, acetic acid, pentanal, hydrogen sulphide, trimethylamine and pentane.

Changes of the measured concetration with storage time can be used to monitor freshens and spoilage and the effect of natural antioxidants in oregano and dill extracts can be observed.

SIFT-MS analyses of a MAP salmon sample.

Hanne Dalsvåg

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