Selenium response to diverse household cooking methods as applied to 15 species of finfish and shellfish caught in the Mediterranean sea

Total selenium contents were determined in the edible portion of several species of blueback fish (European anchovy, European pilchard, sprat, horse mackerel), whitefish (European hake, common sole, red mullet, flathead grey mullet, tub gurnard), molluscs (cuttlefish, Mediterranean mussel, Manila clam, striped venus clam) and crustaceans (caramote prawn, mantis shrimp). Within each species, specimens were analysed both at the raw state and cooked by the most appropriate technique [selected among the following: oven roasting in a partially covered tin (ORO), pan frying (PAF), cooking in parchment (PAR), cooking in a covered non-stick pan (CNS), pressure cooking (PRE), steam cooking (STM)], to gain knowledge about selenium true retention values. Several considerations prompted and justified this study at the same time: the essentiality of selenium, the medium-to-high level of this element known to be present in raw seafood, the attention recently focused on the influence exerted by processing (cooking in particular) on such issues as selenium bioavailability and speciation, the variety of culinary approaches to finfish and shellfish which have been fine-tuned in centuries in the Mediterranean countries and possibly bears on selenium retention. From October to May, 2-to-5 batches per season were collected for each species, the number of specimens per batch depending on their average size and merceological nature. A species-specific procedure was devised in order to have a representative raw reference for each cooked sample. Within species and batch, both raw and cooked flesh were microwave digested and analysed in duplicate by ICP-MS for total selenium content. True retention values (TRVs) of selenium were determined for each species within its own cooking procedure and cooking yield. Season of catch effect was significant for two-thirds of finfish species and for mantis shrimp only among shellfish, the lower levels being in Autumn. Upon cooking, selenium content increased significantly with the exception of PRE cuttlefish, CNS mussel and CNS Manila clam. The richest sources of selenium were ORO pilchard within blueback fish, ORO tub gurnard and ORO red mullet within whitefish, CNS mussel within molluscs and PAF mantis shrimp within crustaceans. When comparing cooking methods as to the selenium TRVs (%) they generated, significant differences did emerge, the average being 106a, 103a, 100a, 95.1ab, 83.9b, and 46.6c, for ORO, PAF, PAR, STM, CNS, and PRE, respectively.