Characteristics of raw and cooked fillets in species of actual and potential interest for Italian aquaculture: rainbow trout (Oncorhynchus mykiss) and meagre (Argyrosomus regius)

Fish is a good source of fat, proteins, vitamins and minerals. It is the major contributor of long-chain omega-3 polyunsaturated fatty acids which are known to have a benefic effect on reducing the incidence of cardiovascular diseases. The world production of farmed fish has raised in the last decades as a consequence of the overexploitation of fishery resources and the wild stocks depletion. Aquaculture is making an important contribution to the demand of seafood and the sector continues to diversify, to use new species and to modify its system and practices towards safe and quality products. In Italy a considerable part of fish is sold fresh and intended for domestic consumption after cooking. Heat treatments such as smoking and parboiling are among the most spread processes applied by fish industry. The effect of cooking on seafood nutritional and organoleptic quality has been described by several researches focusing on both the changes of textural and colorimetric attributes and the retention of nutrients. Heat treatment generally induces structural changes of the muscle involving protein denaturation and gelatinization. Lipid and protein can be also oxidized by heat resulting in losses of nutritional value and formation of volatile molecules responsible for the aromatic profile. Depending on many intrinsic and extrinsic factors, including species, environmental and rearing conditions, storage time after death and type of heat treatment applied, farmed fish qualitative attributes can be subject to changes. The overall aim of this study was to assess the effects induced by cooking on quality of fillets from two different farmed species [meagre (Argyrosomus regius) and rainbow trout (Onchorynchus mykiss)] with reference to changes in physical parameters and nutritional profile. Cooking by boiling was tested and the variation of quality of both raw and cooked fillet depending on species, genetic strain (in rainbow trout), season, rearing system (land-based tank or off-shore cages, in meagre), farming conditions (in rainbow trou) and short-time chilling storage (in meagre) was studied. Specie-specific differences in fillet physico-chemical traits influenced raw flesh quality and the response to cooking. In meagre, which was an emerging species in Italian aquaculture, sampling times differences in macronutrients were nullified by cooking. Boiling method induced loss of some macronutrients, mainly lipids and some fatty acids, but changes detected did not compromise the valuable nutritional traits of this particularly lean species. Morpho-biometric traits of fish and colour, texture, macronutrients, fatty acids and minerals content of raw fillet were affected by rearing system, as a consequence of the diversified environmental parameters and conditions. Short time chilling did not affect nutritional profile and minimal changes, mostly involving colour and texture, were detected. In rainbow trout, which is the major farmed fish species in Italy, cooking by boiling modified physico-chemical profile in a different extent depending on the strain. Differences in some textural properties were nullified by cooking and specific farming conditions resulted to affect fillet quality in a different extent according to the strain.