Biochemical and structural factors contributing to seasonal variation in the texture of farmed atlantic halibut (Hippoglossus hippoglossus L.) flesh

Factors contributing to the texture of fish flesh, including pH, water content, density of fast muscle fibers, and the concentration of collagen and hydroxylysyl pyridinoline (PYD) cross-links, were investigated post-rigor in commercially farmed Atlantic halibut (Hippoglossus hippoglossus L.). The fish was sampled every quarter for a 12 month period from May 2004 to May 2005. Hydroxyproline (HYP) as a measure of collagen and PYD were determined using a high-performance liquid chromatography (HPLC) method. An ANCOVA model with fork length and season as covariates were used to explore the seasonal effects on texture, pH, muscle fiber density, alkaline-insoluble collagen (a-i HYP), alkaline-soluble collagen (a-s HYP), and PYD cross-links. A multiple linear regression (MLR) showed that the most important factors contributing to texture were PYD > water (%) > a-i HYP > fiber density, while pH and a-s HYP did not show any correlation to texture. The contribution of fast muscle fiber density to texture was found to vary between sexes and with the season, contributing more in males and in the spring. The most important parameter affecting texture was PYD, explaining 64% (p < 0.001) of the total variation in a linear regression analysis. It is concluded that cross-linking processes are of great importance for the rigidity and strength of the collagen in Atlantic halibut flesh. Farmed halibut should be harvested in the fall or early winter when texture and nutrition are good to obtain optimal quality.