Color of rainbow trout (Oncorhynchus mykiss) fillets by image and sensory analysis, and correlation with SalmoFan numbers

A total of 72 male and 50 female trout (Oncorhynchus mykiss) fillets were weighed (range 328-794 g, mean 546.2 ± 101.8 g; and range 426-994 g, mean 672.2 ± 106.1 g, respectively), the pictures of whom were taken in a light box, and image analysis was done to measure pixel colors, length, and view area of the fillets. Weight (W) was predicted using view area (V) obtained by image analysis using linear (W = A + BV), and power (W = AV^B ) equations. R² values were between 0.823 and 0.937. Although there was no difference between mean L* and a* values of male and female fillets, significant differences were found between mean b* values (p < 0.05). The colors of SalmoFan™ (SF) mini were also measured by image analysis and their mean L*, a*, b* values, and their entire color index (ECI) and reduced RGB values from 122 images were calculated. A total of 96 untrained panelists were asked to select the SF color of 5 representative fillets and to designate which point on the fillet image best described the SF color chosen. To predict SF numbers of the fillets by image analysis, four cases were considered: (1) whole fillet, (2) whole fillet with pixels a* > 25, (3) a rectangle along the length of the fillet to approximate panelists' selection, and (4) pixels in this rectangle with a* > 25. Mean L*a*b* values, mean reduced RGB values, and mean ECI of the four cases were used to predict fillet SF numbers. Different results obtained imply that image analysis can do repeatable and objective SF color classification of fillets, depending on the pixel selection method, and the color representation. PRACTICAL APPLICATION: Rainbow trout fillets can be assigned SalmoFan (SF) numbers using image analysis of the fillets. However, the selection of pixels and the color representation method affect the results. If these are standardized, SF numbers can be assigned objectively and automatically.

Effect of sodium bicarbonate and varying concentrations of sodium chloride in brine on the liquid retention of fish (Pollachius virens L.) muscle

BACKGROUND

Negative health effects associated with excessive sodium (Na) intake have increased the demand for tasty low-Na products (<2% NaCl) rather than traditional heavily salted fish products (∼20% NaCl). This study investigates the causes of improved yield and liquid retention of fish muscle brined with a combination of salt (NaCl) and sodium bicarbonate (NaHCO3 ).

RESULTS

Water characteristics and microstructure of saithe (Pollachius virens L.) muscle brined in solutions of NaCl and NaHCO3 or NaCl alone were compared using low-field nuclear magnetic resonance (LF-NMR) T2 relaxometry, microscopy, salt content, liquid retention and colorimetric measurements. Saithe muscle was brined for 92 h in 0, 30, 60, 120 or 240 g kg(-1) NaCl or the respective solutions with added 7.5 g kg(-1) NaHCO3 . NaHCO3 inclusion improved the yield in solutions ranging from 0 to 120 g kg(-1) NaCl, with the most pronounced effect being observed at 30 g kg(-1) NaCl. The changes in yield were reflected in water mobility, with significantly shorter T2 relaxation times in all corresponding brine concentrations. Salt-dependent microstructural changes were revealed by light microscopy, where NaHCO3 supplementation resulted in greater intracellular space at 30 and 60 g kg(-1) NaCl.

CONCLUSION

Sodium bicarbonate addition to low-salt solutions can improve yield and flesh quality of fish muscle owing to altered water mobility and wider space between the muscle cells.