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

Abstract

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 = AVB) 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.

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“…These traits can be quantified on a continuous scale. In addition, there are traits quantified on a limited scale, for example survival measured as dead or alive (0 or 1) (Dinh Pham et al, 2021), and color of the fillet as 10 categories (as consecutive numbers from 25 to 34) (Gümüş et al, 2023). An example trait of societal interest is animal welfare, which is quantified as a combination of behavioral traits, disease resistance, and the severity of deformities (Grimsrud et al, 2013).…”