Evaluation of Larimichthys crocea quality grades

To assess the quality differences of Larimichthys crocea and meet the market's demand for finer quality classification, this study developed an evaluation system based on four dimensions: morphology, body color, texture, and nutrition, comprising 12 key quality indicators. Morphological evaluation assessed body shape characteristics through fullness index, body length-to-height ratio, and geometric morphometric analysis; body color was evaluated by measuring the yellow-blue (b^*) and red-green (a^*) values, as well as lutein content to ensure stability; texture evaluation combined microscopic observation and image analysis to calculate the muscle fiber area-to-endomysium area ratio, along with total free amino acid content; nutritional evaluation covered moisture, crude fat, sum of n-6 polyunsaturated fatty acids, and the n-3/n-6 ratio. A breakpoint regression model was used to determine the critical values for each indicator, while random forest algorithms were employed to assign weight to each dimension. Finally, five typical aquaculture areas (A–E zones) with significant market price differences were selected, and 10 professionals conducted sensory evaluations of the fish’s morphology, body color, and texture, which were compared with objective scoring results. Large yellow croakers were classified into nine grades: D (poor), C (below average), C⁺ (average), B (acceptable), B⁺ (good), A (better), A⁺ (excellent), S (superior), and S⁺ (extremely superior). The wild L. crocea performed the best in morphology (92.66), body color (99.09), texture (99.73), nutrition (99.63), and overall score (97.77, S⁺ grade). The E and D zones showed relatively high performance in each dimension, with scores of morphology (92.01/89.08), body color (74.15/72.02), texture (86.87/91.60), nutrition (76.17/83.04), and overall scores ranging from 82.35 to 83.94 (A grade). The C and B zones had moderate scores, with morphology (75.26/75.37), body color (71.91/68.79), texture (77.52/81.56), nutrition (82.48/66.87), and overall scores between 73.15 and 76.79 (B⁺/B grade). The A zone scored the lowest in all dimensions, with morphology (66.87), body color (64.08), texture (50.60), nutrition (58.13), and an overall score of only 59.92 (D grade). Correlation analysis showed strong positive relationships between objective and sensory evaluations of morphology, body color, texture (R²=0.812–0.952), and market price (R²=0.881–0.907), validating the system’s reliability in reflecting quality and market value.. This study established a L. crocea quality evaluation model based on morphology, body color, texture, and nutrition, providing a scientific basis for precise classification of quality grades, standardizing market pricing, and facilitating the realization of high-quality L. crocea farming models.