Prolonging Shelf Life and Meat Quality of Rainbow Trout (<scp><i>Oncorhynchus mykiss</i></scp>) by Immersing in Pine Nut (<scp><i>Pinus gerardiana</i></scp>) Extract During Cold Storage

Rainbow trout (<i>Oncorhynchus mykiss</i>) is a freshwater fish susceptible to chemical and microbial spoilage, limiting its shelf life. This study aimed to enhance and extend the rainbow trout fillets' shelf life stored at 4°C ± 1°C through an immersion treatment using ultrasound-assisted, defatted pine nut (<i>Pinus gerardiana</i> Wallich) extracts at concentrations of 1% and 2% (w/v), compared to the control group (0% pine nut). Evaluations were conducted at storage intervals of 0, 4, 8, 12, 16, and 20 days. The methodology assessed antioxidant activity through 2,2-diphenyl 1-picrylhydrazyl radical scavenging, which showed a linear increase with pine nut extract concentration, reaching 59.24% at 2%. Chemical indicators, such as peroxide values, thiobarbituric acid values, free fatty acids, and total volatile basic nitrogen, decreased significantly (<i>p</i> ≤ 0.05) with higher concentrations of pine nut extract, with the lowest values recorded at 2% across all storage days. Microbial analysis showed a significant reduction (<i>p</i> ≤ 0.05) in the total viable count, psychrotrophic bacteria count, lactic acid bacteria, Enterobacteriaceae, and H₂S-producing bacteria with increasing pine nut concentrations, with the 2% treatment yielding the lowest microbial loads throughout storage. Sensory evaluation indicated that higher pine nut concentrations improved the acceptability of color, odor, and taste (<i>p</i> ≤ 0.05). However, significant degradation (<i>p</i> ≤ 0.05) in chemical, microbial, and sensory parameters occurred with prolonged storage duration. In conclusion, the 2% pine nut extract was the most effective immersion treatment for extending the shelf life of rainbow trout fillets for up to 12 days.