Assessing Red Onion (Allium cepa L.) Peel Extract as an Antioxidant and Antimicrobial Agent for Ice Storage of Tilapia (Oreochromis niloticus) Fillets

This study evaluated the antioxidant and antimicrobial properties of red onion peel extract (ROPE) and its effectiveness as a soaking solution for the ice storage of Nile tilapia fillets for 18 days. The 2,2 ^′-diphenyl-1-picrylhydrazyl (DPPH) free radical–scavenging activity (IC₅₀) of ROPE was 27 μg/mL. The minimum inhibitory concentrations (MICs) of ROPE against Aeromonas hydrophila and Bacillus cereus were 1000 and 500 μg/mL, respectively. The ROPE solutions with IC₅₀ and MICs were used to soak Nile tilapia fillets, while the control was soaked in distilled water. Compared to the control, samples treated with ROPE at MICs exhibited significantly (p < 0.05) lower protein degradation and lipid oxidation levels, suppressed bacterial growth, and enhanced sensory qualities. Based on the microbiological, physicochemical, and organoleptic properties, tilapia fillets treated with 1000 and 500 μg/mL ROPE had a shelf life of up to 18 days, whereas the control and samples treated with 27 μg/mL ROPE had shelf lives of 12 and 15 days, respectively. The treatments with 1000 and 500 μg/mL ROPE demonstrated impressive synergistic antioxidant and antimicrobial effects. Treatment with 500 μg/mL ROPE was recommended to preserve tilapia fillets because it maintained adequate quality and met microbiological parameters for 18 days of ice storage. Although 1000 μg/mL ROPE showed higher bacterial inhibition and less protein disruption after 15 days, samples treated at both concentrations did not substantially differ in lipid oxidation, water-holding capacity, and total volatile basic nitrogen content. The effect of ROPE on protein degradation was investigated. In addition, a strong correlation was observed among the sensory attributes, microbial growth, and physicochemical factors of all samples, and ROPE supplementation was proposed to extend the shelf life of the fish. This study highlights the optimal concentration of ROPE as determined by MIC for storing tilapia fillets in ice.