Natural preservation of Indian mackerel ( <i>Rastrelliger kanagurta</i> ) using bio-oil and chitosan-based edible coatings

Background: This study explores the initial application of chitosan combined with bio-oil to create an edible coating for preserving Indian mackerel (Rastrelliger kanagurta). Methods: Chitosan was extracted from shrimp shells, and bio-oil was produced through the pyrolysis of coconut shells at 350 °C and subsequently purified using adsorption or distillation. Various formulations of the edible coating were created with chitosan concentrations of 0%, 2%, 4%, 6%, and 8%, combined with bio-oil concentrations of 3% and 5%. The Indian mackerel samples were immersed in the edible coating for 20 minutes to promote preservation. The quality and freshness of the Indian mackerel were assessed every 24 hours over a three-day storage period. GC-MS analysis confirmed the presence of phenolic chemicals and acetic acid in the bio-oil, both of which have antibacterial effects. Results: The findings indicated that the optimal edible coating formulation contained 5% bio-oil and 8% chitosan, resulting in a total volatile base (TVB) of less than 30 mg N 100 g of sample and a total plate count (TPC) of less than 1×10³ CFU/mL. Conclusion: The use of chitosan and bio-oil obtained from coconut shells as an edible coating is efficient in preserving mackerel by inhibiting microbial growth and maintaining sensory quality. Pyrolysis, followed by adsorption purification or distillation, provides a natural and environmentally beneficial alternative to synthetic fish preservatives.