Effect of Chitosan and Oregano Oil Edible Coatings on the Physicochemical and Microbiological Quality of Bullfrog Legs (Lithobates catesbeianus) Stored on Ice

The bullfrog (Lithobates catesbeianus) is an aquatic species of increasing commercial importance in Latin America; however, its muscles are highly perishable during ice storage. This study evaluated the effect of three edible coating treatments compared to a control (uncoated)—chitosan (CH), oregano oil (OO) and chitosan + oregano oil (CH-OO) on the physicochemical and microbiological quality of bullfrog legs stored on ice for 24 days. The color (CIE L*, a*, b*), texture (N), water-holding capacity (WHC), pH, total volatile basic nitrogen (TVBN), and mesophilic and psychrotrophic bacterial counts were measured every three days. Compared to the control treatment on day 24, the CH-OO treatment most significantly delayed color changes (3.30) and affected the textural properties (21.29 to 12.28 N). The OO treatment moderated the pH increase (6.2 to 6.65) and controlled TVBN accumulation (13.91 to 29.37 mg N/100 g), while the CH treatment impacted the WHC. However, no treatment was effective in inhibiting bacterial growth, except for the OO treatment on day 9 for mesophilic control, although this effect was not sustained. These results demonstrate that chitosan, oregano oil and chitosan + oregano oil represent effective natural preservation strategies to extend the commercial shelf life of ice-stored bullfrog muscle, although under these experimental conditions, they did not work for controlling microbiological contamination.