Physicochemical Properties of Mechanically Separated Tilapia Meat as Influenced by Rigor Mortis Stages and Weight Classes During Frozen Storage

The aim of this study was to evaluate the quality of mechanically separated tilapia meat (MSM) obtained from fish below commercial size at different rigor mortis stages. One hundred five tilapia specimens donated by a producer in Paraiba, Brazil were classified into two weight classes (<150 g and >150 g) and evaluated at three rigor mortis stages: pre-rigor, rigor mortis, and full rigor. Regarding the proximate composition, MSM from tilapia weighing < 150 g exhibited higher moisture (79.95 ± 1.06%) and ash (1.42 ± 0.09%) contents and a lower lipid content (2.88 ± 0.25%), compared to the >150 g class. The rigor stages only influenced the calcium content, with MSM in the pre-rigor stage showing the highest value (1.48 ± 0.05 mg/100 g) (p < 0.05). In terms of thiobarbituric acid reactive substances (TBARS) values, the smaller tilapia MSM (<150 g) exhibited the lowest value (2.15 ± 0.25 mg MDA/kg of sample) at the end of frozen storage. Among the rigor mortis stages, MSM obtained during the rigor mortis phase showed the lowest value (2.07 ± 0.24 mg MDA/kg of sample) at the end of frozen storage. Specifically, smaller tilapia exhibited better oxidative stability and a more favorable composition, while rigor mortis affected parameters such as calcium and TBARS. These findings highlight the potential for sub-commercial size fish for value-added products.