Due to heterogeneous growth and reproductive precocity, many tilapia do not reach the ideal size for commercialization and are discarded. Despite this, they are characterized as a high quality raw material and have the potential to be used in human food by obtaining mechanically separated meat (MSM). This research aimed to evaluate the yield and quality of MSM from tilapia in different weight classes, outside the commercial size. Animals were obtained from a commercial farm and transported to the laboratory in insulated boxes. They were then washed, weighed, graded, and eviscerated for the production of MSM. The weight classes studied were: A (≥ 50 g < 80 g), B (≥ 80 g and < 110 g), C (≥ 110 g and < 140 g) and D (≥ 140 g and < 170 g). Carcass yield and DMI, physicochemical, calcium, water activity, water retention capacity and fatty acid profile analyses were performed. After 90 days of storage (-18oC), total volatile bases, lipid oxidation and pH of MSM were determined. The highest carcass yield was obtained in weight class D. This variation can be attributed to the difference in size and weight of the fish in both classes. There was no significant difference in MSM performance between weight classes. Proteins were not affected by weight differences, and lipid content increased with fish size, with an inverse relationship with moisture and ash. The water activity values of tilapia MSM did not show significant differences. In the analysis of water retention capacity, the classes showed high retention with a significant difference, in which class B (45.2%) obtained the highest average WHC, while C (30.8%) presented the lowest result. Regarding the results obtained for calcium, it was observed that class A (≥ 50 < 80g) obtained the highest result (1.22%), significantly different from the others. In this study, no significant differences in TBARS and BVT values were observed between different weight classes. Differences in pH were observed among the weight classes, but all were within the regulatory limits. The main fatty acids found in MSM were palmitic acid (C16:0) (31.63 to 37.29%), oleic acid (25.33 to 30.14%), stearic acid (C18:0) (7. 10 to 10.31%), linoleic acid (C18:2n-6) (8.19 to 14.46%), palmitoleic acid (C16:1) (31.63 to 37.29%), and margaric acid (C17:0) (1.14 to 2.27%). MSM from tilapia with low commercial weight showed satisfactory yield in all weight classes and physicochemical quality in compliance with accepted standards after 90 days of storage.
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