The Impact of Diets Supplemented with Different Forms of Rosemary and BHA on Chemical,Microbial and Sensory Properties of Rainbow Trout Fillet

The objective of this study was to evaluate the effect of different forms and doses of rosemary on chemical, microbial, and sensory properties of rainbow trout fed nine different diets: control (C), 20 g.kg^?1 rosemary powder (20RP), 40 g.kg^?1 rosemary powder (40RP), 0.3 g.kg^?1 rosemary extract (0.3RE), 0.6 g.kg^?1 rosemary extract (0.6RE), 0.15 g.kg^?1 rosemary nanopowder (0.15RNP), 0.3 g.kg^?1 rosemary nanopowder (0.3RNP), 0.15 g.kg^?1 butylated hydroxyanisole (BHA) (0.15BHA), and 0.3 g.kg^?1 BHA (0.3BHA). After 8 weeks’ feeding, the fish fillets were sampled on the 1st, 4th, 8th, 12th, and 16th days and then stored on 4°C. Lower value of pH, peroxide value (PV), total volatile base nitrogen (TVB-N), free fatty acids (FFA), and thiobarbituric acid (TBA) were reported in fish fed with RP, RE, RNP, and BHA; among them, RNP groups had the lowest properties (p < 0.05). Furthermore, lower total viable aerobic bacterial counts (TVC) and psychotropic counts (PTC) were observed in the fillets of the fish fed with rosemary treatments, especially in RNP treatments (7.52–9.41 log₁₀ CFU.g^?1), along with a slower spoilage in terms of sensory factors (texture, color, odor, and overall) on the 16th day. Finally, use of natural antioxidant nanorosemary in the diet may positively affect fish fillet quality and delay post-mortem deterioration.