Effect of Low-Temperature (-20°C) Preservation on Pesticide Residues, Biochemical Quality, Microbial Load, Proximate Composition and Sensory Attributes of Indian Major Carps

Abstract

The present investigation evaluated the effect of low-temperature (−20°C) preservation on pesticide residues, biochemical quality, microbial load, proximate composition, and sensory attributes of Indian major carps Catla (Catla catla), Rohu (Labeo rohita), and Mrigal (Cirrhinus mrigala)—during 24 weeks of frozen storage. Although freezing is widely practiced to extend fish shelf life, limited information exists regarding the stability and behavior of pesticide residues under prolonged frozen conditions, representing a significant research gap. Muscle samples analyzed at 0, 4, 8, 12, 16, 20, and 24 weeks using the QuEChERS method followed by GC–MS showed a significant (p≤0.05) increase in pesticide residues during storage; for example, in C. catla, Endosulfan II increased from 0.823 to 1.230 µg/kg and Cypermethrin 2 from 0.437 to 0.663 µg/kg by week 24. This observed increase may be attributed to moisture loss and concentration effects during frozen storage rather than new contamination. Biochemical indices indicated progressive deterioration, with total volatile basic nitrogen rising from 2.980 to 30.710 mg/100 g, peroxide value from 0.756 to 8.453 mg/100 g, and free fatty acids from 0.027 to 0.173 mg/100 g. Microbial load also increased from 2.407 to 6.337 CFU/ml, while proximate composition showed minor changes, including slight moisture reduction (76.90% to ~76.16%) and fat decline (3.73% to 2.73%). Sensory scores decreased from 9.00 to approximately 7.2–7.8 over the storage period. Overall, the study demonstrates that frozen storage at −20°C extends shelf life but does not eliminate pesticide residues or completely prevent biochemical and microbial deterioration during extended preservation.