Influence of ultrasound frequency, processing time, and cold temperature on quality characteristics of mutton subjected to ultrasonic nano-cooling with a preservative film

Refrigeration slows down microbial growth and oxidation in mutton, but it is not enough on its own to fully prevent spoilage. To promote preservation, this research evaluated the effectiveness of combining ultrasound treatment, nanocomposite packaging, and cold storage ― a method known as ultrasonic nano-cooling (UNC) on quality of mutton. Various ultrasound frequencies (40 and 80 kHz) and processing times (2–4 minutes) were applied to process the mutton. Thereafter, the products were packaged in nanocomposite film, made from sorghum starch and Azadirachta indica gum nanoparticles, and then stored under cold temperature condition: 2°C, 4°C, and 6°C. Analysis of the physical and biochemical properties revealed significant improvements in quality due to UNC preservation compared to the control (p < 0.05). Notably, the total bacterial load dropped from 5.4 × 10⁶ CFU/g in the control to 1.9 × 10⁶ CFU/g at 2°C with 80 kHz ultrasound after 4 minutes. This effect may be due to enhanced cavitation effects at higher frequencies, which, according to previous studies, can disrupt microbial cell walls. Lipid oxidation reduced from 0.45 mg MDA/kg to 0.20 mg MDA/kg, likely due to minimized thermal degradation and oxidative reactions, facilitated by lower temperatures and effective packaging. Water holding capacity increased from 70 % to 85 %, due to improved muscle fiber structure from ultrasound treatment, which aids moisture retention. The pH remained steady between 5.8 and 6.0, reflecting minimal spoilage and effective microbial control. This study demonstrates that UNC preservation is an effective method for extending mutton shelf life, aligning with the demand for high-quality, long-lasting mutton products. • UNC reduced bacterial load from 5.4×10⁶ to 1.9×10⁶ CFU/g at 2°C with 80 kHz ultrasound. • Lipid oxidation dropped from 0.45 to 0.20 mg MDA/kg, preserving mutton’s freshness. • Water holding capacity increased from 70 % to 85 %, enhancing moisture retention. • Mutton pH stayed stable at 5.8–6.0, reflecting minimal spoilage. • UNC extended mutton’s shelf life while maintaining quality and freshness.