Enhancing Shelf Life and Quality of Traditional Thai Pork Sausage (Num-Tub) Using Gamma Irradiation

Num-Tub is a traditional Northeastern Thai pork sausage, often consumed fresh or fermented. The ingredients were naturally rich in protein, fat and moisture content. These conditions are conducive to the growth of beneficial and harmful microbes. Its perishable nature poses microbial safety challenges. Irradiation effectively extends the shelf life of Num-tub by reducing microbial contamination and inactivating spoilage microorganisms. This study investigated the effects of gamma irradiation at doses of 0, 5, and 10 kGy on the microbiological, chemical, and color attributes of vacuum-packed Num-Tub during 24 days at 28 ± 2 °C. Irradiation at 5 kGy reduced total viable counts (TVC) and lactic acid bacteria (LAB) to undetectable levels, though microbial regrowth occurred over time and eliminated key pathogens including Salmonella spp, E. coli, C. perfringens, S. aureus. However, this dose could not prevent microbial regrowth. In contrast, irradiation at 10 kGy improved microbial control and color (higher oxymyoglobin and redness) up to day 9 but significantly increased lipid oxidation. Correlation analysis indicated positive associations between microbial growth, acidity, lipid oxidation, and metmyoglobin formation, while pH, myoglobin, oxymyoglobin, and redness were negatively correlated. Gamma irradiation at 10 kGy is a non-thermal method that improves microbial safety by eliminating pathogens, suppressing lactic acid. It also increases oxymyoglobin levels, which enhances product redness. However, it may also lead to increased lipid oxidation during the 9-day storage period at ambient temperature. Further research should focus on integrating gamma irradiation with natural antioxidants or modified atmosphere packaging to mitigate lipid oxidation and pigment degradation. Additionally, sensory evaluation and consumer acceptance studies are essential to establish optimal irradiation protocols that balance safety, quality, and market viability. HIGHLIGHTS Gamma irradiation improved microbial safety and extended shelf life of Num-Tub sausage. Irradiation at 5 kGy eliminated the pathogen and delayed acid production. Irradiation at 10 kGy effectively suppressed microbial regrowth but accelerated lipid oxidation. Irradiation induced oxymyoglobin formation until day 9, preserving redness and color quality. Microbial growth, acidity, and oxidation were closely correlated. GRAPHICAL ABSTRACT