Effect of low dose gamma radiation on the quality of intermediary moisture pet food

Abstract

The effect of low dose gamma irradiation on the quality of intermediary moisture pet food was assessed in the present study. Dog biscuits were prepared using meat cum bone meal, plain flour (Maida), blood, rendered fat, eggs, wheat bran and black gram flour. The mix was baked at different time temperature combinations to attain three different moisture levels of 10, 15 and 25 per cent. The samples were separately packed in High Density Polyethylene (HDPE) packets at a rate of 200g each and then subjected to gamma irradiation using Gamma Chamber 5000 at various doses of zero, 2.0 kGy, 3.0 kGy, 4.0 kGy, 6.0 kGy and 8.0 kGy. After irradiation the samples were kept in ambient temperature for further analysis like proximate composition, development of rancidity, microbiological quality and palatability/ acceptability attributes on the day of preparation and then on 7, 15, 30, 45, 60, 75, 90, 120, 150 and 180 days of storage or till spoilage which ever was earlier. The proximate compositions of the dog biscuits of all moisture levels were not significantly affected by various doses of irradiation and days of storage. The TBARS values were shown a significant (P<0.05) increase with the increase in the doses of irradiation. The days of storage were also affected the TBARS values significantly (P<0.05). The samples irradiated at 6.0 and 8.0 kGy of all moisture level dog biscuits were spoiled between 120 to 150 days where as the samples irradiated at 4.0 kGy showed a higher shelf life in the absence of any developed rancidity changes. The aerobic plate count was shown a significant reduction as the dose of irradiation increased, also a significant (P<0.05) increase was noticed with the days of storage. In 10 per cent moisture level dog biscuits, the samples irradiated at 6.0 and 8.0 kGy revealed 100 per cent reduction of aerobic organisms, where as the same result was obtained for the samples irradiated at 8.0 kGy in case of 15 per cent moisture level dog biscuits. Coliforms and staphylococcal organisms were present only in 25 per cent moisture level dog biscuits and they were completely destroyed at an irradiation dose of 4.0 kGy and above. All the samples under study were found free from E. coli, Salmonella, Clostridium and faecal streptococcal organisms. The yeast and mould count also showed the same trend as aerobic organisms. The samples of 10 and 15 per cent moisture level dog biscuits were found free from yeast and mould when irradiated at 4.0 kGy and above, while the same result was obtained for 25 per cent moisture level samples on irradiation at 6.0 and 8.0 kGy. The palatability/ acceptability studies were conducted using the dog biscuits of 5, 10, 15 and 25 per cent moisture levels irradiated at 4.0 kGy. The dogs preferred intermediary moisture dog biscuits of 15 and 25 per cent moisture levels when compared with dry dog biscuits having 5 and 10 per cent moisture. It was observed that gamma irradiation of dog biscuits significantly reduced the microbial load with out affecting their proximate compositions. But higher doses of irradiation induced the production of oxidative rancidity. The palatability studies revealed that intermediary moisture level food was more preferred by the dogs than dry food. This study also found that the dog biscuits containing 10 per cent moisture and irradiated at 4.0 kGy had got the highest shelf life of more than 180 days.