Irradiation of Milk Products
: Assessment of Gamma Radiation and Evaluation of its Impact on Product Quality and Safety

  • Oluwakemi B Odueke

Student thesis: Master's ThesisMaster of Philosophy


There are growing interests in the consumption of unpasteurised milk due to the perceived health benefits; however, this is associated with increased food safety risks due to the lack of hygiene preservations controls. From a processing perspective, the paradoxical challenge is to select the most appropriate techniques to best preserve the nutritional and organoleptic aspects of raw milk whilst also ensuring a safe product and an increased shelf-life. Therefore, it is necessary to keep contamination to a minimum along the supply chain and to control specific microorganisms with high potential for spoilage. Pasteurisation is the most widely used preservation method for ensuring safety and extending the shelf-life of milk, however, some consumers have described a cooked organoleptic characteristic in pasteurised milk. Pasteurisation also carries the additional environmental burden of maintaining a refrigerated supply chain. Hence the need to investigate alternative approaches. Food preservation by ionizing radiation involves subjecting packaged or bulk foods to a controlled dose of γ-ray, e-beam, or X-ray irradiation. It preserves food product by inactivating spoilage organisms while maintaining sensory and nutritional characteristics and enhancing products durability. Irradiation processing could be a smarter substitute to pasteurisation in assuring milk quality and safety. This study aimed to evaluate the efficacy of irradiation methods on the safety and quality of milk and dairy products, in contrast to traditional techniques such as pasteurisation. In achieving this aim, a dairy analogous –“Kemi block” simulating different macronutrients present in dairy products was developed, stored at refrigerated and frozen temperature (5°C, -5°C and -15°C) prior to been irradiated at 1,3,5, and 10kGy and later stored at 4±1°C throughout the duration of product analysis for shelf-life and compositional assessment. Subsequently, liquid milk –pasteurised and unpasteurised were treated under the same experimental conditions as Kemi block. Kemi block was analysed based on the Aerobic plate count for testing the viability of radiation technology in shelf-life extension while milk samples were analysed for different microbiological composition. Milk samples were tested for Enterobacteriaceae, E.coli, Coagulase-positive staphylococci, salmonella spp, Aerobic Plate count and Listeria spp. Salmonella and listeria were only tested for their presence or absence. Analysis of Kemi block at the end of the shelf-life trial (benchmarked at log 4.3 CFU/g), the total viable count did not exceed log 3.94 CFU/g for samples treated at 10 kGy after 100 days of analysis. These observations indicated that the product could be safely stored aerobically for
vi42 days at (1 kGy), 56days at (3 kGy) and >100days at (5 and 10 kGy), for the irradiated samples and 14 -28 days for the non-irradiated samples without much change in physicochemical and microbiological properties using refrigerated storage. Kemi block irradiated at 3kGy had a shelf-life of 56 days while unpasteurised milk treated at the same dose had a shelf-life of 49 days while the combination of pasteurisation and irradiation significantly extended the shelf-life of milk at 3kGy to have a shelf-life in excess of 100 days. Salmonella spp. and Listeria spp. were not detected in any of the samples over the storage period. Enterobacteriaceae, E.coli, and Coagulase-positive Staphylococci were not detected in any of the samples over the testing period apart from in raw control sample. According to the result of this study, product analysis over storage days showed no apparent effects of irradiation dose on the physicochemical properties of both Kemi block and milk, hence it is evident that macronutrients are not significantly altered. The main findings from this study imply that irradiation extends the shelf-life of milk when compared with pasteurisation treatment and it does not lead to nutrient losses to the extent that there is a compromise on the nutritional value. The research also demonstrated how pre-irradiation temperature regimes could mitigate previously observed losses in the quality of the product post-radiation, especially in relation to fat rancidity challenges
Date of AwardNov 2019
Original languageEnglish
Awarding Institution
  • Coventry University
SupervisorStephen A. Chadd (Supervisor), Richard N Baines (Supervisor) & Farag Karim (Supervisor)

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