Improvement of microbiological quality of milk by UV-C irradiation in milking systems

In this study, it was aimed to reduce the microbial load in milking systems by applying different doses of UV-C radiation without alteration of the structure of milk. The study was carried out in two stages: The reduction of microbial load of raw milk by UV-C radiation application at different temperatures and durations and the examination of the effect of UV-C radiation application on pathogenic bacteria by inoculating certain pathogenic bacteria to the UHT milk proportionately. As a result of the study, it was detected that the application of UV-C caused a decrease of 2-3 log in the total number of Total Mesophilic Aerobic Bacteria (TMAB), while it decreased the number of the total yeast-mold, total coliform group bacteria, Staphlococcus aureus and Escherichia coli to an undetectable level. It was determined that there was a decrease of 1,95-2,81 log for the number of Salmonella Typhimurium, approximately 3 log for the number of Listeria monocytogenes, 1,9-2,76 log for the number of S. aureus in which the number of E. coli reach to an undetectable level in certain pathogenic bacteria inoculated UHT milk. It has been determined that UV-C application does not have an effect on the pH values, while the viscosity of the milk decreases as the applied radiation dose increases. It was determined that UV-C caused a decrease in L and b values and an increase in a value compared to the control group and the total color change (ΔE) values were high in the milk whose color was measured after UV-C application. The free fatty acidity of milk increased with UV-C application, and cholesterol amount decreased during UV-C application depending on the amount of oil remaining on the quartz glass. UV-C application transformed the 7-dehydrocholesterol in milk into vitamin D3, resulting in an increase in D3 concentration. It was determined that UV-C had an effect on milk fatty acid composition. A decrease was occurred in C4:0 and C12:0 amounts as the dose applied increased while a proportional decrease was occurred in C8:0 and C10:0 amounts in all applications. It was determined that UV-C caused an increase in C18:0 and C18:1 amounts, while it caused a proportionally decrease in all aplications for C18:2, C18:3n6 and C18:3n3 amounts except 60 J / mL dosing. UV-C increased the amount of carbon disulfide proportionally detected in untreated milk while it caused the formation of 3-methyl butanal, 2-methyl butanal, isobutyraldehyde, 2-N-propyl-5-oxohexanal, 2,3,5,6 tetra-chloro-phenyl methyl sulfoxide, 2-methyl pentanal components even at a low rate which cannot be detected in unprocessed raw milk. In the sensory evaluation of milk, generally as the applied radiation dose increases, the obtained score values for milk samples decreased. UV-treated samples at a flow rate of 18 mL/min (60 J/mL dose UV-C) received the highest score in all sensory evaluation criteria. With the application of UV-C to raw milk, high doses of microbial load decreased so much but some changes in some physicochemical and sensory properties of milk were detected. As a result, it is thought that the bacterial load can be reduced by 2-3 logs by applying approximately 60 J/mL dose of UV-C without changing the sensory and physicochemical properties of milk. With this level of UV-C application, by reducing the temperature and time norms used in pasteurization of milk with reduced microbial load, both low energy consumption and preservation of unique nutritional and aromatic properties of milk can be achieved. Since the milk flow rate in milking systems is higher than the flow rate used in this study, it indicates that columns with higher UV-C output power and multiple lamps should be used in order to integrate the UV-C system into the milking system. For this reason, it is recommended to work at different flow rates with a pilot/laboratory scale multi-lamp UV-C column before working on an industrial-size UV-C system to achieve more deterministic results.