Effect of atmospheric pressure cold plasma treatment time and composition of feed gas on properties of skim milk

Effect of cold plasma generated using Nitrogen-Oxygen and Nitrogen as feed gases on the properties of skim milk treated for 1, 2, 3, 4 and 5 min was evaluated. Cold plasma treatment with N2-O2 plasma (0.9 mol N2 & 0.1 mol O2 per mol feed gas) significantly decreased the pH and increased the titratable acidity of milk. Furthermore, skim milk treated with N2-O2 plasma showed higher browning intensity at the end of 5 min. Also, the particle size of milk significantly increased with time in case of N2-O2 plasma treatment , indicating aggregation of proteins. SDS PAGE results showing changes in the electrophoretic bands of casein as well as whey proteins also signified denaturation and aggregation of proteins and indicated the formation of insoluble protein aggregates. Apparently, the resultant protein aggregation led to a significant decrease in the surface hydrophobicity of skim milk. FTIR spectroscopy used to study the changes in the secondary structure of milk proteins revealed an overall increase in alpha-helix and aggregated beta-sheet. The results showed that the composition of feed gas had a significant effect on physico-chemical properties, particle characteristics and surface hydrophobicity of skim milk as well as the molecular weight of milk proteins.