Protein fractions in cow milk inhibit decontamination by cold atmospheric plasma

There is a growing body of research on the infection of cow milk by Prototheca algae, a potential human pathogen. This study presents investigations on plasma treatment to inactivate Prototheca directly in milk. However, microbiological tests revealed a surprisingly high survival rate of Prototheca in milk compared to saline solution treated under the same conditions. This phenomenon appears to be due to presence of proteins that act as scavengers of plasma reactive species, with OH^• radicals playing a major role. Studies using MALDI-TOF MS, FTIR, XPS and UV-VIS on a model solution of peptone K (simulating the molecular structure of milk protein fractions) confirmed the high reactivity of peptides with OH^• radicals, leading primarily to the substitution of hydrogen atoms with hydroxyl groups and cleavage of peptide chains. The obtained results encourage a broader consideration of proteins' role in plasma treatment processes, including applications in food products and plasma medicine.