The effects of latoperoxidase system and nitrogen gas flushing on the storage of raw milk

Raw milk storage continues to be a problem for both the developed and developing worlds until new technologies to properly store the milk are readily available to both economies during cold storage. Major causes of spoilage of raw milk are psychrotrophic bacteria belonging to the genus Pseudomonas. In order to extend the shelf life of raw milk, more knowledge of the nitrogen (N2) gas flushing and lactoperoxidase system (LP-s) along with refrigeration on microflora is required and for this reason, a study has been set up. Three experiments where raw milk was stored at 60C for 3 and 7 days under the LP-s and N2-flushing treatment with a control were considered. The milk samples at various conditions were analyzed for total bacterial counts (TBA), psychrotrophs, Gram-negative bacteria, lipase and protease producers; also, the pH was followed. 210 isolates were selected to represent the milk samples for the 3 experiments. All the isolates were characterized by the determination of their spoilage and phenotypic features: proteolytic, lipolytic, phospholipase activities, hemolytic factors and CLP production. In the end, N2-flushing showed a long term (7 days) inhibition of all bacteria types compared to LP-s (which better inhibited bacteria at 3 days) and compared to the control. 11 isolates were further subjected to 16S rRNA partial sequencing to adequately identify them and BLAST GenBank proposed the presence of representatives of the Pseudomonas genus for the 11 isolates. Continuous N2-flushing and activation of LP-s have demonstrated the ability to lower bacterial population in milk to varying degrees