Effect of different ozonation dozes on some physicochemical and microbiological properties in raw and pathogens inoculated milk samples in comparison with conventional heat treatment with emphasis on pathogens was aimed to be investigated.
Raw cow' milk was divided into eight equal portions, 1st portion was heat treated at 72°C for 15 sec then rapidly chilled to room temperature. Other 7 portions were treated with ascending ozonation times, namely, nil (served as a control), 5, 10 15, 20, 25 or 30 min using an ozone generating device from the air at the rate of 400 mg O3/h. In another experiment, five portions of previously autoclaved skimmed milk (at 115°C /15 min) was separately inoculated with 0.1% of 24-h age broth cultured with Staphylococcus aureus ATCC25923, Bacillus cerues ATCC10876, E. coli ATCC25922, S. typhimurium ATCC 14028 or Sh. flexneri ATCC 12022). All inoculated milks were ozonized for nil, 5, 10 15, 20, 25 or 30 min at the same rate and immediately tested for the survival count of the studied pathogenic strains.
The obtained data indicated that, both raw milk treatments studied, namely thermal and ozonation (for more than 5 min) lowered significantly counts of total bacteria, yeasts & molds, Enterobacteriace and psychrotrophic bacteria than those in raw cow' milk. All counts of pathogenic bacteria were less than one cfu/ml after 30 min ozonation., E.coli and S .typhimurium counts were less than one after only 20 min ozonation. No significant differences were detected in all physicochemical properties among all milks treated whether thermally or by ozonation.
As a conclusion, ozonation treatment of raw and pathogenic inoculated milk up to 20 min at the rate of 400mg O3 /h had significantly improved the microbiological quality being able to cause decimal reductions in the milk native flora. Although there has been a marked decrease in the studied pathogenic bacteria as a result of ozonation, this is not enough for assurances, indicating the need for thermal treatment to assure the complete elimination of pathogenic microbes. Additionally, no significant changes were recorded in the physicochemical properties of the ozone treated milk up to 30 min at the same rate. Thus, these findings feature the bubbles of ozonation as a substitute to diminish the load of microbes in the raw milk, improve quality and increase the milk shelf-life before different processing