Application of different orifices for hydrodynamic cavitational effects on deactivation of Escherichia coli and Staphylococcus aureus in milk

Abstract

Thermal processing reduces the nutritional value and flavour of milk due to the application of heat, although it has the benefits for safety and shelf life by eliminating microbes. Also, the growing preference of consumers for natural and minimally processed foods has led to an increase in the use of nonthermal milk processing techniques. Hydrodynamic processing (HC) is one such recent, inventive, scalable, and economically favourable nonthermal technique. Thus, the influence of hydrodynamic cavitation on the deactivation of Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria was investigated using four different orifice plates: ORFP 1 (Ø=4 mm); ORFP 2 (Ø=3 mm); ORFP 3 (Ø=2.27, 3 holes), and ORFP 4 (Ø=2 mm, 5 holes). Milk with cell inoculum was treated at three different pressures (3, 5 and 7 bar) and six different treatment time (5, 10, 15, 20, 30 and 40 min). Multi-hole orifices with higher α-value (plate parameter) were more effective in deactivation of microbial population in comparison to single hole orifices. Multi-hole orifice (ORFP 4) had the highest reduction of microbial cells, with 3.5 and 2.83 Log reduction for E. coli and S. aureus, respectively followed by ORFP 3, ORFP 2, and ORFP 1. Cavitation number in the range of 0.21–0.66 resulted in significant reduction of E. coli and S. aureus. From this study, it can be said that both flow geometry (α, β and flow area) of orifice plates and flow characteristics (flow rate and cavitation number) of the hydrodynamic cavitation system had an impact on the reduction of bacteria. Thus, hydrodynamic cavitation with different configuration of orifice plates can offer a potential option for thermal pasteurization.