Inactivation of Escherichia coli by high-pressure homogenisation is influenced by fluid viscosity but not by water activity and product composition

Inactivation of two strains ofEscherichia coliinoculated into whole and skim milk by ultrahigh-pressure homogenisation

“…In our work the lethality increased by 0.13-0.70 Log 10 cycles depending on the matrix type when the inlet temperature increased from 6 ºC to 20 ºC. However, these lethalities are still far away from the ones described by Vachon et al [23] who reported reductions of approximately 8 Log 10 cycles in cultivable cells in another strain of E. coli (E. coli O157:H7 ATCC 35150) when inoculated into whole raw milk pressurised at 300 MPa with an inlet temperature of 25 ºC, using the same model of UHPH machine employed by Diels et al [7] (Emusiflex C5, Avestin, Ottowa, Canada). They also reported that increasing the milk temperature from 55 ºC to 60 ºC brought an additional reduction of 1.2 logarithmic units in cultivable cells of E. coli O157:H7.…”

“…The inoculated samples of skim milk treated at 6 ºC showed the lowest values of lethality for E. coli ATCC 10536 and E. coli O157:H7 CCUG 44857 (3.15 and 3.32 Log 10 cfu·mL -1 , respectively). Diels et al [7] also reported reductions of around 3.5 Log 10 cycles in E. coli (strain MG1655) when inoculated into skim milk pressurised at 300 MPa in one single cycle, but using a higher inlet temperature (25 ºC). Inlet temperature may influence the maximum temperature reached during the process, and consequently, may affect the lethality reached.…”

“…Information concerning the effect of the matrix on the degree of inactivation showed by the microorganisms is scarce. The available results seem to indicate that UHPH treatments were more effective against microorganisms in saline buffered solutions than in more complex matrices such as milk [7,23].…”

“…Thermal processing has a long tradition in food preservation because it is economical and efficient at achieving microbial inactivation, but it cannot be used to treat heat-labile compounds. Furthermore, high temperatures may lead to undesirable effects in milk such as off-flavours, nonenzymatic browning and denaturation of certain vitamins and proteins [5,7,23].…”

“…The growing trend for fresher, highquality convenience food has generated an increasing interest in nonthermal processing alternatives, such as high-pressure technologies, which are considered to be the most promising emerging food-processing technologies due to recent advances in high-pressure machinery and the successful introduction of pressure-processed foods [5,7,8,12,14]. Ultrahigh-pressure homogenisation UHPH (also called dynamic high pressure in the literature) is based on the same design principles as conventional homogenisation processes that are used in the dairy industry for reducing the size of fat globules [10,22,23], but working at significantly higher pressures (> 200 MPa), resulting in the destruction of large quantities of microorganisms.…”