UV treatment to inactivate Escherichia coli O157:H7 in fruit juices

OTEIZA J. M., GIANNUZZI L. AND ZARITZKY N. E.

Napoles, Italia

Congreso; 2007 CIGR Section VI International Symposium on; 2007

CIGR Section VI International Symposium on FOOD AND AGRICULTURAL PRODUCTS: PROCESSING AND INNOVATIONS

The study analyze the effect of UV radiation: i) in fruit juices with different absorptivities, inoculated with Escherichia coli O157:H7 EDL 933 and ii) in fresh orange juice with different yeast concentrations, inoculated with five individual E.coli O157:H7 strains. For the first objective: orange, apple and multifruit pasteurized juices, and natural fresh orange juice, were inoculated with E. coli O157:H7 EDL 933 using two values of liquid film thickness (0.7 and 2.8mm) and two stirring velocities (0 and 220rpm). For each juices absorptivity coefficients were determined. UV doses ranging between 0 and 6 J/cm2 were applied at 20oC. Doses of UV (J/cm2) necessary to reduce 5D (UV5D) were calculated. In all cases, the highest inhibitory effect was attained using stirring conditions and the lowest film thickness (0.7mm). Stirring of the medium together with the lower liquid film thickness (0.7 mm) showed the higher bactericidal effect. A linear relationship between the absorptivity values and UV5D was obtained. The higher the absorbance of the medium, the greater the values of D required to inactivate E. coli strains by UV. With reference to the second objective: natural fresh orange juice containing four different ranges of background yeast concentrations (1.0x101 - 5.0x102 ; 5.1x102 - 5.0x103 ; 5.1x103 - 8.0x104; 8.1x104 -2.0x106 (CFU/ml)) were inoculated individually with five different E. coli O157:H7 strains. UV doses (ranging between 0 and 2 J/cm2) were applied at two irradiation temperatures (20 and 4ºC). Experiments were carried out using 0.7mm liquid film thickness and stirring conditions (220rpm). Each of the five E. coli strains showed different UV resistance. Higher values of 5D were obtained when yeast concentration increased, regardless the treatment temperature due to the increase of the absorptivity values in the juice. A linear relationship between absorptivities and D values for all E. coli strain was observed, both at 4 and 20°C. Values of D in UV treatments carried out at 4°C were significantly higher (p£ 0.05) than at 20°C, thus all the strains showed higher resistance to UV radiation at the lower temperature.