Death kinetics of Escherichia coli in goat milk and Bacillus licheniformis in cloudberry jam treated by ohmic heating

摘要

In recent years, the world’s food industry has focused increasing attention on electrical techniques offood processing. Ohmic heating is one of these techniques that can be considered as a high temperatureshort time and a purely bulk heating method, having potential applications in processes such asblanching, evaporation and pasteurization in the food industry. However such technology would haveto assure the microbiological safety obtained by the conventional cooking methods. Concerning this,the influence of heat treatment by ohmic and conventional technology on death kinetic parameters (Dand z values) of Escherichia coli ATCC® 25922 was studied in goat milk. In ohmic treatment lower Dvalues were obtained (D60ºC = 4.2 min, D63ºC = 1.9 min, D65ºC = 0.86 min) as compared to conventionaltreatment (D63ºC = 3.9 min, D65ºC = 3.5, D67ºC = 2.8 min, D75ºC = 1.5 min). The increase of temperaturerequired for a ten fold decrease in D value was also lower in the ohmic inactivation (z = 8.4 ºC)comparing with the conventional inactivation (z = 23.1 ºC). The death kinetics for Bacilluslicheniformis ATCC® 14580 spores in cloudberry jam were also studied under both types of heatinactivation (ohmic and conventional) and similar conclusions were drawn for the D values; lower Dvalues were also obtained for ohmic treatment (D70ºC = 57.1 min, D75ºC = 25.2 min, D80ºC = 7.2 min) ascompared to conventional treatment (D70ºC = 85.3 min, D75ºC = 51.0, D80ºC = 18.1 min, D85ºC = 6.0 min,D90ºC = 1.6 min). However, between the z values obtained for those treatments (z ohmic = 11.1 ºC and zconventional = 11.4 ºC) the differences were not significant. In general the results of present work indicatethat the ohmic heating provides quicker death kinetics. This opens the perspective for shorter, lessaggressive treatments.