Inactivation kinetics of Clostridium sporogenes by capillary tube method and thermal food processing

Abstract

This master thesis is a part of the project “KonSpor” (Control of spore-forming bacteria in food with medium and long durability, project number 10415) financed by The Norconserv Foundation. The main objective of this study was to investigate if changes in NaCl concentration would affect the inactivation kinetics of Clostridium sporogenes spores in water and different food matrixes. Clostridium botulinum is a Gram positive, spore forming and anaerobic bacterium that causes botulism. C. botulinum is ubiquitous in the environment and can be found in food products that are not properly handled and stored. At suitable environmental conditions C. botulinum can grow in foods and produce the dangerous botulinum neurotoxin. C. sporogenes is used as a surrogate organism for proteolytic C. botulinum. C. sporogenes is a spore forming, anaerobic bacterium in the same genus as C. botulinum. It is a non-pathogenic bacterium that is often used to investigate the inactivation of Clostridium spores in food products. In this thesis the inactivation kinetics of C. sporogenes was investigated by different methods. The capillary tube method allows rapid heating and cooling and was used to find D-values of the spores at different temperatures in water. The effect of NaCl concentrations on the inactivation of spores was also investigated. A self developed method at laboratory scale was used to investigate the inactivation of C. sporogenes in minced meat with and without added NaCl. Thermal food processing was used to inactivate C. sporogenes spores in liver pate by autoclaving at two different temperatures. The log-reduction of the spores after autoclaving was determined. Germination experiments were also performed using Bioscreen C. Different germinators (L-alanine and Inosine) and NaCl concentrations were applied to C. sporogenes spores to investigate the germination process. The heat tolerance of C. sporogenes CIP 104607 in this thesis was lower than the average heat tolerance of C. sporogenes reported in other studies. The temperatures used in the experiments were between 91 - 97 °C. The D-value at 97 °C varied from 0.53 min in water to 5.33 min in minced meat as a food matrix with no NaCl added. From 0 to 0.9 % NaCl there was a decrease in the inactivation (increase in D-value) of C. sporogenes spores both in water and in the minced meat. NaCl did not increase the inactivation of C. sporogenes in water or in minced meat. The inactivation experiments in water without added NaCl showed decreasing D-values with increasing temperatures. The z-value for C. sporogenes CIP 104607 calculated in this thesis was 9.86 °C. In the germination experiments the C. sporogenes spores were completely germinated under aerobe conditions when L-alanine as germinator and 2.5 or 5.0 % NaCl were combined.