Heat treatment and the defective units’ ratio: surviving active spores in pea puree Original Research Article

The aim of the research work was to develop an experimental method to obtain kinetic data for the thermal inactivation of micro-organisms, with regard to active survivors in the food itself. The method is based on the principle that the number and concentration of surviving active microbes can be assessed from the number of spoiled heat treated units (m) out of a sample containing M units (1⩽m⩽M−1). Clostridium sporogenes spores have been inactivated in pea puree at 115°C and 121°C. The concentration of active surviving spores has been determined from the number of spoiled vials (units) out of samples of 50–50 vials at four-time periods. A very small heat resistant fraction has been detected with DT=6.32 min decimal reduction time at T=121°C, z=10.41°C temperature coefficient, Ni∗=0.36 and 2.2 cm−3 initial concentration of spores. Active survivors are understood as those able to multiply in the specified food after heat treatment, inactive ones do not multiply in the food, but in a suitable culture medium. Total initial concentration (potentially active and inactive survivors) was 1.2×105 spores per cm3. The experimental method is applicable for low survivor concentrations and useful for industrial application, as active survivors are detected in the food itself. Inactive survivors were also found in unspoiled vials.