Citric acid lowers heat resistance of Clostridium sporogenes PA 3679 in HTST white asparagus purée

Summary The heat resistance parameters (DT and z) of Clostridium sporogenes PA 3679 spores were determined from 121 to 145°C (HTST conditions) in Sørensen 0.067 M phosphate buffer (pH 7.0) and in asparagus puree at natural pH (5.8) and at increasing levels of acidification (pH 5.5, 5.0 and 4.5) using citric acid as acidulant. the thermal resistance of the spores was higher when suspended in phosphate buffer pH 7.0 than in asparagus puree at all pH levels. the DT values obtained in asparagus puree decreased as the acidification level of the heating medium was increased by the addition of citric acid. Hie most evident effect was observed at the lower temperatures assayed. There was a general increasing trend in the value of the z parameter as the pH level of the heating medium rose (zpH4.5= 12.9°C; ZpH7.0= 14.5°C). the differences found were significant between z values for pH 4.5 and those calculated for pH 5.8 and 7.0.