Thermal Resistance and Growth of Bacillus licheniformis and Bacillus subtilis in Tomato Juice

Abstract

Bacillus species are common contaminants of soil and can be found with tomatoes and other vegetables and fruits. This research was done to assess the thermal stability of spores of acid tolerant Bacillus licheniformis and Bacillus subtilis in tomato juice. The D values at 90, 95, and 100°C were 29.5, 15.8, and 5.7 min for B. subtilis and 29.9, 12.2, and 5.9 min for B. licheniformis, respectively. The z value for B. subtilis was 14°C and for B. licheniformis was 14.2°C. Aerobically, B. subtilis spores could germinate and outgrow in tomato juice (pH 4.4) within 4 d at 35°C at inoculum levels as low as 1 spore per ml; however, B. licheniformis spores could only germinate and outgrow if levels were 104 spores per mi or higher. Both Bacillus species could raise the pH of tomato juice to above 4.8 when grown aerobically. Neither B. licheniformis nor B. subtilis could germinate and outgrow anaerobically in tomato juice (pH 4.4).