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 10 4 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).
Conditions responsible for growth and pH elevation by selected strains of Bacillus subtilis and Bacillus licheniformis were studied in order to assess the potential hazard of metabiosis occurring between Clostridium botulinum and mesophilic Bacillus species in aseptically packaged tomato juice. The effects of the initial tomato juice pH on the growth of these Bacillus strains were evaluated. Cultures of B. licheniformis previously identified by Fields et al. (6) were reclassified as B. subtilis because none grew under strict anaerobic conditions nor used propionate. B. subtilis did not grow under strict anaerobic conditions but could use oxygen if present in the environment. None of the B. subtilis or B. licheniformis strains grew at pH 4.0 or 4.2. Only B. subtilis 075-T-09 and B. licheniformis 64-83-46 strains isolated from acidic foods were able to grow at pH 4.4 in tomato juice. Anaerobically, B. licheniformis strains did not grow in tomato juice or tomato juice with added nitrate and thiamine and even showed a loss of viability. Both B. licheniformis and B. subtilis require oxygen for growth in tomato juice at pH 4.4.