Thermal Resistance of Selected Heat-Resistant Spore-Forming Bacteria in Philippine Shelf-Stable Foods at Different Syrup Concentrations

Thermal resistance data are important in establishing appropriate thermal processes for shelf-stable foods. However, information on the thermal resistance of heat-resistant spore-forming bacteria in actual food systems, particularly Philippine shelf-stable products, remains limited. This study determined the thermal resistance of selected heat-resistant spore-forming bacteria in commercially processed white beans, chickpeas, and mango in syrup at different syrup concentrations.

Commercial sterility testing was conducted on mango, white beans and chickpeas in syrup. Surviving microorganisms were isolated and identified by 16S rRNA gene sequencing. Bacillus subtilis and Bacillus cereus were selected for Thermal Death Time (TDT) studies. Since no suitable heat-resistant spore-forming bacterium was isolated from mango in syrup, Bacillus coagulans ATCC 8038 was used as the reference microorganism. TDT studies were carried out at 80, 90, and 100 °C using food systems containing 10, 30, and 50 °Bx syrup. Decimal reduction times (D-values) and z-values were determined from survivor curves.

The D-values of all test microorganisms decreased with increasing temperature. For B. coagulans in mango in syrup, D-values ranged from 26.14–39.28 min at 80 °C, 6.18–8.95 min at 90 °C, and 1.60–2.40 min at 100 °C, with the highest thermal resistance consistently observed at 50 °Bx. The corresponding z-values ranged from 16.33 to 17.11 °C. Similar temperature-dependent trends were observed for B. subtilis and B. cereus in chickpeas and white beans. Among the microorganisms evaluated, B. subtilis consistently exhibited greater thermal resistance than B. cereus under comparable test conditions.

The thermal resistance parameters generated in this study provide reference data for selected heat-resistant spore-forming bacteria in Philippine shelf-stable foods. These data may be used in the development and validation of thermal processes for food products with different soluble solids concentrations.