Purpose: This study aimed to assess the efficacy of microwaves on the inactivation of Bacillus coagulans spores, experimentally inoculated into coconut water and to compare its efficacy with conventional heating.
Methods: Experiments were conducted according to the Central Composite Designs (CCD) with four parameters: temperature, 83°C - 95°C; potency, 115 - 135 W; amount of mixture of citric and ascorbic acids added to the coconut water, 73 - 77 mg/100 mL; and the composition of these acids, ascorbic 20% - 30% and citric 67% - 80%. Approximately 1433 B. coagulans spores CCGB (LFB-FIOCRUZ, Rio de Janeiro, Brazil) were inoculated into 100 mL coconut water samples obtained from green fruits and previously acidified (ascorbic and citric acid). After being exposed to microwaves and conventional heating as per the conditions of the CCD central point (89°C, 125 W, and 75 mg of acids [25% ascorbic and 75% citric acid]) for 5, 10, 15, and 20 min, the surviving spores in the coconut water were enumerated.
Results: The average reductions of B. coagulans spores in the coconut water processed by microwave and conventional heating were 3.0±0.6 log CFU/mL and 3.7±0.8 log CFU/mL, respectively. Among the tested parameters, the temperature was the most relevant to the inactivation of this microorganism (p<0.05, Student's t-test). When exposed to microwaves for 5 min at 95°C (lowest time/highest temperature), a reduction of five log CFU/mL was obtained.
Significance: Microwaves have been used to heat foods in commercial sterilization processes. In this study, microwaves showed potential as a process for inactivating of B. coagulans spores in coconut water.