Abstract
The present study evaluated the incidence of B. cereus in samples from 85 refrigerated dairy products through inoculation in selective medium and confirming according to biochemical proofs. Confirmed strains were then inoculated in specific growth medium at 7, 10 and 30°C to test the psychrotrophic behavior, and lipolytic and proteolytic activity. B. cereus was found in 15 of the 85 samples (17.6%); and 12 of them (80%) were let to grow up at 10°C for 7 days. When incubated at 7°C for 10 days, four strains (26.7%) grew up. All isolated B. cereus strains have shown proteolytic activity at 30°C, and 5 (33%) also presented lipolytic activity. At 10°C for 7 days, six strains (40%) showed proteolytic activity, and only one (6.7%), lipolytic activity. The temperature of 7°C for 10 days inhibited the production of proteases and lipases by the strains. The present work confirmed the presence of B. cereus strains with psychrotrophic, proteolytic and lipolytic activities in dairy products, which represents a potential risk for products stored under refrigeration.
Highlights
Bacillus cereus is a gram-positive rod-cell, aerobic and spore-forming bacterium
This study aimed to evaluate the incidence of Bacillus cereus in traded dairy products, verifying the psychrotrophic behavior, proteolytic and lipolytic activities of isolated strains
The results found in this experiment were similar to described by VidalMartins et al (2005), which identified that 11.8% of 110 UHT milk samples were positive for B. cereus
Summary
Bacillus cereus is a gram-positive rod-cell, aerobic and spore-forming bacterium. It is an environmental microorganism and its optimum temperature for multiplication is between 25 and 37°C, while psychrotrophic thermoduric strains can grow from 3 to 75°C (DROBNIEWSKI, 1993; DUFRENNE et al, 1995).This is a thermoduric microorganism because its spores can survive to the thermal processes used in food industry (AIRES et al, 2009; GAILLARD et al, 1998; MAZAS et al, 1999). Bacillus cereus is a gram-positive rod-cell, aerobic and spore-forming bacterium. It is an environmental microorganism and its optimum temperature for multiplication is between 25 and 37°C, while psychrotrophic thermoduric strains can grow from 3 to 75°C (DROBNIEWSKI, 1993; DUFRENNE et al, 1995). This is a thermoduric microorganism because its spores can survive to the thermal processes used in food industry (AIRES et al, 2009; GAILLARD et al, 1998; MAZAS et al, 1999). B. cereus is responsible for two types of food borne diseases: the diarrhea syndrome, caused by an enterotoxin produced in vivo, and the emetic syndrome, related to a preformed toxin in food (AGATA et al, 1995; OMBUI et al, 1997; WIJNANDS et al, 2006)
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