Control of Bacillus licheniformis spores isolated from dairy materials in yogurt production.

To determine the effects of sporulation temperature and period on Bacillus licheniformis spore heat resistance, B. licheniformis strain No.25 spores were sporulated at 30, 37, 42, or 50°C for 11 d and at 50°C for 1.7, 4, 7, or 11 d. The heat resistance of B. licheniformis strain No.25 spores at 110°C increased with an increase in the sporulation temperature. Spores sporulated at 50°C were 1.4-fold more heat resistant than those sporulated at 30°C. Furthermore, the heat resistance of B. licheniformis strain No.25 spores at 110°C increased with an increase in the sporulation period. Spores sporulated for 11 d were 5.3-fold more heat resistant than those sporulated for 1.7 d. The heat resistance of B. licheniformis strain No.25 spores at 110°C increased with increases in the sporulation temperature and sporulation period. The results presented in this study can be applied to the pasteurization process to control B. licheniformis spores. Pasteurization at 110°C for about 60sec. is effective in controlling B. licheniformis spores isolated from dairy materials in yogurt production.

Efficacy of organic acids, bacteriocins, and the lactoperoxidase system in inhibiting the growth of Cronobacter spp. in rehydrated infant formula.

Thirty-three antimicrobial agents, including antimicrobial peptides (nisin, lacticin 3147, isracidin), organic acids, emulsifiers (organic acid esters), glycine, lysozyme, tocopherol, EDTA, milk fat globule membrane, and the lactoperoxidase system (LPOS) were screened for anti-Cronobacter sakazakii activity. The compounds were initially screened individually in parallel in synthetic media. Those showing antimicrobial activity were then tested in reconstituted whole milk and finally in reconstituted powdered infant formula (PIF), using mild temperatures of reconstitution and prolonged storage at room temperature. Propionic acid and monocaprylin (as POEM M-100) in combination showed inhibitory activity at sufficiently low concentrations (0.1 to 0.2%) in milk to be considered as potential antimicrobial additives for the inhibition of C. sakazakii in reconstituted PIF. More interestingly, LPOS, when combined with the broad-spectrum bacteriocins nisin or lacticin 3147, inhibited outgrowth of C. sakazakii at 37°C for 8 h. The combined effects of POEM M-100 and either acetate or propionate and LPOS with lacticin 3147 or nisin were evaluated under the Food and Agriculture Organization of the United Nations-World Health Organization high-risk scenario for PIF, i.e., low temperature of reconstitution and long storage or feeding times at ambient temperature. In the presence of LPOS and lacticin 3147, growth of Cronobacter spp. was inhibited for up to 12 h when the PIF was rehydrated at 40 or 50°C. These results highlight the potential of combinatory approaches to improving the safety of infant milk formula.

Immunomagnetic flow cytometric detection of staphylococcal enterotoxin B in raw and dry milk.

A rapid and sensitive method for detection of staphylococcal enterotoxin B (SEB) in raw and dry milk samples with the use of antibody-based immunomagnetic separation (IMS) in conjunction with flow cytometry (FCM) was developed. Sheep anti-SEB immunoglobulin G (IgG) was immobilized on Dynabeads M-280. The SEB initially binds to the capturing antibody, which is bound on the magnetic beads. The rabbit anti-SEB IgG binds to the captured toxin and is further labeled with a Cy5-labeled goat anti-rabbit IgG antibody. The percentage of the beads that were fluorescent was measured by FCM. FCM was carried out for 1 min, and the data obtained were expressed as histograms for particle size (forward light scatter) and histograms for fluorescence intensity. A peak corresponding to the magnetic beads was clearly distinguished from a peak derived from contaminating particles in the sample solution. In the absence of SEB, about 10% of the beads emitted fluorescence. The percentage of fluorescent beads and the fluorescence intensity increased with increasing SEB concentrations. For this IMS-FCM assay, the lower limits of detection for SEB were estimated to be 0.01 and 0.25 ng/ml for buffer and milk samples, respectively.