The effect of probiotic bacteria on the formation of conjugated linoleic acid (CLA), microbial growth, and organoleptic attributes (acidity, texture, and flavor) of fermented milk products was determined. Four probiotic bacteria, Lactobacillus rhamnosus, Propionibacterium freudenreichii subsp. shermanii 56, P. freudenreichii subsp. shermanii 51, and P. freudenreichii subsp. freudenreichii 23, were evaluated individually or in coculture with traditional yogurt cultures (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus). The lipid source was hydrolyzed soy oil. L. rhamnosus, in coculture with yogurt culture, resulted in the highest content of CLA. Growth and CLA formation of propionibacteria were enhanced in the presence of yogurt cultures. Texture and flavor attributes of fermented milks produced with propionibacteria were significantly different than the fermented milks processed with yogurt cultures. The fermented milks processed with probiotic bacteria in coculture with yogurt cultures demonstrated similar acidity, texture, and flavor as the fermented milk produced with yogurt cultures.

The objective of this research was to study the effects of probiotic bacteria, lipid source, and fermentation time on the CLA content of a milk model system. The evaluation of 11 probiotic bacteria showed that they were able to produce CLA from linoleic acid in a model system containing hydrolyzed soy oil (1%) emulsified in milk, but not in model systems of unhydrolyzed soy oil (1%) emulsified in milk or 1% fat milk. Propionibacterium freudenreichii subsp. shermanii 56, P. freudenreichii subsp. shermanii 51, and P. freudenreichii subsp. freudenreichii 23 demonstrated the greatest increase in CLA content. Propionibacterium freudenreichii subsp. shermanii 51, produced the highest cis-9,trans-11 CLA content and also produced the greatest increase in trans-10,cis-12 CLA content as fermentation time was increased from 24 to 48 h. The fermentation of probiotic bacteria for 24 h was often most effective in increasing the CLA content. Viable counts of probiotic bacteria increased significantly from 0 to 24 h. These results demonstrated that the content of CLA during fermentation was primarily dependent on the strain of probiotic bacteria and the lipid source in the milk model system. This research suggests an efficient approach to produce CLA-enriched cultured dairy products.

Decimal reduction time (time to inactivate 90% of the population) (D) values of Bacillus anthracis spores in milk ranged from 3.4 to 16.7 h at 72°C and from 1.6 to 3.3 s at 112°C. The calculated increase of temperature needed to reduce the D value by 90% varied from 8.7 to 11.0°C, and the Arrhenius activation energies ranged from 227.4 to 291.3 kJ/mol. Six-log-unit viability reductions were achieved at 120°C for 16 s. These results suggest that a thermal process similar to commercial ultrahigh-temperature pasteurization could inactivate B. anthracis spores in milk.In 2001, the intentional release of anthrax spores through the U.S. Postal Service prompted increasing concern for a potential bioterrorist attack, including food terrorism. Due to the vulnerability of the food supply system, food and water could be deliberately contaminated and are considered two of the most viable targets for bioterrorism (7). Milk, as a product consumed every day especially by children, poses a high probability/high severity risk potential if Bacillus anthracis spores were purposely added to it at the farm, truck delivery, or processor level (23). In order to enhance milk safety against purposeful contamination with a biological agent, it is necessary to develop effective heat treatments capable of inactivating biological agents, such as large amounts of anthrax spores, that could be deployed immediately by milk processors in the event of a bioterrorist attack (23).Bacillus anthracis is a spore-forming, gram-positive bacillus that causes anthrax. There is very limited information about heat inactivation of B. anthracis spores in the literature, as most studies have focused on the heat resistance of other Bacillus species. The effects of different heating methods (boiling, moist heat, and dry heat) on heat inactivation of B. anthracis spores have also been reported (6,12,17,19,20). In general, it was reported that in different buffer solutions B. anthracis spore counts could be reduced by at least 10 6 CFU/ml if the spores were heated at 90°C for 20 min, at 100°C for 10 min, and 105°C for 5 to 10 min (12,19). At 120°C, the spores were destroyed after 5 to 15 min (20). The thermal kinetics of B. anthracis inactivation in buffer solutions, however, cannot be used to predict its destruction in foods, because the heat resistance can be increased by food components, such as protein and fat (3, 18).Because milk is not considered a vehicle of natural B. anthracis infections, very few studies have investigated the thermal resistance of B. anthracis spores in milk. In one recent study, standard pasteurization conditions (63°C, 30 min; 72°C, 15 s) killed 4 log CFU/ml vegetative B. anthracis cells but had no effect on spores (14). The authors concluded that standard pasteurization processes had little effect on the viability of B.anthracis spores (14). In another study, Novak et al. (13) reported the inactivation of B. anthracis strain Sterne in skim milk by 0.45 log CFU/ml after 90 min at 72°C, 8.1 log CFU/ml after 60 min at 100°C, and 7.7 log...

The effect of inoculation concentration of Lactobacillus rhamnosus and yogurt cultures and storage time on conjugated linoleic acid (CLA) content and quality attributes of fermented milk products was determined. Yogurt culture (Lactobacillus bulgaricus and Streptococcus thermophilus, 1:1 ratio, YC), L. rhamnosus (LB), and LB co‐cultured with yogurt culture, were inoculated at 106, 107, 108 CFU/mL into a milk with hydrolyzed soy oil as the lipid source. CLA content, microbial counts, acidity, texture, and volatile flavor profile of the fermented milk products were stable during storage at 4 °C for 14 d. Total CLA contents ranged from 0.51 to 1.00 mg CLA/g lipid following 14 d of storage. Inoculation level of L. rhamnosus and yogurt cultures had no significant effect on CLA content and texture, but affected acidity and the volatile flavor profile of the fermented milk products. The fermented milk products produced by L. rhamnosus co‐cultured with yogurt culture with 107 CFU/mL total inoculation level resulted in a high CLA content and desirable quality characteristics. This research demonstrated that the optimal inoculation concentration and the combination of L. rhamnosus and yogurt cultures were important factors to produce fermented milk products with CLA content and acceptable quality attributes.