Survival of Lactobacillus johnsonii La1 and influence of its addition in retail-manufactured ice cream produced with different sugar and fat concentrations

After several studies have proved the benefits deriving from the ingestion of probiotic bacteria, various dairy products containing lactobacilli and bifidobacteria cultures have been formulated in recent years. A 2(4) full factorial experimental design was applied to verify the effects of Lactobacillus johnsonii La1 addition in retail-manufactured ice cream stored at two different freezing temperatures and containing two different levels of sugar and fat. Both fresh and frozen-thawed La1 cells underwent preliminary resistance tests to bile, antibiotics, SDS, and acidity. La1 strain proved to be highly resistant to most of stress factors, thus excluding the possibility to find evidence of cell sublethal injuries caused by freezing. When the microorganism was added to ice cream mixes in the quantity of 10(7) cfu g(-1), it did not modify the overrun and firmness of the finished product. Regardless of formulation, no count decay of La1 cells was observed in ice cream stored for up to 8 months.