Identification and Partial Characterization of a Bacteriocin‐Like Inhibitory Substance (BLIS) from Lb. Bulgaricus K41 Isolated from Indigenous Yogurts

Forty‐two strains of Lactobacillus bulgaricus isolated from locally made yogurts were examined and compared for bacteriocin producing ability using spot on lawn assay which improved by taking photo and image processing. Lb. bulgaricus K41 exhibited the highest inhibition level against indicators. K41 Bacteriocin‐like inhibitory substance is sensitive to proteolytic enzymes (proteinase K, pepsin, and trypsin) but α‐amylase makes slight reduction in its activity and it is resistant to lipase. This antibacterial peptide is extremely heat‐stable (121 °C for 15 min) and remains active over a wide pH range (pH = 2 to 10); also nonionic detergents (Tween‐20, Tween‐80, and Triton X100) showed no effect on its activity. The inhibitory spectrum is against Gram‐positive bacteria (except Staphylococcus aureus) with extremely antilisterial activity and it is almost ineffective against Gram‐negative bacteria. The mode of its action was identified as bactericidal against Listeria monocytogenes. The properties of K41 bacteriocin‐like inhibitory substance add to its safety as a biopreservative produced by a generally recognized as safe (GRAS) bacterium suggesting it can be used in hurdle technology for ready‐to‐eat foods as one of the main sources of Listeria contaminations.     

Nonfermented ice cream as a carrier for Lactobacillus acidophilus and Lactobacillus rhamnosus

Efficiency of a nonfermented ice cream for delivering Lactobacillus acidophilus and Lactobacillus rhamnosus to consumers was evaluated. Both of the microorganisms survived at the populations of greater than 10⁷ CFU g^?1 during 12 weeks of storage at ?19 °C. Addition of the microorganisms had no significant effect on the overrun, viscosity, firmness and melting behaviour; it changed the acidity, pH and sensory properties of the finished product. Resistance to acid and sensitivity to bile of both bacteria were tested separately on fresh harvested cells before inoculation to ice cream and then on the frozen‐thawed cells after 12 weeks of cold storage in ice cream. Ice cream processing followed by cold storage reduced acid resistance of both bacteria at pH 2.5. Resistance to bile in L. rhamnosus was not affected in frozen‐thawed ice cream when compared to fresh cell, whereas resistance to bile in L. acidophilus appeared to be more susceptible to the process and cold storage.