Long-term storage stability of the bacteriocin propionicin PLG-1 produced by Propionibacterium thoenii and potential as a food preservative

Abstract

Propionicin PLG-1, a bacteriocin produced by Propionibacterium thoenii strain P127, was tested for characteristics that could determine its usefulness as a food preservative: long-term storage stability and effectiveness in a food model system. Partially purified propionicin PLG-1 samples, lyophilized and nonlyophilized, were stored at 25, 4, and -20°C. Bacteriocin activity increased by as much as 200% over the first 10 days of storage in nonlyophilized samples stored at 25 or 4°C. Activity then decreased gradually for samples stored at 25°C while samples stored at 4°C retained high activity through 14 weeks of storage. Nonlyophilized samples frozen at -20°C and lyophilized samples stored at all temperatures did not change significantly in activity through 25 weeks of storage. Propionicin was added at 100 and 1,000 arbitrary units (AU)/ml to lactobacilli MRS broth and to skim milk, each inoculated with 105 cells per ml of Lactobacillus delbrueckii ATCC 4797. Upon incubation at 37°C with 1,000 AU/ml, cell numbers were reduced by at least 4 log units within 2 h and no viable cells were detected after 96 h in either medium. With 100 AU/ml of propionicin, viable cells were reduced by 2 log units within 12 h at 37°C, but culture growth resumed after 24 h. At 15°C, no viable cells were detected after 48 h in the presence of 1,000 AU/ml of propionicin, while viable cell counts were gradually reduced to about 10 cells per ml by 168 h in the presence of 100 AU/ml of propionicin.