The antimicrobial effect of organic acids, sour dough and nisin against Bacillus subtilis and B-licheniformis isolated from wheat bread

Prevention of growth in wheat bread for more than 6 d of approximately 10(6) rope-producing Bacillus subtilis spores per gram of dough was achieved by addition of propionic or acetic acids at levels of 0.10% v/w (based on flour weight), or by addition of 15% sour dough fermented with Lactobacillus plantarum C11, Lact. brevis L62, Lact. plantarum ('vege-start 60'), Lact. plantarum (ch 20), Lact. maltaromicus (ch 15), or the commercial sour dough starter culture, Lact. sanfrancisco L99. These cultures resulted in an amount of total titratable acids above 10 in the sour dough and a pH value below 4.8 in the final bread. Bacteriocin-producing lactic acid bacteria added as starter cultures in wheat dough and nisin (Nisaplin) at levels up to 100 p.p.m. g(-1) flour had no effect against B. subtilis and B. licheniformis strains, despite the fact that nisin-producing strains of Lactococcus lactis ssp. lactis among 186 strains of lactic acid bacteria had demonstrated inhibitory activity against B. subtilis and B. licheniformis in an agar spot assay.