The effect of wheat bread contamination by the Bacillus genus bacteria on the quality and safety of bread

Abstract

The aim of the study was to determine the level of contamination of white bread by aerobic spore-forming bacteria that may cause the ropiness and to evaluate the antimicrobial activity of lactic acid bacteria against aerobic sporeforming bacteria during the storage of wheat bread at different temperatures. The contamination of dough samples by aerobic spore-forming bacteria did not affect the quality of bread in the initial storage phase (6–16 h after baking). The critical Bacillus subtilis subsp. spizizenii ATCC 6633 levels that cause ropiness in baked bread were determined: 7.8 × 106 CFU (colony forming units) g-1 after storage of samples for 3 days at 2 ± 2°C, 1.3 × 106 CFU g-1 after storage of samples for 3 days at 18 ± 2°C and 6.0 × 106 CFU g-1 after storage of samples for 1 day at 30 ± 2°C temperature. It was determined that contamination of dough by aerobic spore-forming bacteria should not exceed 1.0 × 103 CFU g-1. The evaluation of antimicrobial activities of lactic acid bacteria from Lactococcus and Lactobacillus genera against aerobic spore-forming bacteria was performed using an agar well diffusion method. In wheat bread, that had been fermented with Lactobacillus delbrueckii subsp. bulgaricus 148/3, L. acidophilus 336 and L. casei subsp. casei, the antimicrobial effects were observed for up to 3 days of storage at 18 and 30°C temperature. Weak signs of ropiness spoilage (sweet rope odour, discoloration of the crumb) were observed during the storage of the bread samples at 18 ± 2°C for 5 days (1.7 × 102 CFU g-1) and at 30 ± 2°C for 3 and 5 days (1.5 × 102 CFU g-1).