Purpose: The aim of this study was to assess the incidence, populations and spoilage ability of sporeforming bacilli (SB) in flour used for bread making.
Methods: Mesophilic and thermophilic aerobic sporeforming bacteria were enumerated in 100 samples of flours (wholemeal, n = 20, white bread flour, n = 40 and white flour cake, n = 40) after heat shock (80°C/30 min and 100°C/5 min, respectively) and plating in Tryptone Glucose Extract (TGE) agar and Dextrose Tryptone agar (DTA). SB isolates were evaluated for their ability to produce amylase and to cause rope spoilage in breads formulated with and without calcium propionate. The amylase positive strains were further identified through 16S rRNA sequencing.
Results: SB were isolated from all 100 flour samples; however, the highest counts were observed in wholemeal flour (3.1 log CFU/g). A total of 327 SB were isolated from flours, and 45 were shown to produce amylase. These isolates were identified as B. licheniformis (62%), B. sonorensis (20%) B. cereus (11%), B. pumilus (2%) and Paenibacillus polymyxa (2%). All 45 SB strains were able to cause bread spoilage by the ninety and third days of storage when formulations with and without preservatives were used for bread making. The response of SB strains with the greater spoilage potential to bread baking and their ability to cause rope in bread will also be reported.
Significance: Most isolates recovered from flour belonged to Bacillus genus. Wholemeal flour was the most contaminated raw material used in bread making, highlighting its importance as a factor that can potentially reduce bread shelf life.