Biological variability of Bacillus species associated to the bread rope.

The raw materials used in the production of bakery products are the main source of sporeforming bacteria associated with the alteration of "bread rope" which occurs predominantly in humid hot weather and which results in significant economic losses in the bakery product sector (Valerio et al., 2012 , Int. J. Food Microbiol, 156, 278-285). The spores, surviving the cooking process, germinate and the vegetative cells start a degrading process of starch and bread proteins leading to the formation of slime. In the present study a screening test was carried out on 176 isolates from raw materials to evaluate which species could cause alteration in bread. Bacillus amyloliquefaciens, together with B. subtilis and B. pumilus, were the main species capable of causing the spoilage. Moreover, among the identified species, strains belonging to the B. cereus group account for 17%, of which 38% were found to be able to cause bread rope. The B. cereus group strains belong to the phylogenetic groups III and IV associated with high risk of intoxication, particularly those of group III, for which a high thermal resistance of the spores has been demonstrated during a test that simulates the thermal profile of the baking process (De Bellis et al., 2015, Int. J. Food Microbiol., 197, 30-39). To estimate the risk of bread spoilage during shelf-life, Symp Previus tool was used: cardinal parameters and growth / no growth boundaries of three strains were determined for three B. amyloliquefaciens strains isolated from bread with clear alteration symptoms, wheat and semolina. In addition, challenge tests were conducted by inoculating the spores of one strain in the mixing phase: various bread formulations were prepared to evaluate their effect on bacterial growth and the experimental results were compared with silica simulations. Finally, to estimate the probability of product contamination during shelf-life, two storage temperatures and a threshold of 5 log cfu / g were considered, a value which could cause alteration and / or represent a risk to consumer health. The characterization of the growth behavior of the three strains showed a difference in the contamination probability and subsequent alteration of the product, demonstrating the need to consider biological variability in predictive microbiological studies in order to obtain a realistic estimate of the risk of contamination. In conclusion, this study demonstrated the applicability of predictive microbiological instruments, known for assessing the risk of food contamination from pathogenic microorganisms, to the study of the behavior of alterative microorganisms to control the quality of food (Valerio et al. 2015 Food Microbiol., 45, 2-9).