Determination of the rope forming species of bacillus in white bread and whole meal bread and kinetic studies on rope development

In this study, white and whole meal breads baked at laboratory conditions were stored at 4, 25, 37 and 45ºC for 7 days to investigate the development of rope spoilage which is one of the main bacterial problems in breads. Microbiological (total mesophilic aerobic bacteria, Bacillus and mold counts), chemical (total free amino acids, total reducing sugar, residual protein contents) and textural (hardness, adhesiveness, cohesiveness, gumminess, chewiness, springiness, resilience) analyses were carried out on these breads in 24 hour intervals. Chemical analyses were determined spectrophotometrically. Also, texture profile analyses were performed to determine bread texture properties.The Bacillus species which were isolated from ropy bread as the disease factor were identified by using classical methods and API identification kits. The changes in the total free amino acids content, and hardness of stored breads were determined as indicators of the degree of hydrolysis. The data thus obtained were used to calculate the kinetic parameters and the mathematical model of rope spoilage.Results of the analysis showed that 37ºC is the optimum temperature for the development of rope spoilage and no symptoms of the disease were observed at 4ºC. It was determined that the visual symptoms of the disease were apparent in the second day of storage at 45ºC and in the fourth day at 25ºC for both types of bread. At 37ºC the disease was perceptible within the first day for whole meal breads and on the third day for white breads. The change in total free amino acids, total reducing sugars and residual protein contents throughout the storage period indicated that the disease factor Bacillus species had a higher amylase activity compared to their protease activity. It was observed that throughout storage, depending on the storage temperature, textural characteristics changed in a different manner.It was observed that there were discrepancies between the results of two identification methods which were used for identifying the Bacillus species isolated from ropy breads. It was understood that definite identification of some of the isolates using these methods was not possible and these strains could only be identified as being most likely a certain species. Isolates from white bread were identified as B. subtilis, B. megaterium, B. licheniformis, B. coagulans and B. pumilus; and isolates from whole meal bread were identified as B. subtilis, B. megaterium, B. licheniformis using biochemical tests. Using the API identification kits, on the other hand, resulted in the identification of B. licheniformis, B. pumilus, B. subtilis/amyloliquefaciens, most likely B. megaterium in white breads and B. licheniformis, Bacillus spp., B. subtilis/amyloliquefaciens, most likely B. megaterium, and most likely B. thuringiensis in whole meal breads. According to the results of the classical methods B.subtilis was the most abundant species in both white and whole meal breads. API kits, on the other hand, confirmed B. licheniformis as the predominant species. It can be concluded that biomolecular methods may provide to be more helpful in obtaining a more exact and credible identification for some of the isolates studied. All of the Bacillus species subjected to identification were also tested for their potential to be the causative agents in rope spoilage and were confirmed as being so.