Rope in bread - a critical challenge for the bakery industry
Fieseler, Lars; Gantenbein-Demarchi, Corinne; Miescher Schwenninger, Susanne; ; Kleinert, Michael (2013). Rope in bread - a critical challenge for the bakery industry: Posterpräsentation. In: 4th MoniQA International Conference. Kongress. (26. Februar - 1. März 2013). Budapest: MoniQA Association.
Rope formation is a serious, but underreported food security problem in the bakery industry. Although ropiness has been recognized for many years, no effective means of prevention have yet been determined. Ropiness can occur in wheat bread, mixed grain bread or yeast-raised baked goods. It is initially characterized by an unpleasant fruity odor accompanied by a bitter taste. Subsequently the bread crumb discolors, the bread appears greasy and sticky and, when broken apart, extended threads develop which stretch out from the crumb. Ropiness is particularly prevalent in organic products and is caused by several bacterial species of the genus Bacillus (B. subtitlis, B. licheniformis, B. pumilus, B. megaterium, and B. cereus). Bacillus spp. are Gram-positive, rod-shaped, spore-forming bacteria omnipresent in the environment and in various raw materials. The spores are often introduced into the dough via contaminated flour or after reuse of dried and milled bakery residues. Analysis of ca. 200 grain samples in Switzerland confirmed that virtually all samples were associated with Bacillus spores at a level of 101 to 104 spores per gram. Because spores exhibit a high heat resistance they normally survive the baking process inside the bread crumb. After cooling, spores germinate in the warm moist matrix. During subsequent storage of the bread (in particular during the summer months in tightly closed containers), the germinated vegetative cells multiply rapidly. Rope spoilage becomes visible if the bacteria multiply to 107 to 108 colony forming units per gram of crumb. A survey carried out among small and medium-sized bakeries in Switzerland confirmed that 61% of the respondents were familiar with rope spoilage and 30% thereof referred to spoilage incidents in their own bakeries. However, because of the long time for ropiness to develop, spoilage is often only detected once the product has been purchased by the consumer and consequently the bakery industry is unaware of the full extent of the problem.
Ropiness is related to protease and amylase activity and correlates with the presence of an inverted repeat within the promoter region of the amylase encoding gene (amyE) in the corresponding Bacillus spp.. It is thought that the inverted repeat features a binding site for regulatory proteins, which control amylase expression. However, the activity of the amylase alone is not sufficient to cause ropiness. Hence, other so far unidentified factors may be involved in symptom development.
The main strategy to prevent rope spoilage is control of the processing parameters. The use of additives, such as sodium diacetate, has also been successful in the past. However, additive use is becoming restricted due to the consumers’ increasing demand for preservative-free products, which poses a significant challenge for the baking industry. The effectiveness of lowering the pH of the dough to prevent rope spoilage could be demonstrated. Non-acidified bread samples displayed ropiness within 24 hours after artificial inoculation of the dough with 102 to 103 rope-forming Bacillus spores per gram. Spoilage could be prevented for several days if the pH in the dough was reduced to 5.0-5.1 (5.2-5.4 in the baked bread) by the addition of a 6% pre-ferment. While lowering the pH is an effective method in sourdough bread, new strategies like the addition of protective cultures to the dough are required for other bakery products where acidification is not appropriate due to sensorial or other factors.
Specific and reliable, but also quick and simple screening methods for the detection of a contamination with rope-forming Bacillus strains should be the subject of further investigations. A deeper comparison of rope-forming and other Bacillus strains based on morphological, biochemical and genetic characteristics could provide the necessary background for the development of a rapid detection system for rope formers.