Contaminant Aerobic Sporeforming Bacteria

contamin.pdf (application/pdf-tiedosto)

Papermaking, production and handling of modified starches, and dairy and some other food processes share the sensitivity of the raw materials and process conditions often favourable for microbial growth. Process equipment has large surfaces for microbes to settle and to form biofilms.

Helge: I see that Juha Mentu has been involved in this.

Heat in the dry end of the paper machine or during the ‘cooking’ of industrial starches inactivate fungi and vegetative bacteria whereas heat resistant bacterial spores not only survive but may become activated. Similar selection for heat resistant contaminants occurs by the
pasteurization of liquid foods. Effective cleaning and preservation techniques and good manufacturing practices are required in these processes to maintain high hygienic quality in the end product.

Helge: Keep it clean!

Aerobic endospore forming bacteria are widely distributed in nature. The spores are resistant to heat, desiccation, disinfectants, ionizing radiation and UV light. Bacilli are frequent contaminants in biomaterial-based industrial processes. They represent the major hygienic problem in processes where heat or other treatments kill the competing, non-sporeforming microflora.

Helge: Ok.

The significance of bacilli in foods such as milk products has been studied intensively, but little information is available on their role in industrial processes, e.g. in the production of food packaging materials.

Helge: I see.

Paper and paperboard is produced in large volumes worldwide: in 1999 the production was 12.6 million tons in Finland and 79.5 million tons in Europe. Biocides are used to reduce accumulation of slimes and the subsequent production downtime and deterioration of the technical and hygienic quality of paper and board. One kg of each (effective substance) ton-1 of paper is commonly dispensed into the process at the different stages of production.

Helge: Biocides, yes.

Considering the economic importance of paper and paperboard manufacture, surprisingly little published information is available on the microbes contaminating these processes and the products. This study focuses on the production of food packaging paper and board and a dairy process bringing new knowledge on diverse bacterial contaminants in these biomaterial-based industries.

Helge: Why?

Aerobic bacteria producing heat-tolerant spores (named bacilli in this thesis), are the main contaminant group. The properties of these bacteria relevant to hygiene, food spoilage and food poisoning were studied in this work. The most prevalent pathogenic bacillus in industrial
processes is Bacillus cereus, classified to hazard category 2 (Anon., 1995; European Commission, 1993). An industrially applicable method for differentiating the potentially dangerous, emetic toxin producing strains of B. cereus from the non-producing strains, did not exist when this work was initiated.

Helge: Heat-tolerant...

Strains of B. cereus isolated from food poisoning incidents, from the products and process of food packaging paper and board manufacture and from dairy processes were characterized chemically, biochemically and genotypically. Starch constitutes one to two percent of the dry weight of paper products other than newsprint and some brands of grease proof paper.

Helge: Food poisoning?

Paper industry is thus a major user of modified starches. Over 90 % of the starches used in Finland are used by paper industry, 250 000 tons in 1999. Preservation of industrial starches against microbial deterioration is difficult. The organisms responsible for spoilage have seldom been identified. This gap of knowledge hampered the design of rational strategies for preserving industrial starches against microbial spoilage. Good novel preservation methods with minimal usage of toxic or sensitising chemicals are needed.

Helge: Starches and microbial deterioration.