Overview
ISO 8784-2:2023 - "Pulp, paper and board - Microbiological examination - Part 2: Enumeration of bacteria, yeast and mould on surface" establishes a standardized contact-plate method for measuring surface microbiological contamination on paper, paperboard, dry market pulp (sheet form) and packaging materials. The method uses RODAC/contact plates to transfer microorganisms from defined test pieces onto nutrient media and reports results as colony‑forming units (CFU) related to a defined surface area.
Key Topics and Requirements
- Method principle: Surface printing (contact‑plate/RODAC) transfers microorganisms to agar; colonies are incubated and enumerated as CFU.
- Test pieces and sampling: Representative sampling per applicable sampling standards; typically five test pieces (cut without touching, commonly 60 × 60 mm) are used so the total analysed surface meets the document’s minimum.
- Contact procedure: Press convex agar onto the test surface for 10 s using a 500 g weight, then maintain contact at room temperature for a defined contact time before incubation.
- Culture media:
- Tryptic Soy Agar (TSA) contact plates for bacteria.
- Sabouraud 4% Dextrose Agar with chloramphenicol (SDA + chloramphenicol) for yeast and mould.
- Contact plates: Use standard RODAC/contact plates (55 mm commonly available); follow manufacturer instructions for storage and shelf life.
- Incubation conditions:
- Bacteria: incubate TSA plates at 37 °C ± 2 °C for ~48 h.
- Yeast and mould: incubate SDA plates at 25 °C ± 2 °C for 3–5 days (enumerate at 3 d and 5 d to avoid overgrowth).
- Enumeration and reporting:
- Sum colony counts from the set of plates, calculate CFU per 100 cm² (CFU/100 cm²).
- Report when no colonies are observed (below detection) or when enumeration is not possible due to overgrowth.
- Aseptic technique: Work in aseptic conditions; a laminar flow hood is recommended. Sterilize tools and follow ISO 7218 general microbiology rules.
Practical Applications and Users
This standard is essential for quality control, hygiene monitoring and specification compliance in:
- Pulp, paper and paperboard manufacturers
- Packaging material producers and converters (food/medical packaging)
- Industrial QC and microbiology laboratories performing surface microbial assays
- Procurement and regulatory teams specifying hygiene criteria for paper-based products
Benefits include reproducible, comparable results for surface contamination assessments, supplier qualification, product release testing and investigation of microbial-related defects.
Related Standards
- ISO 186 - Paper and board - Sampling to determine average quality
- ISO 7213 - Pulps - Sampling for testing
- ISO 7218 - Microbiology of food and animal feeding stuffs - General rules for microbiological examinations
Keywords: ISO 8784-2:2023, microbiological examination, contact plate, RODAC, CFU, paper microbiology, TSA, SDA chloramphenicol, surface enumeration, pulp and paper quality.