Overview
EN 1788:2001 (CEN) specifies a validated laboratory method for the detection of irradiated food by thermoluminescence (TL) analysis of contaminating silicate minerals. The standard applies to foodstuffs from which a sufficient amount of silicate minerals can be isolated. It was developed and tested in interlaboratory trials on herbs and spices, shellfish (shrimp/prawn), fresh and dehydrated fruits and vegetables, potatoes and many other food types.
Key topics and technical requirements
- Principle: Silicate minerals in foodstore trapped charge when exposed to ionizing radiation. Controlled heating of isolated minerals produces TL glow curves whose shape and intensity indicate prior irradiation.
- Glow analysis: Two measurements are required - Glow 1 (sample as extracted) and Glow 2 (same sample after a fixed known radiation dose). The TL glow ratio (Glow 1 / Glow 2) is used to discriminate irradiated vs non‑irradiated samples.
- Minimum Detectable Level (MDL): Defined as the full process blank (Glow 1) plus three standard deviations; Glow 2 integrated intensity should be at least 10× MDL.
- Sample preparation: Isolation techniques include wet sieving, density separation (e.g., sodium polytungstate solution at 2 g·ml−1), and acid hydrolysis where applicable. Samples must be protected from light and not exposed to temperatures >100 °C.
- Apparatus & reagents:
- TL reader with data recording, heating rate ≈ 6 °C/s, max temperature ≥ 350 °C, suitable photomultiplier and optical filters.
- Stainless steel sample discs (≈9–10 mm), radiation source for Glow 2 (interlaboratory tests used 60Co γ-rays at fixed doses such as 1 kGy; potatoes used 250 Gy).
- Ultrasonic bath, centrifuge, nylon sieves (125–250 µm), sodium polytungstate, HCl (1 M, or 4–6 M for special cases), NH4OH, oxygen‑free nitrogen for flushing.
Practical applications
- Routine screening of spices, herbs, seafood, fruits, vegetables and other commodities for undeclared irradiation.
- Regulatory compliance testing by national food control laboratories and customs authorities.
- Quality control by producers and trade laboratories to verify labeling and processing claims.
- Research and forensic investigations into food treatment history.
Who would use this standard
- Food testing laboratories and analytical chemists
- Public health and regulatory agencies enforcing irradiation labeling
- Spice and seafood industry testing facilities
- Accreditation and interlaboratory validation teams
Related standards
- EN ISO 3696 (Water for analytical laboratory use) is referenced for reagent water quality.
- EN 1788 supersedes EN 1788:1996 and is published under CEN procedures.
Keywords: EN 1788:2001, thermoluminescence, TL detection, irradiated food, silicate minerals, food analysis, TL glow ratio, sodium polytungstate, CEN.