ISO 11289:1993 PDF

Overview

ISO 11289:1993 specifies a potentiometric method for the determination of pH in heat‑processed foods in hermetically sealed containers. The method measures the potential difference between a glass electrode and a reference electrode immersed in a prepared test sample. It is intended primarily for verification of the biological stability of canned and other hermetically sealed food products.

Key topics and technical requirements

• Scope and purpose: Applies to the aqueous phase of four product classes -

1. homogeneous liquid or thick products; 2) homogeneous pastes or heterogeneous products requiring homogenization; 3) heterogeneous products with large solid components; 4) products whose liquid phase is mainly oil or oil/water emulsion.

• Measurement principle: Potentiometric pH measurement using a glass electrode and a reference electrode; results reported to 0.1 pH unit.
• Temperature: Measurements may be made at 20 °C or 25 °C (temperature must be recorded).
• Reagents and buffers: Use analytical‑grade reagents and Type 1 water (ISO 3696). Standard buffer solutions are required for calibration - example recipes are given (e.g., pH 4 buffer from 10.120 g potassium hydrogen phthalate per 1 L; pH ~6.88 buffer from specified phosphate salts).
• Apparatus: pH‑meter with minimum display resolution of 0.01 pH, temperature compensation; thermometer (±1 °C); homogenizer or Stomacher; laboratory glassware.
• Sample preparation: Procedures differ by class - direct measurement for class 1, homogenization for classes 2 and 3 components, separation of aqueous phase for class 4 (oil/water emulsions). For large containers, a representative 200 g sample is recommended.
• Calibration and quality control: Calibrate pH‑meter with two buffers at measurement temperature; control calibration during series every 30 minutes.
• Electrode care: Rinse with acetone and warm water (30–35 °C); periodic deeper cleaning per manufacturer; enzymatic cleaning or 70% ethanol recommended for biological contamination.
• Replicates and repeatability: Single determination is sufficient for class 1 and some aqueous phases; perform three determinations for homogenized products (classes 2 and 4) and for solid components of class 3. Repeatability criterion: absolute difference between two independent results should not exceed 0.15 pH unit.
• Reporting: Report sampling method (if known), measurement temperature, method used, individual results and final results (mean where applicable), and any deviations or operational details.

Applications and users

ISO 11289:1993 is used by:

• Food quality and safety laboratories for pH control and shelf‑life/stability testing
• Canning and food processing manufacturers for process validation
• Regulatory authorities and auditors verifying biological stability of hermetically sealed foods
• R&D teams assessing formulation changes affecting pH and preservation

Keywords: ISO 11289:1993, pH determination, heat‑processed foods, hermetically sealed containers, potentiometric method, food safety, homogenization, buffer calibration.

Related standards

• ISO 3696 - Laboratory water specifications (referenced for reagent water quality).