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ISO 27608:2010 – Lovibond Colour of Fats and Oils (Automatic Method)
Animal and vegetable fats and oils — Determination of Lovibond colour — Automatic method
1. Automatic Determination of Lovibond Colour in Oils and Fats
ISO 27608:2010 specifies an automatic method for the determination of Lovibond colour of animal and vegetable fats and oils using automatic instrumentation. The Lovibond colour scale is a traditional and widely used parameter for assessing the quality and grade of edible oils and fats, correlating with refining degree, bleaching efficiency, and overall product acceptability.
The standard was developed in response to industry demand for an automated alternative to the manual method (ISO 15305), which relies on visual comparison and is subject to operator variability. While complete agreement between automated and manual methods is not achievable, the automated method specified in ISO 27608 provides results within the repeatability and reproducibility limits of the manual method for most commercial applications.
The automatic method is particularly well-suited for production quality control where high throughput and operator-independent results are essential. For oils with colour intensity above 4 Lovibond red units, the manual reference method remains the preferred approach.
| Colour Component | Typical Range | Significance | Acceptance Criteria (Refined Oil) |
|---|---|---|---|
| Red | 0.1 – 4.0 | Primary quality indicator | Less than 1.5 |
| Yellow | 1.0 – 70.0 | Supplementary measurement | Less than 15 |
| Blue | 0.0 – 5.0 | Indicates unusual processing | Less than 0.5 |
| Neutral | 0.0 – 3.0 | Darkness indicator | Less than 1.0 |
2. Instrumentation and Measurement Procedure
The automatic instrument uses a spectrophotometric or colorimetric measurement principle with standardized illumination (CIE Standard Illuminant C) and observation geometry. The instrument compares the sample’s transmission spectrum against the Lovibond glass standards and reports the colour in terms of Lovibond red, yellow, blue, and neutral units. The cell path length is typically 1 inch (25.4 mm) for most oils, with 5.25 inch (133.35 mm) cells used for very pale oils.
The procedure requires the oil sample to be filtered and heated to a specified temperature (typically 50-60 degrees C for liquid oils or above the melting point for solid fats) to ensure complete melting and homogeneity. The sample is placed in the measurement cell, and the instrument automatically performs the colour measurement and displays results. Annex A provides guidance on instrument installation, calibration, and maintenance.
The instrument’s calibration must be verified using certified Lovibond glass standards or reference filters. Regular calibration checks are essential to ensure measurement accuracy, particularly for critical trading applications where colour specifications are part of contractual agreements.
3. Engineering Applications and Quality Control
The Lovibond colour measurement is a critical quality parameter throughout the edible oil supply chain. Crude oils typically have high colour values due to the presence of pigments (chlorophylls, carotenoids, gossypol). During refining, the bleaching step removes these pigments, and the bleached oil colour is a key indicator of bleaching efficiency. The final refined, bleached, and deodorized (RBD) oil colour determines its suitability for specific food applications.
From an engineering perspective, the transition to automatic colour measurement offers several advantages: elimination of operator subjectivity, integration with laboratory information management systems (LIMS), automated data recording for traceability, and higher sample throughput. The standard’s note regarding limitations with strongly colored samples (above 4 red units) and unusual hues (blue, green, brown) provides important guidance for selecting the appropriate method.
Implementing ISO 27608 in quality control laboratories enables consistent colour measurement across production shifts and between different factory locations. The automated method reduces analysis time from approximately 5 minutes (manual) to under 1 minute per sample, significantly improving laboratory efficiency.
Do not use automatic colour instruments for oils containing suspended solids or turbidity without prior filtration. Particulate matter will scatter light and produce erroneously high colour readings, potentially leading to incorrect quality classification and unnecessary reprocessing.
4. Frequently Asked Questions
Q: What types of oils and fats can be measured with this method?
A: The method is suitable for both animal fats (tallow, lard) and vegetable oils (palm, soybean, rapeseed, sunflower, olive, etc.) within the colour range specified. Solid fats must be melted and measured at a temperature above their melting point.
A: The method is suitable for both animal fats (tallow, lard) and vegetable oils (palm, soybean, rapeseed, sunflower, olive, etc.) within the colour range specified. Solid fats must be melted and measured at a temperature above their melting point.
Q: How do the automatic method results compare with manual visual results?
A: While complete agreement is not possible due to fundamental differences in measurement principles, the automatic method produces results within the repeatability and reproducibility limits of the manual method for most oils with colour intensity below 4 red units and without unusual hues.
A: While complete agreement is not possible due to fundamental differences in measurement principles, the automatic method produces results within the repeatability and reproducibility limits of the manual method for most oils with colour intensity below 4 red units and without unusual hues.
Q: What is the measurement cell path length used in this standard?
A: The standard uses a 1-inch (25.4 mm) cell as the standard path length. For very pale oils, a 5.25-inch (133.35 mm) cell may be used to obtain measurable colour values, and the results are reported with the cell length specified.
A: The standard uses a 1-inch (25.4 mm) cell as the standard path length. For very pale oils, a 5.25-inch (133.35 mm) cell may be used to obtain measurable colour values, and the results are reported with the cell length specified.
Q: Can this method be used for refined oils with very low colour values?
A: Yes, the automatic method is particularly suitable for very pale oils, as the instrument’s photometric detection provides better sensitivity at low colour levels than the human eye. Using the longer path length cell further improves sensitivity for these applications.
A: Yes, the automatic method is particularly suitable for very pale oils, as the instrument’s photometric detection provides better sensitivity at low colour levels than the human eye. Using the longer path length cell further improves sensitivity for these applications.
The automatic determination of Lovibond colour in animal and vegetable fats and oils using ISO 27608 represents a significant improvement over traditional manual methods for quality control applications. The automatic method eliminates operator subjectivity, reduces analysis time, and provides digital data that can be integrated with laboratory information management systems for comprehensive quality tracking and traceability.
The measurement principle is based on spectrophotometric analysis of the oil sample in the visible spectrum (400-700 nm). The instrument compares the transmission spectrum of the sample against the spectral characteristics of standard Lovibond glass filters and calculates the colour values in terms of red, yellow, blue, and neutral units. The use of standardized illumination conditions (CIE Standard Illuminant C) and observation geometry ensures consistency between different instruments and laboratories.
Sample preparation significantly affects measurement accuracy. Oil samples must be free from turbidity, suspended solids, and water droplets, which can scatter light and produce erroneously high colour readings. Filtration through a suitable filter medium at the measurement temperature is essential. For solid fats, the sample must be melted and maintained at a temperature above its melting point throughout the measurement to ensure complete homogeneity and reproducible results.
The standard provides guidance on instrument calibration and maintenance to ensure long-term measurement accuracy. Certified Lovibond glass standards are used to verify instrument performance, with regular calibration checks recommended based on the frequency of use and the criticality of the measurements. The instrument should also be checked for stray light, wavelength accuracy, and photometric linearity as part of a comprehensive quality assurance program.
While the automatic method offers many advantages, users must be aware of its limitations. The method is not suitable for oils with colour intensity above 4 red units or for samples with strong blue, green, or brown hues. For these samples, the manual reference method specified in ISO 15305 should be used. Understanding these limitations is essential for selecting the appropriate method for each application and ensuring the reliability of quality control measurements.
