Application of Gardner Colorimeter in the Determination of Oil and Fat Color

Principle of Garth colorimeter

Garth colorimeter is a special instrument for determining the color of liquids by visual colorimetry, and its core principle is based on the comparison of the color of the standard glass color standard with the color of the sample to be tested. In the determination of grease color, the operator will visually compare the grease sample that has been pretreated and injected into a standard cuvette to the standard glass color plate built into the instrument that meets the Garth color scale classification. When the color of the sample is closest to a standard color plate, the number of the color plate is recorded as the color value of the sample. This method transforms subjective color perception into relatively objective grade values, which is based on the application of Lambert-Beale's law in a specific wavelength range, that is, the absorption of light by the solution is related to the concentration of colored substances and the thickness of the liquid layer, which can be roughly expressed as:A = εlc, among themAis absorbance,εis the absorbance coefficient,lfor the optical path,cis the concentration. The concentration of pigment substances (such as carotenoids, chlorophyll derivatives, etc.) in oils and oils directly affects their color depth.

Operation process in oil color determination

The determination of oil color using a Garth colorimeter requires a standardized procedure to ensure reproducibility and comparability of results. First, the grease sample to be tested is pre-treated, which typically involves heating and melting (for solid greases), filtration to remove suspended impurities, and ensuring that the sample is clear and transparent. The sample is then injected into a clean, dry standard cuvette to the specified height. In a colorimeter cabinet with a constant light source, the operator visually compares the sample from the viewing hole to a slidable standard color sheet series. Comparisons should be carried out under specified light conditions, usually avoiding direct sunlight. Record the standard color plate number that matches the sample color and report the range value if the sample color is between two standard color plates. The whole operation process needs to pay attention to the consistency of cuvette cleaning, sample temperature control and visual judgment of the operator.

Method characteristics and scope of application

The Garth colorimetric method is a classic and widely recognized color evaluation method in the oil and oil industry. It is characterized by simple instrument structure, quick operation, and can provide a common color language between industries. This method is particularly suitable for color quality control of vegetable oils (such as soybean oil, rapeseed oil, peanut oil), refined animal fats, and edible oil products in the production and trade process. However, this method relies on human eye judgment, has a certain subjectivity, and is sensitive to the distinction between red and yellow tones, and has limited ability to distinguish blue or green tones. It primarily reflects the overall level of fat-soluble pigments in the oil and is not suitable for samples that are too dark or opaque.

Key influencing factors and control points

The accuracy of the measurement results is affected by multiple factors and needs to be strictly controlled. Sample state is key, and moisture, impurities, or turbidity can significantly interfere with colorimetry, so the sample must be clear. The cuvette must meet the specifications and cleanliness of the cuvette, and any scratches or stains will cause deviations. The stability of the ambient light source is crucial, and the instrument should be placed in an environment with uniform light and no direct bright light. The operator's visual judgment ability and experience will also affect the results, so it is recommended to operate by trained personnel or use the method of averaging the judgment of multiple people. In addition, the degree of oxidation of grease can sometimes affect the color, so it should be measured in time after sample preparation.

Comparison with other assays

In addition to the Garth colorimetric method, the Luo Weipeng colorimetric method and spectrophotometry method are often used for the determination of oil color. To clearly demonstrate their main differences, a brief comparison is made below.

The Garsler colorimetric method is widely used in trade contracts because of its long history and unified standards. The Luo Weipeng method can provide a more detailed description of the tone; The spectrophotometric method is more objective and deeply studied. The choice of method depends on the specific standard requirements, precision requirements, and application scenarios.

Epilogue

As a classic color measurement tool, the Garth colorimeter continues to play a role in production control, quality inspection and trade pricing in the grease industry. Its value lies in standardizing sensory evaluation, providing a simple and economical way to quantify color. Although more sophisticated instrumentation methods continue to develop, mastering the standardized operation of the Garth colorimetric method and understanding its principles and limitations are still of practical significance to ensure the quality of oil products and the smooth circulation of the market. In practical applications, the provisions of relevant product standards or testing method standards should be strictly followed.

References

GB/T 22460-2008, Determination of color of Luo Weipeng in animal and vegetable oils.

AOCS Official Method Cc 13b-45， Color of Fats and Oils (Lovibond Method)。

Comparative Study on the Methodology of Determination of Food Oil and Oil, China Oil, 2020.

Bailey's Industrial Oil and Fat Products, 6th ed., Wiley-Interscience.