Discussion on improvements to AOCS Cc 13j-97 color of fats and oils, automated method

Abstract: The current method of assessing the color of fats and oils requires turbidity-free samples. Turbidity is caused by particulate matter and moisture and appears cloudy, reducing lightness and chroma, thereby affecting color measurement values. Two optical cells of different path lengths are required due to the insensitivity of the current instrumentation.

We propose using a colorimetric spectrometer that assesses liquids’ optical properties. A spectrometer is an analytical, scientific instrument that measures the photometric optical properties in International Units.

We describe a new method of measuring and assessing turbidity derived from the US & European pharmacopeias. The Nephelometric Turbidity Unit, NTU, describes a specimen's ability to scatter light. Its units are grouped by turbidity level, from transparent (0 NTU) to opaque (10,000 NTU). The turbidity (figure 1) and color are simultaneously measured and reported, properly assessing the samples’ optical properties.

We describe a methodology and derive the mathematics providing equivalent colorimetric results (figure 2), allowing the user to measure in an optical cell of any pathlength from 10mm to 76mm, and report results in terms of AOCS-Tintometer Color, Lovibond Color, in any pathlength optical cell. This unique feature is innovative. Measured results correlate to NIST-calibrated artifact standards greater than 0.990. Predicted results in different path length optical cells less than 0.01 color units. Reproducibility on multiple HunterLab spectrometers less than 0.02 color units. We demonstrated that these values are industrially robust and statistically significant, giving the assessor confidence that reported values are true and accurate to a high degree of certainty.

Spectrometry advances the science and analysis of liquid fats and oils in any state, significantly increasing precision, accuracy, flexibility, and reliability.