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2025-02-25
The color of oils and fats is often an important basis for determining the grade, pricing and consumer selection. When we buy edible oils, we will use color to identify the quality of oils and fats. Therefore, color has become one of the important indicators of edible oil quality. So, how to measure the color of oils and fats? This article introduces the method of measuring the color of oils and fats.
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Color is one of the most important quality indicators of oils and fats. It is also the basis for determining the price of oils and fats and the appearance of oils when consumers choose them from the shelves. Therefore, it has become a routine item in oil quality inspection. Processing companies must also control the color of finished oils according to national standards to obtain the best decolorization conditions for oil processing technology and obtain the maximum profit.
The color of oil is a comprehensive reflection of various pigments in oil. It is mainly due to the transfer of oil-soluble pigments contained in oil seeds into oil during the oil production process. A small part comes from the substances generated by the decomposition products of reducing sugar substances in oil seeds combined with amino acids or proteins during the oil production process. In addition to the above pigments, there is also a substance called chromogen in the cells of oil seeds. It is colorless in itself, but can be oxidized by air and show color under the action of special reagents.
The main factors affecting the color of oils and fats are as follows: different types of oils and fats have different colors; the influence of raw material purity; the higher the impurity content in the oil, the darker the color; the influence of the powder size during rough rolling of the oil; if the powder size is too large during rough rolling, the powder will easily burn during steaming and frying, causing the oil color to darken; the influence of steaming and frying temperature; the oil color is light at low temperatures; the influence of oil temperature during dehydration; when the temperature is low, the dehydration effect is not good; when the temperature is high, it will affect the color; phospholipids will deepen the color of the oil; quality changes during oil storage also have a certain impact on the color.
Therefore, the determination of oil color is of great significance for improving oil processing technology and conditions, producing high-quality oil, and evaluating the quality of oil. In particular, edible oil or oil for certain industrial purposes generally requires a lighter color. Therefore, the depth of oil color is one of the important indicators of its quality.
Desktop Colorimeter
Common methods for determining the color of oils and fats include visual method, potassium dichromate method and Lovibond colorimeter method. The visual method relies on the direct observation of the color of oils and fats with the human eye; the potassium dichromate method compares the oil sample with the prepared potassium dichromate sulfuric acid standard solution, and the color value when the color is equal is the potassium dichromate color value; the Lovibond colorimeter method compares the color of the oil sample with the color of the standard color glass piece, and the depth of the color is indicated by the number marked on the required standard color glass piece. This method is currently the internationally accepted inspection method. These methods are greatly affected by the subjectivity of the operator and the surrounding environment. Therefore, an objective measuring instrument is needed to replace them to eliminate the errors caused by subjectivity. The use of a liquid colorimeter to measure the color of oils and fats can not only accurately measure the color of oils and fats, but also measure the changes in color during oil processing, so as to compare the differences and determine the advantages and disadvantages.
According to the theory of modern colorimetry, for any given object color, its characteristics can be described by various color systems. From the color matching test, we know that any color can be obtained by mixing and matching three single colors. Experiments have shown that using red, green and blue as single colors can most conveniently obtain different mixed colors. We call these red, green and blue used to produce mixed colors the three primary colors, and the three primary colors required to match a specific color: the three stimulus values, which are represented by X, Y and Z respectively. In actual expression, we often use the relative proportion of one of the three stimulus values in its total amount to express it. This relative proportion is the chromaticity coordinate, which is represented by x, y and z.
According to the research on the tolerance of color discrimination, it is found that using CIE1931x,y chromaticity diagram to express color differences is not ideal. Because the x,y coordinate system is not a perceptually uniform color space, the spatial distance on the diagram is not visually equidistant, that is, the equal distance on the x,y coordinates does not represent the visually equal color difference, so the visual effect of reflecting color is not ideal. In order to further evaluate color differences, CIE recommends two color spaces and their related color difference formulas. These two color spaces are called CIE1976LUV space and CIE1976Lab color space.
When measuring color, the colorimeter uses the internationally used Lab color space. In the Lab color space, L is lightness, a and b are chromaticity. The colorimeter simulates the process of human eyes seeing color. By analyzing the incident and reflected light, it converts abstract color information into easily distinguishable color parameters. According to the colorimetry theory, the three stimulus values XYZ are calculated and converted into the color-uniform CIE Lab color space. Users only need to analyze the Lab values to accurately evaluate the color of the oil used and the total color difference range, thereby effectively controlling the color quality of the oil used.
Compared with the Lovibond colorimeter, the use of a liquid colorimeter to measure the color of oils and fats has the following advantages:
1. The colorimeter is more comprehensive than the Lovibond colorimeter in expressing color. The colorimeter uses three values, L, a, and b, to express the color of an object. a and b represent the color of the object, and L represents the brightness of the object. The Lovibond colorimeter only uses two values, the total number of red and yellow glass pieces, to express the color of the oil.
2. The numbers of the colorimeter are more accurate than those of the Lovibond colorimeter. The numbers of the colorimeter are accurate to two decimal places, while the numbers of the Lovibond colorimeter are only accurate to one decimal place.
3. The testing speed of the colorimeter is faster than that of the Lovibond colorimeter. Due to the high degree of automation of the colorimeter, zero adjustment, standard white plate adjustment, data collection and processing are all performed by a microcomputer. The color of an object can be measured in a few seconds, saving time and workload.
