The abstract: With the continuous improvement of people's living standards, the requirements for the quality of edible oil have also been greatly improved. The appearance, transparency, and color of oil products are the most intuitive basis for consumers to judge the quality of oil products. Due to the influence of climate and other factors, the chlorophyll content of the raw material oil obtained from different raw materials of soybeans is different. Since the quality of the raw oil is a key factor affecting the quality of the refined oil, how much chlorophyll content in the refined oil affects the appearance and quality of the oil. Therefore, this article analyzes and judges the chlorophyll content in the refined oil, its appearance, color, and oil stability (color reversion experiment).
Key words: freezing test, color, oil stability (color reversion test), chlorophyll
Freezing experiment: Keep the oil sample under constant temperature of 0℃ for a certain period of time to observe its clarity. The freezing test is used to test whether the first-class oil crystallizes out in winter (below 0°C) and the cold resistance of the oil sample。
The color of oil: The color carried by the oil itself, mainly from the oil - soluble pigments in the oil. The color of oil is an important physical index of oil color. The color of oil is different with different varieties and different processing grades.
Oil stability (color reversion test): by measuring the degree of color change of oil in 6 hours at 105°C.
Chlorophyll Definition: Chlorophyll is a green pigment found in higher plants and all other photosynthetic organisms. The various colors of edible vegetable oils are mainly due to the pigment dissolved in the oil. The main fat soluble pigments are chlorophyll, lutein, carotene and so on.
Generally, the chlorophyll content in oil is very small, but a large number of data prove that due to the influence of climate and environmental factors, the soybean is often mixed with immature green soybean, and the extracted oil has a little more green color. The first grade soybean oil produced by refining soybean crude oil with higher chlorophyll content will appear green in color and its chlorophyll content is relatively high. What effect will chlorophyll have on the quality of first-grade soybean oil during storage? This article mainly monitored the quality of first-grade soybean oil with different chlorophyll content, and collected data to determine the effect of chlorophyll on oil quality
一. The purpose of the experiment
By monitoring the quality of first-class soybean oil with different chlorophyll content and collecting data, the effect of chlorophyll on oil quality was determined.
Refining workshop produces first-class soybean oil
三．Inspection basis and experimental method
1. Frozen experiment: GB/T 35877-2018 "Frozen test of grain and oil inspection of animal and plant fats"
（1）Experimental principle
Under the specified temperature and time, the anti-crystallization ability of the sample was determined, and the patency was used as an evaluation index for the process of oil wintering and stearin removal.
（2） Instruments and utensils
1) Oil sample bottle: 50ml colorimetric tube, which should be clean, dry and dust-free, with a sealed cap.
2) Circulating bath: equipment model DC-300F.
3) Neutral filter paper: 125mm.
1) When the evenly mixed oil sample (200 mL～300 mL) is heated to 130°C, filter it with filter paper while it is hot.
2) Pour the filtered oil sample into the colorimetric bottle, cover and seal the bottle, and then cool to room temperature.
3) Immerse the oil sample bottle in a circulating bath at 0°C. The liquid level of the ice-water bath should exceed the oil sample liquid level and start timing.
The test results are expressed in terms of "clear and transparent", "minor precipitates", "slightly turbid" or "turbid", and record the experimental time.
2. Chlorophyll: SN/T 0801.21-2001 "Method for Chlorophyll Inspection of Import and Export Animal and Plant Fats"
The chlorophyll determined by this method: is the total content of chlorophyll and pheophytin in the rapeseed oil, measured by spectrophotometry, and calculated with chlorophyll a.
（2）Instruments and reagents
1) carbon tetrachloride: chromatographic pure.
2) UV spectrophotometer: equipment model
3) neutral filter paper: 125mm.
（1）Filter the oil sample with neutral filter paper in a beaker.
Turn on the switch of the instrument, select the wavelength range from 620nm to 720nm, adjust the oil temperature to 25 ℃± 2 ℃, pour the oil sample into the colorimetric tank carefully with proper optical path, pay attention not to make the oil sample produce bubbles, take carbon tetrachloride as reference, and conduct absorbance scanning in the range of 620nm to 720nm, so that the absorbance of the peak falls between 0.3 and 0.8, Record the absorbance of peak and valley.
Note: if the peak value of the oil sample still exceeds 0.8 when the colorimetric cell with the shortest optical path is used, the oil sample can be diluted with carbon tetrachloride. The oil sample should be clarified or filtered.
In the formula: X——the content of chlorophyll in the sample, mg/kg;
Amax——the absorbance of the peak;
A630——Absorbance of peak and valley near 630nm;
A710——Absorbance of peak and valley near 710nm;
L——length of colorimetric cell, cm;
δ——constant, which is 0.1 when calculated with chlorophyll a.
Note: If the oil sample is diluted with carbon tetrachloride, the calculation result should be multiplied by the corresponding dilution factor.
The calculation result is kept to one decimal place.
3. Color: GB/T 22460 "Determination of the color of Luo Weipeng for animal and vegetable oils"
（1）Experimental principle
Under the same light source, the light and color of the liquid grease product passing through the known optical path are matched with the color of the light passing through the standard glass color chip, and the Lovibond color value is used to represent the measurement result.
（2） Instruments and utensils
1) Lovibond colorimeter: equipment model UV-3000
2) Glass cuvette: 133.4mm (5.24 inches)
1) Take the clarified (or filtered) sample and pour it into the colorimetric cell and put it into the instrument.
2) Turn on the light source and move the red piece to adjust the color until the glass piece color is exactly the same as the oil sample color.
Note down the yellow, red or yellow, red, blue glass number of the respective sum that is to measure the color and lustre of oil sample.
4. Oil stability (color reversion test): 105℃ electric oven method
（1） The purpose of the experiment
By measuring the degree of color change of oil within 6 hours at 105°C.
（2） Instruments and utensils
1) Blast drying oven: equipment model DGX-9243B-I
3) Lovibond colorimeter: equipment model UV-3000
4) Glass cuvette: 133.4mm (5.24 inches)
1) Weigh 400g of oil and put it in a beaker, and place it in a blast drying oven at 105°C-110°C for 6 hours.
2) Cool the oil to room temperature and check the color.
3) Compare the red change value of the oil color before and after the test, and record the data.
Table 1. Summary of experimental data
1. The effect of chlorophyll content in oil on color
Table 2. Summary of chlorophyll and color data of first-grade soybean oil
Figure 1 is a graph of the chlorophyll content of a sample, and Figure 2 is a graph of the color of the same sample. By comparing the two figures, it can be seen that the chlorophyll content has no correlation with the shade of the finished oil. For example: two samples with a chlorophyll content of 0.23mg/kg and a chlorophyll content of 0.06mg/kg in the sample, their color is both yellow 10 red 0.9; the sample with the highest chlorophyll content is 0.48mg/kg and the sample with the lowest chlorophyll content The red value of the two samples at 0.06mg/kg differs by 0.1, which is within the effective error range. Therefore, the chlorophyll content has no effect on the color quality of the finished oil.
2. The influence of chlorophyll content in oil on freezing experiment
Table 3. Summary of first-grade soybean oil chlorophyll and freezing experiment data
Figure 3 is a graph of the chlorophyll content of the sample, and Figure 4 is a graph of the freezing experiment of the same sample. By comparing the two graphs, it can be seen that the chlorophyll content has no correlation with the length of the product oil freezing time. For example, the chlorophyll content of the B3001-2020.5.29 sample and the B3004:5012=1:1-2020.5.29 sample are the same, but the freezing time is 7 hours and 14.5 hours, and the value is doubled. The freezing time of the B3004: A5012=1:1-2020.6.1 sample and the B3001-2020.5.29 sample is 10 hours, but the chlorophyll content is 0.275mg/kg and 0.13mg/kg respectively, the value is doubled. Therefore, the chlorophyll content has no effect on the freezing time of the refined oil.
3. The influence of chlorophyll content in oil on oil stability (color reversion experiment)
Table 4. Summary of experimental data of chlorophyll and color reversion of first-grade soybean oil
Figure 5 is a graph of the chlorophyll content of a sample, and Figure 6 is a graph of the increase in the red value of the same sample in the color reversion experiment. By comparing the two figures, it can be seen that the chlorophyll content has no correlation with the color recovery of the finished product. For example, compare the A5012-2020.6.1 sample, A5012-2020.6.1 sample, and B3002-2020.6.2 sample. The chlorophyll content of the A5012-2020.6.1 sample is 0.06mg/kg, and the chlorophyll content of the B3002-2020.6.2 sample is 0.137mg/kg, the difference is 1.28 times. The red value of sample A5012-2020.6.1 increased by 0.4, and the red value of sample B3002-2020.6.2 increased by 0.5, and the value was within the effective error range. The chlorophyll content of the B3004-2020.6.1 sample is 0.48mg/kg, which is the highest value of chlorophyll in all samples, but the red value of the recolor experiment increases by 0.3, which is the smallest increase in the red value of the recolor experiment of all samples. The increase in red value of the three samples in the color reversion experiment is similar, but the chlorophyll content data are quite different. Therefore, the chlorophyll content has no effect on the color recovery test of the refined oil.
4. The effect of chlorophyll content in oil on the appearance of oil
Table 5. Summary of comparison data of chlorophyll content and color plus blue
From the analysis of the existing data in Table 5 and Figure 7, it can be seen that when the chlorophyll content is less than or equal to 0.195mg/kg, the color plus blue is 0; when the chlorophyll content is between 0.210mg/kg-0.315mg/kg, the color plus Blue is 0.1; when the chlorophyll content is greater than or equal to 0.45mg/kg, the color plus blue is 0.2. The change of oil color blue value increases with the increase of chlorophyll content, which is in direct proportion. The higher the blue value of the color, the more obvious the greenish appearance of the oil.
五. Experimental conclusion
1. The chlorophyll content does not affect the color of the finished oil.
2. The chlorophyll content has no effect on the freezing time of the refined oil.
3. The content of chlorophyll does not affect the stability of refined oil products (color reversion test).
4. The change of oil color blue value increases with the increase of chlorophyll content, which is in direct proportion. When it is difficult to visually judge whether the color and appearance of the oil are green, this conclusion can be used as a basis for judgment and play a guiding role.
