Commonly used oil color determination methods include visual method, Lovibond visual Colorimeter method, potassium dichromate method, etc. The Lovibond visual Colorimeter method is to compare the color of the standard color glass sheet with the grease. This method is currently an internationally accepted inspection method. There are the following problems in the determination of the color and luster of oil by the Lovibond visual Colorimeter method :
①Oil samples need to be clear and transparent, and turbid samples are difficult to measure.
② The "background color" of the same type of oil itself is inconsistent, and the reference value of yellow is fixed when measuring. For example: foreign literature reports that the yellow color of rapeseed oil is not fixed at the same value, and the yellow color has different values such as 30, 31, 32, 35, 39, etc., which is caused by the inconsistent background color of the oil itself.
③ If the yellow value is not fixed, then the color of the oil will have two variables (such as three variables when adding a blue film), which is not convenient for comparison, so the yellow film has to be fixed. However, according to the principle of the Lovibond Colorimeter method, when the yellow color changes, the red color will also change, so the current Lovibond Colorimeter method is a relative value measured under a fixed yellow condition.
④ For the same sample, different operators will get inconsistent measurement results due to differences in visual judgment, that is, personal bias.
⑤ For oil products of the same variety and different grades, colorimetric cells of different sizes are used for measurement, which is troublesome to operate.
⑥The Lovibond Colorimeter method can only be operated intermittently, and cannot be continuous and automated.
⑦ The color of the standard glass color chip will gradually become "out of alignment" with the prolongation of use time, and the bulb and reflector need to be replaced regularly, otherwise the accuracy of the measurement result will be affected [1]. Therefore, it is necessary to have an objective measuring instrument to replace the Lovibond visual Colorimeter method.
PFX995 Lovibond Automatic Colorimeter is a spectrophotometric Colorimeter, its principle is that 16 interference filters separate the light with a wavelength in the range of 420-710nm, and the measurement system reads by comparing with the built-in data. This instrument is used for color analysis and provides objective color data according to almost all established industrial color scales. In this paper, by comparing the PFX995 Lovibond automatic Colorimeter and the F-type Lovibond visual Colorimeter in the determination of oil color, the possibility of the application of the Lovibond automatic Colorimeter in the determination of oil is analyzed.
1 Materials and methods
1.1 Experimental materials
Bohai oil first grade soybean oil Ⅰ; Bohai oil first grade soybean oil II; Jilin Deda third grade soybean oil; Huanglong food Fuzhong whole corn oil; Laiyang Luhua peanut oil;
1.2 Experimental Instruments
PFX995 Lovibond Automatic Colorimeter, F-Type Lovibond Visual Colorimeter, Tintometer Company, UK.
1.3测定方法
1.3.1PFX995型罗维朋自动比色计法制备的样品应透明、不浑浊、无气泡。比色池的端窗应清洁。测量基线校正之后,放入样品至样品室的右手边,关闭样品室盖,进行测定,结果自动显示在屏幕上。
1.3.2F型罗维朋目视比色计法通过调节红、黄、蓝及灰色标准色阶玻璃片与油样的颜色进行比较,当二者颜色相当时,分别读取各色片上的数字作为色泽测定结果。
1.4实验方法
1.4.1相同比色槽的色泽比较相同比色槽下,同时用PFX995型罗维朋自动比色计与F型罗维朋目视比色计测定不同品种油脂的色泽,比较二者之间的差异。
1.4.2不同比色槽的色泽比较分别选用25.4(1英寸)、50.8(2英寸)、76.2(3英寸)、101.6(4英寸)、133.4mm(5.25英寸)比色槽,同时用PFX995型罗维朋自动比色计与F型罗维朋目视比色计测定油脂的色泽,比较二者之间的差异。
2结果与讨论
2.1相同比色槽的色泽测定结果相同比色槽下,PFX995型罗维朋自动比色计与F型罗维朋目视比色计的测定结果见表1、表2。
从表1、表2可以看出,在浅色油色泽测定中,PFX995型罗维朋自动比色计可以取得与F型罗维朋目视比色计相同的结果;在深色油测定中,二者之间有微小差别。
2.2 不同比色槽的色泽测定结果用PFX995型罗维朋自动比色计与F型罗维朋目视比色计测定油脂的色泽,不同长度比色槽的测定结果见表3、表4、表5、表6。
从表3、表4、表5、表6可以看出,在浅色油的测定中,不论比色槽长短,PFX995型罗维朋自动比色计与F型罗维朋目视比色计的测定结果基本一致。在深色油的测定中,随着比色槽长度的增加,二者之间有一定的差异,但这种差异并不是很大。
3 结 论
In the determination of oil color, there is a small difference in the measurement results of the PFX995 Lovibond automatic Colorimeter and the F-type Lovibond visual Colorimeter, and they have a good correlation. Using the Lovibond automatic Colorimeter to measure the color of oil can obtain results similar to those of the Lovibond visual Colorimeter, and the measurement reproducibility is good, no manual reading is required, and sensory and human errors are eliminated. It is objective and fair, and can be popularized use.
