Comparison of Waste Oil Detection Methods

(1) Sensory testing

Sensory evaluation is usually performed from five aspects: seeing, smelling, tasting, listening, and asking, that is, to see the transparency and color of the fat, whether it has an unpleasant smell, taste whether it has a peculiar smell, and listen to whether it is in the burning process.

(2) Routine testing

1.

The source of cooking oil includes kitchen waste oil, so it usually contains animal fat

2.

After the oil is oxidized, it will produce alcohol, aldehyde, ketone, acid and other substances.

3.

SDBS is a chemically synthesized surfactant, which is impossible to exist in natural oils, so it can be used as a specific detection component of waste oil

4.

Even if the waste oil is repeatedly processed, many trace volatile substances cannot be completely removed.

5.

When light enters another medium from one medium, and its propagation direction is not perpendicular to the interface of the two media, the phenomenon of light refraction occurs at the interface, and the refractive index is a measure of the phenomenon of light refraction

(3) New detection methods

1.

In the process of collection and processing, the waste oil will undergo oxidation, acidification and other reactions under the action of various factors to cause the deterioration of the oil, the ionic compounds produced by rancidity, low molecular weight acids, etc.

Many people in China have conducted research in this area

2.

The content of free fatty acids in edible oil is less, but as heating will cause the hydrolysis of triglycerides, the generated volatile products contain free fatty acids, the deeper the rancidity, the higher the free fatty acid content

3.
NMR identification method

Waste oil contains a lot of animal fats.
At a certain temperature, the solid fat content (SFC value) of waste fats is higher than qualified edible vegetable oil
.
Nuclear magnetic resonance (NMR) identification method is that when NMR is generated, liquid molecules move rapidly relative to each other, which will cause obvious movement to narrow the spectrum and increase the resonance peak; on the contrary, the resonance peak of solid molecules is low, and after a period of time , The test will get two sets of NMR signal values, from which the signal intensity value can be used to calculate the solid fat content
.
Wang Le et al.
measured the SFC values ​​of waste oil, swill oil, peanut oil, rapeseed oil, and soybean oil at 10°C and 0°C by pulsed NMR, and found that as the amount of waste oil and tear oil added increases, The SFC value increases, and the amount of adulteration reaches 1%, it can be detected
.
NMR is not affected by the technical level of the operator, the test accuracy is high, relatively fast, and can be used for the detection of waste oil, but the NMR instrument is more expensive and not easy to promote
.

4.
Near infrared spectroscopy

Waste oil is the reuse of waste oil, which contains more oxidation products, so the detection of peroxide value has been used as a means of judging the degree of oil rancidity
.
Near-infrared spectroscopy is a convenient analytical technique developed in recent years, which can perform quantitative and qualitative analysis quickly and efficiently
.
Zhang Juhua et al.
used partial least squares method to detect the relative content of saturated fatty acid , oleic acid, and linoleic acid in rapeseed oil.
The correlation coefficients (RP2) of the prediction sets of the above three components were 0.
996, 0.
999 and 0.
999 respectively
.
Rao et al.
established a near-infrared quantitative model for the acid value and peroxide value of peanut oil, and used an acid value greater than 3mg/kg as unqualified oil
.
The near-infrared spectroscopy detection process does not require sample pre-processing, and has the advantages of fast analysis speed and good reproducibility.
Based on the direct reading method of the total polar substance sensor, it can quickly detect the acid value, peroxide value, aflatoxin and other indicators of the cooking oil.

.
As a new detection technology, near-infrared spectroscopy has achieved certain development and will gradually be optimized to identify the degree of oxidation of oils
.

Related Links: Research Progress of Different Detection Techniques for Waste Oil