Identification of vegetable oils and fats (5)
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31, the identification of incorporation of croton oil 1 principle: croton oil is a highly toxic non-edible oil, the croton oil mixed with potassium hydroxide solution heating, in the two-liquid junction will produce a red-brown ring, according to this A special phenomenon can determine the presence of croton oil.
2 Operation method: Inject 1mL of oil sample into a small test tube and add 5mL of absolute ethanol. After mixing well, add this solution slowly to the tube wall containing 3mL of potassium hydroxide saturated solution. The tube was heated in a warm water bath for 30 minutes. A brown ring appeared at the interface of the two liquids, indicating the presence of croton oil. 3 Description: The color of the ring is from reddish brown to brownish black due to the incorporation of Croton oil: This method can detect 2.5% of Croton oil.
32. Identification of adulterated green oil or linseed oil
1 Principle: Green oil (pressed oil, cedar oil), linseed oil contains high-grade unsaturated fatty acids, which can precipitate with bromine to form insoluble hexabromo compounds, thus detecting green oil and linseed oil.
2 Operation method: Take 2mL oil sample in the test tube, add 5mL ether to dissolve, slowly inject the bromine test solution to the mixture to maintain a clear red color, shake it and put it in a water bath below 15°C for 15 minutes, if precipitation occurs, It means that there is green oil or linseed oil. The detection rate of this law is 2.5%.
33. Identification of varieties of vegetable oil
(1) Concentrated sulfuric acid reaction
The concentrated sulfuric acid was applied to the pit of the white porcelain reaction plate, and two drops of the oil sample to be inspected were added. After the reaction, the color of the surface was observed. The peanut oil was brownish red, the sesame oil was brownish black, and the sunflower oil was brownish red. Tea seed oil, soybean oil, rapeseed oil, and cottonseed oil are brown and palm oil is orange and yellow.
(2) Freezing test
The oil sample to be tested was poured into the test tube to two-thirds, placed in the refrigerator at 10°C for 4 hours, and then taken out. The peanut oil was solidified and flowed slightly. The brown oil was a milky yellow solid, and the other vegetable oils were clear liquids.
(3) Qualitative reactions
1 Refined cottonseed oil - Take 2 ml of the oil sample, and add 2 ml of the mixture of amyl alcohol and carbon disulfide with 1% sulfur. After heating in a boiling water bath for 20 minutes, red color appears.
2 Peanut oil - Take 1 ml of oil sample, place it in a 50 ml rubber stoppered test tube, add 1.5 mol/L potassium hydroxide and ethanol mixed solution 5 ml, and heat in a 90-95°C water bath for 5 minutes, then add 10 Ethanol (50 ml) and hydrochloric acid (0.5 ml) are shaken and all precipitates are dissolved (heated if necessary). The test tube is placed in 11-12°C water and cooled for 20 minutes. A large amount of precipitation or turbidity should occur.
3 Soybean Oil - Take 5 ml of the oil sample in a test tube, add 2 ml of chloroform and 3 ml of 2% potassium nitrate solution, vibrate vigorously, and turn into a lemon yellow milky liquid.
4 Sesame Oil - Take 2 drops of oil sample, add 3 ml of petroleum ether, add sucrose hydrochloride solution (1 g of sucrose dissolved in 100 ml of hydrochloric acid, and use as required) 3 ml, slowly shake for 15 minutes, add distilled water 2 In milliliters, it is red after shaking and standing.
34, the impact of humidity on oil and grease quality
The storage of vegetable oils and fats in a relatively humid environment will not only increase the water content but also change the internal quality of the oil. In particular, vegetable oils, which have been stored under high humidity conditions for a long period of time, can cause them to become moldy and even spoil. Therefore, vegetable oils and fats should be stored in a well-ventilated, dry place.
35. Effects of temperature and light factors on oil quality and oil quality
The fatty acids contained in vegetable oils and oils are easily oxidized and rancid. The increase in temperature and direct light can accelerate the oxidative deterioration of fatty acids, resulting in the appearance of oily rancidity. Therefore, in addition to the requirement of environmental drying, vegetable oils and greases should also pay attention to the adverse effects of temperature and light on their quality during storage.
36, the impact of vegetable oil raw materials on the quality of oil
The quality of the vegetable oil can directly affect the quality of the extracted vegetable oil. Such as moldy, sprouts, worms, frostbite, and heat wounds of vegetable oils, can make the oil color of the pressed vegetable oil deepen, and the appearance of bad smell and taste such as musty taste and bitterness. In addition, if various kinds of pesticides contaminate the vegetable oil, drying the vegetable oil on asphalt can cause the pollution of 3,4-benzopyrene in the bitumen to be transferred to oil during oil extraction. Peeling directly with shelled peanuts will give a peanut shell flavor to peanut oil.
37. The influence of processing factors on the quality of fats and oils
Poor mastery of processing can also affect the quality of vegetable oils. If organic oil is used to extract the vegetable oil, if it is not completely dissolved, a small amount of organic solvent will remain in the oil. If the refining process is poor, the grease will have a deep color, and the phospholipids, sterols, lipids, saponins, etc. cannot be effectively removed and the quality of the oil is not qualified. In the process of steaming and frying, such as frying the oil coke will make the oil with a burnt taste, sesame, peanuts, etc. If not steamed or not enough directly on the cold press made oil, although the color is light, but its fragrance is also relatively light. 38. Principles of sensory identification and consumption of vegetable oils and fats
Vegetable oils and fats are indispensable food materials and essential consumer goods in the daily life of our people. The main components of vegetable oils and fats are fatty acids, which are easily oxidized and deteriorated. Vegetable oils are mostly grains, and they are also easily contaminated by molds, resulting in poor quality changes. Therefore, in order to ensure food safety, after organoleptic identification of vegetable oils and oils, the grades can be consumed or treated as described below. (1) Vegetable oils and fats that have been identified as good by sensory identification can be consumed or sold, and vegetable oils can also be used to extract edible oils.
(2) Physicochemical tests must be performed on vegetable oils and fats that are organoleptically identified as secondary. For the qualified physical and chemical indicators, they can be sold or eaten. The oil can also be used to extract edible oil. However, it must be sold out or used up within a time limit, and it cannot be stored for a long time. Unqualified vegetable oils and fats after physical and chemical inspection shall not be used for food, and shall be changed to non-food industry materials (such as soaps, etc.). For the secondary plant oils, there are only impurities and poor grain problems, which can be selected, and the impurities and bad grains can be removed for sale or squeezed.
(3) For vegetable oils and fats that are poorly perceived by the senses, they must not be eaten by humans. They can be used as non-food industry raw materials or destroyed.
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