Feed oil is a high energy feed. Due to the high price, the market for feed oil adulteration is serious. The adulterants detected were mainly water, and flour and salt were also detected in the animal oil with higher melting point. The following is a brief introduction to the general sensory method to determine whether the oil is adulterated, and then introduce the fats and oils commonly used in the feed.
(1) Oil and fat testing project
1, total fatty acids
This includes the total amount of free fatty acids and fatty acids bound to glycerol. The amount of animal or vegetable oil is usually 92% to 94%. Most of the fat energy is supplied by fatty acids, so the total fatty acid amount is an indicator of the energy value.
2, free fatty acids
Free fatty acids are produced after decomposition of fat, so the amount can be used as the basis for judging the freshness. The fat used in complete feed is generally about 15% to 35%. In terms of nutrition, free fatty acids are harmless to animals, but too high free fatty acids (more than 50%) indicate that the fat and oil raw materials are not good, are corrosive to metal machinery and equipment, and reduce the palatability.
3, moisture
The oil contains moisture, which not only causes corrosion of processing equipment, but also causes the oil to hydrolyze to produce free fatty acids, accelerate the rancidity of fat, and reduce the energy content of fat.
4, insoluble matter or impurities
It includes substances such as cellulosic, wool, skin/bone, metal, and sand that cannot be dissolved in petroleum ether. These materials have no energy value and can block screens and nozzles or cause deposits in storage chairs. The amount should be limited to 0.5 or less.
5, unsaponifiable
Including white enzymes, hydrocarbons, pigments, fatty alcohols, vitamins and other substances that do not react with alkali, most of the ingredients still have feeding value, no adverse effects on animals, but wax, tar, etc. have no nutritional value. Even some ingredients are harmful to animals, such as edema factors.
6, acid price
Although the acid value is easy to measure, it is usually not possible to evaluate the quality of the oil simply. It must be combined with other methods for signing. The increase in the acid value of fats and oils is partly due to the hydrolysis of oils and fats to form free fatty acids. In part, the free fatty acids are produced by the reoxidation of hydroxyl compounds produced by the decomposition of peroxides. Therefore, the free fatty acid production mechanism varies with conditions and is not easy to be used as the degree of oxidation of oils. Judging indicators.
7, peroxidation price
The carbonyl oxide is formed during the oxidation of the oil, and the peroxide price can be judged by the degree of oxidation. However, peroxides are easily decomposed in the presence of water or under high humidity, so that when the oil is oxidized to a certain extent, the peroxide price will decrease. Therefore, we should understand that the peroxide price == the difference between the amount of peroxide and the amount of decomposition, so it is necessary to cooperate with other oxidation determination methods to judge the quality.
8, carbonyl compounds
Determination of the content of carbonyl compounds produced by rancidity in oils and fats is also a method for determining the degree of oxidation of fats and oils.
9, TBA test (thio barbituric acid test), the general requirement is not more than 2.
Usually, TBA reacts with the above-mentioned oil oxidizing product to form a red color, and absorbance is measured at 530 mm to determine the degree of rancidity. The TBA test can measure the content of malonaldehede. Malondialdehyde is the second stage product in the oxidation process of fats and oils. Therefore, the initial oxidation change cannot be detected in this test. In addition, the malondialdehyde itself is unstable and can be reoxidized. Malonic acid causes misjudgment of oxidation.
10, Kreis test
This is a simple color reaction of aldehydes and ketones, which can be used as a qualitative reaction for oxidative deterioration of oils.
11, AOM (Active Oxygenmethod)
The grease is maintained at a certain high temperature and passed through a metered amount of air to promote oxidation. The stability of fats and oils is expressed by the time required for the peroxide price to reach a certain value. Different types of oils have different peroxide standards. Usually, the peroxide standard for vegetable oils is 100meg/kg; for animal oils, 20meg. /kg (such as lard), and no more than 20 hours for feed grade grease specifications. Since the AOM measurement system uses photoelectric colorimetry, the effectiveness of some dark-colored feed-grade oils is still open, but it is still the best method.
12, safety and other
Pesticides, polychlorinated biphenyls, pesticides, chlordoxime and other toxic substances may be transferred to oils and fats. To prevent possible poisoning, Liberman Buchard reaction and Hdphen reaction and other test tests should be carried out. Out.
(B) the identification of oil and fat
1, different oils and physical properties are also different
Therefore, whether the oil is pure or not can be identified by viscosity, refractive index, color, iodine value, saponification value, solubility, specific gravity, melting point, boiling point and the like.
2, the identification of animal and vegetable oils and fats
The identification of animal and vegetable oils is based on the characteristics of the ingredients, such as animal oil containing cholesterol (Cholesterlo) and vegetable oil is phytosterol. The unsaponifiable matter of animal fats and oils contains cholesterol, while the unsaponifiable matter of vegetable oils and fats contains phytosterols. The distinction between animal and vegetable oils can be determined by its character.
3, fish oil identification
Fish oil contains highly unsaturated fatty acids. The ether-insoluble oxides produced by oxidation reaction are usually insoluble in hot benzene, and the ether-insoluble polyhexaoxide formed by linolenic acid is soluble in hot benzene.
4, the identification of hardened oil
Hardened oil usually contains trace catalyst (such as nickel and hydrogenated to produce isole-Oleic acid. It can be judged by the presence or absence of these substances.
5, the identification of lard containing lard
The Boemer value of lard and butter is different and can be discerned by the measured value. Usually, the value of pure lard is 73.4-78.1 °C; the butter is 62.8-67.1 °C, and the lard + 10% butter is 67.7-75.4 °C. Lard plus 20% butter is 65.3-73.9 °C.
6, mineral oil identification
Generally, the mineral oil has a specific gravity of 0.84-0.93, an iodine value of 6-12, and a refractive index of 1.490-1.507. It is insoluble in alcohol, and can be used as a basis for identifying the proportion of unsaponifiable matter in the oil, the iodine value, and the solubility of the alcohol.
7, the identification of paraffin hydrocarbons
This product is extracted from petroleum as a waste hydrocarbon, weighed 1.43 grams of sample, placed in a test tube (with 0.1 mm scale, length 15 cm, inner diameter 10 mm), adding glycerol dichlorohydroxide 7 mm and water 1.2 mm at 65 ° C After heating and shaking, it was allowed to stand for 10 minutes (65 ° C), and then the volume of the insoluble portion was measured to determine the presence of paraffinic hydroxyl, and its capacity of 0.1 mm was approximately equal to 5% paraffin hydroxy.
(III) Inspection of the acid value of oil and fat
Determination principle: The oil sample is dissolved by a neutral ethanol and acetic acid mixed solvent, and then the free fatty acid is titrated with the alkali standard solution, and the acid value of the oil is calculated according to the quality of the oil sample and the amount of the alkali liquor consumed.
The instruments used are: burette: 25 ml; triangular flask: 250 ml; balance: 0.001 g; volumetric flask, pipette, weighing bottle, reagent bottle, etc.
The reagents used were: 0.1 mol/L potassium hydroxide (or sodium hydroxide) standard solution; neutral ether: ethanol (2:1) mixed solvent: neutral to 0.1 mol/L alkali droplets before use.
Specific operation steps: Weigh 3-5 grams of mixed sample, inject into a conical flask, add 50 ml of mixed solvent, shake to dissolve the sample, add three drops of phenolphthalein indicator, and set with 0.1 mol / liter of alkali droplets. The reddish color did not disappear in 30 seconds, and the number of milliliters of alkali consumed was recorded.
The calculated acid value (mg KOH / gram of oil) = V × C × 56.1 / m.
Where: V - volume of potassium hydroxide solution consumed by titration, ml; C - concentration of potassium hydroxide solution, mole / liter; m - mass of sample, gram; 56.1 - 1 mole per liter of alkali solution equivalent to hydr The mass of potassium is 56.1 mg.
The double test results allow the difference to be no more than 0.2 g KOH / liter of oil, and the average is the measurement result. A significant number is retained after the decimal point of the measurement.
(4) General sensory detection method for oils and fats
1, odor check
Pay attention to whether it is rancid, that is, whether there is halal smell: 1 The mouth of the container containing grease is used to close the mouth of the container with the nose and smell it; 2 Take 1-2 drops of oil on the palm or back of the hand, fasten the hands and rub it to heat. Smell the smell; 3 use steel spoon to take about 25 grams of oil sample, heated to 50 ° C up and down to smell its smell.
2, taste inspection
Each grease has its own unique taste. Through the identification of taste, you can know the type of oil, the quality of the oil, the degree of rancidity, whether it can be used. Try the oil with your mouth. The abnormally deteriorated oil will have the taste of acid, bitterness, spicy and bitterness. The good quality oil will have no odor. The method is to take a little oil sample with a glass rod and apply it on the tongue that has been licked to distinguish its taste.
3, color inspection
Each grease has its inherent color. Based on this, it is possible to identify whether the grease has the normal color of the grease. In terms of grease composition, the pure grease is colorless, transparent, and slightly viscous at room temperature. However, because the oil itself has various pigments, during the processing, these pigments are dissolved in the oil, so that the oil has a color, the national standard stipulates that the lighter the color, the better the quality.
The method for identifying the color is as follows: Generally, a clarified residue-free oil is extracted from a glass oil pipe having a diameter of 1 to 1.5 m. The oil column is about 25-30 cm long (can also be transferred into a test tube or a colorimetric tube) and reflected in front of a white background. Observe under light. In winter, the temperature is low, the oil is easy to solidify, and about 250 grams of oil can be taken. It is heated to 35-40 ° C to make it liquid, and cooled to about 20 ° C, and identified according to the above method.
4, transparency
The normal quality oil should be completely transparent. If the oil contains alkali grease, lipid, wax and water content, it will appear turbid, which will reduce the transparency. Generally, the oil will be sucked out by the oil pipe. Judging transparency, clear and transparent. It is slightly turbid, turbid, extremely turbid, with or without suspended matter, and how much suspended matter.
5, sediment
The mechanical impurities (mud sand, powder, fiber, etc.) and the non-greasy substances such as alkali grease, protein, fatty acid mucilage, resin, sterol, etc., which are mixed in the process of oil and fat, sink into the lower layer of the oil under certain conditions, called Precipitate. For high-quality grease, there is no sediment. Generally, the glass oil pipe is inserted into the bottom to suck out the oil, and it can be seen whether there is any precipitation or sediment.
6, sensory identification of plant oils moisture and impurities
Grease is a hydrophobic substance. It is generally not easy to mix with water. However, oils and fats often contain a small amount of alkali, sterol and other impurities to absorb water, and can form colloidal substances suspended in oil, so there is still a small amount in oil. Moisture, this part of the water is usually mixed in the process of oil production. At the same time, some impurities are mixed. When the moisture and impurities in the oil are too much, not only the quality is lowered, but also the hydrolysis and rancidity of the oil are accelerated, which affects the stability of oil storage. Plant oils and fats and impurities and identification are based on the degree of transparency and turbidity of oils and fats, the amount of suspended solids and sediments, and various phenomena that occur after changing conditions, and are analyzed and judged by human sensory organs. The identification method is as follows:
(1) Sampling determination method. Take a dry and clean oil pipe, press the glass tube with your thumb, insert it into the oil container to the bottom, then release the thumb, shake it slightly, then hold the tube with your thumb. , extract and observe the oil column. At normal temperature, the grease is clear and transparent, and the moisture impurity content is below 0.3%; if turbidity occurs, the moisture impurity content is above 0.4%; if the oil shows obvious turbidity and suspended matter, the moisture impurity content is above 0.5%. Put the oil from the oil pipe back to the original container and observe that the oil pipe is unclear, the oil moisture is between 0.3% and 0.4%.
(2) Burning paper test method. Take a dry, clean oil pipe, press the upper end of the oil pipe with the index finger, insert it into the static oil container, until the bottom, release the upper mouth, take a little sediment at the bottom, ignite it on the flammable paper, and listen to it. The sound of the sound is observed. When burning, bubbles appear on the paper surface, and the sound is "å±å±", the moisture is between 0.2% and 0.25%; if the oil star is splashed when burning, the sound of "beep" is emitted, and the moisture is about 0.4% or more; if the paper burns normally, the moisture is about 0.2%. This method is mainly used to check the clear water (if the container mouth of the oil is not tightly sealed, leaking into the rain or the container is originally caused by water).
(3) Reinforced spoon heating method. Use a common steel spoon, take a representative oil sample of about 250 grams, heat it to 150-160 ° C on a fire or alcohol lamp, watch its foam, listen to its sound and observe its precipitation (mold, frostbite The oil is the exception of the oil. If there is a lot of foam, it will make a "beep" sound, indicating that the water is larger, about 0.5% or more. If there is foam, it is stable and does not emit any sound, indicating that the water is less. , generally around 0.25%. After heating, remove the oil foam and observe the color of the oil. If the oil color does not change, there is no precipitation, indicating that the impurities are generally around 0.2%; if the oil color becomes darker, the impurities are about 0.49; if there is a precipitate at the bottom of the spoon, More impurities, about 1% or more. In this way, the heating temperature should not exceed 160 °C.
7, the identification of salt into the
Method 1: Take a little oil sample from the bottom of the oil drum and taste it with your mouth. If it is salty, it means that the oil is mixed with salt.
Method 2: Take a little oil sample from the bottom of the oil drum into a clean test tube (washed with distilled water), add 5 ml of distilled water, heat to boiling, continue heating for 1-2 minutes, cool slightly, filter hot, or let stand After cooling, the layered liquid was taken up by a pipette, and 1-2 drops of a 1.7% silver nitrate solution (weighed 1.7 silver nitrate in 100 ml of distilled water) was added to the filtrate (or the lower layer of liquid). If a white precipitate is produced, it can be confirmed that the test oil is mixed with salt.
8, the identification of the incorporation of flour
Take a small amount of oil from the bottom of the oil drum and put it into a clean test tube (washed with distilled water). Add 2 drops of iodine solution after heating and melting. If it turns blue, it means that the oil sample contains starch.
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