Determination of Smoke Point of Edible Vegetable Oils and Fats
Overview
Edible vegetable oils and fats are esters formed by the reaction of higher fatty acids with glycerol, widely used in cooking, food processing, pharmaceuticals, chemical engineering and other fields. Their quality is directly related to food flavor, edible safety and processing applicability. As an important physical and chemical index of vegetable oils and fats, the smoke point refers to the temperature at which oils and fats start to emit a small amount of continuous blue smoke during heating. It is a key basis for evaluating the refining degree, oxidative rancidity and thermal stability of oils and fats.
Experimental Purpose
By detecting the smoke point value of edible vegetable oils and fats, the refining quality, freshness and applicable scope of thermal processing of oils and fats can be determined. A low smoke point indicates that the oils and fats contain a large amount of free fatty acids, colloids, impurities, etc., which tend to produce harmful substances when heated, affecting edible safety and food quality. This detection is carried out in accordance with the second method (visual determination) in the national standard GB/T 20795-2006 Determination of Smoke Point of Vegetable Oils and Fats. The ST123 Smoke Point Tester for Oils and Fats is a special testing instrument specially developed for this standard, which can accurately complete the determination of the smoke point of vegetable oils and fats.
Experimental Samples and Instruments
- Experimental samples: Edible vegetable oils and fats (soybean oil, rapeseed oil, peanut oil, etc.)
- Experimental instruments:
1. ST123 Smoke Point Tester for Oils and Fats
2. Auxiliary items such as cleaning reagents (e.g., anhydrous ethanol) and samplers
Operating Steps
1. Pour the vegetable oil/fat sample to be tested into the matching copper sample cup of the instrument, making the liquid level exactly at the scale line of the sample cup. Place the sample cup on the heating furnace of the instrument, adjust the position of the spotlight to make the spotlight beam pass through the center of the sample cup, ensuring a clear observation field of vision.
2. Hang the PT100 temperature sensor vertically at the center of the sample cup, with the sensor probe about 6 mm away from the bottom of the sample cup, and the small hole of the probe fully immersed in the oil sample. Connect the power cord of the instrument, and turn on the power switch and the spotlight switch.
3. Set the preset temperature value through the plus, minus and function keys of the instrument according to the estimated smoke point range of the oil to be tested. The instrument will automatically enter the temperature control mode when the temperature rises to 42 ℃ below the set value, and heat up uniformly at a rate of 5-6 ℃ per minute.
4. During the heating process, carefully observe the smoke emission of the oil sample in a windproof and dark environment. When the sample emits a small amount of continuous light blue smoke, quickly press the temperature lock button, and the instrument will lock the current temperature value immediately.
5. If the temperature is locked by mistake due to observation error, press the lock button again to unlock, and the instrument will continue heating until the clear smoke judgment point is observed, then press the lock button again to complete effective temperature locking. If no smoke is emitted when the temperature exceeds the preset value, keep the preset value unchanged and continue observation until smoke is emitted before locking.
6. To ensure the accuracy of test results, conduct duplicate tests on the same sample. After completion, turn off the power of the instrument, clean the sample cup and sensor probe with cleaning reagents, and set aside for later use after drying.
Data Analysis and Result Evaluation
Conduct duplicate smoke point tests on edible vegetable oil/fat samples with the ST123 Smoke Point Tester for Oils and Fats. The error between the two test results shall not exceed 2 ℃, and the average of the two results shall be taken as the final smoke point test result of the sample.
After testing, the smoke point values of qualified refined edible vegetable oils and fats meet the relevant national quality standards (e.g., smoke point of soybean oil ≥ 230 ℃, smoke point of peanut oil ≥ 225 ℃), indicating that the oils and fats meet the refining standard, have low impurity content and good thermal stability, and can meet the thermal use requirements of daily cooking and food processing. If the smoke point value is low, it indicates that the oils and fats have problems such as substandard refining or oxidative deterioration, and further testing is required to determine their application value.
