Determination of sulphite in foods and beverages Sulfur dioxide is used as a preservative in the food industry, particularly fruit juices, beer, red wine, preserved fruit, sausages, burgers and vegetables, due to serious health hazards. EC regulations stipulate concentrations of >10 mg/kg. Or 10mL/L must be marked. The total sulfur dioxide was detected by the Kjeldahl tester and distilled through an acidic (60% phosphoric acid) vapor, which was then received and oxidized by a hydrogen peroxide solution to form sulfuric acid, which was titrated with standard NaOH (detection limit 5 mL/L). Sample preparation requires shaking or ultrasonic shaking to remove carbon dioxide.
In the fermentation process of the feed industry, some volatile nitrogenous substances are produced due to protein decomposition, and the volatile nitrogen content in the base will increase. For example, the total volatile nitrogen content of soybean meal is 30-50 mg/100 g before fermentation, which increases after fermentation. Since animal protein, such as fishmeal, and particularly low-grade fishmeal, have relatively high volatile base nitrogen, fermented soybean meal products may contain high levels of volatile base nitrogen and may be incorporated into animal protein such as inferior fish meal or corrupted during fermentation. To. The Kjeldahl nitrogen analyzer uses magnesium oxide instead of sodium hydroxide, and the other steps are exactly the same as Kjeldahl.
Determination of Volatile Base Total Nitrogen An important indicator in fresh foods, especially meat foods, is the total nitrogen content of volatile salts. For meat foods, it will produce a certain amount of quality in the process of deterioration. Alkaline nitrogenous substances under the premise of decomposing protein, this will cause certain harm to the human body's health, so it is very useful and convenient to use the Kjeldahl apparatus for the quality inspection of such foods. The conversion of nitrogen into certain forms of ammonium salts by the instrument's distillation can be used to calculate the total nitrogen content of volatile bases in foods. In general, when it exceeds 30 mg/100 g, it is considered to be a deteriorated food.
What are the 3 main uses of Kjeldahl?
The main mechanism of Kjeldahl is to determine the content of protein through the determination of nitrogen content in the sample, which also shows that the instrument can be used for various types of samples, such as food, feed, dairy products and soil The nitrogen content and so on are more applicable. The most important part of Kjeldahl is the distillation. It can be known from the summary of the distillation apparatus's knowledge and application that the instrument is usually applied in the following three aspects.