5 Ways to Make the Kjeldahl Method a More Approachable Topic for Students

Usama Attiq

Introduction: Kjeldahl Method

Proteins are macromolecules that consist of a long chain of amino acids. There are twenty types of amino acids naturally present in the protein. The proteins can be differentiated from each other according to the number of amino acids, the number of amino acids, and the sequence of amino acids. Protein plays an important functional role in our body. It is necessary for the growth of children and during pregnancy. The protein present in the food helps to repair the cells of the body.

Amino acids have two main types; essential amino acids and nonessential amino acids. The essential amino acids cannot be synthesized within the body and obtained from food. The nine essential amino acids are leucine, histidine, isoleucine, threonine, tryptophan, valine, methionine, lysine, and phenylalanine. The nonessential amino acids can be synthesized within our body, so you do not need to take them through a diet. The eleven nonessential amino acids are proline, arginine, tyrosine, cysteine, aspartic acid, alanine, asparagine, glycine, glutamine, serine, and tyrosine.

The Kjeldahl method is an analytic method used to quantify and estimate the protein content in food. The principle of the Kjeldahl method is that when a certain food is digested by using a strong acid, it releases nitrogen gas that can be determined with the help of titration. The Kjeldahl method is a standard method for the determination of protein content in food. Moreover, it is important to evaluate the protein quantification which can be helpful to understand the total protein content of the resulting product. 

There are several aspects of the Kjeldahl method that may be confusing for students as well as for teachers. At Labster, we will explain all the difficulties that students experience during learning the Kjeldahl method. Additionally, we provide information that can help teachers properly explain the topic. At the end of the topic, we will convince you why a virtual lab simulation is important for conveying the Kjeldahl method in class.

Explore Kjeldahl Method Estimate the protein content in food Virtual Lab Simulation

Figure: An image of titration process from the Labster virtual laboratory of the Kjeldahl Method

Why Kjeldahl Method can be tricky to learn

The Kjeldahl method is a complicated topic for some learners. There are top three reasons that make the Kjeldahl method difficult to learn.

1. Use of different acids

Since the Kjeldahl method consists of several steps. Different acids are used in each step. For instance, concentrated acid is used in the first step. Students need to learn the names of multiple acids used in the Kjeldahl method. It is hard for the learners to remember the several acids while reading this topic.

2. It’s complicated

The Kjeldahl method has several steps, chemical reactions, the formula for percentage protein, and the formula for percentage nitrogen. Each process is done in a different apparatus and different chemicals are used in each process. It is difficult for students to learn the complexities of the Kjeldahl method. 

3. You need to remember the chemical reactions

The Kjeldahl method is an analytic chemistry process that has several chemical reactions. In this process, you need to remember the different chemical reactions. Students find it difficult to understand and write the chemical reactions of the Kjeldahl method. It is the main reason that makes the Kjeldahl method a boring and time-consuming topic.

5 ways to make Kjeldahl Method a more approachable topic to understand

As we are familiar with the difficulties that students experience during learning. There are five ways that make the Kjeldahl method a simpler and easier topic to understand.

1. Talk about the people behind that science

Johan Kjeldahl (1849 – 1900)

Johan Kjeldahl was a chemist who introduced a method for the determination of nitrogen from the organic compounds in the laboratory. In the beginning, he developed a two-step method for the estimation of protein content. These steps are distillation and back titration. In the first step, he produced ammonium salts after the reaction of the organic compound with sulfuric acid. Then, Kjeldahl used caustic soda in the solution to indirectly measure the amount of nitrogen present in the sample. In 1883, he presented the Kjeldahl method at the Danish Chemical Society. The Kjeldahl method is a universally accepted technique for the estimation of protein and nitrogen content in compounds.

2. Explain the process of the Kjeldahl Method

Generally, the Kjeldahl method has three main steps. It is important to follow the proper sequence of this method. Traditionally, the apparatus of the Kjeldahl method consists of a manual laboratory heater or round bottle flask. But now several advanced instruments are available for this process. The large cast iron racks, block digestion units, and steam distillation units are available to estimate the protein content from the food sample by using the Kjeldahl method. The steps include:

  1. Digestion
  2. Distillation
  3. Titration

Digestion: In this step, the sample of organic food is heated at a high temperature in the presence of concentrated acid, usually sulfuric acid (H2SO4). The concentrated acid solution digests the sample and produces ammonium sulfate. Different catalysts including mercury, copper, and selenium are used to increase the process of digestion. Potassium sulfate is also added in the process to enhance the boiling point. In the digestion step, we obtain an utterly colorless solution.

Distillation: Distillation is the second step of the Kjeldahl method, which combines condensation and boiling. In distillation, a small amount of sodium peroxide is added to the solution. It helps to convert ammonium sulfate into ammonia gas. The distilled vapors formed in the solution are trapped by the solution of hydrochloric acid (HCl) and water.

Titration: Titration is the last step of the Kjeldahl method. It is a process that is used to measure the concentration of an unknown substance sample by using a solution with a known concentration. In the Kjeldahl method, titration is done to determine the nitrogen present in the sample.  

digestion process of the Kjeldahl method

Figure: An image of the digestion process of the Kjeldahl method from the Labster virtual laboratory on the Kjeldahl Method.

3. Relate to the real world

The Kjeldahl method is valid in various applications. It is an accurate and reliable method to determine the nitrogen component present in organic compounds. It is used for the analysis of multiple samples such as fish, milk, grain, meat, beverages, vegetables, fertilizers, rubber, plastic, and paper. The Kjeldahl method is effective for the evaluation of all the nitrogen components present in the organic substances. Additionally, the total nitrogen content, nitrite, nitrate, and ammonium can be determined from the sample by using the Kjeldahl method.

  • The nitrogen present in the organic compounds is called total Kjeldahl nitrogen. Total Kjeldahl Nitrogen is the sum of ammonium, ammonia, and organic nitrogen. This method is accurate to check the wastewater and soil water. Therefore, the Kjeldahl method is used for water treatment plants and monitoring several plant operations.
  • The Kjeldahl method is used to check the protein content present in several foods. For that, it is necessary to determine the fraction of protein made up of nitrogenous amino acids. For example, the value of nitrogen for eggs and meat is 6.38, rice has a 5.83 value, and sorghum has a 6.25 value.
  • The original process of the Kjeldahl method comprises two steps that are not reliable. It is important to combine different other methods such as titration, ion chromatography, and zone capillary electrophoresis with the Kjeldahl method to obtain the desired results.

4. Seeing is believing

Students can understand a topic like the Kjeldahl method when they see the apparatus or experiment in person. Kjeldahl’s flask, stone fume hoods, micro-Kjeldahl equipment, ceramic heating blocks, block digestor, and condenser are mainly used in the Kjeldahl method. Using color diagrams to show these apparatuses' structure can help students remember the procedure in their minds. When students see color images, it will be effective in understanding complex topics like the Kjeldahl method.

The color diagram, like the one used below, represents the test tube containing the sample. It shows the last step for the Kjeldahl method which is titration by using hydrochloric acid (HCl). 

Kjeldahl Method virtual lab check protein

Figure: An image of the Kjeldahl method to check the protein content of the sample from Labster virtual simulation on the Kjeldahl Method.

5. Use of virtual lab simulation

A virtual lab simulation is a better way to teach a tough topic, like the Kjeldahl method, to the students. At Labster, we provide you with an advanced lab simulation with gamification elements like storytelling and a scoring system to provide complete detail about the topic.

Labster simulation about the Kjeldahl method explains the Kjeldahl method's steps, evaluates the food sample's nitrogen content, calculates protein content from the nitrogen value, and applies the principles of spiking. Therefore, it helps to make the topic easier for students to understand and for teachers to convey it.

Check out the simulation for the Kjeldahl method here, or get in touch to find out how you can start using virtual labs with your students. 

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