Difference Between Casein and Lactose

The key difference between casein and lactose is that casein is a family of phosphoproteins found in mammalian milk while lactose is a disaccharide (sugar) found in milk.

Lactose is a disaccharide made from two simple sugars: glucose and galactose. It is the main carbohydrate in dairy products. It is also found in breast milk. Casein is the most important protein component in milk. Casein is able to provide all essential amino acids. Therefore, both lactose and casein are components of milk that have a high nutritional value. Some people can be intolerant to both lactose and casein; they need to avoid consuming food containing these two components.

1. Overview and Key Difference
2. What is Casein
3. What is Lactose
4. Similarities Between Casein and Lactose
5. Side by Side Comparison – Casein vs Lactose in Tabular Form
6. Summary

What is Casein?

Casein is a milk protein found in dairy products. It is a white solid which is tasteless and odourless. It is a complete protein that can provide all the essential amino acids we need for growth and repair. The chemical formula of casein is C₈₁H₁₂₅N₂₂O₃₉P, and the molecular weight is 2062 g/mol.

Figure 01: Casein

Casein is a slow-digesting protein which shows a slow absorption rate on the gut. Moreover, casein is poorly soluble in water. Hence, it is relatively hydrophobic. Casein is useful for muscle growth since it provides a high amount of leucine, which initiates muscle protein synthesis. Some people may be intolerant to casein, showing symptoms such as gas, bloating and diarrhoea.

What is Lactose?

Lactose is a type of sugar found in the milk of mammals. In fact, it is a disaccharide composed of galactose and glucose subunits. The chemical formula of lactose is C₁₂H₂₂O₁₁. The molecular weight of lactose is 342.3 g/mol. Lactose is a white, water-soluble, non-hygroscopic solid with a mildly sweet taste.

Figure 02: Lactose

In humans, lactase is the enzyme that digests lactose during the digestion. Lactose intolerance is a digestive disorder that refers to the inability to digest lactose in dairy products. Bloating, diarrhoea, gas and abdominal cramps are the common symptoms of lactose intolerance.

What are the Similarities Between Casein and Lactose?

Both casein and lactose are two components found in mammalian milk.
Some people can be intolerant to both lactose and casein.
Therefore, both can result in symptoms such as gas, bloating and diarrhoea.

What is the Difference Between Casein and Lactose?

Casein is a milk protein, while lactose is a milk sugar (carbohydrate). Thus, this is the key difference between casein and lactose. Furthermore, casein is water-insoluble while lactose is water-soluble. So, this is also a significant difference between casein and lactose.

Moreover, casein is a slow-digesting protein while lactose is a fast-digesting sugar. Trypsin digests casein while lactase digests lactose. In addition to these, casein is tasteless while lactose has a mildly sweet taste.

The below infographic tabulates the differences between casein and lactose in more detail.

Summary – Casein vs Lactose

Casein and lactose are two ingredients of milk. Casein is a protein that is very rich in essential amino acids. Lactose, on the other hand, is a disaccharide composed of two sugar molecules. Trypsin is the enzyme that digests casein while lactase is the enzyme that digests lactose. Casein is water-insoluble while lactose is water-soluble. Casein has a high molecular weight compared to lactose. Moreover, casein contains phosphorus, unlike lactose. Thus, this summarizes the difference between casein and lactose.

Reference:

1. “Casein | Protein”. Encyclopedia Britannica, 2020, Available here.
2. “5 Signs And Symptoms Of Lactose Intolerance”. Healthline, 2020, Available here.

Image Courtesy:

1. “Micelle caseine” By Pancrat – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Beta-D-Lactose” By Yikrazuul – Own work (Public Domain) via Commons Wikimedia