Bubbles in Saliva

In the potato staining experiments, Aditi (DC-Micronaut) wondered what would happen if we spit on the potato, would we see the amyloplasts being digested? More on those experiments in a different post.  What caught our attention were the salivary bubbles. You could see bubbles through bubbles and it made for a dainty sight. Coming to think of it, why should Saliva bubble?

Saliva is mainly composed of water (99.5%), the remaining 0.5% is made up of glycoproteins (proteins linked to sugars), digestive enzymes like amylases and  lipases, protective proteins such as lysozyme,peroxidin, lactoferrin and immunoglobulins that kill bacteria, carbonic anyhydrase that has a role in taste physiology and various ions that maintain a pH balance between 6.2 and 7.4. The term “licking your wound”s is based on the observation that animals (humans included) are often seen licking their wounds and experiments have shown the saliva of various animals to possess antibacterial molecules that disinfect wounds. Saliva is extensively used across vertebrates for distinct purposes and it is fascinating to read.

One thing that proteins in solution do is to froth, e.g. Milk Froth. So the bubbling is likely to be due to the proteins in saliva. But does the type of protein in solution influence the type of the bubble? Could we detect secretory differences between humans by just studying the stability of salivary bubbles?  Are the salivary enzymes better off on a bubble surface as compared to being suspended in a more watery interface? Never thought about bubbles as much until we saw this. Perhaps the experts on our forum have interesting answers.

-Aditi and Laks

4 Comments Add yours

  1. Saad Bhamla says:

    @Aditi and @laks,

    Fantastic observation on the bubbles in saliva. What you are asking are very insightful questions and there are subtle points in here that soft matter scientists are still figuring out.

    Just to give you an example that pharmaceutical industry faces is the adsorption of proteins (think anti-bodies) at air-water interfaces (in bubbles) which causes the drug to denature and ultimately lose efficacy. Imaging a vial containing a drug with a little air-head at the top – and if bubbles form during transportation (jiggling and movement), then the patient receives a drug that is ineffective.

    Proteins and lipids tend to stabilize air-water interfaces and hence create stable bubbles – this has both positive and negative consequences. To give you a positive one to counteract the negative example above, imagine lipids/proteins in your alveoli or your tear film – every time you breathe or blink, you are create stable thin film layers at the air-water interface to protect your cornea or allow exchange of gas. Problems in the chemical composition of either proteins or lipids can lead to dry eyes or respiratory syndrome.

    Coming back to saliva – the proteins also do a very good job of lubricating and keeping your oral cavity hydrated – of course when air enters, they form bubbles – but the original design is to keep your internal cells wet and happy..

    You guys are really asking awesome questions!! 🙂


  2. laksiyer says:

    And you have given us an awesome set of things to talk about @Saad…. from medicine bottles to tears and alveoli. Thank you for your detailed explanation. Now I am beginning to wonder what hot liquids do to your oral cavity!

  3. Matthew Rossi says:

    I’m on tenterhooks waiting to find out about the potatoes!

  4. Yash says:

    reminds me of the soap bubbles I did a little while ago

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