Mouthwash: A case of disrupting the balance of the human-hosted bacterial ecosystem

It is well known the our bodies are inhabited by billions of microorganisms, mostly bacteria. The majority of those are benign and don't pose any threat to us, provided that we are reasonably healthy. Having said that, current thinking suggests that maintaining one 's health is tightly connected to the maintenance of properly functioning bacterial communities in our bodies.

'Vintage 80's Scope Mouthwash'
by twitchery under a CC license

Most of the things we do in our normal life affect the microorganisms living within us. Whatever we eat, for instance, affects our gut flora. Eating food with lots of fibre equals giving more food to the microrganisms of the gut - it may be even possible to fine tune gut flora this way. Showering and bathing alter the composition of our skin microbiota (there are times when clean skin becomes too clean, in a risky kind of way). Brushing our teeth changes the bacterial demographics of the oral cavity, etc.

Some - and, hopefully, most - of those changes have negligible effect of human health. Major disruptions, however, may lead to more pronounced outcomes. For instance, courses of antibiotics strongly reduce the gut flora populations, leaving ground for more resistant species to settle in and, if the are pathogens, to cause trouble to their host.

A common practice with potentially detrimental effects, which seems to go unnoticed, is the use of mouthwashs. Some of those, strongly impact the baterial populations within the mouth. That is a good thing if we are talking about bacteria that cause cavities or gingivitis but probably not so good if we are talking about the bacteria that can reduce dietary nitrate to nitrite.

What?

OK, let's have a quick close look at that.

The topic of dietary nitrite (which originates from the nitrate that exists in foods, mostly leafy vegetables, which is converted to nitrite by the mouth bacteria) is still a bit controversial. The reason for that is that nitrites, which are further converted to nitrous oxide in the acidic environment of the stomach, can have good properties but also, possibly, some bad ones.

The good ones have to do with the function of the immune system, especially the organism 's defence in the gastrointestinal track against pathogens, the function of the cardiovascular system (improving blood flow, lowering blood pressure) and also the improvement of performance in moderate aerobic exercise. The bad ones are associated with cases where nitrosamine is formed, which is a carcinogen. The latter is, of course, of great concern. Nitrosamine can be formed by nitrites in the presence of secondary amines under the effect of high temperature or strongly acidic environment. Adding antioxidants (such as ascorbic acid) or keeping food processing temperature at lower level can help reduce considerably foodborne nitrosamine. Practically, nitrosamine levels from food intake are very low, though (e.g., considerably lower than the nitrosamine smokers receive from tobacco products).

So what is the bottom line?

As usual, it is a question of the right balance (as in the case of nutrition). Some mouthwashes can have an effect on nitrate-reducing bacteria and that may be not-so-good. But there may be very good reason to use them. Dental or gum problems pose considerable risks both in the long and in the short term. Really, a dentist should be the one to advise. Under normal circumstances, however, I thing that not overdoing it is quite important!

The science in the (kitchen) cupboard

It is interesting that when people want to describe something complex they refer to it as "rocket science". On those grounds, I guess introducing oneself as a "rocket scientist" (or as an aerospace engineer) in most social occasions would cause plenty of heads to turn to oneself. Now, I wonder if introducing oneself as a "food scientist" would have the same effect.....

I admit - I've never tried it. But my gut feeling is that "food science" scores really low on the coolness scale most people maintain. And that is totally unfair!

Food science is not an isolated island in the sea of knowledge. Instead, it would be better described as a large group of islands: food science is about chemistry, physics and biology applied onto systems of considerable complexity. I know. It doesn't sound convincing. So let me give you a couple of simple examples:

Example 1: Pop-corn physics. You know the story: You take dry corn seeds; you throw them in a saucepan with a bit of oil; you warm the saucepan; after a while the corn seeds violently explode into yummy white-ish flakes. So what has happened? Well, basically, two things have happened: Firstly, the water inside the seed turned into steam, which, with when heated up to about 170-200 ^oC, it raises the pressure inside the corn seed to very high levels, until the seed hull finally breaks with a explosion. Secondly, the starch inside the corn seed changes it structure to a higher volume "jelly" form. When the seeds explode, the water steam - starch mixture breaks loose and rapidly expands; at the same time, the steam escapes to the atmosphere leaving back the familiar, starch-made, foamy structure that we call pop-corn.

Example 2: Corn flour physics. Corn flour is a rather popular ingredient. In cooking, water-dispersed corn flour often functions as a thickening agent, which, when warm is thin-flowing, but when it gets colder it assumes a jelly-like behaviour. Kids are a bit more familiar with the corn flour slime, which, is unarguably considerably more fun: Just slowly start adding corn flour to a bowl with a bit of water, while stirring to ensure homogeneity; once you reach equal amounts of water and corn flour, the mix will become thicker; keep adding corn flour slowly and you will reach a point (which depends on the type of corn flour you use and the temperature), where the mix will be changing to a "solid" form under rapid stirring and melting back to the liquid form when the stirring stops.

Why that strange behaviour? Well, corn flour contains a lot of corn starch. Starch is carbohydrate molecule, comprised by lots of glucose molecules linked together, forming a long chain. Starch chains also feature smaller glucose chains (branches) attached onto the main chain. When in solution, the neighbouring starch chains can interact with each other. At a certain starch concentration, stirring or agitating the solution helps the individual starch chains hit and -briefly- stick to a high number of nearby chains, thus creating solid-looking blobs of starch. When the agitation stops, the chains go back to their original, "untangled" state, thus giving the solution its liquid-like look.

Corn-starch solutions are non-Newtonian fluids, which at certain starch concentrations behave as rheopectic (shear-thickening) ones. As you may suspect, depending on the corn starch solution and the agitation frequency, a number of cool effects can be seen. Check out the video below:

Beyond plain fun, fluids with such properties have a wide range of practical applications, from power transmission in mechanical systems to enhanced performance in bulletproof vests (traditionally employing polymer fibres).

I guess that the humble corn flour doesn't look that naive anymore, does it?

:-)

(Photo by http://www.flickr.com/photos/ryantron/ / CC BY-ND 2.0)