Yum, There's a Science Behind That!

By Dr. Mehmood Asghar BDS, M Phil., Ph.D.

Saliva is 99% water. It helps us chew foods, contains certain antibacterial agents, and prevents teeth cavities - basic facts many of us already know. But did you also know that saliva impacts how we perceive food and develop a specific "taste" for our favorite meals?

The fact is that saliva is so much more than just a lubricant that helps us digest food. "It is a liquid, but it's not just a liquid," says Guy Carpenter, an Oral Biologist at King's College London. Researchers are now discovering that saliva also serves as a mediator (Matsuo, 2000), helps move food through the oral cavity, and perhaps influences how to develop tastes for different foods.

There's a Science to "Yummy"

Saliva is not too salty, so it lets us enjoy salted potato chips. It's neither too acidic, so a lemonade tastes refreshing and stimulating. At the same time, saliva contains different enzymes that help digest food. Due to its lubricating function, scientists have discovered that it also dissolves the chemical components of taste, the so-called tastants. These tastants travel in and interact with taste buds, allowing us to enjoy different flavors of foods. "We detect chemical information of food: the flavor, the taste," says Jianshe Chen, a food scientist at Zhejiang Gongshang University in Hangzhou, China.

So rich is the influence of saliva on how we perceive the taste of food that Chen coined a new scientific field, "oral food processing," which is an amalgamation of food science, the physics of food ingredients, and the body's physiological and psychological response to food. He expressed his views in the Annual Review of Food Science and Technology journal in 2022 (He et al., 2022). In this co-authored publication, he explains that when we eat food, we are not savoring the food itself but the mixture of the food and saliva, which forms the taste. So, for someone to perceive the taste of their food, it must first come in contact with salivary glands on the saliva-coated tongue.

Saliva also plays a vital role in texture perception. We often encounter astringency, a feeling of dryness in the mouth when drinking red wine or biting on unripe food. Is it because these foods make our mouths drier? No, the presence of certain molecules in these foods called tannins causes the proteins in the saliva to precipitate out, taking away its lubrication function.

That's not all; saliva also differentiates between low- and high-fat foods. Professor Anwesha Sarkar, a food scientist at the University of Leeds, UK, believes there is a difference between the tastes of high- and low-fat yogurts, even though they have the same consistency and appearance. "What you're trying to understand is not the property of the food, but how the food is interacting with the surface," Sarkar says. He adds that milk fat combines with saliva, creating a layer of surface droplets on the mouth's surface that tends to mask astringency and adds richness to the yogurt.

But what's the underlying cause of differences in taste perceptions in different individuals? One factor is the varying rates of salivary flow during the day. Typically, saliva flows slower in the morning, and its release peaks during the afternoon. This means the number of specific proteins and the so-called tastants will also vary during the day and, therefore, the taste of food.

Elsa Lamy, an Oral Biochemist at the University of Évora in Portugal and CEO at FoodAccept, scientifically demonstrated this phenomenon. Lamy asked ten blindfolded individuals to smell a piece of bread for four minutes, monitoring their salivary flow. She found that the concentrations of two types of salivary proteins, amylases, and cystatins – linked with taste perception and sensitivity – followed exposure to the bread.

Taste Perception

What's more interesting is that our perception and taste of different foods are also linked to our previous food choices and preferences. For example, Ann-Marie Torregrossa, an Associate Professor and a behavioral neuroscientist at the University at Buffalo, fed rats bitter-tasting diet additives. Interestingly, she observed increases in specific salivary proteins. Furthermore, as these salivary proteins increased, she observed that the rats became more likely to accept the bitterness in their food. "The way we think about this is, if you eat broccoli all the time, broccoli doesn't taste bad to you," says Torregrossa.

The implications of these findings are far-reaching. For example, if we could precisely identify the proteins in saliva affecting salivary taste sensitivity and acceptability, we could make bitter-tasting vegetables more palatable for kids.

What if their first experience of food that is generally perceived as bitter is not bitter or bad? This would help us encourage healthy diet maintenance in our kids. "How," says Torregrossa, "can we turn the haters into people who love these foods? That's what I'm obsessed with, and that's where the focus of future research should be."

We can only hope scientists will make broccoli as palatable as fast food in the future. Kids (and their parents) have their fingers crossed!

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References

1. He, Y., Wang, X., & Chen, J. (2022). Current Perspectives on Food Oral Processing. Annual Review of Food Science and Technology, 13(1), 167-192. https://doi.org/10.1146/annurev-food-052720-103054
2. Matsuo, R. (2000). Role of saliva in the maintenance of taste sensitivity. Crit Rev Oral Biol Med, 11(2), 216-229. https://doi.org/10.1177/10454411000110020501
3. Saliva is much more than we think it is! In addition to helping us chew food through lubrication, functioning as an antibacterial agent, a pH buffer, and an ant-caries agent, scientists have recently discovered that saliva plays a multi-factorial role in food taste perception and sensitivity.

Author: Dr. Mehmood Asghar is a dentist and Assistant Professor of Dental Biomaterials at the National University of Medical Sciences, Pakistan. Dr. Asghar received his undergraduate and postgraduate dental qualifications from the National University of Science and Technology (NUST). He has recently received a Ph.D. in Restorative Dentistry from Universiti Malaya, Malaysia. Besides his hectic clinical and research activities, Dr. Asghar likes to write evidence-based, informative articles for dental professionals and patients. Dr. Asghar has published several articles in international, peer-reviewed journals.