Saturday, July 19, 2014

The Inner Processes Of Eating

English: diagram of action of swallowing a bol...
English: diagram of action of swallowing a bolus of food (Photo credit: Wikipedia)

by Mary Roach

WAGENINGEN, the Netherlands - In Food Valley, a cluster of universities and research facilities, nearly 15,000 scientists are dedicated to improving - or, depending on your sentiments about processed food, compromising - the quality of our meals.

Here I am, in the Restaurant of the Future, a cafeteria at Wageningen University where hidden cameras record diners as they make decisions about what to eat. And here is a bowl of rubbery white cubes the size of salad croutons. Dr. Andries van der Bilt has brought them from his lab at the nearby University Medical Center Utrecht.

"You chew them," he said.

An oral physiologist, Dr. Van der Bilt uses the cubes to quantify "masticatory performance" - how effectively a person chews.

He and his colleagues study the mouth's role as the human food processor.

Chewing is as unique and consistent as the way you walk. There are fast chewers and slow chewers. Some of us chew straight up and down, and others chew side-to-side, like cows.

Dr. Van der Bilt studies the neuromuscular elements of chewing. You often hear about the impressive power of the jaw muscles. In terms of pressure per single burst of activity, these are the strongest muscles we have. But it is the jaw's nuanced ability to protect that fascinates Dr. Van der Bilt.

Think of a peanut between two molars, about to be crushed. At the precise millisecond the nut succumbs, the jaw muscles sense the yielding and let up. Without that reflex, the molars would continue to hurtle reckelessly toward one another.

To keep your jaw muscles from smashing your teeth, the body evolved an automated braking system. The faster and more recklessly you close your mouth, the less force the muscles are willing to apply. Without your giving it a conscious thought.

The study of oral processing is about the entire "oral device" - teeth, tongue, lips, cheeks, saliva, all working together toward a singular revolting goal, bolus formation.

"Bolus," here, refers to a mass of chewed, saliva-moistened food particles - food that is in, as one researcher puts it, "the swallowable state."

Bolus formation and swallowing depend on a highly coordinated sequence of neuromuscular events and reflexes, researchers have found. The larynx (voice box) usually blocks the entrance to the esophagus. When food or drink is ready to be swallowed, the larynx has to rise out of the way, both to allow access to the esophagus and to close off the windpipe and prevent the food from "going down the wrong way."

To allow this to happen, the bolus is held momentarily at the back of the tongue, a sort of anatomical metering light. If the larynx doesn't move quickly enough, the food can head down the windpipe instead.

A more more entertaining swallowing missteps is nasal regurgiration. Here the soft palate fails to seal the opening to the nasal cavity. This leaves milk or chewed peas in peril of being expelled through the nostrils. Nasal regurgiration is more common with children, because they often laugh while eating and because their swallowing mechanism isn't fully developed.

"Immature swallowing coordination" is the reason 90 percent of food-related choking deaths befall children under 5. Also contributing: immature dentition. Children grow incisors before they have molars; for a brief span of time, they can bite off pieces of food but cannot chew them.

Round foods are particularly treacherous because they match the shape of the trachea. If a grape goes down the wrong way, it blocks the tube so completely that no breath can be drawn around it. Hot dogs, grapes and round candies take the top three slots in a list of killer foods published in the July 2008 issue of The International Journal of Pediatric Otorhinolaryngology.

Those who can chew want to chew. We especially enjoy the crunch. A colleague of Dr. Van der Bilt, Dr. Ton van Vliet, has spent seven years figuring out how crunch works.

"It's all bubbles and beams," he said, sketching networks of water-filled cells and cell walls. When you bite into an apple, the flesh deforms and at a certain moment the cull walls burst. And there is your crunch. In crispy snack foods, the bubbles are filled with air. As a piece of produce begins to decay, the cell walls break down and water leaks out. Now nothing bursts.

For a food to make an audible noise when it breaks, there must be what's called a brittle fracture: a sudden, high-speed crack. Dr. Van Vliet takes a puffed cassava chip from a bag and snaps it into two.

"To get this noise, you need crack speed of 300 meters per second," he said. The speed of sound. The crunch of a chip is a tiny sonic boom inside your mouth.

Crispiness and crunchiness appeal to us because they signal freshness, Dr. Van Vliet said. Old, rotting, mushy produce can make you ill. "You eat physical properties with a little bit of taste and aroma," Dr. Van Vliet said. "And if the physics is not good, then you don't eat it."

Mary Roach is the author of the new book "Gulp: Adventures on the Alimentary Canal," from which this article is excerpted.

Taken from TODAY Saturday Edition, 06-April-2013