Why We Love Ice Cream

December 8th, 2010 | Sources: PLoS Medicine, Science Daily, Wall Street Journal

Scientists know that our perceptions about taste and texture drive our food preferences. They know quite a lot about the role of taste in this regard, and the results of some recent experiments have shed new light on the role of texture as well, particularly as it relates to foods containing starch.

Starch is a major component of potatoes, rice, corn, wheat and the enormous variety of foods derived from them. It is also added to many other products from maple syrup to pudding. In fact starch accounts for 40-60% of the calorie content in the average Western diet, and more than that in many Asian and third-world diets. 

Humans begin digesting starch in the mouth, where the salivary glands secrete an enzyme known as amylase. This enzyme breaks down starch and other complex carbohydrates into simpler sugar molecules which end-up being absorbed from the small intestine into the bloodstream.

For years, scientists knew that people’s DNA contains between 2 and 15 copies of AMY1, the gene that codes for amylase. Recently, Abigail Mandel and colleagues at the Monell Chemical Senses Center in Philadelphia hypothesized that the number of copies of the AMY1 gene that a person has might impact the speed with which that person breaks down starch in his or her diet. This in turn might affect the way that person perceives the texture of starchy foods, and ultimately his or her preferences for that food.

To test their theory, Mandel’s team determined the number of AMY1 genes and the amount and activity of salivary amylase in 62 healthy volunteers. Sure enough, the team found that people with more AMY1 genes produced more salivary amylase. Then, the team asked the volunteers to swish-and-swirl starch-containing solutions in their mouths and rate the “runniness” of these solutions after 60 seconds. The high-amylase producers found the solutions to be “more runny” than the low amylase producers.

So what, you ask? Well, Mandel’s team believes this finding helps explain why people experience starch-containing foods as creamy vs. slimy, or sticky vs. watery. In the case of ice cream and hard chocolate for example, Mandel’s team had shown in a separate study that people who really dig these treats seem to be particularly enthralled by creamy sensations that start off as “solid” and then subsequently melt away in the mouth.

“We all have had the experience of liking a food that someone else complains is too tacky, or slippery, or gritty, or pulpy,” Breslin explained to the Wall Street Journal. “This is why a given line of product often comes in different textural forms,” like orange juice with and without pulp, he added.

Of course, an abundance of salivary amylase is just a part of a much larger food preference story. Scientists have, for example, identified another gene that renders bitter tastes more intense and shown that people who have this gene tend not to consume bitter-tasting vegetables like kale and spinach. And learned phenomena also play a role: people who don’t initially like scotch for example, can wind up enjoying it with “practice.”

Breslin’s amylase study appears in PLoS ONE.


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