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How sweet it is.

Bosco chocolate syrup--notable for its cameo as fake blood in Alfred Hitchcock's 1960 Psycho shower scene--is still around, though it has undergone a significant transformation over the years. First introduced in 1928, the sweet sauce's main ingredients were corn syrup and cocoa with sugar and malt extract added for taste and xanthan gum as a thickener. The main difference from the 1960s is that high fructose corn syrup is now one of the ingredients because it achieves the same degree of sweetness with less sugar, a more expensive ingredient.

The substitution of high-fructose corn syrup for cane sugar is a pattern that became common in the food industry in the decades that followed Hitchcock's landmark film. Sugar tariffs and large subsidies introduced in the 1970s for corn growers in the U.S. made the technology for producing high fructose corn syrup popular as a cheaper way to add sweetness to foods and beverages. Since high fructose corn syrup is a liquid, it is easier to transport and blend than granulated sugar, particularly when it comes to formulating beverages. Its popularity is waning today as its ubiquity in things like carbonated beverages has been pointed to as a contributor to obesity, cardiovascular disease, diabetes and non-alcoholic fatty liver disease.

Corn syrup and high fructose corn syrup are not identical products. Corn starch, which is used to make both products, is a white powder, chemically composed of polymers of glucose. This means it consists of hundreds of glucose molecules joined together either in a straight chain known as amylose or in a branched chain version called amylopectin. Treating the starch with dilute hydrochloric acid breaks down the chains, yielding a mix of individual glucose molecules along with maltose, which is two glucose units joined together, and various short glucose chains known as oligosaccharides. To make corn syrup commercially, instead of using an acid, a mixture of corn starch and water is treated first with alpha amylase, a bacterial enzyme that breaks the starch down into oligosaccharides, followed by the addition of gammaamylase, an enzyme isolated from the Aspergillus fungus that converts some of the oligosaccharides to glucose. In the case of high fructose corn syrup, another bacterial enzyme, D-xylose isomerase, is used to convert some of the glucose into fructose. Fructose is sweeter than glucose, so an equivalent amount of high fructose corn syrup is sweeter than regular corn syrup.

While corn syrup is made of corn starch, the two substances are different in more ways than you may think. You can't walk on corn syrup, but you can walk on a liquidy mix of water and corn starch. Well, maybe not walk, but you can run. That's because a mixture of water and corn starch is a non-Newtonian fluid.

Isaac Newton did more than watch apples fall. He was also interested in the viscosity of liquids and determined that the viscosity can be changed by altering the temperature. Try warming up some honey in the microwave and see how easily it then flows. Non-Newtonian fluids can changed their viscosity not only in response to temperature change but also in response to pressure. When pressure is applied to a viscous water-starch mixture, it momentarily becomes a solid but quickly reverts to a liquid. That's why you can run across a basin filled with water and corn starch. Your weight provides enough pressure to solidify the corn starch. But you can't dilly-dally. You have to take the next step before the mixture reverts to a liquid state.

If making a pool of corn starch is too big a challenge, which it probably is, you can impress your friends by making a small batch in a bowl. (For a Hitchcockian twist, add some food dye and it looks like blood.) Then slap it hard with your hand. Everyone will expect the guck to fly all over the place, but if done right, the fluid's non-Newtonian nature guarantees that nothing happens. (But if your slap is too timid, you'll end up with a bloody mess!)

Joe Schwarcz is the director of McGill University's Office for Science and Society. Read his blog at
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Title Annotation:CHEMFUSION
Author:Schwarcz, Joe
Publication:Canadian Chemical News
Date:Sep 1, 2012
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