Food chemists identify organic structure for maximum 'pop' in popcorn

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Related tags: Popcorn, Chemistry, Starch, Us

Food chemists bring new knowledge to cut costs in the steady
European popcorn market, identifying a key crystalline structure in
popcorn that appears to determine its popping quality, reports
Lindsey Partos.

Researchers at Purdue University in the US conclude kernels with the best 'popability', are composed of a stronger, 'more highly ordered crystalline arrangement of the cellulose molecules', than the pericarp of poorer performing varieties.

The finding could lead to a better microwave popcorn variety with fewer, or no unpopped kernels, they say.

Adding the 'pop' to corn occurs because each kernel of popcorn contains a small drop of water stored inside a circle of soft starch. The soft starch is surrounded by the kernel's hard outer surface.

As the kernel heats up, the water begins to expand, and pressure builds against the hard starch. Eventually, this hard surface gives way, causing the popcorn to explode. As it explodes, the soft starch inside the popcorn becomes inflated and bursts, turning the kernel inside out.

Processors consider the minimum expansion ratio for good popcorn to be 35 to 38 to one. However, some of today's improved hybrids will expand to over 40 times the original volume.

"We think the secret to maximising 'popability' is found in the special chemistry of the corn kernel,"​ says food chemist Bruce Hamaker.

"We believe that the amount and location of the cellulose component of the kernel are critical for crystallinity, and think that this property can be transferred to corn kernels to improve their popping performance."

Manufacturers have tried to reduce the number of unpopped kernels through trial and error breeding of the better performing corn kernels, but the problem persists, especially in microwave popcorn.

Unpopped kernels, also called 'old maids', not only represent unnecessary costs on wastage, they can break teeth, destroy fillings and cause choking.

The new study could bring cost-savings that could lead to new gains in the slipping microwave popcorn market worth$1.3 billion microwave popcorn in the US, the largest global market for this snack.

Retail sales in the US have dropped off recently after 20 years of steady increases. According to the Popcorn Board​ sales of unpopped popcorn reached 1.15 billion pounds in the US in 1993, but by 2000 sales had dipped to 980 million pounds.

Microwave popcorn hit the shelves in the 1980s, profiting from the explosion in this new domestic appliance: more than 80 per cent of US consumers households now own microwaves, representing over 73 million microwaves.

Market researchers Datamonitor claim the European popcorn market, the smallest of Europe's snack markets, is generally showing strong and steady rates of growth, of about 2 per cent up to 2006.

Particularly high growth is expected in the accelerating economies of Eastern Europe, although the UK has by far the largest popcorn market in the region, worth about £24 million and dominated by Cadbury Schweppes' Butterkist brand that has a 44 per cent market share.

For the 'popability' study, Hamaker and colleagues analysed 14 different genetic varieties of yellow popcorn and compared their microwave popping performance. They determined that the number of unpopped kernels ranged from 4 per cent (best) to 47 per cent (worst), depending on the variety.

They found that the key factor that appears to influence popping quality is the chemical structure of the pericarp, which is composed partly of cellulose (a polymer of glucose).

During heating, the corn pericarp acts like a pressure cooker that locks moisture inside the corn kernel. The heated moisture leads to a pressure buildup until the kernel eventually ruptures and pops, to about 45 times its original volume.

According to the chemists, in the best popping kernels, the pericarp is composed of a stronger, more highly ordered crystalline arrangement of the cellulose molecules than the pericarp of the poorer performing varieties.

In laboratory studies, the researchers demonstrated that these stronger crystalline structures tend to maximise moisture retention, leading to a more complete rupture and fewer unpopped kernels.

"We're not sure yet exactly how this will be achieved, but we're optimistic that enterprising researchers will be able to do this in the near future,"​ says Hamaker.

Possible techniques include selective breeding of the kernel varieties show the best optimal crystalline structure; chemical modification of corn kernels to produce the desired structure; and even genetic engineering of the corn plant.

Hamaker predicts the new corn could be available to consumers in three to five years.

Although the new popcorn will be slightly different chemically than conventional microwave popcorn, mainly from the presence of more cellulose, it will look and taste just like any other popcorn, he says.

Full findings of the study will be published in the 11 July print version of the American Chemical Society's BioMacromolecules​, and available online from 7 April.

Related topics: Ingredients

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