Issue 121 / January - February 2018
Mmm, Mmm, Popcorn!
Who doesn't love popcorn! Eating popcorn is fun for everybody especially for kids. James H├Ârner’s  poem below might express feelings of Americans for popcorn that they consume 16 billion quarts annually .
Popcorn crowding all around,
Hot air blows them round and round,
Yellow corn kernels poppity pop,
One after another, when will they stop?
Whirling, swirling the popcorn pops,
In a bowl they quickly drop,
Fluffy popcorn, grab a bunch,
Light and tasty, eat them crunch.”
Popcorn is one of the most nutritious and economical foods available. You can see people enjoying huge buckets of popcorn at movie theaters, amusement parks, festivals, gamesÔÇŽ basically, anywhere associated with fun. How all this popcorn craziness started in the first place is uncertain and the exact birthplace of corn (Zea mays ssp. mays, maize) is not very clear either. According to Lance Gibson and Garren Benson of Iowa State University, Department of Agronomy archeological evidence shows corn has been in the Western Hemisphere for at least 80,000 years. Corn pollen samples were obtained from drill cores 200 feet below Mexico City. Radiocarbon dating revealed that the corncobs found in the bat caves in New Mexico were 5,600 years old .
Scholars agree that, thousands of years ago, maize was domesticated from a Mexican grass called teosinte (Zea mays spp. parviglumis). They know this mostly due to 1958 Nobel Prize winner George W. Beadle’s extensive genetic studies. It was not easy for him to convince others that teosinte, a wild grass with just a dozen dark kernels in a seed coat that was hard as a stone, was domesticated and turned into juicy and soft corn by early cultivators, who worked like agriculturalists and geneticists thousands of years ago . Their extraordinary selective breeding effort, talent, and patience generated today’s corn, which has more than 500 different uses, including industrial ones .
Most of the world's popcorn is grown in the United States’ corn belt of Iowa, Illinois, Indiana, Kansas, Kentucky, Michigan, Missouri, Nebraska, and Ohio. Each spring, farmers use a corn planter to place the seeds about 1 ┬Ż inches deep and 6 inches apart in the soil. That's nearly 28,000 seeds per acre .
According to DuPont Pioneer, a large U.S. producer of hybrid seeds for agriculture, maize is a warm-season crop, so germination and emergence are optimal when soil temperatures are approximately 85 to 90 degrees F; cool conditions during planting impose significant stress on corn emergence and seedling health. Elwynn Taylor and Roger Elmore, from the Department of Agronomy of Iowa State University, say that “Corn typically requires 90 to 120 Growing Degree Days (GDD) from planting to emergence.”
Anatomy and reproduction of corn
A typical corn plant is often 2.5 m (8 ft.) in height, though some natural strains can grow 12 m (40 ft.) high . Corn produces individual male (tassel) and female (ear) flowering parts on the same plant, unlike all other major grain crops. The immature ear consists of a cob, eggs that develop into kernels after pollination, and silks. From each egg, a hair-like structure called a silk grows and eventually emerges from the tip of the husk, which is a group of leaves attached to the shank that encloses the entire ear . Approximately 1,000 individual spikelets form on each tassel and each one holds two florets (small flowers making up a composite flower head) encased in two large glumes (husks of grain), and each floret has three anthers hanging from the tassel during pollination (pollen bearing parts) . Each tassel contains from 2 to 25 million pollen grains, and pollen grains released from tassels can travel as far as 1Ôüä2 mile (800 m) in 2 minutes with only a 15 mph wind . When pollen falls on the silk’s fine, sticky hairs, which serve to catch and anchor pollen grains, it hydrates and a pollen tube, including two male gametes (mature sexual reproductive cells) from a single pollen grain emerges and grows down to the egg, with a growth rate of some 0.5 cm/h. Male gametes fertilize two female gametes, the egg and central cells, resulting in the formation of the embryo and endosperm, together called a kernel. The average ear of corn has approximately 400 to 600 kernels. Approximately 83% of the mature kernel is endosperm composed of about 88% starch and 8% protein , and functions as a key carbon and nutrient source during germination and early seedling growth. Other than endosperm and embryo (germ), a corn kernel also includes pericarp (bran) and the tip. During the industrial processing of corn, the endosperm is separated from the other parts, and the germ and pericarp are generally used for oil extraction and animal feed, due to the high density of nutrients, particularly lipids, proteins, and fibers .
We’ve learned corn’s anatomy, but now the really important question: How does corn pop when it is exposed to heat? How does the yellow, hard kernel turn into a puffy, delicious, white, tender flake?
When the kernel is heated, the moisture inside it turns to steam, and because the pericarp is hard, pressure builds up within the kernel, so each kernel becomes like a pressure cooker. The starch in the endosperm becomes soft like gelatin and the moisture vaporizes until the pressure in the kernel reaches 135 pounds per square inch. The pressure increases until the pericarp breaks and the gelatinized starch granules puff out, thus the kernel turns inside out. Consequently, the starch or endosperm forms the white part of the popped kernel, while the pericarp is the darker, flaky bit at the center of the kernel .
Because corn is not only a staple crop but also important for many industrial uses, including biofuel or biodegradable plastic production, it is of great interest to scientists, mainly plant geneticists. Corn has a large genome of about 2.4 gigabases, with 10 chromosomes (n=10). The total genetic length of these chromosomes is roughly 1500cM (centimorgan, distance between chromosome positions). The complete genome sequence of Zea mays cv. B73 was published in 2009 by the Maize Genome Sequencing Project which was funded by the National Science Foundation . This was very exciting for maize researchers and breeders. However, it has also reignited the debate over food safety and scientific responsibility. In the summer of 2012, large quantities of Monsanto’s genetically modified organism (GMO) sweet corn appeared on grocery store shelves and roadside produce stands. GMO sweet corn is genetically engineered to be herbicide resistant (Roundup Ready) and to produce its own insecticide (Bt Toxin). Furthermore, in 2013, Monsanto launched the first transgenic drought tolerance trait in a line of corn hybrids, called DroughtGard. The developers of GMO foods claim that they help combat the world’s malnutrition and starvation problems, whereas antiGMO groups battle against them, thinking they are dangerous, since their effects are not well studied. Many studies show genetically modified foods are safe for human consumption; however, it is broadly accepted that the long-term health effects are unknown. The Food and Drug Administration generally recognizes these foods as safe, and the World Health Organization has said no ill health effects have resulted on the international market .
Genetically modified or not, corn is the most-produced grain worldwide and provides about 21 percent of human nutrition across the globe. It is involved in just about every aspect of our lives , including our movie nights, holidays, or other fun social activities.
- Glover DV, Mertz ET (1987) Corn. In RA Olson, KJ Frey, eds, Nutritional Quality of Cereal Grains: Genetic and Agronomic Improvement. American Society of Agronomy, Madison, WI, pp 183-336
- Naves MMV, Castro MVL, Mendonca AL, Santos GG, Silva MS (2011) Corn germ with pericarp in relation to whole corn: nutrient contents, food and protein efficiency, and protein digestibility-corrected amino acid score. Ci├¬nc. Tecnol. Aliment., Campinas, 31(1): 264-269