Nut of the Week - Peanuts

Roasted peanuts as snack food

The peanut, or groundnut (Arachis hypogaea), is a species in the legume or "bean" family (Fabaceae). The peanut was probably first cultivated in the valleys of Peru. It is an annual herbaceous plant growing 1.0 to 1.6 ft tall. The leaves are opposite, pinnate with four leaflets (two opposite pairs; no terminal leaflet), each leaflet 1⅜ to 2¾ in long and ⅜ to 1 inch broad. The flowers are a typical peaflower in shape, 0.8 to 1.6 in ¾ to 1½ in across, yellow with reddish veining. Hypogaea means "under the earth", after pollination, the flower stalk elongates causing it to bend until the ovary touches the ground. Continued stalk growth then pushes the ovary underground where the mature fruit develops into a legume pod, the peanut – a classical example of geocarpy. Pods are 1.2 to 2.8 in long, containing 1 to 4 seeds.

Peanuts are known by many other local names such as earthnuts, ground nuts, goober peas, monkey nuts, pygmy nuts and pig nuts. Despite its name and appearance, the peanut is not a nut, but rather a legume.

The domesticated peanut is an amphidiploid or allotetraploid, meaning that it has two sets of chromosomes from two different species, thought to be A. duranensis and A. ipaensis. These likely combined in the wild to form the tetraploid species A. monticola, which gave rise to the domesticated peanut. This domestication might have taken place in Paraguay or Bolivia, where the wildest strains grow today. Many pre-Columbian cultures, such as the Moche, depicted peanuts in their art.

Archeologists have dated the oldest specimens to about 7,600 years, found in Peru. Cultivation spread as far as Mesoamerica where the Spanish conquistadors found the tlalcacahuatl (Nahuatl = 'peanut,' whence Mexican Spanish, cacahuate and French, cacahuète) being offered for sale in the marketplace of Tenochtitlan (Mexico City). The plant was later spread worldwide by European traders.

The orange-veined, yellow-petaled, pea-like flower of the Arachis hypogaea is borne in axillary clusters above ground. Following self-pollination, the flowers fade and wither. The stalk at the base of the ovary, called the pedicel, elongates rapidly, and turns downward to bury the fruits several inches in the ground, where they complete their development. The entire plant, including most of the roots, is removed from the soil during harvesting. The fruits have wrinkled shells that are constricted between pairs of the one to four (usually two) seeds per pod.

Peanuts grow best in light, sandy loam soil. They require five months of warm weather, and an annual rainfall of 20 to 39 in or the equivalent in irrigation water.

The pods ripen 120 to 150 days after the seeds are planted. If the crop is harvested too early, the pods will be unripe. If they are harvested late, the pods will snap off at the stalk, and will remain in the soil. They need an acidic soil to grow preferably with 5.9-7 pH

Thousands of peanut cultivars are grown, with four major cultivar groups being the most popular: Spanish, Runner, Virginia, and Valencia. There are also Tennessee red and white groups. Certain cultivar groups are preferred for particular uses because of differences in flavor, oil content, size, shape, and disease resistance. For many uses the different cultivars are interchangeable. Most peanuts marketed in the shell are of the Virginia type, along with some Valencias selected for large size and the attractive appearance of the shell. Spanish peanuts are used mostly for peanut candy, salted nuts, and peanut butter. Most Runners are used to make peanut butter.

The various types are distinguished by branching habit and branch length. There are numerous varieties of each type of peanut. There are two main growth forms, bunch and runner. Bunch types grow upright, while runner types grow near the ground.

Each year new cultivars of peanuts are bred and introduced. Introducing a new cultivar may mean change in the planting rate, adjusting the planter, harvester, dryer, cleaner, sheller, and method of marketing.

While peanuts are nutritional as an everyday food, during expeditions on foot into the wilderness, especially regions of sub-zero temperatures like the South and North Poles, having peanuts has been the deciding factor between life and death. After learning from the mistakes of other adventurers, especially the tragically ill-prepared Discovery and Terra Nova expeditions to the South Pole led by Captain Robert Falcon Scott and Captain Oates from 1901 to 1912 (during which the majority of the expedition died), where starvation and lack of the proper amount of calories needed to keep from freezing were a constant danger, adventurers had to decide on a type of food that was dense, portable, high in protein and calories and could be eaten at any time without preparation. Subsequent expeditions thus settled on peanut butter as the ideal foodstuff, freeing explorers from the transport and kindling of cooking fuel (a near-impossibility in the frigid polar winds), and high enough in protein and calories to fuel the party and keep them from freezing to death in the harsh weather and freezing nighttime temperatures. Peanut butter was further favored for speed and ease of use because it could be eaten while walking if necessary.

Peanut oil is often used in cooking, because it has a mild flavor and a relatively high smoke point. Due to its high monounsaturated content, it is considered more healthy than saturated oils, and is resistant to rancidity. There are several types of peanut oil including: aromatic roasted peanut oil, refined peanut oil, extra virgin or cold pressed peanut oil and peanut extract. In the United States, refined peanut oil is exempt from allergen labeling laws.

Peanut flour is lower in fat than peanut butter, and is popular with chefs because its high protein content makes it suitable as a flavor enhancer. Peanut flour is used as a gluten-free solution.

Boiled peanuts are a popular snack in the southern United States, as well as in India, China and Ghana.

In the U.S., peanuts are used in candies, cakes, cookies, and other sweets. They are also enjoyed roasted and salted. Peanut butter is one of the most popular peanut-based foods in the U.S., and for four hundred years, recipes for peanut soup have been present in the South, Virginia in particular. In some southern portions of the U.S., peanuts are boiled for several hours until soft and moist. Peanuts are also deep fried, shell and all.

Peanuts are rich in nutrients, providing over 30 essential nutrients and phytonutrients. Peanuts are a good source of niacin, folate, fiber, magnesium, vitamin E, manganese and phosphorus. They also are naturally free of trans-fats and sodium, and contain about 25% protein (a higher proportion than in any true nut).

Recent research on peanuts and nuts in general has found antioxidants and other chemicals that may provide health benefits. New research shows peanuts rival the antioxidant content of many fruits. Roasted peanuts rival the antioxidant content of blackberries and strawberries, and are far richer in antioxidants than carrots or beets. Research conducted by a team of University of Florida scientists, published in the journal Food Chemistry, shows that peanuts contain high concentrations of antioxidant polyphenols, primarily a compound called p-coumaric acid, and that roasting can increase peanuts' p-coumaric acid levels, boosting their overall antioxidant content by as much as 22%.