Peanuts as functional food: a review
Peanut is an important crop grown worldwide. Commercially it is used mainly for oil production but apart from oil, the by-products of peanut contains many other functional compounds like proteins, fibers, polyphenols, antioxidants, vitamins and minerals which can be added as a functional ingredient into many processed foods. Recently it has also revealed that peanuts are excellent source of compounds like resveratrol, phenolic acids, flavonoids and phytosterols that block the absorption of cholesterol from diet. It is also a good source of Co-enzyme Q10 and contains all the 20 amino acids with highest amount of arginine. These bioactive compounds have been recognized for having disease preventive properties and are thought to promote longevity. The processing methods like roasting and boiling have shown increase in the concentration of these bioactive compounds. In the present paper an overview on peanut bioactive constituents and their health benefits are presented.
Keywords: peanut, functional ingredients, health benefits
Peanut or “groundnuts” as they are known in some parts of the world are the edible seeds of a legume. India is second largest producer of peanut in world, with total production of approximately 7,131,000 million metric tons per year (USDA, 1996-2000, PS&D database). Peanut (Arachis hypogaea) is technically considered as pea and belongs to the family (fabaceae) of bean/legume. Although a legume; it is generally included amongst the oilseeds due to its high oil content. Peanuts are rich in protein, oil and fibers (Suchoszek et al., 2011). Apart from oil, peanuts are widely used for production of peanut butter, confections, roasted peanuts, snack products, extenders in meat product formulation, soups and desserts (Rustom et al., 1996).
There are thousands of peanut cultivars around the world. Certain cultivars 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 however, the most popular cultivars are Spanish, Runner, Virginia and Valencia. Most peanuts marked 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 Runner are used to make peanut butter (Woodroof, 1983).
China leads in production of peanuts, having a share of about 45% of overall world production, whereas India has (16%) share and the United States of America has (5%) (USDA, 2012)
Peanuts are consumed all over the world in a wide variety of forms most of which are traditional cuisine. Peanuts are being used as the complete dietary source for people on expeditions to areas like Antarctica, space and trekking. It has notably been the source of elimination of malnutrition amongst the population in many African countries in the recent years (Guimón et al., 2012).
History of peanuts
The history of peanuts dates back to the times of the ancient Incas of Peru. They were the first to cultivate wild peanuts and offered them to the sun God as part of their religious ceremonials. They use to call peanut as ynchic. The modern history of peanut popularization began with the civil war of the 1860s in America. George Washington Carver who is known as the “father of peanut industry’’ as he developed more than three hundred products derived from the peanut (Carver, 1925).
Peanut butter was created in the 1890s by the St. Louis physician as the soft protein substitute for people with poor teeth. In 1895, Dr. John Harvey Kellogg patented a “Process of preparing nut meal” and used peanuts to serve the soldiers. According to John Mariana’s ‘Encyclopedia of american food and drink,’ a process for roasting shelled peanuts in oil was developed in the early 1900s and packed in the airtight bags under the “Planters’’ label. Joseph L. Rosenfield licensed his invention to the pond company, the makers of peter pan peanut butter , in 1928, Rosenfield began making his own brand of peanut butter, this was the beginning of commercialization and popularization of peanut butter in the America which gradually spread all over the Europe and Asia.
Recent developments on peanut based products
Peanut consumption all over the world varies in large proportions hence the commercial products too are variant and generally localized. Peanuts has been developed into the variety of products like roasted peanuts, peanut butter, peanut oil, peanut paste, peanut sauce, peanut flour, peanut milk, peanut beverage, peanut snacks (salted and sweet bars) and peanut cheese analog. Raw peanut are consumed all over the world. Roasted peanuts are processed by heating the peanuts up to temperature of 180⁰C for around 12-15 minutes or at 160⁰C for 40-60 minutes depending on the moisture content.
The influence of boiling, roasting and frying on the digestion of peanuts in simulated gastric environment was studied and the results show that processing improved the gastric disintegration of peanuts, and the disintegration rate was in an order of fried > roasted > boiled > raw peanuts (Kong et al., 2013). Effect of addition of peanut skin into peanut butter on antioxidant and total phenolic content was studied by Ma et al., (2014). They observed a significant increase in the fiber, phenolics and antioxidant content of butter prepared.
Peanut oil is obtained by different extraction methodologies and is mainly consumed in the Asian subcontinent especially India. Maximum amount of the peanut production around the world is utilized for oil production. The world production of peanut oil has risen from 4.53 million metric tons in 2000 to 4.91 in 2010. Production across the countries of the world, where China (44%), Indian (20%), and Nigeria (11%) are the largest producers, is expected to account for almost 75% of the world’s peanut oil (FAS-USDA, 2011).
Peanut snacks (salted/unsalted) are consumed mainly in the Asian subcontinent, particularly India. These are prepared mainly by frying and coating of the peanut kernel. (Varela et al., 2011).
Peanut flour, generally produced by grinding the defatted peanut meal after oil extraction is generally used in other preparations like soup, cookies, curries (Tate et al.,1990) due to its emulsifying properties and as a composite flour (Singh and Singh, 1991). It is also used for coating meat products. Peanut flour can be used for making composite flours with non-wheat cereals or supplementing its flour with protein-rich sources, such as legume flours, especially in countries in which the production of wheat is insufficient, can improve the nutritional value of bread. (Stefano et al.2011)
Peanut bars are consumed all over the world in different forms. They are prepared after coating the partially ground peanuts with sugar or jaggery after blanching and demoisturizing the kernels. In India, it is popularly called as “chikki” (Narayan et al., 1994)
Other peanut products like peanut milk, fermented peanut products, cheese analogs, peanut beverages are still not very popular to be utilized for their production and commercialized for e.g. according to Chandrasekhara et al., (1971), peanut milk is made from sludge produced by grinding one volume of raw peanuts with 6 volumes of water for 30 min. The pH is adjusted to 9.0, and using a cream separator, the fat is removed from the starch and fiber. This process provides a yellow liquid nearly fat free and constitutes high proteins milk.
Beuchat and Nail (1978), Salunkhe and Kadam (1989), Van (1992), Maltz (1981), Chandrasekhara et al. (1987), showed peanut milk which can be fermented by lactic acid bacteria. Rubico et al. (1987), showed methodology to prepare beverage from the filtrate of the soaked, blanched and grinded peanut.
Table 1. Popular peanut based branded products available in the local market (Mumbai):
Peanut Product Brand and company details Price in Rs/100 g
Roasted Peanuts Planters
Bhikharam Chandmal Bhujiawala (Plain peanut)
Haldirams (Salted nuts) 110
Peanut snacks Haldirams tasty nuts
Gardens fried nuts
Snackup Masala peanuts(MTR) 42
Peanut Butter Skippy (Unilever)
Peterpan (ConAgra Foods)
Savoury (Bajaj foods)
American Garden Foods
Navadarshanam handmade peanut butter
Sundrop creamy peanut butter 78
Peanut Caramel Bars Paypals (Hersheys)
National Chikki 100
Peanut Nutrition Profile
Protein, fats, and fiber are the major components that make up peanuts (Table 2). All these components are present in their most beneficial forms. The protein is plant-based: the fat is unsaturated, and the fiber is complex carbohydrate which are all proved to be the best for human nutrition.
Table 2. Groundnuts (Arachis hypogaea), All types, Nutritional value per 100 g.ce: USDA National Nutrient data base)
Principle Nutrient Value Percentage of RDA
Energy 567 Kcal 29
Carbohydrates 16.13 g 12
Protein 25.80 g 46
Total Fat 49.24 g 165
Cholesterol 0 mg 0
Dietary Fiber 8.5 g 22
Folates 240 µg 60
Niacin 12.066 mg 75
Pantothenic acid 1.767 mg 35
Pyridoxine 0.348 mg 27
Riboflavin 0.135 mg 10
Thiamin 0.640 mg 53
Vitamin A 0 IU 0
Vitamin C 0 0
Vitamin E 8.33 mg 55.5
Sodium 18 mg 1
Potassium 705 mg 15
Calcium 92 mg 9
Copper 1.144 mg 127
Iron 4.58 mg 57
Magnesium 168 mg 42
Manganese 1.934 mg 84
Phosphorus 76 mg 54
Selenium 7.2 µg 13
Zinc 3.27 mg 30
According to the American peanut council, peanut fat profile contains about 50% monounsaturated fatty acids (MUFAs), 33% Paraformaldehyde (PFAs) and 14% saturated fatty acids which is a heart friendly combination of fatty acids (Feldman, 1999).The amount of trans fat in peanut butter with 2% stabilizer is 156 times less than what is needed to reach the 0 g trans fat cut-off on food labels (Sanders, 2001).
Kris-Etherton, et al. (1999) showed that peanut products (raw, butter and oil) were more beneficial to heart health when compared to the low fat diets. The high monounsaturated fat peanut diets lowered their total body cholesterol by 11% and bad LDL cholesterol by 14%, while their good HDL cholesterol was maintained with reduction in triglycerides (Pelkman et al. 2004).The benefits of the peanut diets on cholesterol were comparable to the olive oil diet. There is strong evidence supporting an association between monounsaturated fat as well as overall nut intake and reduction in the risk of coronary heart disease (Mente et al, 2009).
Figure 1. Fat Profile of Peanuts (Source: American Journal of Clinical Nutrition,1999)
Emerging data clearly shows that type of fat can impact health in various ways at different stages of life. The fat in peanuts and peanut butter provides healthy calories to malnourished infants and children at their time of need.
Peanuts are actually a legume and have more protein than any other nut with levels comparable to or better than serving of beans. After the peanut oil is extracted, the protein content in the cake can reach 50% (Zhao et al, 2011). Peanuts contain all the 20 amino acids in variable proportions and is the biggest source of the protein called “arginine” (USDA, 2011). According to Protein Digestibility Corrected Amino Acid Score (PDCAAS) peanut proteins and other legume proteins such as soy proteins are nutritionally equivalent to meat and eggs for human growth and health (FAO 1991). The amino acid profile of the peanut meals shows that it can be an ingredient for protein fortification (Yu et al. 2007). Since the proteins in peanuts is plant based, it carries with it additional components that have positive health benefits like fiber and unique bioactive components, unlike animal protein. The peanut proteins have been found to have good emulsifying activity, emulsifying stability, foaming capacity, excellent water retention and high solubility, and can also provide a new high protein food ingredient product formulation and protein formulation in food industry (Wu et al. 2009). Based on these observations, recently peanut protein has been incorporated into noodles (Xiaodong and Ying, 2010) and infant formula, (Nimsate et al. 2010). There is a renewed interest in the studies related to the flavors in the peanut kernel and skin.
Figure 2. Total Protein in Various Grains and Legumes Per Half Cup
The components in peanuts are highly digestible. The true protein digestibility of peanuts is comparable with that of animal protein (Singh and Singh, 1991). The limiting amino acid in peanuts varies based on the study i.e. lysine, methionine or threonine, (McOsker, 1962; et al,Venkatachalam and Sathe,2006;Sarwarg, 1987). Protein quality is defined based on the amino acid pattern and percent of digestibility of proteins. The PDCAAS for peanuts has been estimated to be about 0.70 out of 1 where as for whole wheat PDCASS is 0.46 (Table 3).
Table 3. Percent Digestibility and Average PDCAAS for Peanuts and other grains.
Food Item True Digestibility PDCAAS References
Peanuts 94 0.70 Suárez López MM, et al.(2002)
Soy 86 0.91 Schaafsma G.(2006)
Whole Wheat 86 0.46 Schaafsma G.(2006)
Maize 85 0.43 Micheal j.Gibney et al.(2009)
Fat digestibility varies based on the structure of different fatty acids. Peanuts contain over 50 percent monounsaturated fats, which are easily digested due to single unsaturated hydrogen bond which is easily broken (American Peanut Council, 2008). Since peanuts are legumes, they contain phytic acid which is associated with decreasing the bioavailability of other nutrients due to their binding properties, but the amount in peanuts is lower than compared to other legumes such as soybean (Schlemmer, et al., 2009). The fiber in peanuts is mainly insoluble, with lower amounts of soluble fiber (Higgs, 2003). It contributes to daily intake, but has not been shown to bind nutrients and restrict their absorption. In fact, the small amount of soluble fermentable fiber may improve adsorption of some minerals (Gregor, 1999).
Peanuts are also a good source of fiber, according to the Food and Drug Administration. Sucrose and starch constitute the major while reducing sugars form the minor proportion of the peanut carbohydrates (Tharanathan et al., 1975). This may contribute to the fact that peanut have a low glycemic index (GI) and glycemic load (GL) (Foster-Powell, 2002).On a 100 –point scale, the GI of peanuts is 14, and the GL of peanuts is one. Additional research has shown that when peanuts or peanut butter are added to a high glycemic load meal ,such as with a bagel and a glass of juice ,they actually keep the blood sugar stabilized so that it does not rise too high too quickly(Johnston , 2005). Peanuts contain carbohydrates, and all foods that contain carbohydrates elevate blood-glucose levels. Some carbohydrates, such as simple sugars, have a swift, dramatic effect on your blood sugar. Carbohydrates that contain fiber or starch, these two types of carbohydrates have a slower, less pronounced effect on blood sugar. The American Diabetes Association ranks peanuts and other nuts as diabetes superfoods. To make the list, foods must supply important nutrients such as fiber, calcium, potassium, magnesium and vitamins A, E and E. Foods on the list must also rank low on the glycemic index. Peanuts make the list because they contain magnesium, fiber and heart-healthy oils and do not overly affect your blood glucose.
Table 2 provides the detail regarding the amounts of vitamin present in 100 g of peanuts and their levels as per the RDA.
According to the table 4, 100 g peanuts consumption is capable of providing up to 75% RDA of Niacin, 60% RDA of folate, 53% RDA of thiamin, 10% RDA of Riboflavin, 35% RDA of pantothenic acid, 27% RDA of pyridoxine, 55.5% RDA of vitamin E.
It has been recognized as a great source of niacin, which is important for functioning of the digestive systems, skin, nerves, helps in conversion of food to energy and supposed to protect against Alzheimer’s disease and cognitive decline (Morris, 2004). Peanut is an excellent source of vitamin E is considered a hard-to-get nutrients as it was shown that over 90% of men and women were not meeting the recommendations for intake (Gao, 2006). New research shows that there is more vitamin E in peanuts that was realized (Shin, 2009). And its consumption in low quantities can lead to benefits against coronary heart disease (Bramley et al., 2000). Peanut also contains good amounts of folate which is especially important in infancy and pregnancy, in production and maintenance of cells. Research shows that people who take in higher dietary folate may have an advantage when it comes to prevention of heart disease (Rimm, 1998).
Table 2 illustrates that small amounts of peanut consumption can meet the most part of RDA of many minerals which are crucial for health and proper functioning of the body. It is clear from the dates that 100 g of peanut can provide RDA levels of 127% copper, 84% manganese, 57% iron, 54% phosphorus, 42% magnesium intake is associated with reduced inflammation (King, 2005: Song, 2005) and a decreased risk of metabolic syndrome (Song, 2005) and type II diabetes (Kao, 1999: Lopez-Ridaura, 2004: Huerta, 2005: Larson, 2007).
Compact source of energy
Peanuts provide high energy levels for lesser consumptions level (Holt et al .1995; Kirkmeyer and mattes, 2000; Burton-freeman, 2000). They are also referred to as energy-dense (Alper and Mattes, 2000). Peanuts contains about 50 % fat (table 3), which at 9 calories per gram, contribute more calories than traditional foods used in humanitarian relief such as milk, corn, soybean, wheat and other grains. The majority of fat in peanuts is heart healthy monounsaturated fat, with balanced levels of polyunsaturated and saturated fats (American peanut council).
Peanuts are rich in multiple natural micronutrients (Table 2) including vitamins, minerals, and bioactive compounds such as resveratrol that are beneficial to health, making them a viable option for improving the nutrition status of those who are malnourished, developing, growing, or in need of critical nutrients in peanuts are integral to growth, development, metabolism, and immunity (Gulcin, 2010). It is likely that the individual nutrients in peanuts work by multiple mechanisms and that they have synergistic effects toward improving towards improving health status.
In more than 15,000 people who consumed peanuts and peanut products, it was found that levels of vitamin A, vitamin E, folate, magnesium, zinc, iron, calcium, and dietary fiber were higher than those who did not consume peanuts (Griel, 2004).
Recent focus is on the proper utilization of the by-products from peanut processing. It has been found that peanut hull, peanut skin, peanut leaves, and stems are all nutrients rich parts of the crop with their own functional component. It has been reported that for 1000kg of peanut for the cold procedure can generate 700kg of peanut meals, while the hot crushing procedure can produce 500kg. Usually, only a little peanut skin are utilized to extract polyphenolic compounds or make the cattle feed, most of the skins are as the wastes of peanut processing industry and discarded (Sobolev and Cole, 2003). While peanuts skins can provide an inexpensive source of polyphenols for use as functional ingredients in food or dietary supplements, and make a positive contribution to nation’s health (Yu et al. 2006). An estimated 35-45g of peanut skin is generated per kg of shelled peanut kernel. Over 0.74 million metric tons of peanut skins are produced annually worldwide as a by-product of the peanut processing industry (Sobolev and Cole, 2003). The production of peanut hull has been estimated to be 230-300g of peanut hull per kg of peanut. The production of peanut vine from harvested peanut has been estimated to be 60-65 %of the peanut production peanut vines are rich in dietary fibers and flavonoid components (Du and Fu 2008). The peanut vines include roots, stem, leaves and flowers.
Health Benefits of Peanuts
The consumption of either peanuts or processed peanuts has been shown to be beneficial to health, due to their desirable lipid profile, which is higher in unsaturated fatty acids than in saturated fatty acids peanut oil is naturally trans- fat-free, cholesterol-free, and low in saturated fats. It shows many positive biological effects, which are mostly connected with its high oleic acid content. A number of studies have shown the unique properties of this fatty acid and the importance of maintaining its intake at as high a level as possible. Many studies have revealed that consumption of peanuts or peanut oil is associated with reduced cardiovascular disease (CVD) risk and may improve serum lipid profiles, decrease LDL oxidation, and exert a cardioprotective effect. Peanut and peanut products (peanuts, peanut butter, and peanut oil) can be used in designing a high-MUFA, cholesterol-lowering diet that is preferable to a low-fat diet in regard to CVD protection. Peanuts also proved to be beneficial in lowering the risk of type 2 diabetes. People with this type of diabetes do not produce adequate amounts of insulin for the needs of the body and/or cannot use insulin effectively. Processed peanuts and by-products from the production of peanut products also exhibit health-promoting and preventive effects. Frequent intake of peanut and its products may reduce the risk of colorectal cancer. Some people have allergic reactions to peanuts (Suchoszek-Lukaniuk, 2011)
Peanuts contain all the 20 amino acids (USDA SR-21) and more than 20 vital nutrients (vitamins and minerals) in every seed. Apart from the daily nutrition peanut consumption leads to long term health benefits. Compared to well-known foods like green tea and red wine, peanuts have higher antioxidant capacity (Halvorsen, 2006; Zhang 2011; Kane 2012). Peanut skins contain potent rich antioxidants. It has been noted that the when peanuts are consumed with their skins, their antioxidant capacity doubles and roasting can at times actually increase this capacity as well (Craft, 2010; Yu et al 2006). Recent research studies suggest that boiling enhances antioxidant concentration in the peanuts. It has been found that boiled peanuts have two and four fold increase in isoflavone antioxidants biochanin A and genistein content, respectively (Craft, 2010).
As much as 40% reduction in mortality due to any factor has been reported when peanuts were included as an integral part of the routine diet (Fraser et al, 1997). Reduction in deaths due to cardio vascular diseases in particular was found in population who consume peanut or peanut butter regularly (Fraser et al.1992). It has been reported that peanut consumption reduces the risk factors of heart diseases amongst all ages, across both genders and even in patients who have multiple risk factors including diabetes (Fraser et al, 1997; Hu et al, 1998; Li et al, 2009). High blood pressure is associated with greater risks of heart disease and stroke .Scientists have learned that the dietary choices we make can have an impact on the blood pressure .Peanuts and peanut butter contain health monounsaturated fatty acids, plant proteins, magnesium, potassium , fiber arginine , and many bioactive components ,each of which could be contributing to lowering blood pressure (Appel, 2005).Population studies consistently showed the risk of heart disease when peanuts were consumed in small amounts on a daily basis(Sabate ,2006;2009)