- Email: [email protected]
Walnut
C H A P T E R
49 Walnut Zarghouna Chudhary1, Rasheed Ahmad Khera1, Muhammad Asif Hanif1, Muhammad Adnan Ayub2, Lamia Hamrouni3 1
Department of Chemistry, University of Agriculture, Faisalabad, Pakistan; 2 Department of Chemistry, University of Okara, Okara, Pakistan; 3 Laboratory of management and valorisation of forest resources, INRGREFUniversity of Carthage, Ariana, Tunisia
O U T L I N E 1. Botany 1.1 Introduction 1.2 History/Origin 1.3 Demography/Location 1.4 Botany, Morphology, Ecology
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2. Chemistry
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3. Postharvesting Technology
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4. Processing
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5. Value Addition
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6. Uses
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7. Pharmacological Uses 7.1 Antimicrobial Activity 7.2 Antioxidant Activity 7.3 Antimutagenic Activity 7.4 Anticancer Activity
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Copyright © 2020 Elsevier Ltd. All rights reserved.
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7.5 7.6 7.7 7.8 7.9 7.10 7.11
Cholesterol Lowering Activity Antidiabetic Activity Antiaging Effects Antiviral Activity Antianesthetic/Depressant Activity Anti-Alzheimer Activity Effects on Bone Health
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8. Side Effects and Toxicity
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References
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1. BOTANY 1.1 Introduction Juglans regia L. is commonly known as walnut tree, a deciduous plant of Juglans specie, that can attain a height up to 40 m. The bark of walnut tree is grayish black and intensely furrowed (Williams, 1990). English as well as Persian walnut belongs to Juglandaceae family and is highly valuable due to its good quality timber, nuts, and nut oil (Malvolti et al., 1995). There are more than 15 species of walnut trees, and the most common are Juglans cinerea (white or butter walnut), English or Persian walnut (J. regia), and Juglans nigra (black walnut) (LA, 1909). In English J. regia is typically called walnut or common walnut. In Urdu, it is commonly known as akhrot (Fig. 49.1). In German, it is called walnub, and in Spanish and French, known as nogal and noyer, respectively.
1.2 History/Origin The word nut derives from the Latin word “nux” that means an edible kernel surrounded by hard shell. J. regia is the botanical name of walnut tree given by Romans, and Juglans means “acorn of Jupiter” and regia means royalty (Manchester, 1987). In Afghani language, it is pronounced as charmarghz, meaning “four brains,” as it looks like a human brain (Menninger, 1977). Walnut is a native plant of central Asia that spread throughout Europe, western China, Afghanistan, Persia, and Caucasus, where it is found in semicultivated as well as wild state (Dandekar et al., 2005). Walnut and its oil were used by Egyptians for the embalming of mummies and for making the strings of musical instruments (Facciola, 1990). In ancient
1. BOTANY
FIGURE 49.1
Leaves, stems, trees and fruits of Walnuts.
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FIGURE 49.1
49. WALNUT
(Continued)
times, people used the bark of walnut tree to make dark brown or black dye (Galey et al., 1991).
1.3 Demography/Location J. regia is found in different countries of Asia including Iran, Iraq, Turkey, Azerbaijan, Bhutan, Myanmar, Uzbekistan, Kazakhstan, Nepal, Armenia, Kyrgyzstan, China, Pakistan, Afghanistan, Bangladesh, Russia, Tajikistan, Georgia, and India (Kolov, 1998). Walnut is the second major nut-producing plant after almond. According to an international survey, the global walnut production in year 2010 was 1,500,000 tons, and China is one of the leading producers and exporters of walnuts, followed by America, which covers 34% of global walnut production (Frederick et al., 2014). Global demand and consumption of walnuts are increased day by day due to extensive health benefits. It has been reported that regular consumption of walnut fruit reduces the risk of heart diseases (Hemery, 2004).
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1.4 Botany, Morphology, Ecology J. regia is a large, deciduous tree attaining heights of 25e40 m, and a trunk up to 2 m diameter, commonly with a short trunk and broad crown, though taller and narrower in dense forest competition. It is a lightdemanding species, requiring full sun to grow well. Walnut trees flourish in a well-drained and loamy soil that is free from alkali. Soil needs to be moist all the time. The pH of the soil should be in the range of 6e8 (Cogliastro et al., 1997). Walnuts need protection from wind (Polunin, 1977). The bark is smooth, olive-brown when young and silvery-grey on older branches, and it features scattered broad fissures with a rougher texture (Jackson and Looney, 1999). Like all walnuts, the pith of the twigs contains air spaces; this chambered pith is brownish in color. The leaves are alternately arranged, 25e40 cm long, odd-pinnate with five to nine leaflets, paired alternately with one terminal leaflet (Gleeson, 1982). The largest leaflets are the three at the apex, 10e18 cm long and 6e8 cm broad; the basal pair of leaflets is much smaller, 5e8 cm long, with the margins of the leaflets entire. The male flowers are in drooping catkins 5e10 cm long, and the female flowers are terminal, in clusters of two to five, ripening in the autumn into a fruit with a green, semifleshy husk and a brown, corrugated nut (Abrams, 1997). Walnuts grows best in a Mediterranean climate, with a growing temperature in the range of 0e10 C during winter, a frost-free period during flowering, and temperatures below 38 C during summer.
2. CHEMISTRY Juglone is a major chemical component present in almost all of parts of walnut tree. It is a toxic isomer of lawsone that acts as a growth stunner. A small amount of alpha-hydrojuglone is also present in walnut (Kong et al., 2008). L-arginine, a precursor to nitric oxide, is also present in significant quantity in walnut trees (Crews et al., 2005). Walnut kernels have high nutritional value, containing 63%e65% kernel oil, 3%e4% water, around 7% dietary fiber, 14%e15% protein, and 12%e14% carbohydrates. The majority of nut oils contain highly unsaturated fatty acids that are not beneficial to human health, but in contrast, walnut oil contains a large amount of polyunsaturated fatty acids like 58% linoleic acid and 14% alpha-linolenic acid (Jackson and Looney, 1999). Walnut is a rich source of phytochemicals and contains a significant amount of phenols, flavonoids, sterols, tannins, phospholipids, terpenes, essential fatty acids, sphingolipids quinines, hydrocarbons, triterpenes, quinones, and oils (Crews et al., 2005). It is also contains essential minerals a-tocopherol, cellulose, albumin, and mucilage. Gallic acid, ethyl gallate, pyrogallol, vanillic acid,
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OH
O
HO
OH
HO
OH
OH
O
Juglone
OH
Alpha hydrojuglone O
OH
Gallic acid
HO OH
HO HO
HO
OCH
Vanillic acid
Pryogallol
O HO
Linoleic acid
FIGURE 49.2
Important bioactive compounds of walnuts.
proto-catechuic acid, and p-hydroxybenzoic acid are the main phenolic acids present in walnut (Davis et al., 2007). Walnut seed oil contains sterols, acrid resin, myristin, free fatty acids, sterol esters, palmitin, and stearin (Calzoni et al., 1990). Important bioactive compounds of walnuts are shown in Fig. 49.2.
3. POSTHARVESTING TECHNOLOGY Before the age of mechanization, the traditional September harvesting of walnuts consisted of shaking the trees by hand using long hooked poles to knock the nuts to the ground, from where they could be easily collected. This breaks off many of their points, thereby causing the production of new spurs, which will probably bear fruit-bearing flowers (Jackson and Looney, 1999). Today, the trees are shaken by a machine, while another machine uses vacuum suction to collect the fallen nuts. Commercial hot air dehydrators with blower fans circulate warm air to reduce the moisture of the walnuts between 12% and 20% to preserve their shelf life.
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In past centuries, walnuts were simply left on drying racks away from the sun, until they were properly dried (Gandev, 2007). Postharvest treatment involves sieving the walnuts to remove sticks and leaves, hulling to remove hulls, washing, and then grading into different sizes. Hand sorting of nuts is used to remove damaged nuts. The nuts are then put into a drier to reduce the moisture content of the kernel from 10%e30% to around 5%e8%.
4. PROCESSING Once the walnuts are harvested, precleaners are used to clean the walnuts so they are ready for hulling. A huller removes the outer green hull, and the nut is mechanically dehydrated (air dried) to the optimum 8% moisture level, preventing deterioration of the nut and protecting its quality during storage. Hulled walnuts are transported to nearby packing plants and are stored until needed for cracking (Mapelli et al., 1995). Drying may be done in the sun, in kilns, portable field bins, or in fruit bins. In all but the first method, heat applied from a gas or oil burner may be used up to 110 C. Above this temperature, kernel quality is decreased. Some growers prefer to use fan-forced air, without heating, to maintain nut quality at the expense of drying time. Packaging should be moistureproof. Shelled products should be packaged in airtight, moisture-proof, opaque, or foil packages to maximize shelf life. Unroasted kernels are less likely to take up moisture than roasted kernels. Dried nuts last for about 4 months at room temperature before becoming rancid, and 1e2 years when stored in the freezer. The primary objectives of storage are to maintain the low water content attained after preliminary drying (to suppress enzyme activity, retain texture, and reduce microbial activity) and to limit exposure to O2 (to minimize rancidity). The optimum temperature range for storage is 0e10 C (32e50 F), with the lower temperature being better.
5. VALUE ADDITION Walnuts are delicious way to add extra flavor, nutrition, and crunch to a meal. Walnuts can ‘be taken with onions, salt, and honey. Walnuts are a common food source and are used in cooking and baking (Rosengarten, 1984). Green walnuts are completely edible but are a bit sour. They form an ideal ingredient for pickles, jams, and marmalades (Payne, 1985).
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6. USES Walnuts have various benefits that are useful for humans. They are considered a major source of U-3fatty acid. They have been used as nuts from ancient time, and walnut oil is considered beneficial for our health, skin, and hair. In last few decades, walnut consumption has seen several changeable developments (Hocking, 1997). Several commercial industries use the finely ground walnut shells, in the aeronautical industry for polishing of metals, for removal of graffiti and paints, and for cleaning of electronic circuits, jet engines, and of automobiles. Walnut is used in face powder, exfoliating cleanser, and soaps. Shells of walnut are used in cleaning of stone, plastic, wood, fiberglass, and soft metals (Bown, 1995).
7. PHARMACOLOGICAL USES 7.1 Antimicrobial Activity Walnut tree is a potent source of antimicrobial agent. It has been reported that different parts of this plant show strong antimicrobial activity against various fungal as well as bacterial strains. Aqueous extract of six different green husk varieties were found potentially active against Bacillus subtilis, Cryptococcus neoformans, Escherichia coli, Bacillus cereus, Candida albicans, Pseudomonas aeruginosa, and Staphylococcus aureus strains (Oliveira et al., 2008). Walnut ethyl acetate extract exhibited potential antifungal activity against the Candida albicans strains (Noumi et al., 2010). Powerful antimicrobial activity was shown from the pyroligneous acid, which is obtained from the branches of pyrolyzing walnut tree (Wei et al., 2010). Leaves and barks of walnut, especially its aqueous and other solvent extracts, showed antifungal potential against a vast range of fungal strains, determined by using agar dilution reddish method and disc diffusion method (Pereira et al., 2008). Acetone, methanol, chloroform, and ethyl acetate extract of bark exhibited antifungal activity against Aspergillus niger, Alternaria alternata, Trichoderma virens, Fusarium solani, Pichia guiliermondii, and Pichia jadinii (Ahmad et al., 1973).
7.2 Antioxidant Activity Antioxidant potential of walnut seeds alcoholic extract assessed by DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity assays that showed positive results with high scavenging of free radicals (Carvalho et al., 2010). A similar pattern is mentioned in another literature report in which walnut stem and bark showed significant scavenging of free radicals (Ngoc et al., 2008). Moreover, the aqueous extract of walnut
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green husk exhibited in vivo antioxidant potential against cyclophosphamide-induced urotoxicity in the mice. Walnut extract restored all antioxidants significantly in the bladder (Bhatia et al., 2006).
7.3 Antimutagenic Activity Walnuts extracts, i.e., aqueous and acetone, are quite effective and exhibited antimutagenic activity. These extracts were considered very efficient for inhibiting the 2-aminoflourene 2-AFeinduced mutagenicity in strains of Salmonella (Kaur et al., 2003).
7.4 Anticancer Activity Prostate cancer is one of the most common types of cancer reported in men. It has been reported that regular consumption of walnut seeds reduces the risk of prostate cancer in males (Spaccarotella et al., 2008). Juglone is one of the major components of walnut tree and is reported to have anticancer potential against melanoma cell lines (Aithal et al., 2009). In another study, it was reported that walnut extract and fractions with excess amount of juglone and ellagic acid impressively reduced the cancer cell proliferation. Walnut seed is a rich source of omega-3 that may decrease the risk of breast cancer (Hardman and Ion, 2008).
7.5 Cholesterol Lowering Activity High cholesterol level in blood is one of the major factors of cardiovascular diseases. It has been reported that daily consumption of walnut seed significantly reduces the body cholesterol level (Sabate et al., 1993). Up to 70% risk of arteries clogging and stroke is reduced by consuming high amount of walnuts (De Lorgeril et al., 1994). Endothelial dysfunction coupled with the cardiovascular disease is restored by several food components. Walnut diet showed improved endothelial function in hypercholesterolemic patients. Walnut significantly minimized total cholesterol and low-density lipoprotein (LDL) cholesterol level (Ros et al., 2004). Similarly, it reduces the concentration of triglyceride and serum cholesterol (Rajaram et al., 2009).
7.6 Antidiabetic Activity It has been reported that daily use of the diet rich in walnut seeds significantly reduced the sugar level in patients with diabetes mellitus type 2 (Gillen et al., 2005). Dietary fats can be influenced with the walnuts to produce the reductions in fasting insulin levels. The plant extract of
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walnuts inhibited efficiently alpha-glycosidase activity for both sucrose and maltase enzymes and showed no change in the insulin and glut-4 genes expression (Teimori et al., 2010).
7.7 Antiaging Effects Walnut seed oil is a rich source of omega-3 natural antioxidants. Therefore, it has been used as a natural moisturizing and antiaging agent in beauty products (Espı´n et al., 2000). Moreover, the ethanolic extract of its leaves could be suggested as a good and new source of skin-lightning agents. Walnuts polyphenolic constituents showed significant skin lightning and were found more superior to the skin-lightning agents such as arbutin and ascorbic acid (Aitani and Shimoda, 2005).
7.8 Antiviral Activity It has been illustrated that walnut leaf extracts prepared from 95% ethanol as well as ethyl acetate significantly reduced the production of tobacco mosaic virus (Zhai et al., 2006). Methanol extract of walnut at a minimum concentration of 1.5 mg/mL inhibited the Sindbis virus (Mouhajir et al., 2001).
7.9 Antianesthetic/Depressant Activity The in vivo study results showed that walnut extracts significantly reduced depression. The walnut extracts open the closed coronary arteries of rabbit’s heart (Auyong et al., 1963). The hexane extract of walnut fruit exhibited efficient antidepressant activity at 100 and 150 mg/kg doses of body weight of male Wistar rat compared with the standard drug fluoxetine. Tail suspension and forced swimming tests were used to evaluate the antidepressant activity (Rath and Pradhan, 2009).
7.10 Anti-Alzheimer Activity In traditional medicinal systems, different parts of walnut have been used to reduce Alzheimer disease. It has been reported in different scientific reports that walnut extracts exhibited anti-Alzheimer activity. In one of the scientific reports, it was mentioned that walnut extract strongly defibrillated the beta-amyloid plaques (Chauhan et al., 2004). In another in vivo study, walnut significantly enhance the cognitive as well as motor performance in rats (Willis et al., 2009). Similarly, methanol extract of walnut has the ability to reduce the b-amyloid protein formation in Alzheimer patients. Moreover, it has been reported that the polyphenolic
REFERENCES
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compounds present in walnut may attribute for its antiamyloidogenic activity (Chauhan et al., 2004).
7.11 Effects on Bone Health Walnuts promote bone health. Walnut oil is a rich source of a-linoleic acid and U-3 fatty acids, which are essential for normal bone growth. It has been reported that the consumption of walnut in daily food stuff significantly reduced a marker of bone break down, i.e., N-telo-peptides serum concentration. Moreover, walnuts have osteoblastic potential that improves bone formation (Griel et al., 2007).
8. SIDE EFFECTS AND TOXICITY Walnuts have been reported to have extensive toxic effects on different organisms, and it has been studied widely for its toxicity. The mechanism of walnut toxicity is well understood by either electrophilicity or by oxidative stress (Gant et al., 1986). Generally, juglones were more cytotoxic than the parent compound 1, 4-naphthoquinone (Doherty et al., 1987). Walnut promoted skin tumors in female Swiss mice that were pretreated with a subcarcinogenic dose of DMBA (di-methyl benzene anthracene), which was followed by juglone’s dermal applications for a year. Though, the skin tumor was not observed, followed by the treatment of juglone without pretreatment with DBMA (Van Duuren et al., 1978). Juglone is considered an equivocal tumorigenic agent (thorax, lungs, respiration, appendages, and skin) by the Registry of Toxic Effects of Chemical Substances based on the 29-week skin painting study of mice.
References Abrams, D., 1997. Sexual Symbolism and Merkavah Speculation in Medieval Germany: A Study of the Sod ha-egoz Texts. Mohr Siebeck, 13, 147. Ahmad, S., Wahid, M.A., Bukhari, A., 1973. Fungistatic action of Juglans. Antimicrobial Agents and Chemotherapy 3, 436. Aitani, M., Shimoda, H., 2005. The effect of ascorbic acid and arbutin on B16 melanoma cells. Japan Food Science 44, 58e63. Aithal, B.K., Kumar, M.S., Rao, B.N., Udupa, N., Rao, B.S., 2009. Juglone, a naphthoquinone from walnut, exerts cytotoxic and genotoxic effects against cultured melanoma tumor cells. Cell Biology International 33, 1039e1049. Auyong, T., Westfall, B., Russell, R., 1963. Pharmacological aspects of juglone. Toxicon 1, 235e239. Bhatia, K., Rahman, S., Ali, M., Raisuddin, S., 2006. In vitro antioxidant activity of Juglans regia L. bark extract and its protective effect on cyclophosphamide-induced urotoxicity in mice. Redox Report 11, 273e279. Bown, D., 1995. The Royal Horticultural Society Encyclopedia of Herbs & Their Uses. Dorling Kindersley Limited.
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Calzoni, G., Speranza, A., Caramiello, R., Piccone, G., Zannini, P., 1990. Wall ultrastructure and biochemical features of the Juglans regia L. and Juglans nigra L. male gametophyte. Sexual Plant Reproduction 3, 139e146. Carvalho, M., Ferreira, P.J., Mendes, V.S., Silva, R., Pereira, J.A., Jero´nimo, C., Silva, B.M., 2010. Human cancer cell antiproliferative and antioxidant activities of Juglans regia L. Food and Chemical Toxicology 48, 441e447. Chauhan, N., Wang, K., Wegiel, J., Malik, M.N., 2004. Walnut extract inhibits the fibrillization of amyloid beta-protein, and also defibrillizes its preformed fibrils. Current Alzheimer Research 1, 183e188. Cogliastro, A., Gagnon, D., Bouchard, A., 1997. Experimental determination of soil characteristics optimal for the growth of ten hardwoods planted on abandoned farmland. Forest Ecology and Management 96, 49e63. Crews, C., Hough, P., Godward, J., Brereton, P., Lees, M., Guiet, S., Winkelmann, W., 2005. Study of the main constituents of some authentic hazelnut oils. Journal of Agricultural and Food Chemistry 53, 4843e4852. Dandekar, A., Leslie, C., McGranahan, G., Litz, R., 2005. Juglans regia walnut. Biotechnology of Fruit and Nut Crops 307e323. Davis, L., Stonehouse, W., Mukuddem-Petersen, J., van der Westhuizen, F.H., Hanekom, S.M., Jerling, J.C., 2007. The effects of high walnut and cashew nut diets on the antioxidant status of subjects with metabolic syndrome. European Journal of Nutrition 46, 155e164. De Lorgeril, M., Renaud, S., Salen, P., Monjaud, I., Mamelle, N., Martin, J., Guidollet, J., Touboul, P., Delaye, J., 1994. Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. The Lancet 343, 1454e1459. Doherty, M.D.A., Rodgers, A., Cohen, G.M., 1987. Mechanisms of toxicity of 2-and 5-hydroxy-1, 4-naphthoquinone; absence of a role for redox cycling in the toxicity of 2-hydroxy-1, 4-naphthoquinone to isolated hepatocytes. Journal of Applied Toxicology 7, 123e129. Espı´n, J.C., Soler-Rivas, C., Wichers, H.J., 2000. Characterization of the total free radical scavenger capacity of vegetable oils and oil fractions using 2, 2-diphenyl-1-picrylhydrazyl radical. Journal of Agricultural and Food Chemistry 48, 648e656. Facciola, S., 1990. Cornucopia: A Source Book of Edible Plants. Frederick, C., Tang, C., Wu, B., 2014. China Tree Nuts Annual. USDA, Foreign Agricultural Service. GAIN CH14051. http://gain.fas.usda.gov. Galey, F., Whiteley, H., Goetz, T., Kuenstler, A., Davis, C., Beasley, V., 1991. Black walnut (Juglans nigra) toxicosis: a model for equine laminitis. Journal of Comparative Pathology 104, 313e326. Gandev, S., 2007. Budding and grafting of the walnut (Juglans regia L.) and their effectiveness in Bulgaria (review). Bulgarian Journal of Agricultural Science 13, 683. Gant, T.W., Doherty, M.d.A., Odowole, D., Sales, K.D., Cohen, G.M., 1986. Semiquinone anion radicals formed by the reaction of quinones with glutathione or amino acids. FEBS Letters 201, 296e300. Gillen, L.J., Tapsell, L.C., Patch, C.S., Owen, A., Batterham, M., 2005. Structured dietary advice incorporating walnuts achieves optimal fat and energy balance in patients with type 2 diabetes mellitus. Journal of the American Dietetic Association 105, 1087e1096. Gleeson, S.K., 1982. Heterodichogamy in walnuts: inheritance and stable ratios. Evolution 892e902. Griel, A.E., Kris-Etherton, P.M., Hilpert, K.F., Zhao, G., West, S.G., Corwin, R.L., 2007. An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans. Nutrition Journal 6, 2. Hardman, W.E., Ion, G., 2008. Suppression of implanted MDA-MB 231 human breast cancer growth in nude mice by dietary walnut. Nutrition and Cancer 60, 666e674.
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Rosengarten Jr., F., 1984. The Book of Edible Nuts. Walker Publishing, New York, New York, USA, pp. 239e262. Sabate, J., Fraser, G.E., Burke, K., Knutsen, S.F., Bennett, H., Lindsted, K.D., 1993. Effects of walnuts on serum lipid levels and blood pressure in normal men. New England Journal of Medicine 328, 603e607. Spaccarotella, K.J., Kris-Etherton, P.M., Stone, W.L., Bagshaw, D.M., Fishell, V.K., West, S.G., Lawrence, F.R., Hartman, T.J., 2008. The effect of walnut intake on factors related to prostate and vascular health in older men. Nutrition Journal 7, 1. Teimori, M., Montasser Kouhsari, S., Ghafarzadegan, R., Hajiaghaee, R., 2010. Study of hypoglycemic effect of Juglans regia leaves and its mechanism. Journal of Medicinal Plants 1, 57e65. Van Duuren, B., Segal, A., Tseng, S., Rusch, G., Loewengart, G., Mate´, U., Roth, D., Smith, A., Melchionne, S., Seidman, I., 1978. Structure and tumor-promoting activity of analogs of anthralin (1, 8-dihydroxy-9-anthrone). Journal of Medicinal Chemistry 21, 26e31. Wei, Q., Ma, X., Dong, J., 2010. Preparation, chemical constituents and antimicrobial activity of pyroligneous acids from walnut tree branches. Journal of Analytical and Applied Pyrolysis 87, 24e28. Williams, R.D., 1990. Juglans nigra L., black walnut. Silvics of North America 2, 391e399. Willis, L.M., Shukitt-Hale, B., Cheng, V., Joseph, J.A., 2009. Dose-dependent effects of walnuts on motor and cognitive function in aged rats. British Journal of Nutrition 101, 1140e1144. Zhai, M.-z., Zhang, F.-y., Wei, H., Wang, W., 2006. A study on the bioactivity of secondary metabolites from walnut green gull. Journal of Northwest Forestry University 21, 122.
49 Walnut Zarghouna Chudhary1, Rasheed Ahmad Khera1, Muhammad Asif Hanif1, Muhammad Adnan Ayub2, Lamia Hamrouni3 1
Department of Chemistry, University of Agriculture, Faisalabad, Pakistan; 2 Department of Chemistry, University of Okara, Okara, Pakistan; 3 Laboratory of management and valorisation of forest resources, INRGREFUniversity of Carthage, Ariana, Tunisia
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7. Pharmacological Uses 7.1 Antimicrobial Activity 7.2 Antioxidant Activity 7.3 Antimutagenic Activity 7.4 Anticancer Activity
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7.5 7.6 7.7 7.8 7.9 7.10 7.11
Cholesterol Lowering Activity Antidiabetic Activity Antiaging Effects Antiviral Activity Antianesthetic/Depressant Activity Anti-Alzheimer Activity Effects on Bone Health
679 679 680 680 680 680 681
8. Side Effects and Toxicity
681
References
681
1. BOTANY 1.1 Introduction Juglans regia L. is commonly known as walnut tree, a deciduous plant of Juglans specie, that can attain a height up to 40 m. The bark of walnut tree is grayish black and intensely furrowed (Williams, 1990). English as well as Persian walnut belongs to Juglandaceae family and is highly valuable due to its good quality timber, nuts, and nut oil (Malvolti et al., 1995). There are more than 15 species of walnut trees, and the most common are Juglans cinerea (white or butter walnut), English or Persian walnut (J. regia), and Juglans nigra (black walnut) (LA, 1909). In English J. regia is typically called walnut or common walnut. In Urdu, it is commonly known as akhrot (Fig. 49.1). In German, it is called walnub, and in Spanish and French, known as nogal and noyer, respectively.
1.2 History/Origin The word nut derives from the Latin word “nux” that means an edible kernel surrounded by hard shell. J. regia is the botanical name of walnut tree given by Romans, and Juglans means “acorn of Jupiter” and regia means royalty (Manchester, 1987). In Afghani language, it is pronounced as charmarghz, meaning “four brains,” as it looks like a human brain (Menninger, 1977). Walnut is a native plant of central Asia that spread throughout Europe, western China, Afghanistan, Persia, and Caucasus, where it is found in semicultivated as well as wild state (Dandekar et al., 2005). Walnut and its oil were used by Egyptians for the embalming of mummies and for making the strings of musical instruments (Facciola, 1990). In ancient
1. BOTANY
FIGURE 49.1
Leaves, stems, trees and fruits of Walnuts.
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FIGURE 49.1
49. WALNUT
(Continued)
times, people used the bark of walnut tree to make dark brown or black dye (Galey et al., 1991).
1.3 Demography/Location J. regia is found in different countries of Asia including Iran, Iraq, Turkey, Azerbaijan, Bhutan, Myanmar, Uzbekistan, Kazakhstan, Nepal, Armenia, Kyrgyzstan, China, Pakistan, Afghanistan, Bangladesh, Russia, Tajikistan, Georgia, and India (Kolov, 1998). Walnut is the second major nut-producing plant after almond. According to an international survey, the global walnut production in year 2010 was 1,500,000 tons, and China is one of the leading producers and exporters of walnuts, followed by America, which covers 34% of global walnut production (Frederick et al., 2014). Global demand and consumption of walnuts are increased day by day due to extensive health benefits. It has been reported that regular consumption of walnut fruit reduces the risk of heart diseases (Hemery, 2004).
2. CHEMISTRY
675
1.4 Botany, Morphology, Ecology J. regia is a large, deciduous tree attaining heights of 25e40 m, and a trunk up to 2 m diameter, commonly with a short trunk and broad crown, though taller and narrower in dense forest competition. It is a lightdemanding species, requiring full sun to grow well. Walnut trees flourish in a well-drained and loamy soil that is free from alkali. Soil needs to be moist all the time. The pH of the soil should be in the range of 6e8 (Cogliastro et al., 1997). Walnuts need protection from wind (Polunin, 1977). The bark is smooth, olive-brown when young and silvery-grey on older branches, and it features scattered broad fissures with a rougher texture (Jackson and Looney, 1999). Like all walnuts, the pith of the twigs contains air spaces; this chambered pith is brownish in color. The leaves are alternately arranged, 25e40 cm long, odd-pinnate with five to nine leaflets, paired alternately with one terminal leaflet (Gleeson, 1982). The largest leaflets are the three at the apex, 10e18 cm long and 6e8 cm broad; the basal pair of leaflets is much smaller, 5e8 cm long, with the margins of the leaflets entire. The male flowers are in drooping catkins 5e10 cm long, and the female flowers are terminal, in clusters of two to five, ripening in the autumn into a fruit with a green, semifleshy husk and a brown, corrugated nut (Abrams, 1997). Walnuts grows best in a Mediterranean climate, with a growing temperature in the range of 0e10 C during winter, a frost-free period during flowering, and temperatures below 38 C during summer.
2. CHEMISTRY Juglone is a major chemical component present in almost all of parts of walnut tree. It is a toxic isomer of lawsone that acts as a growth stunner. A small amount of alpha-hydrojuglone is also present in walnut (Kong et al., 2008). L-arginine, a precursor to nitric oxide, is also present in significant quantity in walnut trees (Crews et al., 2005). Walnut kernels have high nutritional value, containing 63%e65% kernel oil, 3%e4% water, around 7% dietary fiber, 14%e15% protein, and 12%e14% carbohydrates. The majority of nut oils contain highly unsaturated fatty acids that are not beneficial to human health, but in contrast, walnut oil contains a large amount of polyunsaturated fatty acids like 58% linoleic acid and 14% alpha-linolenic acid (Jackson and Looney, 1999). Walnut is a rich source of phytochemicals and contains a significant amount of phenols, flavonoids, sterols, tannins, phospholipids, terpenes, essential fatty acids, sphingolipids quinines, hydrocarbons, triterpenes, quinones, and oils (Crews et al., 2005). It is also contains essential minerals a-tocopherol, cellulose, albumin, and mucilage. Gallic acid, ethyl gallate, pyrogallol, vanillic acid,
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49. WALNUT O
OH
O
HO
OH
HO
OH
OH
O
Juglone
OH
Alpha hydrojuglone O
OH
Gallic acid
HO OH
HO HO
HO
OCH
Vanillic acid
Pryogallol
O HO
Linoleic acid
FIGURE 49.2
Important bioactive compounds of walnuts.
proto-catechuic acid, and p-hydroxybenzoic acid are the main phenolic acids present in walnut (Davis et al., 2007). Walnut seed oil contains sterols, acrid resin, myristin, free fatty acids, sterol esters, palmitin, and stearin (Calzoni et al., 1990). Important bioactive compounds of walnuts are shown in Fig. 49.2.
3. POSTHARVESTING TECHNOLOGY Before the age of mechanization, the traditional September harvesting of walnuts consisted of shaking the trees by hand using long hooked poles to knock the nuts to the ground, from where they could be easily collected. This breaks off many of their points, thereby causing the production of new spurs, which will probably bear fruit-bearing flowers (Jackson and Looney, 1999). Today, the trees are shaken by a machine, while another machine uses vacuum suction to collect the fallen nuts. Commercial hot air dehydrators with blower fans circulate warm air to reduce the moisture of the walnuts between 12% and 20% to preserve their shelf life.
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In past centuries, walnuts were simply left on drying racks away from the sun, until they were properly dried (Gandev, 2007). Postharvest treatment involves sieving the walnuts to remove sticks and leaves, hulling to remove hulls, washing, and then grading into different sizes. Hand sorting of nuts is used to remove damaged nuts. The nuts are then put into a drier to reduce the moisture content of the kernel from 10%e30% to around 5%e8%.
4. PROCESSING Once the walnuts are harvested, precleaners are used to clean the walnuts so they are ready for hulling. A huller removes the outer green hull, and the nut is mechanically dehydrated (air dried) to the optimum 8% moisture level, preventing deterioration of the nut and protecting its quality during storage. Hulled walnuts are transported to nearby packing plants and are stored until needed for cracking (Mapelli et al., 1995). Drying may be done in the sun, in kilns, portable field bins, or in fruit bins. In all but the first method, heat applied from a gas or oil burner may be used up to 110 C. Above this temperature, kernel quality is decreased. Some growers prefer to use fan-forced air, without heating, to maintain nut quality at the expense of drying time. Packaging should be moistureproof. Shelled products should be packaged in airtight, moisture-proof, opaque, or foil packages to maximize shelf life. Unroasted kernels are less likely to take up moisture than roasted kernels. Dried nuts last for about 4 months at room temperature before becoming rancid, and 1e2 years when stored in the freezer. The primary objectives of storage are to maintain the low water content attained after preliminary drying (to suppress enzyme activity, retain texture, and reduce microbial activity) and to limit exposure to O2 (to minimize rancidity). The optimum temperature range for storage is 0e10 C (32e50 F), with the lower temperature being better.
5. VALUE ADDITION Walnuts are delicious way to add extra flavor, nutrition, and crunch to a meal. Walnuts can ‘be taken with onions, salt, and honey. Walnuts are a common food source and are used in cooking and baking (Rosengarten, 1984). Green walnuts are completely edible but are a bit sour. They form an ideal ingredient for pickles, jams, and marmalades (Payne, 1985).
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6. USES Walnuts have various benefits that are useful for humans. They are considered a major source of U-3fatty acid. They have been used as nuts from ancient time, and walnut oil is considered beneficial for our health, skin, and hair. In last few decades, walnut consumption has seen several changeable developments (Hocking, 1997). Several commercial industries use the finely ground walnut shells, in the aeronautical industry for polishing of metals, for removal of graffiti and paints, and for cleaning of electronic circuits, jet engines, and of automobiles. Walnut is used in face powder, exfoliating cleanser, and soaps. Shells of walnut are used in cleaning of stone, plastic, wood, fiberglass, and soft metals (Bown, 1995).
7. PHARMACOLOGICAL USES 7.1 Antimicrobial Activity Walnut tree is a potent source of antimicrobial agent. It has been reported that different parts of this plant show strong antimicrobial activity against various fungal as well as bacterial strains. Aqueous extract of six different green husk varieties were found potentially active against Bacillus subtilis, Cryptococcus neoformans, Escherichia coli, Bacillus cereus, Candida albicans, Pseudomonas aeruginosa, and Staphylococcus aureus strains (Oliveira et al., 2008). Walnut ethyl acetate extract exhibited potential antifungal activity against the Candida albicans strains (Noumi et al., 2010). Powerful antimicrobial activity was shown from the pyroligneous acid, which is obtained from the branches of pyrolyzing walnut tree (Wei et al., 2010). Leaves and barks of walnut, especially its aqueous and other solvent extracts, showed antifungal potential against a vast range of fungal strains, determined by using agar dilution reddish method and disc diffusion method (Pereira et al., 2008). Acetone, methanol, chloroform, and ethyl acetate extract of bark exhibited antifungal activity against Aspergillus niger, Alternaria alternata, Trichoderma virens, Fusarium solani, Pichia guiliermondii, and Pichia jadinii (Ahmad et al., 1973).
7.2 Antioxidant Activity Antioxidant potential of walnut seeds alcoholic extract assessed by DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity assays that showed positive results with high scavenging of free radicals (Carvalho et al., 2010). A similar pattern is mentioned in another literature report in which walnut stem and bark showed significant scavenging of free radicals (Ngoc et al., 2008). Moreover, the aqueous extract of walnut
7. PHARMACOLOGICAL USES
679
green husk exhibited in vivo antioxidant potential against cyclophosphamide-induced urotoxicity in the mice. Walnut extract restored all antioxidants significantly in the bladder (Bhatia et al., 2006).
7.3 Antimutagenic Activity Walnuts extracts, i.e., aqueous and acetone, are quite effective and exhibited antimutagenic activity. These extracts were considered very efficient for inhibiting the 2-aminoflourene 2-AFeinduced mutagenicity in strains of Salmonella (Kaur et al., 2003).
7.4 Anticancer Activity Prostate cancer is one of the most common types of cancer reported in men. It has been reported that regular consumption of walnut seeds reduces the risk of prostate cancer in males (Spaccarotella et al., 2008). Juglone is one of the major components of walnut tree and is reported to have anticancer potential against melanoma cell lines (Aithal et al., 2009). In another study, it was reported that walnut extract and fractions with excess amount of juglone and ellagic acid impressively reduced the cancer cell proliferation. Walnut seed is a rich source of omega-3 that may decrease the risk of breast cancer (Hardman and Ion, 2008).
7.5 Cholesterol Lowering Activity High cholesterol level in blood is one of the major factors of cardiovascular diseases. It has been reported that daily consumption of walnut seed significantly reduces the body cholesterol level (Sabate et al., 1993). Up to 70% risk of arteries clogging and stroke is reduced by consuming high amount of walnuts (De Lorgeril et al., 1994). Endothelial dysfunction coupled with the cardiovascular disease is restored by several food components. Walnut diet showed improved endothelial function in hypercholesterolemic patients. Walnut significantly minimized total cholesterol and low-density lipoprotein (LDL) cholesterol level (Ros et al., 2004). Similarly, it reduces the concentration of triglyceride and serum cholesterol (Rajaram et al., 2009).
7.6 Antidiabetic Activity It has been reported that daily use of the diet rich in walnut seeds significantly reduced the sugar level in patients with diabetes mellitus type 2 (Gillen et al., 2005). Dietary fats can be influenced with the walnuts to produce the reductions in fasting insulin levels. The plant extract of
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walnuts inhibited efficiently alpha-glycosidase activity for both sucrose and maltase enzymes and showed no change in the insulin and glut-4 genes expression (Teimori et al., 2010).
7.7 Antiaging Effects Walnut seed oil is a rich source of omega-3 natural antioxidants. Therefore, it has been used as a natural moisturizing and antiaging agent in beauty products (Espı´n et al., 2000). Moreover, the ethanolic extract of its leaves could be suggested as a good and new source of skin-lightning agents. Walnuts polyphenolic constituents showed significant skin lightning and were found more superior to the skin-lightning agents such as arbutin and ascorbic acid (Aitani and Shimoda, 2005).
7.8 Antiviral Activity It has been illustrated that walnut leaf extracts prepared from 95% ethanol as well as ethyl acetate significantly reduced the production of tobacco mosaic virus (Zhai et al., 2006). Methanol extract of walnut at a minimum concentration of 1.5 mg/mL inhibited the Sindbis virus (Mouhajir et al., 2001).
7.9 Antianesthetic/Depressant Activity The in vivo study results showed that walnut extracts significantly reduced depression. The walnut extracts open the closed coronary arteries of rabbit’s heart (Auyong et al., 1963). The hexane extract of walnut fruit exhibited efficient antidepressant activity at 100 and 150 mg/kg doses of body weight of male Wistar rat compared with the standard drug fluoxetine. Tail suspension and forced swimming tests were used to evaluate the antidepressant activity (Rath and Pradhan, 2009).
7.10 Anti-Alzheimer Activity In traditional medicinal systems, different parts of walnut have been used to reduce Alzheimer disease. It has been reported in different scientific reports that walnut extracts exhibited anti-Alzheimer activity. In one of the scientific reports, it was mentioned that walnut extract strongly defibrillated the beta-amyloid plaques (Chauhan et al., 2004). In another in vivo study, walnut significantly enhance the cognitive as well as motor performance in rats (Willis et al., 2009). Similarly, methanol extract of walnut has the ability to reduce the b-amyloid protein formation in Alzheimer patients. Moreover, it has been reported that the polyphenolic
REFERENCES
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compounds present in walnut may attribute for its antiamyloidogenic activity (Chauhan et al., 2004).
7.11 Effects on Bone Health Walnuts promote bone health. Walnut oil is a rich source of a-linoleic acid and U-3 fatty acids, which are essential for normal bone growth. It has been reported that the consumption of walnut in daily food stuff significantly reduced a marker of bone break down, i.e., N-telo-peptides serum concentration. Moreover, walnuts have osteoblastic potential that improves bone formation (Griel et al., 2007).
8. SIDE EFFECTS AND TOXICITY Walnuts have been reported to have extensive toxic effects on different organisms, and it has been studied widely for its toxicity. The mechanism of walnut toxicity is well understood by either electrophilicity or by oxidative stress (Gant et al., 1986). Generally, juglones were more cytotoxic than the parent compound 1, 4-naphthoquinone (Doherty et al., 1987). Walnut promoted skin tumors in female Swiss mice that were pretreated with a subcarcinogenic dose of DMBA (di-methyl benzene anthracene), which was followed by juglone’s dermal applications for a year. Though, the skin tumor was not observed, followed by the treatment of juglone without pretreatment with DBMA (Van Duuren et al., 1978). Juglone is considered an equivocal tumorigenic agent (thorax, lungs, respiration, appendages, and skin) by the Registry of Toxic Effects of Chemical Substances based on the 29-week skin painting study of mice.
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Calzoni, G., Speranza, A., Caramiello, R., Piccone, G., Zannini, P., 1990. Wall ultrastructure and biochemical features of the Juglans regia L. and Juglans nigra L. male gametophyte. Sexual Plant Reproduction 3, 139e146. Carvalho, M., Ferreira, P.J., Mendes, V.S., Silva, R., Pereira, J.A., Jero´nimo, C., Silva, B.M., 2010. Human cancer cell antiproliferative and antioxidant activities of Juglans regia L. Food and Chemical Toxicology 48, 441e447. Chauhan, N., Wang, K., Wegiel, J., Malik, M.N., 2004. Walnut extract inhibits the fibrillization of amyloid beta-protein, and also defibrillizes its preformed fibrils. Current Alzheimer Research 1, 183e188. Cogliastro, A., Gagnon, D., Bouchard, A., 1997. Experimental determination of soil characteristics optimal for the growth of ten hardwoods planted on abandoned farmland. Forest Ecology and Management 96, 49e63. Crews, C., Hough, P., Godward, J., Brereton, P., Lees, M., Guiet, S., Winkelmann, W., 2005. Study of the main constituents of some authentic hazelnut oils. Journal of Agricultural and Food Chemistry 53, 4843e4852. Dandekar, A., Leslie, C., McGranahan, G., Litz, R., 2005. Juglans regia walnut. Biotechnology of Fruit and Nut Crops 307e323. Davis, L., Stonehouse, W., Mukuddem-Petersen, J., van der Westhuizen, F.H., Hanekom, S.M., Jerling, J.C., 2007. The effects of high walnut and cashew nut diets on the antioxidant status of subjects with metabolic syndrome. European Journal of Nutrition 46, 155e164. De Lorgeril, M., Renaud, S., Salen, P., Monjaud, I., Mamelle, N., Martin, J., Guidollet, J., Touboul, P., Delaye, J., 1994. Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. The Lancet 343, 1454e1459. Doherty, M.D.A., Rodgers, A., Cohen, G.M., 1987. Mechanisms of toxicity of 2-and 5-hydroxy-1, 4-naphthoquinone; absence of a role for redox cycling in the toxicity of 2-hydroxy-1, 4-naphthoquinone to isolated hepatocytes. Journal of Applied Toxicology 7, 123e129. Espı´n, J.C., Soler-Rivas, C., Wichers, H.J., 2000. Characterization of the total free radical scavenger capacity of vegetable oils and oil fractions using 2, 2-diphenyl-1-picrylhydrazyl radical. Journal of Agricultural and Food Chemistry 48, 648e656. Facciola, S., 1990. Cornucopia: A Source Book of Edible Plants. Frederick, C., Tang, C., Wu, B., 2014. China Tree Nuts Annual. USDA, Foreign Agricultural Service. GAIN CH14051. http://gain.fas.usda.gov. Galey, F., Whiteley, H., Goetz, T., Kuenstler, A., Davis, C., Beasley, V., 1991. Black walnut (Juglans nigra) toxicosis: a model for equine laminitis. Journal of Comparative Pathology 104, 313e326. Gandev, S., 2007. Budding and grafting of the walnut (Juglans regia L.) and their effectiveness in Bulgaria (review). Bulgarian Journal of Agricultural Science 13, 683. Gant, T.W., Doherty, M.d.A., Odowole, D., Sales, K.D., Cohen, G.M., 1986. Semiquinone anion radicals formed by the reaction of quinones with glutathione or amino acids. FEBS Letters 201, 296e300. Gillen, L.J., Tapsell, L.C., Patch, C.S., Owen, A., Batterham, M., 2005. Structured dietary advice incorporating walnuts achieves optimal fat and energy balance in patients with type 2 diabetes mellitus. Journal of the American Dietetic Association 105, 1087e1096. Gleeson, S.K., 1982. Heterodichogamy in walnuts: inheritance and stable ratios. Evolution 892e902. Griel, A.E., Kris-Etherton, P.M., Hilpert, K.F., Zhao, G., West, S.G., Corwin, R.L., 2007. An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans. Nutrition Journal 6, 2. Hardman, W.E., Ion, G., 2008. Suppression of implanted MDA-MB 231 human breast cancer growth in nude mice by dietary walnut. Nutrition and Cancer 60, 666e674.
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Rosengarten Jr., F., 1984. The Book of Edible Nuts. Walker Publishing, New York, New York, USA, pp. 239e262. Sabate, J., Fraser, G.E., Burke, K., Knutsen, S.F., Bennett, H., Lindsted, K.D., 1993. Effects of walnuts on serum lipid levels and blood pressure in normal men. New England Journal of Medicine 328, 603e607. Spaccarotella, K.J., Kris-Etherton, P.M., Stone, W.L., Bagshaw, D.M., Fishell, V.K., West, S.G., Lawrence, F.R., Hartman, T.J., 2008. The effect of walnut intake on factors related to prostate and vascular health in older men. Nutrition Journal 7, 1. Teimori, M., Montasser Kouhsari, S., Ghafarzadegan, R., Hajiaghaee, R., 2010. Study of hypoglycemic effect of Juglans regia leaves and its mechanism. Journal of Medicinal Plants 1, 57e65. Van Duuren, B., Segal, A., Tseng, S., Rusch, G., Loewengart, G., Mate´, U., Roth, D., Smith, A., Melchionne, S., Seidman, I., 1978. Structure and tumor-promoting activity of analogs of anthralin (1, 8-dihydroxy-9-anthrone). Journal of Medicinal Chemistry 21, 26e31. Wei, Q., Ma, X., Dong, J., 2010. Preparation, chemical constituents and antimicrobial activity of pyroligneous acids from walnut tree branches. Journal of Analytical and Applied Pyrolysis 87, 24e28. Williams, R.D., 1990. Juglans nigra L., black walnut. Silvics of North America 2, 391e399. Willis, L.M., Shukitt-Hale, B., Cheng, V., Joseph, J.A., 2009. Dose-dependent effects of walnuts on motor and cognitive function in aged rats. British Journal of Nutrition 101, 1140e1144. Zhai, M.-z., Zhang, F.-y., Wei, H., Wang, W., 2006. A study on the bioactivity of secondary metabolites from walnut green gull. Journal of Northwest Forestry University 21, 122.