INTRODUCTION:

Oxygen free radicals or reactive oxygen species (ROS), are products of normal cellular metabolism. Free radicals can be defined as molecules or molecular fragments containing one or more unpaired electrons in atomic or molecular orbitals. This unpaired electron(s) usually gives a considerable degree of reactivity to the free radical. Radicals derived from oxygen represent the most important class of radical species generated in living systems.¹ During the process of oxygen utilization in a normal physiological and metabolic process, approximately 5% of oxygen gets univalently reduced to oxygen derived free radicals like superoxide, hydrogen peroxide, hydroxyl and nitric oxide radicals. All these radicals known as reactive oxygen species (ROS), exert oxidative stress towards the cells of human body. The oxidative damage caused by free radical is related to pathogenesis of many chronic degenerative diseases like cancer, diabetes, neurodegenerative disease, atherosclerosis, cirrhosis, malaria and AIDS.² Most living species have an efficient defense system to protect themselves against the oxidative stress induced by Reactive Oxygen Species (ROS) ³.Although the human body produces antioxidant enzymes to neutralize free radicals, a diet rich in edible antioxidants is recommended to assist the human body to protect itself.

Medicinal plant parts are commonly rich in phenolic compounds, such as flavonoids, phenolic acids, stilbenes, tannins, coumarins, lignans and lignins. These compounds have multiple biological effects including antioxidant activity.⁴There are a number of clinical studies suggesting that the antioxidants in fruits, dried fruits, vegetables, tea and red wine are the main factors for the observed efficacy of these foods in reducing the incidence of chronic diseases including heart disease and some cancers.⁵ Dried fruits are widely used in confectionaries, bakery products and sweet industries. As almost all dried fruits have healthy protective bioactive ingredients and essential nutrients they help to reduce the risk of chronic illnesses and also prevent them. As dried fruits have all the nutritive value like fresh fruits, they are now highly recommended and are taken as dietary supplements. This review outlines the antioxidant activity of three dried fruits, raisins, almonds and walnut that are used by us commonly.⁶

Almond (Family: Rosaceae)

Almonds are called the “King of nuts.”Almond is an important food crop, varying in use from local consumption as an edible nuts in its natural state to inclusion as a major ingredient in manufactured food products.⁷Almonds contain monounsaturated fats and some polyunsaturated fats and hence they help to lower the low-density lipoprotein (LDL) or the bad cholesterol, while maintaining healthy high-density lipoproteins or good cholesterol levels.⁸ Almonds are natural sources of Vitamin E. Vitamin E is a powerful antioxidant. It protects our cells from damage by preserving the integrity of cell membrane. Both sweet and bitter almonds have similar chemical composition and contain 35–55% fixed oil. The only difference appears to be the presence of amygdalin (3–4%) in bitter almond and its absence or presence in trace amounts in sweet almonds. Other constituents reported to be present in sweet and/or bitter almonds include protein (18–25%); emulsin; prunasin (0.005% in bitter almond); daucosterol, and other sterols (e.g., sitosterol, citrostadienol, 24-methylene-cycloartanol); calcium oxalate; tocopherols (mostly α); trace amounts of vitamins A, B complex, and E; and amino acids, including glutamic acid, aspartic acid, and arginine^. 9

Antioxidant property:

Almond nuts possess high levels of phenolics, an important class of antioxidants in human nutrition, with most of this diverse range of compounds being found in the seed coat. Most are thought to have powerful effects on health.¹⁰ Consumption of almonds increases the flavonoids level in the body as also the level of vitamin E. The flavonoids are really helpful antioxidants and have many different health benefits such as having an anti-tumor effect and an anti-inflammatory effect in our body. Moreover, almonds are also known to be high in other antioxidants such as Epicatechin, Catechin and even Kaempferol that are very powerful and protect our body from different diseases, abnormalities and ailments at different stages of life and even during the course of our daily activities. Researchers have proved that consumption of a handful of almonds as part of the daily diet even helps in reducing the LDL levels in the body without causing any substantial weight gain.¹¹ They protect the body by deactivating the free radicals that are known as compounds that destroy cells leading to various complications like skin ailments, cardiac diseases, strokes and even cancer.

Almonds are also beneficial in treatment of constipation since they increase the fiber content of the food as well. Almonds has antioxidant properties and are hence very beneficial for the health. Almonds contain alpha-tocopherol, which is a major source of vitamin E and is hence really great for healthy hair and skin. Almonds also increase the blood flow to the vital organs and are also used as aphrodisiacs. Almonds decrease the after-meal rises in blood sugar and are hence help in maintaining a healthy blood sugar level.¹² Almond oil also possesses laxative properties and helps to produce soft stools and avoid any other problems of the digestive system.

The main biochemical function of tocopherols is believed to be the protection of polyunsaturated fatty acids against peroxidation. In almond, tocopherol concentration plays an important role in protecting lipids against oxidation and thus lengthening their storage time Alpha-tocopherol is the form of vitamin E that is most efficiently used by the human body yet is often deficient in modern diet. The vitamin E from almonds has been shown to be efficiently absorbed and produces a significant increase in plasma g-tocopherol levels.¹³

Raisins (Family : vitaceae )

A raisin is a dried grape. Raisins are made by dehydrating grapes in a process using the heat of the sun or a mechanical process of oven drying. Raisins have wrinkled skins surrounding chewy flesh that tastes like a burst of sugary sweetness.¹⁴ Raisins are cholesterol-free, low in sodium, high in fiber and totally fat-free. Apart from that, they contain a lot of vitamins and minerals, making their nutritional value very high. Raisins are the best source of quick energy, as they contain 70 percent pure fructose, which gets digested by the body easily and gives instant energy.¹⁵They contain a reasonable level of tartaric acid that works together with fiber to help proper elimination and keep the colon healthy. Raisin have been successfully used as part of diets to lower blood cholesterol and prevents its damaging oxidation.¹⁶

Antioxidant Property:

The phenols found in fruit have been shown to have antioxidant activity and prevent oxygen-based damage to cells in the body. The total antioxidant activity of many fruits and vegetables has been found to be exactly parallel to their total phenol content, and raisins take their place in this list right alongside prunes and apricots as an antioxidant-rich fruit.¹⁷ The flavonols (one type of phenol belonging to the flavonoid family) in raisins appear to be least affected by the grape-drying process, but raisins do contain fewer phenols than grapes since many of grape's phenols are largely lost in the conversion of grapes to raisins. These phenols include hydroxycinnamics (caftaricand coutaric acids), procyanidins, and flavan-3-ols. Raisins have high levels of catechins, which are polyphenolic antioxidants.¹⁸ They scavenge the free radicals that float around the body and wreak havoc on the organ systems and cells. These are also very good for ocular health, as they protect eyes from the damage caused by free radicals (oxidants), in the form of macular degeneration, age-related weakening of vision, and cataracts.¹⁹

In addition to their antioxidant qualities, raisins contain significant amounts of vitamin-A, A-Beta Carotene and A-Carotenoid, all of which are essential for good ocular health. Raisin contains flavonoids, which can have antioxidant effects, lower the levels of low density lipoproteins (LDLs, or “bad cholesterol”), relax blood vessels²⁰ and reduce the risk of coronary heart disease. Resveratrol, a polyphenol component of raisin has anti-oxidant, has anti-inflammatory, anti-cancer, blood cholesterol lowering activities. Studies suggest that resveratrol has been found to have protective action against cancers like melanoma, colon and prostate, and diseases such as coronary heart disease (CHD), degenerative nerve disease, Alzheimer's disease and viral/ fungal infections. Like in grapes raisins, especially those derived from red/purple grapes, are very high in anthocyanins, another class of polyphenolic anti-oxidants. Raisins are dense sources minerals like calcium, iron, manganese, magnesium copper, fluoride, and zinc. Copper and manganese are an essential co-factor of antioxidant enzyme, superoxide dismutase. ^{21 -23}

Therefore, by including raisins in your diet and increasing the level of these powerful antioxidants in your system, you can prevent cancer from forming, or slow down its progress if you have already developed a number of forms of that deadly disease.

Walnut (Family : Juglandaceae)

A walnut is an edible seed of any tree of the genus Juglans. Walnut seeds are a high density source of nutrients, particularly proteins and essential fatty acids. Walnuts are one of the most popular and versatile of all nuts. When picked young, they're known as wet and their milky white kernels are mainly used for pickling. Far more common is the dried nut, either shelled or unshelled. The brown-skinned kernel has a ridged surface, which looks like two halves of the brain. Slightly bitter in flavour, walnuts are good eaten raw or cooked, in either sweet or savoury dishes, and are particularly useful for baking.²⁴ Walnuts contain 60% oil,and 15% to 20% protein, bearing approximately 700 calories per 100g. The chief known chemical constituent in walnut is juglone. Also present are alpha-hydrojuglone and its glycoside beta-hydrojuglone, along with caffeic acid, ellagic acid, hyperin, and kaempferol, and the tannins galloylglucose and ellagitannis. Gamma lactones are present in walnut oils.²⁵

Antioxidant Property:

Walnuts and walnut oil have been cited as one of the best antioxidant sources among the tree nuts. Walnuts are especially dense in the antioxidant ellagic acid, which aids in controlling the replication of malignant tumors and has anti-bacterial, anti-inflammatory, antiviral and antiseptic properties. Gallic acid and malic acid, both antioxidants, are present in smaller quantities and have similar protective effects. Nuts constitute a good source of vitamin E with antioxidant properties, so they will be very effective to avoid the negative influence of free radicals in health. The presence of zinc in nuts, together with their content in vitamin B and polyphenols, helps to maintain the good state of the skin, preventing some anomalies like eczema or avoiding it to become dry. Of all the tree nuts, walnuts, pecans, and chestnuts contain the greatest amount of antioxidants. Although peanuts are technically legumes, they are nutritionally similar to nuts. Like walnuts, peanuts are packed with high levels of antioxidants. The study found that the antioxidants in walnuts were up to 15 times as potent as those found in vitamin E. A great deal of research has shown that regular consumption of nuts has many beneficial effects including the reduction of the risk of heart disease, diabetes and some forms of cancer.^26-29

CONCLUSION:

Dried fruits are rich with unusual and interesting facts from history. Dried fruits also have the advantage of being easy to store and distribute, available around the year, readily incorporated into other foods and recipes, and present a healthy alternative to salty or sugary snacks. Various researches indicate that majority of the fresh and dry fruits studied are rich in phenolic antioxidants with potent free radical scavenging activity. The three dried fruits Raisins, Almonds and Walnuts, reviewed in this article contains a lot of phyto nutrients that make them a very powerful anti oxidants.

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Received on 21.07.2014 Modified on 16.08.2014

Research J. Pharm. and Tech. 7(11): Nov. 2014 Page 1319-1322