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Essay on Anti-Oxidants
Essay Contents:
- Essay on the Meaning of Anti-Oxidants
- Essay on the Effect of Anti-Oxidants in Disease Prevention
- Essay on the Effect of Cooking on Anti-Oxidants
- Essay on the Measurement of Anti-Oxidant Potential
- Essay on the Dietary Intake of Anti-Oxidants
- Essay on the Other Applications of Anti-Oxidants
Essay # 1. Meaning of Anti-Oxidants:
An anti-oxidant is a molecule that inhibits the oxidation of other molecules. Anti-oxidants terminate the chain reactions by removing free radical intermediates, and inhibiting other oxidation reactions. They do this by being oxidized themselves.
The body possesses an enzymatic mechanism against oxidative stress, which is made up of free radical scavengers like superoxide dismutase (SOD), catalase (CAT), and the glutathione- dependent enzymes such as glutathione peroxidase (GPx), glutathione S-transferase (GSH), and Glutathione reductase (GR). GR and enzymatic anti-oxidant mechanisms play an essential role in preventing oxidative damage in cells and tissues.
Moreover, several nutritional and phytochemical constituents of food also protect the body against oxidative stress. These include vitamins A, C and E, carotenoids and flavonoids, all of which are available from foods. Anti-oxidants are often reducing agents e.g. thiols, ascorbic acid or polyphenols. Thus, the antioxidant defense system of the body is composed of antioxidant enzymes and food constituents.
Oxidative stress results from a persistent imbalance between antioxidant defenses and the production of highly reactive oxygen species (ROS). Anti-oxidants prevent and protect the body cells from the damage caused by free radicals. Currently, there has been an increased global interest to identify anti-oxidant compounds that are pharmacologically potent and have low or no side effects, for use in preventive medicine. A wide range of nutritional and non-nutritional anti-oxidants including vitamins A, C and E, carotenoids and flavonoids are all available from fruits and vegetables.
The importance on anti-oxidant activities of phenolic compounds in fruits and vegetables as natural anti-oxidants has reached a new high in recent years. Vegetables belonging to the Brassicaceae family are rich in polyphenols, flavonoids and glucosinolates, and their hydrolysis products, which may have anti-bacterial, antioxidant and anti-cancer properties.
Dietary polyphenols may exert their anti-cancer effects through several possible mechanisms, such as removal of carcinogenic agents, modulation of cancer cell signaling and anti-oxidant enzymatic activities, and induction of apoptosis. The pro-oxidant effect of dietary polyphenols may contribute to the activation of anti-oxidant enzymes and protective proteins in cultured cells and animal models because of the adaptation of cells and tissues to mild/moderate oxidative stress.
Because of increased safety concerns about synthetic anti-oxidants, exploitation of cheaper and safer sources of anti-oxidants based on natural origin is the focus of research now a days. As plants produce significant amount of anti-oxidants to prevent oxidative stress, they represent a potential source of new compounds with antioxidant activity.
A lot of medicinal plants, traditionally used for thousands of years, are present in a group of herbal preparations of the Indian traditional health care system, Ayurveda. Among the medicinal plants used in ‘Ayurvedic Rasayana’ for their therapeutic action, some have been thoroughly investigated.
Plant foods provide more than 25,000 bioactive constituents (World Cancer Research Fund/American Institute for Cancer Research, 2007). Judging the historical, etymological, morphological, phytochemical and pharmacological aspects of Emblica officinalis L., Curcuma longa L., Mangifera indica L., Momordica charantia L., Santalum album L., Swertia chirata Buch-Ham, Withania somnifera Dunal) all of them were found to contain antioxidant principles that explain and justify their use in traditional medicine.
Essay # 2. Effect of Anti-Oxidants in Disease Prevention:
Anti-oxidants can eliminate free radicals and other reactive oxygen and nitrogen species which contribute to most chronic diseases, and also induce mechanisms related to anti-oxidant defense, such as radical scavenging ability, complex formation with DNA and direct binding to proteins, longevity, cell maintenance and DNA repair, cancer chemo-preventive potential antibacterial and wound healing properties. Antioxidants offer protection against several diseases including CVD, Alzheimer’s Disease, asthma, eye disorders, skin disorders, wrinkles, osteoporosis, gall stones, menstrual disorders etc.
The protective effect of antioxidants against certain diseases has been discussed below:
i. Heart Disease:
Deficiencies of vitamins A, C, E, beta carotene and lycopene have been linked to heart disease. A high intake of fruits and vegetables containing beta carotene, lycopene, and other carotenoids may reduce the risk of heart attack. All of these nutrients have anti-oxidant effects and other properties that may benefit the heart. Mattioli et al (2011) reported high intake of anti-oxidants to be significantly associated with an increasing probability of spontaneous alleviation of arrhythmia (P < 0.01).
Vitamin E had an anti-oxidant effect when administered at low doses over short time periods (biweekly intramuscular administration of 100,300 and 600 mg/kg at a baseline time point, and additionally at 2, 4 and 6 weeks later) increased the activity of anti-oxidant enzymes. However, at higher doses and over longer time periods, it increased the level of lipid peroxidation, and attenuated the activity of anti-oxidant enzymes.
ii. Cancer:
Besides preventing heart disease, fresh fruits and vegetables also help fight cancers, including lung, breast, colon, and prostate cancers. Most chemo-preventive agents are antioxidant in nature. Examples of important cancer-fighting foods include various cruciferous vegetables (e.g., cabbage, sprouts and broccoli).
Although supplements of vitamins A, C, and E appear to have no advantages, studies have reported an association between low blood levels of these anti-oxidant vitamins and a higher risk for cancer. Some studies have suggested that certain vitamin D compounds may inhibit certain cancer cells, specifically prostate cancer, from proliferating.
There is some evidence that anti-oxidants including vitamins E and C, beta carotene, isoflavones (found in soy), and quercetin (found in red wine and purple grape juice) may enhance the anti-cancer effects of chemotherapy.
Naziroðlu et al (2004) reported that intra-peritoneally injected selenium combined with a high dose of vitamin E produced a significant improvement on anti-oxidant concentrations in rats treated before, simultaneously and after with cisplatin (one of the most active cytotoxic agents in the treatment of cancer). Interestingly, resveratrol, a polyphenol present in grapes and red wine exhibit anti-cancer and chemo-preventive properties due to its pro-oxidant action.
iii. Lung Disease:
Bentley et al (2011) reported that the intake of anti-oxidant nutrients may modulate lung function decline in older adults exposed to cigarette smoke by delaying the rate of forced expiratory volume (FEV1).
Kayan et al (2009) investigated the effects of Vitamins C and E administration on X-ray-induced oxidative toxicity in blood of smoker and nonsmoker X-ray technicians and found that both of these vitamins prevented the smoke and X-ray-induced oxidative stress and strengthened anti-oxidant vitamin concentrations in the blood of the technicians. Vitamin E and selenium also have protective effects on the cigarette smoke-induced blood toxicity by supporting the enzymatic anti-oxidant redox systems.
iv. Epilepsy:
Topiramate, a voltage-gated calcium channel inhibitor, has an evident effect in the treatment of childhood epilepsy; however, topiramate may cause nephrotoxicity. But treatment with topiramate combined with vitamin E showed protective effects on pentylenetetrazol-induced nephro-toxicity by inhibition of free radicals and by supporting the anti-oxidant redox system. There is convincing evidence for the proposed crucial role of selenium and deficiency of GSH-Px enzyme activity in epilepsy pathogenesis.
Just as Vitamin E, selenium also in combination with topiramate showed protective effects on pentylentetrazol (PTZ)-induced brain toxicity (seizures) in rats by inhibiting free radical production, regulating calcium- dependent processes, and supporting the anti-oxidant redox system, and epilepsy.
Demirci et al. (2013) have reported that selenium alone could also provide protective effects on oxidative stress in neuronal PC12 cells by modulating cytosolic Ca2+ influx and anti-oxidant levels. Selenium induced protective effects on oxidative stress, (Ca2+)(c) release and apoptosis in dorsal root ganglion cells since selenium deficiency is a common feature of oxidative stress- induced neurological diseases of sensory neurons.
v. Cataract:
The presence of the direct oxidation product of lutein and 3′-epilutein (metabolite of lutein and zeaxanthin) in human retina suggests that lutein and zeaxanthin may act as antioxidants to protect the macula against short-wavelength visible light. Oxidized lutein may be highly reactive, since oxidation results in radical ions, which can combine with similar reactive oxidative species that could lead to higher anti-oxidant effect.
Lakshminarayana et al. (2010) demonstrated that anti-oxidant property of oxidized lutein was higher than lutein that correlated with free radical scavenging activity and cytotoxic effects on HeLa cells. Further, Lakshminarayana et al. (2013) reported that oxidation by 2,2′-Azobis (2- methylpropionamidine) dihydrochloride (AAPH) Resulted in peroxyl radical ions, which can react with conjugated polygene chain of lutein that could lead to higher anti-oxidant and cytotoxic effects on HeLa cells.
Essay # 3. Effect of Cooking on Anti-Oxidants:
In general, anti-oxidant contents are preserved fairly well during most types of processing, but there are some exceptions. Boari et al (2013) observed that cooking did not always have negative effect on product quality, since in certain cases, it even enhanced the nutritional value of wild edible plants by increasing their total antioxidant activity and reducing the nitrate content.
The anti-oxidant content increased in products such as carrots, spinach, mushrooms, asparagus, broccoli, cabbage, red cabbage, green and red peppers, potatoes, and tomatoes during microwave cooking, steaming, or boiling. Anti-oxidant values also increased after toasting or baking of bagels, French bread, wheat bread, whole-wheat bread, and pie crust.
Stir-frying increased anti-oxidant capacities in bamboo shoots as compared to boiling and steaming and hence may be considered suitable method of cooking the same. On the other hand, Pellegrini et al (2010) demonstrated that fresh brassica vegetables retain phytochemicals and total anti-oxidant capacity better than frozen samples.
According to Ng et al. (2011) boiling generally improved the overall anti-oxidant activity in all the vegetables while pressure cooking did not cause any significant decline in the anti-oxidant property, thus suggesting that prudence in selecting an appropriate cooking method for different vegetables may improve/preserve their nutritional value.
Essay # 4. Measurement of Anti-Oxidant Potential:
Several assays have been used to assess the total anti-oxidant content of foods, e.g. the 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) equivalent anti-oxidant capacity (TEAC) assay and the oxygen radical absorbance capacity assay (ORAC) assay the ferric-reducing ability of plasma (FRAP).
Anti-oxidant activity is measured using the linoleic acid system, metal chelating activity, ferric thiocyanate method, and lipid peroxidation, total reducing power by potassium ferricyanide reduction method, scavenging effect on 1,1- diphenyl-2-picrylhydrazyl free radical, and superoxide anion radical scavenging activity as the parameters for assessment of anti-oxidant potential of methanolic extracts.
The bioavailability of phytochemical anti-oxidants is influenced by many factors such as, the food matrix, absorption and metabolism. The methods measuring total antioxidant capacity do not identify single anti-oxidant compound, and thus cannot help in determining the mechanisms involved.
These different anti-oxidant assays for measuring anti-oxidant capacity make it difficult to compare whole lists of foods, products and product categories. But a food that has a high total anti-oxidant capacity (TAC) in one assay will most likely show the same in another assay. But, though the exact values differ, the ranking of the products will not differ.
Anti-Oxidant Capacity of Different Foods:
Foods from all the food groups have been identified with anti-oxidant constituents. Breakfast cereals, grains, legumes, nuts and seeds are poor in antioxidant capacity. Among cereal products, whole meal buckwheat and wheat bran had the greatest total anti-oxidant capacity (TAC). Pellegrini et al (2006) expanded the data base for TAC of different foods and reported that among pulses and nuts, broad bean, lentil and walnuts had the highest anti-oxidant capacity, whereas chickpeas, pine nuts and peanuts were less effective.
The contribution of bound phytochemicals to the overall TAC was relevant in cereals as well as in nuts and pulses. Among the oils soybean oil has the highest anti-oxidant capacity followed by extra virgin olive oil and groundnut oil having the least capacity.
Most of the dairy products are low in anti-oxidant content, in the range of 0.0 to 0.8 mmol/100 g. Eggs are almost devoid of anti-oxidants with the highest anti-oxidant values found in egg yolk (0.16 mmol/100 g). Especially high anti-oxidant capacity was found in dried amla (Indian gooseberry, 261.5 mmol/100 g).
Mean anti-oxidant contents increased with increasing content of cocoa in the chocolate product. Chocolate products with cocoa contents of 24-30 per cent, 40-65 per cent and 70-99 per cent had mean anti-oxidant contents of 1.8, 7.2 and 10.9 mmol/100 g, respectively.
Walnuts, with pellicle and nut shell intact contains 33.3 mmol/100 g. Pecans with pellicle, sunflower seeds and chestnuts with pellicle, have mean anti-oxidant content in the range of 4.7 to 8.5 mmol/100 g.
Fresh fruits and vegetables have been considered the most important sources of antioxidants. Examples of anti-oxidant rich berries are fresh, black currants, wild strawberries, blackberries and cranberries. Certain dried fruits and vegetables such as dried apples, lemon skin, plums, apricots, dates, mango, black and green olives, red cabbage, guava, plums, prunes and red beets, paprika, red and green chilly were also found to be rich in antioxidants. However, the antioxidant content in these dried foods was reported to be in the medium range.
Other anti-oxidant rich products are Triphala, Amla and Arjuna from India and Goshuyu-tou, a traditional kampo medicine from Japan, with anti-oxidant values in the range of 132.6 to 706.3 mmol/100 g.
Although spices, herbs and condiments such as fennel seeds are consumed in very small quantities, they may still be important contributors of the total anti-oxidant intake, especially in India where spices and herbs are used in cookery regularly.
Several foods showed improved antioxidant potential when consumed along with individual antioxidant nutrients, e.g. Phyllanthus emblica L., Santalum album L., Syzygium cumini L. and Trigonella foenum-graecum L. presented highly significant antiradical efficiency (AE) singly and in combination with either vitamin A, C or E.
Further, Curcuma longa L., Momordica charantia L., S. cumini, T. foenum-graecum, Moringa oleifera Lam. and S. album have also shown fairly significant AE in a vitamin combination dose of 0.001mM concentration.
Essay # 5. Dietary Intake of Anti-Oxidants:
The relation between dietary anti-oxidants and oxidative stress-induced diseases can be established with the anti-oxidant content coupled with an estimate of antioxidant intake. There are several thousand-fold differences in anti-oxidant content of foods, some with exceptionally high values.
A comprehensive food database consisting of the total anti-oxidant content of typical foods as well as other dietary items such as traditional medicinal plants, herbs and spices and dietary supplements is helpful in planning diets. For example, soybean oil has the highest anti-oxidant capacity, followed by extra virgin olive oil, whereas peanut oil is less effective of the oils.
Beverages account for a very high proportion of dietary anti-oxidant intake as compared to intake of anti-oxidant vitamins C and E in the Spanish diet where coffee is the main contributor (61-66 per cent respectively), followed by red wine (16-22 per cent), fruit juices (5-6 per cent), beer (4-5 per cent), tea (3-5 per cent) and milk (1-4 per cent).
In general, vegetarian diet contains more anti-oxidant vitamins i.e. vitamin C, vitamin E, and beta-carotene and copper than that of non-vegetarian diet. Intake of zinc in vegetarians is generally comparable to that of non-vegetarians. However, the bioavailability of zinc in vegetarian diets is generally low.
Dietary intake of selenium is variable in both groups and depends on the selenium content of the soil. Anti-oxidant status in vegetarians shows higher anti-oxidant vitamin status (vitamin C, vitamin E, beta-carotene) but variable anti-oxidant trace element status as compared to the non-vegetarians.
In Rural Mexico, Hervert-Hernández and Go i (2011) found soft drinks to be the most commonly consumed beverage (280 ml/d), followed by coffee and fresh fruit beverages among pre-menopausal obese women. Polyphenol intake and dietary antioxidant capacity from beverages was 181 mg/person per day and > 1000 µmol. Trolox equivalents /person per day respectively. The items that contributed most to this intake were coffee, roselle drink, peach and guava juices and infusions.
Essay # 6. Other Applications of Anti-Oxidants:
Traditionally, the age old practice of improving the stability of ghee (clarified butter) or oils is to use curry leaves or Drumstick leaves as a source of anti-oxidant. The leaves of M. oleifera have been reported to be a valuable source of both macro and micro-nutrients, calcium, and potassium and especially β-carotene, vitamin C, and thus act as a good source of natural anti-oxidants; and thus enhance the shelf-life of fat-containing foods.
Sánchez de Medina et al. (2011) used phenolic extracts from olive tree leaves and olive pomace to enrich refined oils (namely, maize, soy, high-oleic sunflower, sunflower, olive, and rapeseed oils) at two concentration levels (200 and 400 µg/mL, expressed as gallic acid) for their preservation. All the oils experienced either a noticeable or a dramatic improvement of their quality-stability parameters (e.g., peroxide index and Rancimat) as compared with their non-enriched counterparts.
According to Mohamad et al. (2011) fennel seeds could be used as a safe, effective, and easily accessible source of natural anti-oxidants to improve the oxidative stability of fatty foods during storage.
Fennel seed methanolic extract showed strong free radical-scavenging activity (100 per cent). Thus, fennel seeds may reduce oxidative stress and protect mouse cells from damage caused by reactive oxygen species.
Conclusions:
Anti-oxidant nutrients and foods play a fundamental role not only in prevention and cure of CVD but also in anti-ageing along with several other degenerative diseases. Interestingly, the anti-oxidant content in human breast milk is comparable to that in pomegranate juice, strawberries and coffee and on average higher than the antioxidant content observed in the commercially available infant formulas analyzed.
The benefits of anti-oxidants have raised commercial and research interest in foods with anti-oxidant components resulting in ascertaining their role in health and disease.