Primarily the pigments are present in plants for photosynthesis, to capture the light of all hues. Some are synthesized by the plant to assist in various other functions like attracting pollinators, repelling pest or for defense purposes. Lycopene is one of the pigments having its relevance and significance beyond the plant's life, particularly in human health.
Lycopene is a tetraterpenic C40 carotenoid with a molecular weight of 536 Da and having very high antioxidant potential. It is a non- pro vitamin A carotenoid, which has upto twice the antioxidant capacity of β- carotene (Bohm et al., 2002). Red coloured lycopene pigment was first discovered in tomato by Millardet in 1876 and was named by Schunck as lycopene. As far as physico-chemical properties of lycopene is concerned, both cis & trans isomeric forms of lycopene occur in nature. It has conjugated double bonds in 11 places and non-conjugated double bonds in two places.
It is more stable in alkaline pH compared to acidic pH and is highly prone to oxidation. Tomato is a very important and abundant source of lycopene. In tomato 90% of it occurs as free crystal in protoplasm, and about 10% as complexes with proteins in the cells.
Significance of Lycopene in human health
Lycopene attracted commercial attention due to its significance in human health. As several biological processes involve oxidation and reduction a balance between oxidants and antioxidants is essentially required for maintaining the balance in metabolism. During the process of oxidative metabolism and release of energy, large amounts of ROS & RNS are released that damage the genetic material (DNA) by knocking out or adding an electron. Normally the body protects itself against these damages through an ‘antioxidant enzyme network’ that is part of body’s defense system. Several small biomolecules/pigments like anthocyanins, carotenoids, and vitamins like A & E, some minerals and phytochemicals that are ingested through food are contributing to ‘antioxidant defence’, either being a part of enzymes or by quenching free radicals like ROS and RNS.
Studies have indicated that higher intake of tomatoes as vegetable or as tomato product resulted in lower risk of chronic diseases like hypertension, diabetes, and cancer. In certain studies, an inverse relationship was seen between the serum and tissue lycopene levels and the cancer risks (Cohen et al, 2000; Kucuk et al, 1999). Currently health professionals and nutritionists have been recommending increased consumption of fruits and vegetables, from sources such as citrus, cruciferous vegetables, and other that have different colours like green and yellow. It is emphasized that each class of these foods have unique phytochemicals that confer preventive benefits by interacting with the host through regulation of enzymes that are important in metabolizing carcinogens and xenobiotics. It is said that the mechanism of action is directly through modulation of nuclear receptors, interfering in cellular signaling and apoptosis. Indirectly, it also happens by antioxidant actions of these molecules which reduce the proliferation and damage to DNA (Kucuk et al, 1999).
Research in recent past claim that many lifestyle diseases like HTN, cardiac diseases, hyperglycemia, cancer, and other diseases related to vision are due to oxidative stress caused over a long period of time. Several epidemiological studies have indicated that most of these types of diseases are prevalent in populations where intake of fresh fruits and vegetables is very low and consumption of junk foods, low in fibres and beneficial phytochemicals, is more. Many trials have shown that consumption of more of carotenoid rich foods, has resulted in lesser occurrence of diseases like prostate cancer and diabetes. Among the carotenoids, lycopene was found to be the most potent antioxidant, which the researchers thought are responsible for prevention of diseases. Lycopene has been ranked as being most potent among the antioxidants: lycopene > α-tocopherol > α-carotene > β-cryptoxanthin > zeaxanthin > β-carotene > lutein (Heber and Lu, 2002).
Reviews on mechanism of action of lycopene suggest that ‘lycopenoids’, may be the important metabolite that contribute to the decrease in risk of chronic diseases. While the antioxidant property of lycopene has been attributed to its positive effect in countering many disorders, its cancer preventing property has been attributed to its ability to induce apoptosis in cancer cells. It is said that molecular signalling between cells takes place through ‘channels’ that are formed by gap junction proteins such as ‘connexion 43’. Some studies have found a positive association between gap junction communication protein or ‘connexion 43’ and lycopene consumption, while some others have found no such correlation in certain other types of cancers. Lycopene because of its high number of conjugated dienes, is the most important singlet oxygen quencher among the carotenoids (Di Mascio et al., 1989). Its ability to scavenge nitrogen dioxide (NO2*), thiyl (RS*) and sulphonyl (RSO2*) radicals and protect lymphocytes from damage is reported to be twice when compared to β-carotene ( Bohm et al., 1995).
Tomato is the second most consumed vegetable in the world after potato and onion. About 8-10% of tomato fruit consists of its peel, which can yield between 20-30 mg lycopene/100g tomato peel when extracted using solvents like ethyle acetate, acetone, petroleum ether or their mixtures. When pre-treated with enzymes like pectinase, it can increase upto 44-57mg of lycopene/100g peels (Prathibha et al, 2015; Prathibha and Narayana, 2016 ; Prathibha et al, 2014).
HPLC is being used for separation of carotenoids, including lycopene, using C1s Column. Its demerit is that it fails to separate trans and cis isomers of lycopene. Flash purification is a method, that allows large amounts of sample size to be injected and later the solvent can be quickly evaporated (Xu et al, 2006).
Compared to conventional method of solvent extraction, enzyme-assisted extraction is another potential alternative where the enzymes that catalyze reactions have high specificity, region-selectivity and an ability to function under mild processing conditions and in aqueous phase (Gardossi, 2009). Prathibha et al (2014) compared the solvent and enzymatic extraction methods and reported higher yields (56.76 mg/100g wet peels) when peels were pre-treated with 0.1% pectinase enzyme followed by solvent extraction.
SFE (Supercritical Fluid Extraction), is currently finding a lot of industrial applications, particularly for extraction of natural pigments from vegetable matrices, essential oils, etc. In SFE carbon dioxide is used as supercritical fluid, which besides being low in cost has high purity and low critical temperature. It is highly useful for compounds that are thermolabile or unstable at higher processing temperatures like steam distillation.
Usage and Bioavailability
Lycopene is ingested through consumption of fresh tomatoes or its various types of processed products like crushed tomatoes, tomato juice, ketchup, paste, puree, sauce, passata, sundried tomato, osmo-dried tomato, tomato powder, ready-to-eat products, etc. Pure lycopene extracted from plant sources are marketed in several forms, like softgels, colouring agents and fortificant additive in various food products. Bioavailability of lycopene was found to be 2.5 times more when ingested as processed product like tomato paste compared to fresh tomatoes. The heating process during the processing has been found to increase it bioavailability, both in all-trans and cis-form.
Commercial prospects of lycopene
Ever since synthetic colours have been found to cause cancer in laboratory test animals, a search for safe and natural alternative was intensified around the world (Amr and Tamimi, 2007). Pigments from natural sources are considered as alternates among which, lycopene occupies a prime place. Lycopene has been approved as a food colorant in several parts of the world. US FDA approved the use of lycopene as a colorant in food and beverages including dairy products. Compared to synthetic, lycopene from natural organic source is preferred due to its wide application in pharmaceutical, cosmetic and food industry. The lycopene demand is driven by growth in the food and beverage industry and health supplement segments where natural health benefits associated with lycopene are the market triggers. In 2018 functional food ingredients market is estimated to be valued at USD 68.60 billion. By 2023, this is expected to reach USD 94.21, at a CAGR of 6.6%. Extensive research activities are underway in different parts to increase the applications of lycopene, including the development of anti-cancer drugs and other health products. As of 2017, the food and coloring agents segment dominated the market with a majority share. This dominance is anticipated to continue during the next 3-5 years.
India being the second largest producer of tomato in the world, has enormous potential for processing of tomato as well as, volarization of its wastes like peels and seeds for value added products and by-products. Demand for organic / natural sources of lycopene is expected to increase due to lower risks involved in development of products with lycopene as an ingredient. These developments are positive indicators of growth for the important segment of functional foods and food additives/food colors.
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