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2.1 Sky Fruits
Herbs have been used for many centuries ago to maintain health and also been used in enhancing the flavour, colour and aroma and also to improve physical and chemical characteristics of food. They also have known for their antioxidant and antimicrobial agent action on our body and food products. In food, they can be used to replace synthetic antioxidant and antimicrobial agent that increasing demand in the market.
Our rain forest has thousand kinds of plant that are potential to act as herbs. One of them is Swietenia Macrophylla King or Big leaf Mahogany. It is a tree from the family of Meliaceae. This tree is widely distributes native to Mexico, Central and northern South America. It also have extensively been planted mainly in Southern Asia and the Pacific and also in the West Africa. Mahogany is well known in furniture industry and it is one of the most valuable furniture timbers in the world.
The fruits of mahogany also been known as "Sky Fruit" or "Tunjuk Langit" in Malays language that means "pointed to the sky". This because the fruits are pointed to the sky and located at the end of the shoots. The fruits have 5 segments that are about 15 cm long, greyish brown in colour and have smooth woody outer skin that is 5 - 7 mm thick. When they are ripe and dry, the fruits will split open from their base and disperse their seeds by wind. There are 35 - 45 seeds in every fruit. The seed is brown in colour and 7.5 - 15cm long with extensive air space like a wing. There are 1800 to 2500 seeds in 1 kg of them. (Lars Schmidt, Dorthe joker)
The seed has been used as a folk medicine in Malaysia for treating diabetes and high blood pressure and also have a lot of healing effects. The active ingredients that as antioxidant and antimicrobial in the seed of sky fruits are flavonoids and saponins.
2.2 Lipid oxidation
Lipids are important in food. A food product's nutritional value as well as its flavor, texture, physical characteristic, and storage stability are affected by the amount of lipids.
Lipid oxidation is one of the most major problems in the storage of fatty foods. Oxidative changes can result in imparting bad flavours, destruction of valuable nutrients and production of toxic compounds. This reaction occurs by several molecular mechanisms which lead to chain-propagating of free radicals. The better understanding of lipid oxidation achieved should assist in improving the food processing and food handling.
Lipid oxidation always occurs to unsaturated fatty acids due to the presence of double bond. There are a wide variety of organic molecules that are susceptible to chemical attack by oxygen, the attention recently been focused on lipids because of the implications of their oxidative damage have a big effect. In our body, the oxidation of lipids can give damage to membranes, vitamins and hormones, which are important components for the normal cell activity. The oxidation of fatty constituents is the major chemical factor that affects the nutritional level in the food that can cause loss of food wholesomeness by deterioration of flavour and aroma, and decrease the nutritional and food safety qualities. Oxidation of lipids can occur in foods containing high amounts of fat, like milk and meat products, oils, nuts and also foods that contain small amounts of lipids, such as vegetable products. All quality attributes of food can be affected by oxidation process. (food chemistry note)
Fats in foods are susceptible to oxidation or rancidity resulting in off flavours, off-odours and sometimes off-colours. Although for good health unsaturated fat is preferred to saturated fat, it is more prone to oxidation leading to undesirable changes in the food. Oxygen, certain metals such as copper and iron, and heat, are known to aid in this type of deterioration of fats and fatty foods. Exclusion of one or more of these factors may therefore lessen the risk of rancidity. Foods often implicated include meats, fish and poultry. In addition, dried foods containing small amounts of fats (e.g., vegetables) and foods processed in oil are also susceptible to oxidative rancidity. (Audrey Morris, Audia Barnett and Olive-Jean Burrows, 2006)
Oxidative rancidity process can occur in low temperature because it is a chemical reaction which requires low activation energy. The free radical route is an oxidation reaction producing free radicals that lead to peroxides that in turn are converted to alcohols, aldehydes, ketones, and free fatty acids. Many of these compounds have very bad flavors and odors and are what can reduce the quality of a food. They also may harm our health and cause many health problems. Usually oxidation of lipids and lipid containing food stuffs such milk refers the lipid autooxidation. The autooxidation process is initiated by radical reaction involving unsaturated fatty acids. It takes place at the double bonds of unsaturated fatty acids. The initial reaction or initiation step for the free radical route requires the presence of a catalyst, such as heat, light or high-energy radiation or metal ions for example copper ions. This process will proceed by the propagation steps that are chain reactive or autocatalytic through formation of more free radicals. Free radicals may be the initiators of and products of these propagation reactions. At some point during this propagation process, free radicals themselves can combine to form products that eventually can terminate the reaction. (Mark Sewald and Dr. Jon DeVries)
Initiation: RH RÂ· (1)
Propagation: RÂ· + O2 ROOÂ· (2)
ROOÂ· + RH ROOH + RÂ· (3)
Termination: ROOÂ· + ROOÂ· molecular product
2.2.1 Initiation stage
During the oxidation of fatty acid, the methylene group which is located adjecent to two double bond become primary site of oxygen attack. Therefore, it is easily converted to free radical. Free radicals often formed by cleavage of a hydroperoxide molecule. They are produced by singlet oxygen or enzyme-catalysed oxidation. They can be present in trace quantity in raw lipid material.
The initiation process is the process of the production of free radicals RÂ·. This reaction can be initiated by heat, light or ionising radiation. This initiation process is commonly due to the degradation of hydroperoxides that is highly susceptible to light and to particular metal ions.
2.2.2 Propagation stage
When the unsaturated fatty acid radical formed, it will absorb a molecule of oxygen and form a peroxy radical. This free radical is very reactive as it react with a hydrogen atom from another molecule of a polyunsaturated fatty acid forming a hydroperoxide and an alkyl free radical. This molecule will cleave with formation of a free peroxy or alkoxy radical. This reaction sequence will repeat many times and it is also known as chain reaction.
2.2.3 Termination stage
This oxidation process ends when all of the fat molecules have reacted with a radical or when two unstable radical species react with each other or when an antioxidant react with a radical which stops the chain reaction.
Antioxidants are traditionally added to the food to prevent lipid oxidation. Antioxidant means any substance that is capable of delaying, retarding or preventing the development of rancidity in food or other flavour deterioration due to oxidation. There are three classes of antioxidants based on their function, primary or chain breaking antioxidant, synergistic antioxidant and secondary or preservative antioxidant.
Primary antioxidant been used to inhibit or retard the oxidation process which can interfere with either chain propagation or initiation. The function of primary antioxidant is to interrupt the free radical chain mechanism. It acts as a hydrogen donor or free radical acceptor.
RÂ· + AH RH + AÂ·
ROÂ· + AH ROH + AÂ·
ROOÂ· + AH ROOH + AÂ·
RÂ· + AÂ· RA
ROÂ· + AÂ· ROA
Free radicals are molecules that are electrically charged which have unpaired electron. This causes them to seek and bind other substances in order to neutralize themselves to become more stable. But, in the initial attack will cause the free radical to become neutralized, but another new free radical form causing this reaction will continue to react. This process is also known as chain reaction. Anti oxidant can help to stabilize and deactivating free radical before they can attack other molecules thus will stop the initiation process. (Dr. Mark Percival, 1998)
2.4 Phenolic compound
All plants produce an amazing diversity of secondary metabolites. One of the most important groups of these metabolites are phenolic compounds. Phenolics are characterized by at least one aromatic ring (C6) bearing one or more hydroxyl groups. (A. Michalak, 2006)
Plant phenolics are known group of natural antioxidants. They are present in almost all plants make our consumption in diet is about 1 g. They consist mostly of phenolic acids, flavonoids, anthocyanins and their glycosides. Less polar substances, such as tocopherols, lignans or resins, may be added to fats and oils product to increase their stability on storage and heating. More polar phenolics may be use in stabilization of food dispersions. High content of phenolics are found in spices, tea leaves, roasted coffee and cocoa beans, and in red wine. Phenolic antioxidants react with free lipidoxy or lipidperoxy free radicals, that may prevent further autoxidation. The inhibition of lipid autoxidation is important not only in foods storage or heating, but also to reduce the oxidation of lipids after been absorbed in our body.
Phenolic compounds may be found widely in seeds and other parts of the plant. Most seeds contain large amounts of polyunsaturated oils and phenolic antioxidants necessary to protect polyunsaturated fatty acids in oil against autoxidation that may occur to the seed. (Pokkorny et al., 2008)
Flavonoids are plant secondary metabolites widely distributed in the plant kingdom, and can be subdivided into six classes: flavones, flavanones, isoflavones, flavonols, flavanols, and anthocyanins based on the structure and conformation of the heterocyclic oxygen ring of the basic molecule.
Flavonoids are phenolic substances isolated from a wide range of vascular plants, with over 8000 compounds are known. In plants, they may act as antioxidants, antimicrobials, photoreceptors, visual attractors, feeding repellants, and for light screening. Many studies shows that flavonoids may perform variety of biological activities, such as antiallergenic, antiviral, antiinflammatory, including vasodilating actions. However, most of the interest is on the antioxidant activity of flavonoids, which is due to their ability to reduce free radical formation and to bind with free radicals. Many studies has been made in the past years on the capacity of flavonoids to act as antioxidants in vitro, and important structure-activity relationships of the antioxidant activity have been established. (Pier-Giorgio Pietta, 2000)
Saponins are a major family of secondary metabolites that occur in a wide range of plant species. These molecules are synthesised from evalonic acid via the isoprenoid pathway and are derived from triterpenoid or steroid cyclisation products of 2,3-oxidosqualene. Saponins are differentiate by their surfactant properties and give stable, soap-like foams in aqueous solution. The name saponinis derived from sapo, that means soap in Latin word. Many compounds of this saponins family are being used commercially for a variety of purposes including as drugs and medicines, precursors for hormone synthesis, adjuvants, foaming agents, sweeteners, taste modifiers and also including in the cosmetics. Many saponins have potent antimicrobial activity, and this make the natural role of these molecules in plants is likely to protect against attack by potential pathogens. (Anne E. Osbourn, 2003)
Saponins are steroid or triterpenoid glycosides, common in a large number of plants and plant products that are so important in human and animal nutrition. Several biological effects have been ascribed to saponins. Most research has been carried out in the membrane-permeabilising, immunostimulant, hypocholesterolaemic and anticarcinogenic properties of saponins and they also have been found thay may have significantly effect in the reproduction in animals. These structurally diverse compounds have also been studied in killing protozoa and molluscs, to have an effect on cold blooded animals, also to have the analgesic, anti-nociceptive, antioxidant activity, to impair the digestion of protein, to cause hypoglycemia and to act as antifungal and antiviral agents. (Sapna D. Desai, Dhruv G. Desai, Harmeet Kaur, 2009)