LITERATURE REVIEW

2.1 Coconut (Cocos nucifera)

The coconut tree (cocos nucifera) is a member of the family Arecaceae (palm family). It is the only accepted species in the genus cocos. The term coconut can refer to the entire cocnut palm, the seed or the fruit, which botanically is a drupe, not a nut. The spelling coconut is an archaic form of the word. The term is derived from the 16th-century Portuguese and Spanish word coco meaning “head” or “skull” from the three indentations on the coconut shell that resemble facial features.

The coconut is known for its great versatility as seen in the many uses of its different parts and found throughout the tropics and subtropics. Coconuts are the part of the daily diets of many people coconut is different from any other fruits because they contain a large quantity of “water” and when immature they are known as tender-nuts or jelly-nuts and may be harvested for drinking. When mature, they still contain some water and can be used as seed-nuts or processed to give oil from the kernel, char coal from the hard shell and coir from the fibrous husk. The endosperm is initially in its nuclear phase suspended within the coconut water. As development continues, cellular layers of endosperm deposit along the walls of the coconut, becoming the edible coconut “flesh” when dried, the coconut flesh is called copra. The oil and milk derived from it are commonly used in cooking and frying, coconut oil is also widely used in cooking and cosmetic. The clear liquid coconut water within is potable. The husks and leaves can be usedd as materials to make a variety of products for furnishing and decorating, it also has cultural and religious significance in many societies that use it.

DESCRIPTION

Plant Cocos nucifera is a large palm, growing up to 30m (98ft) tall, with pinnate leaves 4-6m (13-20ft) long and pinnae 60-90 long old leaves break away cleanly, leaving the trunk smooth. Coconut stems are generally classified into two general types, tall and dwarf. On very fertile land, a tall coconut palm tree can yield up to 75 fruits per year, but more often yields less than 30, mainly due to poor cultural practices. Given proper care and growing conditions coconut palms produce the first fruits in six to ten years, it takes 15-230 years to reach peak production.

Fruits botanically, the coconut fruit is a drupe not a true nut like other fruits, it has three layers the exocarp, mesocard and endocarp. The exocarp and mesocarp make up the “husk” of the coconut. Coconuts sold in the shops of nontropical countries often have had the exocarp (outermost layer) removed. The mesocarp is composed of a fiber, called coir, which has many traditional and commercial uses. The shell has three germination pores (stoma) or “eyes” that are clearly visible on its outside surface once the husk is removed.

A full size coconut weighs about 1.44kg (3-216). It takes around 6,000 full grown coconuts to produce a tone of corpa.

Roots unlike some other plants, the palm tree have neither a tap root nor root hairs, but have fibrous root system.

The coconut palm root system consists of an abundance of thin rooks that grow outward from the plant near the surface. Only a few of the root penetrate deep into the soil for stability. The type of root system is known as fibrous or adventitious and is a characteristic of grass species. Other types of large trees produce a single downward-growing tap root with a number of feeder roots growing from it.

Coconut palms continue to produce roots from the base of the stem throughout its life. The number of roots produced depends on the age of the tree and the environment, with more than 3,600 roots possible on a tree that is 60 to 70 years old. Roots are uniformly thick from the tree trunk to the root tip.

Inflorescence: The palm produces both the female and male flowers on the same inflorescence; thus the palm is monoecious. Other sources use the term polygamomonoecious. The female flower is much larger than the male flower. Flowering occurs continuously. Coconut palms are believed to be largely cross pollinated, although some dwarf varieties are self-pollinating.

Taxonomy

Cellular organisms Eukaryote-Viridiplantae

Streptophyta –Streptophyta-Euphyllophyta

Spermatophyte-Tracheophyta-liliopsida

Commelinids – Arecales-Arecaceae

Arecoideae – Cocoseae- Attaleinae-cocos-Cocos nucifera

CLASSIFICATION

Kingdom Plantae

Division Magnoliophyta

Class Liliopsida

Family Arecaceae

Genus Cocos

Species C. nucifera

CULTIVATION

V palms are grown in more than 90 countries of the world, with a total production of 62 millions tones per years. Most of the world production is in tropical Asia. Coconut trees are very hard to establish in dry climates, and cannot grow there without frequent irrigation, in drought conditions, the new leaves do not open well, and older leaves may become desiccated, fruits also tends to be shed.

2.2 Technical Requirement of Coconut Cultivation

Agro-climate requirements

Coconut is essentially a tropic plant but has been found to grow under varying agro climatic conditions. The mean annual temperature for optimum growth and maximum yield is stated to be 270c with a diurnal variation of 60c to 70c and relative humidity more than 60%. The coconut palm thrives well up to an altitude of 600m above MSL. The coconut palm thrives well under an evenly distributed annual rainfall ranging from 100mm to 3000mm. However, a well distributed rainfall of about 2000mm is the ideal rainfall for proper growth and higher yield.

Soil

The coconut palm can tolerate wide range of soil conditions. But the palm does show certain growth preferences. A variety of factors such as drainage, soil depth, soil fertility and layout of the land has great influence on the growth of the palm. The major soil types that support coconut in India are laterite, alluvialred sandy loan, coastal sandy and reclaimed soils with a pH ranging from 5.2 to 8.0.

Selection of site

Soil with a minimum depth of 12m and fairly good water holding capacity is preferred for coconut cultivation. Shallow soils with underlying hard rock, low lying areas subjected to water stagnation and clayey soils should be avoided. Proper supply of moisture either through well distributed rainfall or irrigation and sufficient drainage are essential for coconut.

Preparation of land

Size of the pit depends on the soil type and water table. In laterite soils large pits of the size 1.2m x 1.2m x 1.2 may be dug and filled up with loose soil, powered cow dung and ash up to a depth of 60cm before planting. In loaming soils, pits of size 1m x 1m x 1m filled with top soil to height of 50cm is recommended, while filling the pits, two layers of coconut husk can be arrange at the bottom of the pit with concave surface fusing upwards for moisture conservation. After arranging each layer, BHC 10%/DP should be sprinkled on the husk to prevent termite attack. In laterite soils, common salt at 2kg pit may be applied, six months, prior, on the floor of the pit to soften the hard pans.

Spacing

In general square system of planting with a spacing of 7.5m x 7.5m is recommended for coconut. This will accommodate 177 palms per hectare. However, spacing of 7.5 to 10m is practiced in various coconut growing regions of the country.

Harvesting

Coconuts are harvested at varying intervals in a year. The frequency differs in different areas depending upon the yield of the trees in well maintained and high yielding gardens, bunches are produced regularly and harvesting is done once a month. Coconut becomes mature in about 12months after the opening of the spathe. It is the ripe coconut which is the source of major coconut products nut which are eleven months old give fibre of good quality and can be harvested in the tracts where green husks are required for the manufacture of coir fibre. Economic life of the coconut palm is about 60 years.

2.3 Overview of Coconut oil

Coconut oil is one of the most important edible oils for domestic use. The oil is rich in medium chain fatty acids (MCFA) and exhibits good digestibility (Shahidi 2006). Coconut oil is produced by crushing copra, the dried kernel, which contains about 60–65% oil. The oil has the natural sweet taste of coconut and contains 92% of saturated fatty acids (in the form of triglycerides), most of them (about 70%) are lower chain saturated fatty acids known as MCFA. MCFA are not common to different vegetable oils with lauric acid (45–56%) as a main MCFA in coconut oil. Various fractions of coconut oil have medium chain triglycerides which considered as an excellent solvent for flavors, essences, and emulsifiers. These fatty acids are used in the preparation of emulsifiers, as drugs and also in cosmetics (Krishna et al. 2010).

Fig 2.1: Coconut oil and tree

Various methods have been developed to extract coconut oil, either through dry or wet processing. Dry processing is the most widely used form of extraction. Clean, ground and steamed copra are pressed by wedge press, screw press or hydraulic press to obtain coconut oil, which then goes through the refining, bleaching, and deodorizing processes (O’Brien and Timms 2004).

2.4 Preparation of Different Oils from Coconut

Different coconut oils are produced from different parts of coconut by different methods. Copra as well as refined, bleached and deodorized (RBD) oils are produced from dried coconut kernel, with a difference that RBD oil undergoes chemical refinement and bleaching. The brown testa of the coconut is used for the preparation of coconut testa oil (CTO), which is actually a byproduct of coconut oil preparation. Compared to corpa oil (CO) and RBD oils, virgin coconut oil (VCO) is extracted depend on a “wet method” using fresh coconut milk. As there is no specific method of preparation of VCO has been established, all types of preparations that do not involve refinement and alterations in the oil are considered as a virgin (Narayanankutty et al. 2018).

2.4.1 Corpa Oil

Copra is the dried coconut kernel. The fresh coconut kernel is dried in the oven or sunlight and the oil is collected by mechanical milling. The oil is collected and sun- dried to remove the moisture content (Narayanankutty et al. 2018).

2.4.2 Testa Oil

Coconut testa oil (CTO) is the emerging form, which can be extracted using isopropyl alcohol from the coconut testa (Zhang et al. 2016). CTO is best obtained at a temperature of 60 °C for a period of 3 h with the substrate to solvent ratio of 1:4 and having a yield up to 63–76%. Since the extraction involves chemical solvents, CTO has not yet been widely used for edible purposes.

2.4.3 Virgin Coconut Oil

Virgin coconut oil (VCO) is extracted naturally from the fresh coconut kernel without the application of high temperature or chemical treatment. Based on the mode of preparation, several types of VCO are available (Narayanankutty et al. 2018).

2.5 Methods of extraction

2.5.1 Cold Extraction (C-VCO)

Cold processing is the method of VCO extraction without the aid of heat. In this method, the coconut milk is subjected to chilling (2–8 °C) overnight and the separated oil is collected by centrifugation, filtered and stored. This is a simpler and cheapest method available (Narayanankutty et al. 2018).

2.5.2 Hot Extraction (H-VCO)

Hot extraction is traditionally used in Southern India for VCO preparation. In this method, the coconut milk is subjected to a moderate temperature of up to 100 °C. The processing lasts for 60 min or until the oil get completely separated from the milk then the oil is collected by filtration. This heating process helps to increase the release of bound phenolic acids into the oil and also yield is much higher. The oil prepared in this way is being used conventionally in the Ayurvedic system of medicine for skin ailments, especially for children (Narayanankutty et al. 2018).

2.5.3 Fermentation Technique (F-VCO)

The fermentation method uses bacterial activity to generate VCO has also been proposed. It is mainly of two types-natural fermentation as well as induced fermentation. In the natural fermentation method, the freshly grated coconut kernel is extracted with its water to collect the coconut milk. It is then kept for 24–48 h under room temperature (or up to a temperature of 45 °C) to allow fermentation and separation of oil layer, which is scooped out, filtered and stored (Nevin and Rajamohan 2010). Masyithah (2017) prepared VCO by induced fermentation technique, where they used Saccharomyces cerevisiae and Lactobacillus plantarum (strain 1041 IAM) for the extraction of VCO from coconut milk. L. plantarum, and L. delbrueckii are also used in the fermentation process. However, studies using induced fermentation are quite rare and VCO produced by natural fermentation method is often regarded as F-VCO.

2.5.4 Enzymatic Extraction Technique

Extraction of oil can be carried out using the enzymes in the aqueous extraction process. This is due to the fact that plant cell walls consist of complex carbohydrate molecules such as cellulose, hemicellulose, mannans, galactomannans, arabinogalactans, pectin substances and protein (Shah et al. 2005). Coconut meat contains about 10% of carbohydrate, in which 50% is cellulose and 75% of the cellulose is made up with α-cellulose (Rosenthal et al. 1996). Oil can be found inside plant cells, linked with proteins and a wide range of carbohydrate such as starch, cellulose, hemicellulose, and pectins. Cell-wall degrading enzymes can be used to extract oil by solubilizing the structural cell wall components of the oilseed. Man et al. (1996) successfully extracted coconut oil with 1% enzyme mixture of cellulase, α-amylase, polygalacturonase, and protease with an oil yield of 74%. The polygalacturonase hydrolyses α-linkages of polygalacturonic acid of the polymer randomly from the ends. An α-amylase randomly hydrolyzed α-linkages to liquefy starch and produced maltose, whereas bacterial proteases were used to hydrolyze the plant protein. The study showed that different enzymes were required to degrade components of the structural cell wall including mannan, galactomannan, arabinoxylogactan and cellulose.

2.5.5 Wet Extraction

Wet processing or aqueous processing is the term used for the extraction of coconut oil directly from coconut milk. This method eliminates the use of a solvent, which reportedly may lower the investment cost and energy requirements. Furthermore, it eliminates the RBD process (Villarino et al. 2007). Even though the concept appears potentially attractive, however, the method yields comparatively low content of oil, which has discouraged its commercial application (Rosenthal et al. 1996). The wet processing can only be carried out by means of coconut milk by breaking the emulsion. This is rather difficult due to the high stability emulsion of coconut milk. Destabilization can be done through three mechanisms. The first stage is creaming by the action of gravitational force resulting in two phases, with the higher specific gravity takes place at the top phase and the lower specific gravity phase moves downward. The second stage is flocculation or clustering in which the oil phase moves as a group, which does not involve the rupture of the interfacial film that normally surrounds each globule and therefore does not change the original globule. The last stage, coalescence is the most critical phase in destabilization. During this stage, the interfacial area is ruptured; the globules joined together and reduced the interfacial area (Onsaard et al. 2005). The wet process appears more desirable due to the free usage of chemical solvents, thus more environmental friendly than the solvent extraction. The method is also much simpler, which can be carried out at home by anyone who is interested in producing natural oil.

2.5.6 Chilling, Freezing and Thawing Techniques

Attempts have been made to break the protein stabilized oil-in-water emulsion including heating and centrifugation, freezing and thawing, chilling and thawing wherein the coconut cream obtained after centrifugation (Seow and Gwee 1997). The emulsion was centrifuged before chilling and thawing to allow better packing of the coconut oil globules. The temperature used were 10 °C and −4 °C for chilling and freezing process, respectively while the thawing process was carried out in a water bath at 40 °C until the coconut cream reached room temperature (25 °C). In addition, this action also helps in removing undissolved solids after extraction. The removal of solids present in high percentages in the dispersion of oilseed was important for efficient recovery of oil by centrifugation (Rosenthal et al. 1996). The centrifugation step was followed to enable the packing of cream oil globule to crystallize on lowering the temperature. Centrifugation process was carried out from 2000 to 5000 g up to 6 min. During thawing, the oil coalesced due to loss of spherical shape and formed large droplets of varying sizes. Robledano-Luzuriage and Krauss- Maffei were two processes known to apply freeze and thaw operation in the extraction of coconut oil (Marina et al. 2009). In the Robledano-Luzuriage process, fresh coconut kernel was comminuted and pressed to obtain approximately equal amounts of emulsion and residue. The residue was pressed again to obtain more emulsion and residue. The emulsion was centrifuged to obtain a cream, skim milk and some solids or protein. The cream was subjected to enzymatic action under closely controlled temperature and pH conditions. After the freeze-thaw operation, the cream was centrifuged again to obtain the oil. The protein in the skim milk was coagulated by heating, subsequently filtered and dried to produce protein concentrate. The oil recovery reported in the Krauss-Maffei was 89%, which was less than the conventional expeller process (95%). In this technique, husked coconuts were autoclaved, shelled, and the coconut meat (the white solid endosperm inside the coconut fruit) first sent through cutter and subsequently through a roller mill. Then it was pressed in a hydraulic press and the emulsion was centrifuged to obtain the cream and skim milk. The cream was heated to 92 °C and filtered to obtain high-quality oil. The skim milk is heated to 98 °C in a flow heater to coagulate protein, which was separated by centrifuging then drying. The residue from the hydraulic press was dried and ground to obtain edible coconut flour. The study showed that a high recovery of oil was obtained but the temperature employed was slightly high which might destroy some of its minor components such as phenolic compounds.

2.6 Chemical Composition of Coconut Oil

2.6.1 Triacylglycerol and Fatty Acid Composition

Coconut oil contains a high proportion of glycerides of lower chain fatty acids. The oil is highly stable towards atmospheric oxidation. The oil is characterized by a low iodine value, high saponification value, high saturated fatty acids content and the oil is liquid at 27 °C. Medium chain triglycerides (MCT) are a class of lipids in which three saturated fats are bound to a glycerol backbone. What distinguishes MCT from other triglycerides is the fact that each fat molecule is between 6 and 12 carbons in length (Babayan 1988). MCT are a component of many foods, with coconut and palm oils being the dietary sources with the highest concentration of MCT. MCT are also available as a dietary supplement (Heydinger and Nakhasi 1996). MCT have a different pattern of absorption and utilization than long-chain triglycerides (LCT) that makeup 97% of dietary fats. For absorption of LCT to occur, the fatty acid chains must be separated from the glycerol backbone by the lipase enzyme. These fatty acids form micelles, are then absorbed and reattached to glycerol, and the resultant triglycerides travel through the lymphatics en route to the bloodstream. Up to 30% of MCT are absorbed intact across the intestinal barrier and directly enter the portal vein. This allows for much quicker absorption and utilization of MCT compared to LCT. MCT are transported into the mitochondria independent of the carnitine shuttle, which is necessary for LCT mitochondrial absorption. Oxidation of MCT provides 8.3 calories per gram, while LCT provides 9.2 calories per gram (Hoagland and Snider 1943). All fats and oils are composed of triglyceride molecules, which are triesters of glycerol and fatty acids. The fats upon hydrolysis yield fatty acids and glycerol. There are two methods of classifying fatty acids, monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA). The second method of classification is based on molecular size or length of the carbon chain in the fatty acid. The vast majority of the fats and oils whether they are saturated or unsaturated or from an animal or a plant, are composed of LCT. All fats we eat consist of LCT while, coconut oil is unique because it is composed predominantly of MCT. The size of the fatty acid is extremely important because physiological effects of medium-chain fatty acids in coconut oil are distinctly different from the long-chain fatty acids more commonly found in our diet (Furman et al. 1965). It is the MCT in coconut oil that makes it different from all other fats and for the most part gives it its unique character and healing properties. Almost all of the medium- chain triglycerides used in research, medicine, and food products come from coconut oil. MCT are easily digested, absorbed, and put to use nourishing the body. Unlike other fats, they put little strain on the digestive system and provide a quick source of energy necessary to promote healing. This is important for patients who are using every ounce of strength they have to overcome serious illness or injury. It’s no wonder why MCT are added to infant formulas. MCT is not only found in coconut oil but also are natural and vital components of human breast milk. MCT are considered essential nutrients for infants as well as for people with serious digestive problems like cystic fibrosis (St-Onge et al. 2003). Like other essential nutrients, one must get them directly from the diet. Bhatnagar et al. (2009) recorded that the coconut (Cocos nucifera) contains 55–65% oil, having C12:0 as the major fatty acid. Coconut oil has 90% saturates and is deficient in monounsaturates (6%), polyunsaturates (1%), and total tocopherols (29 mg/kg). However, coconut oil contains medium chain fatty acids (58%), which are easily absorbed into the body.

Fatty acid profiles (Figs. 2.2 and 2.3) are found to be similar in all the different varieties of coconut oils such as CO, VCO or RBD oil. In CTO, there is comparatively

Fig. 2.2 Saturated fatty acids profiles in the different varieties of coconut oils

Fig.2.3 Unsaturated fatty acid profiles in the different varieties of coconut oils

a higher level of unsaturated fatty acids than CO and VCO, with a c oncomitant reduction in the medium-chain saturated fatty acid (MCFA) (Appaiah et al. 2014). The other oils contain high amounts of MCFA. Among these, lauric acid (C12:0) forms the predominant fatty acid (45–52%), followed by myristic acid (15–19%) and palmitic acid (10–11%). As indicated by the triglyceride composition of these oils, the major triacylglycerol is formed by tri-lauryl glycerols (22.2–23.9%). On the other hand, CTO contains higher levels of Capryl-lauryl-lauric glycerol (18.7%), followed by tri-lauryl glycerol (14.3%) and lauryl-lauryl-oleic glycerol (13.4%) (Appaiah et al. 2014).

Fig. 9.3 The common phenolics in coconut oils

2.6.2 Phenolic Compounds Composition

Phenolics are another main group of bioactive compounds present in edible oils prepared from coconut. Several studies have analyzed the phenolic content and composition in various types of coconut oils, among which VCO prepared by hot pressing and fermentation methods have higher levels of phenolic antioxidants (Narayanankutty et al. 2016; Seneviratne and Sudarshana Dissanayake 2008). Individual phenolics present in coconut oil are p-coumaric acid, ferulic acid, caffeic acid, quercetin and catechins wherein the level of these are found to be higher in fermented-VCO compared to CO and RBD oil (Illam et al. 2017).