The coconut (Cocos nucifera
L.) is an important fruit tree in the tropical regions and the fruit can be made into a variety of foods and beverages (Figure 1
). The edible part of the coconut fruit (coconut meat and coconut water) is the endosperm tissue. Endosperm tissues undergo one of three main modes of development, which are the nuclear, cellular and helobial modes [1
] and the development of coconut endosperm belongs to the nuclear mode. Initially, the endosperm is a liquid containing free nuclei generated by a process, in which the primary endosperm nucleus undergoes several cycles of division without cytokinesis (the process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells). Cytokinesis then occurs, progressing from the periphery towards the center, thus forming the cellular endosperm layer. At first, the cellular endosperm is translucent and jelly-like, but it later hardens at maturity to become white flesh (coconut meat). Unlike the endosperms of other plants (e.g., wheat and corn), the cellularization process in a coconut fruit does not fill up the entire embryo sac cavity, but instead leaves the cavity solution-filled. This solution is commonly known as coconut water and it is of cytoplasmic origin [2
]. Nutrients from coconut water are obtained from the seed apoplasm (surrounding cell wall) and are transported symplasmically (through plasmodemata, which is the connection between cytoplasms of adjacent cells) into the endosperm [3
Coconut water should not be confused with coconut milk (Figure 1
a), although some studies have used the two terms interchangeably (e.g., [4
]). The aqueous part of the coconut endosperm is termed coconut water (Figure 1
b), whereas coconut milk, also known as “santan” in Malaysia and Indonesia, and “gata” in the Philippines (Figure 1
a), refers to the liquid products obtained by grating the solid endosperm, with or without addition of water [6
]. Coconut water is served directly as a beverage to quench thirst (Figure 1
b), while coconut milk is usually used as a food ingredient in various traditional cooking recipes (Figure 1
a). The main components of coconut milk are water (ca.
50%), fat and protein [7
], whereas coconut water contains mainly water (ca.
94%, Table 1
). Unlike coconut water, coconut milk, which is the source of coconut oil, is generally not used in plant tissue culture medium formulations [8
Compared to coconut water, there are only limited studies on the aqueous extract of coconut solid endosperm (coconut meat or copra). Mariat et al.
used coconut meat extract in orchid tissue culture to study its effects on orchid seed germination [9
]. Subsequently, Mauney et al.
purified a growth factor from the aqueous extract of coconut meat which was found to be very potent in promoting growth of tissue cultured plants [10
]. Another group, Shaw and Srivastava demonstrated the presence of purine-like substances in coconut meat extract [11
]. The purine-like substances were able to delay senescence (the process of ageing in plants) in detached cereal leaves, which exhibited similar known physiological effects of cytokinins. Zakaria et al.
showed that the aqueous extract of coconut meat exhibited anti-inflammatory and wound healing properties when tested on mice [12
Conversely, coconut water has been extensively studied since its introduction to the scientific community in the 1940s. In its natural form, it is a refreshing and nutritious beverage which is widely consumed due to its beneficial properties to health, some of which are based on cultural/traditional beliefs [2
]. It is also believed that coconut water could be used as an important alternative for oral rehydration and even so for intravenous hydration of patients in remote regions [13
]. Coconut water may also offer protection against myocardial infarction [15
]. Interestingly, a study has shown that regular consumption of either coconut water or mauby (a liquid extracted from the bark of the mauby tree, Colubrina arborescens
), or particularly, a mixture of them, is effective in bringing about the control of hypertension [16
Apart from that, coconut water is widely used in the plant tissue culture industry [17
]. The extensive use of coconut water as a growth-promoting component in tissue culture medium formulation can be traced back to more than half a century ago, when Overbeek et al.
first introduced coconut water as a new component of the nutrient medium for callus cultures in 1941 [17
]. From a scientific viewpoint, the addition of coconut water to the medium is rather unsatisfactory, as it precludes the possibility for investigating the effects of individual components of the medium with any degree of accuracy. The question of which components cause the growth stimulation arose immediately. Besides its nutritional role, coconut water also appears to have growth regulatory properties, e.g., cytokinin-type activity [8
Some of the most significant and useful components in coconut water are cytokinins, which are a class of phytohormones [21
]. The first cytokinin, N6
-furfuryladenine (kinetin) was isolated from an autoclaved sample of herring sperm DNA in 1955 [22
]. In 1963, Letham isolated trans
-zeatin, the first naturally-occurring cytokinin, from a plant source (unripe corn seeds) [24
]. In addition to various plant-related functions, it was also found that some cytokinins (e.g., kinetin and trans
-zeatin) showed significant anti-ageing, anti-carcinogenic, and anti-thrombotic effects [25
Furthermore, micronutrients (nutrients needed in small quantities) such as inorganic ions and vitamins in coconut water play a vital role in aiding the human body antioxidant system [27
]. Hypermetabolism gives rise to an increased production of reactive oxygen species (or free radicals), as a result of increased oxidative metabolism. Such increase in free radicals will cause oxidative damage to the various components of the human cell, especially the polyunsaturated fatty acids in the cell membrane, or to the nucleic acids in the nucleus [27
]. Fortunately, living organisms have well developed antioxidant systems to neutralize the most detrimental effects of these oxidizing species. Micronutrients have important functions in this aspect. For example, they act directly to quench free radicals by donating electrons, or indirectly as a part of metallo enzymes (a diverse class of enzymes that require a catalytic metal ion for their biological activity) such as glutathione peroxidase (selenium) or superoxide dismutase (zinc, copper) to catalyse the removal of oxidizing species [28
Other components found in coconut water include sugars, sugar alcohols, lipids, amino acids, nitrogenous compounds, organic acids and enzymes [20
], and they play different functional roles in plant and human systems due to their distinct chemical properties. The myriad of compounds, both known and unknown, provide coconut water with the special biological properties that is known to the typical layman. In this paper, we will present a summary on the chemical composition of the known compounds in coconut water.