CHARACTERIZATION AND COMPARATIVE ASSESSMENT OF THE PHYSICO- CHEMICAL PROPERTIES OF COCONUT (COCOS NUCIFERA) AND WALNUT (TETRACARPIDIUM CONOPHORUM) OILS

ABSTRACT

Characterization   and   comparative   assessment   of   Cocos   nucifera   and   Tetracarpidium conophorum seeds and the oils were evaluated in this work using standard techniques. The percentage proximate analysis of the samples revealed that the moisture, ash, fibre and protein contents of coconut sample were significantly lower (p<0.05) than that of walnut while the fat, carbohydrate and energy value of walnut sample were significantly lower (p<0.05) than that of coconut sample. The phytochemical constituents of the samples were also qualitatively and quantitatively analysed. The quantitative phytochemical constituents of the samples showed that the amount of alkaloids (2.29 mg/100g), saponins (8.07 mg/100g) and glycosides (2.19 mg/100g) were significantly higher (p<0.05) in walnut than that of coconut sample. On the other hand, the amount of reducing sugar (10.07 mg/100g), flavanoid (1.864 mg/100g) and tannins (2.77 mg/100g) were significantly increased (p<0.05) in coconut sample when compared with that of walnut sample. Soluble carbohydrate, hydrogen cyanide and tepernoids show no significant differences (p>0.05) between the samples. The mineral analysis of the seed samples revealed that the  manganese (3.20±0.02 mg/100g), zinc (6.78±0.08 mg/100g), iron (2.89±0.02 mg/100g), phosphorus (265.92±0.32 mg/100g) and calcium (44.99±0.14 mg/100g) contents of the walnut sample were significantly higher (p<0.05) than that of the coconut sample while the opposite was the case when magnesium, potassium and sodium are considered. However, the amount of copper (1.24±0.02 mg/100g and 1.87±0.02 mg/100g) observed showed no significant difference (p>0.05) between the samples. The result of the vitamin analysis revealed an appreciable amount of vitamin A (3.12±0.06 mg/100g and 2.24±0.06 mg/100g) and vitamin C (14.71±0.02 mg/100g and 5.08±0.00 mg/100g) in  both Cocos nucifera and Tetracarpidium conophorum samples. However, it was observed that walnut sample contains a great amount of vitamin E (70.00±0.08mg/100g). The result also revealed that the amount of vitamin A, C, B2 and B6 were significantly lower (p<0.05) in walnut sample than that of coconut sample while vitamin E content significantly increased (p<0.05) in walnut sample than that of coconut sample. Other vitamins detected in the respective samples though in trace amount, were reported in Table 10. The oils of Cocos nucifera and Tetracarpidium conophorum were extracted by cold method and the percentage oil yields gave 42.5% and 24% respectively. The physicochemical properties of the coconut and walnut oils were determined and the result revealed that the oils have agreeable odour with a colour, yellow and golden yellow, specific gravity of 0.89 and 0.91, refractive index of 1.46 and  1.48, viscosity of 10.96 mm2/s and 21.69 mm2/s at  40oC, acid  value of 5.54 mgKOH/g and 19.2 mgKOH/g, saponification value of 267.90 mgKOH/g and 186.95 mgKOH/g, peroxide value of 0.13 meq/kg and 0.93 meq/kg, iodine value of 7.87 mI2/g and 29.44 mI2/g for Cocos nucifera and Tetracarpidium conophorum respectively. All the physical properties observed  for  the  oils  were  in  agreement  with  those  recommended by Codex Standard  for Vegetable oils (1999) and as such indicate edibility. The chemical properties of oils extracted from Cocos nucifera and Tetracarpidium conophorum seeds were compared well with selected commercially available oils in the Nigerian market.

CHAPTER ONE

INTRODUCTION

1.1       Background of Study

Nigeria is a country blessed with abundant seeds rich in oil. These seeds are readily available  from  virtually  all  farmlands  including  thick  forests  across  the  nation. Despite the availability of these seeds,   lack   of   adequate scientific,  industrial and potential  nutritional    information    on  these  plant  seed    resources    have    made Nigerians  to depend very much on vegetable oils (Yusuf et al., 2006). The nutritive and  calorific  values  of  seeds  make  them  good  sources  of  edible  oils  and  fats (Odoemelam, 2005; Akubugwo et al., 2008). Seed oils have extensive demands both for human consumption and for industrial uses (Kyari, 2008) and have also been rated as the second most valuable commodity in the world trade today (Ige et al., 1984).

Coconut (Cocos nucifera L. Family-Palmae)  is one of the most extensively grown and used nuts in the world and is rated as one of the most important of all palms (Popenoe, 1969; Onifade and Jeff-Agboola, 2003). A lot of products are directly or indirectly  made  from coconuts.  These  include  whole  coconut  copra,  coconut  oil, coconut oil cake, coir, desiccated shredded coconut, coconut skin milk and coconut protein  (Onifade  and  Jeff-Agboola,  2003).  Coconut  can  also  be  used  to  produce desired texture in cookies, candies, cakes pies, salads and desserts. It is commercially viable because of its rich nutritive values (Child, 1964; Akubugwo et al., 2008; Kyari,

2008).

Tetracarpidium  conophorum otherwise known as walnut is an edible seed of a tree which belongs to the genus juglans and the family juglandaceae. Walnut is known in the Eastern Nigeria as Ukpa (Igbo), Western Nigeria as asala (Yoruba) and Northern Nigeria as gawudi bairi (Hausa) and it is cultivated principally for its nuts which are cooked and consumed.

Previous works conducted on coconut and walnut seeds and their seed oils show that the oils  have  numerous  nutritional  and  industrial  qualities  and can serve  as non- conventional sources of oil for human consumption and industrial uses (Obasi et al.,

2012). As a result,  numerous  researchers  amongst  whom are  Akpan  et al.,  1999; Yusuf et al., 2006; Akubugwo et al., 2008 and Kyari, 2008 have also carried out a lot of studies on these seeds primarily because of increasing demand for them, both for human  consumption  and  for  numerous  industrial  uses.  This  study  therefore,  was designed to assess the nutritional values of coconut and walnut seeds and seed oils for maximum utilization of the products for food and animal feeds.

1.2       Description of Coconut and Walnut Seeds

1.2.1    Coconut

The spelling coconut is an archaic form of the word meaning “head” or “skull”, named from the three small holes on the coconut shell that resemble human facial features. The  coconut  palm  (also,  cocoanut),  Cocos  nucifera,  is  a  member  of  the  family Arecaceae (palm family). The term coconut can refer to the entire coconut palm, the seed, or the fruit, which, botanically, is a drupe, not a nut. Fig. 1 shows the coconut fruit on a tree.

Cocos nucifera is a large palm, growing up to 30 meters (98 ft) tall, with  pinnate leaves 4–6 meters (13–20 ft) long, and pinnae 60–90 cm long; old leaves break away cleanly, leaving the trunk smooth. Coconuts 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. In recent years, improvements  in  cultivation practices and breeding have produced coconut trees that can yield more.

Like  other  fruits,  it  has  three  layers:  the  exocarp,  mesocarp,  and  endocarp.  The exocarp and mesocarp make up the “husk” of the coconut. Coconuts sold in the shops of non-tropical 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-sized coconut weighs about 1.44 kilograms (3.2 lb). It takes  around 6000 full-grown coconuts to produce a tonne of copra (Bourke et al., 2009).

Coconut is found throughout the tropic and subtropic area, it is known for its great versatility  as  seen  in  the  many  domestic,  commercial,  and  industrial  uses  of  its different parts including the dietary use of its parts by many people. Coconuts contain a large quantity of “water” and when immature they are known as tender-nuts or jelly- nuts and may be harvested for drinking and this differentiates them from any other fruits. When mature they still contain some  water and can be used as seed nuts or processed to give oil from the kernel, charcoal 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 soaps and cosmetics. The clear liquid coconut water within is a refreshing drink. The husks and leaves can be used as material to  make  a variety of products  for furnishing  and  decorating.  It  also  has cultural and religious significance in many societies that use it.

Fig. 1: Bunch of coconuts on a coconut tree.

Source: (Chan and Elevitch, 2006).

1.2.2    Walnut

Tetracarpidium conophorum otherwise known as walnut is an edible seed of any tree of the genus juglans and the family juglandaceae. It is a large deciduous tree attaining the height of 25-35m and a trunk up to 2m diameter, commonly with a short trunk and broad crown, though taller and narrower  in dense forest  competition (Caglarimark,

2003). It is a light-demanding  species, requiring  full sun to grow well  (Brinkman, 1974).

Walnut comprises such families as Juglandaceae (English walnut), Euphorbiaceae and Olacaceae (African walnut). The English walnuts are called Juglan regia  while the black  walnuts  are  known  as  Juglans  nigra.  Each  family  has  its  own  peculiar characteristics but they have some things in common such as the nuts. Tetracarpidium conophorum  (family  Euphorbiaceae)   is  found  in  Nigeria   and  Cameroon  while Coulaedulis (family Olacaceae) which is also referred to as African walnut is found in Congo, Gabon and Liberia. Tetracarpidium conophorum is a climbing shrub 10-20ft long, it is known in the Eastern Nigeria as ukpa (Igbo), Western Nigeria as awusa or asala  (Yoruba)  and  Northern  Nigeria as gawudi  bairi (Hausa).It  is known  in the

littoral and the western Cameroon as kaso or ngak. It is found in Uyo,  Akamkpa, Akpabuyo,  Lagos,  Kogi,Ajaawa-Ogbomoso   and  Ibadan.  The  plant   is  cultivated principally for the nuts which are cooked and consumed as snacks.

Walnuts are round, single-seeded stone fruits of the walnut tree. The walnut fruit is enclosed in a green, leathery, fleshy husk. This husk is inedible. After  harvest, the removal of the husk reveals the wrinkly walnut shell, which is in two halves. This shell is hard and encloses the kernel, which is also made up of two halves separated by  a  partition.  The  seed  kernels  –  commonly  available  as  shelled  walnuts  –  are enclosed in a brown seed coat which contains antioxidants. The antioxidants protect the oil-rich  seed  from atmospheric  oxygen  so  preventing  rancidity.  Fig.  2  shows

Figure 2: Walnut tree as climber.

Source: Ayoola et al. (2011).

1.2.3 Scientific Classification of Coconut and Walnut

Table 1: Scientific Classification of Coconut and Walnut

Scientific Classification	Coconut	Walnut
Kingdom-	Plantae	Plantae
Subkingdom-	Tracheobionta	Tracheobionta
Superdivision-	Spermatophyta	Spermatophyta
Division	Magnoliophyta	Magnoliophyta
Class-	Monocots	Magnoliopsida
Subclass-	Arecidae	Rosidae
Order-	Arecales	Euphorbiales
Family-	Arecaceae	Euphorbiaceae
Genus-   Species-	Cocos   C. nucifera	Tetracarpidium   Tetracarpidium
		conophorum

Source: (Chan and Elevitch, 2006).

1.3       Origin and Natural Habitat

1.3.1    Coconut

There are several opinions on the origin of coconut (Cocos nucifera). Many scholars suggest that coconut has its origin either around Melanesia and Malesia or the Indian Ocean, while others believe it originated in northwestern South America. The oldest fossils known of the modern coconut dated from around 37 to 55 million years ago and were found in Australia and India. However, older palm fossils have been found in the Americas.

The coconut palm thrives on sandy soils and is highly tolerant of salinity. It prefers areas with abundant sunlight and regular rainfall (150 cm to 250 cm annually), which makes  its colonizing  shorelines  of the tropics understandable.  Coconuts  also  need high humidity (70–80 %+) for optimum growth, which is why they are rarely seen in areas  with  low humidity,  or even where  temperatures are high enough  (regularly above 24°C or 75.2°F).

Coconut palms require warm conditions for successful growth, and are intolerant of cold weather. Optimum growth is obtained with a mean annual temperature of 27 °C (81 °F). Growth is reduced below 21 °C (70 °F). Some seasonal variation is tolerated, with  good  growth  where  mean  summer  temperatures  are  between  28  and  37  °C

(82 and 99 °F), and survival is possible in winter, as long as winter temperatures are above 4–12 °C (39–54 °F); they will survive brief drops to 0 °C (32 °F). Severe frost is usually fatal, although they have been known to recover from temperatures of −4

°C (25 °F). They may grow but not fruit properly in areas with insufficient warmth, such as Bermuda.

The conditions required for coconut trees to grow without any care are:

     mean daily temperature above 12–13°C (53.6–55.4°F) every day of the year

     mean yearly rainfall above 1000 mm (39.37 in)

     no or very little overhead canopy, since even small trees require direct sun

The main limiting factor for most locations which satisfy the rainfall and temperature requirements  is canopy growth,  except  those  locations  near  coastlines,  where  the sandy soil and salt spray limit the growth of most other trees.

1.3.2    Walnut

Black walnut (Juglans nigra L.), also known as eastern black walnut or  American walnut, is a fine hardwood species of the family juglandaceae, section Rhysocaryon (Manning, 1978). Black walnut is a large tree and on good sites may attain a height of

30 to 38m, diameter of 76 to 120 cm, and can exceed 100 years of age  (Williams

1990; Dirr 1998; USDA-NRCS 2004). Black walnut grow best on moist, deep, fertile, well-drained, loamy soils; although it also grows quite well in salty clay loam soils, in good agricultural soils without a fragipan (Williams, 1990; Cogliastro et al., 1997). These  sites  include  coves,  bottomlands,  abandoned  agricultural  fields,  and  rich woodlands.  J.  regia  has  its  origins  in  Eastern  Europe,  Asia  Minor,  and  points eastward to the Himalayan Mountains.  However, there are native Juglans in North, Central, and South America, Europe and Asia.

1.3.3    Nutritional Benefit of Coconut and Walnut

Walnuts are one of the several high nutrient density foods. About 100g of walnuts contain 15.2g protein,  65.2g  fat, and 6.7g dietary fibre.  Walnuts  protein provides many essential amino acids.

Though English walnut is the predominant commercially distributed nut because of the ease with which it is processed,  its nutrient density and profile is  significantly different from black walnut. The table below compares some of the major nutrients between coconut and walnut.

Table 2: Nutritional Benefit of Coconut and Walnut

Nutritional     Value     per   100g.	Coconut	Walnut
Energy   Carbohydrates	354Kcal (1,480 KJ)   24.23	654Kcal (2, 738 KJ)   13.71
Sugars	6.23	2.61
Dietary fibre	9	6.7
Fat	33.49	65.21
Protein	3.33g	15.23
Water   Thiamine (Vit. B1)	47   0.066mg (6%)	4.07   0.341 mg (30%)
Riboflavin (Vit. B2)	0.02 mg (2%)	0.15 mg (13%)
Niacin (Vit. B3)	0.54 mg (4%)	1.125 mg (8%)
Pantothenic acid (Vit. B5) Vitamin B6 Folate (Vit. B9)	1.014 mg (20%)   0.05 mg (4%)   –	0.570 mg (11%)   0.537 mg (41%)   98ug (25%)
Vitamin B12   Vitamin D Vitamin C	–   –   3.3 mg (4%)	0 ug (0%)   0 ug (0%)   1.3 mg (2%)
Vitamin E	–	0.7 mg (5%)
Vitamin K	–	2.7 ug (3%)
Calcium	14 mg (1%)	98 mg (10%)
Iron	2.43 mg (19%)	3.1mg (16%)

Percentages       are       relative       to       US       recommendations       for       adults. Source: USDA Nutrient Database

1.4 LIPIDS

Lipids  consist  of  numerous  fatlike  chemical  compounds  that  are  insoluble  in water but soluble  in organic solvents  (Boelsma et al., 2001). Lipid  compounds include  monoglycerides,  diglycerides,  triglycerides,  phosphatides, cerebrosides, sterols, terpenes, fatty alcohols, and fatty acids (Burgess et al., 2000). Dietary fats supply  energy,  carry  fat-soluble  vitamins  (A,  D,  E,  K),  and  are  a  source  of antioxidants  and  bioactive  compounds.  Fats  are also  incorporated  as structural components of the brain and cell membranes.

Table 3: Chemical Names and Descriptions of some Common Fatty Acids

Common name	Structure	Carbon   Skeleton	Systematic names
Caproic acid Caprylic acid Capric acid	CH3(CH2)4COOH CH3(CH2)6COOH CH3(CH2)8COOH	C6:0   C8:0   C10:0	n-Hexanoic acid n-Octanoic acid n-Decanoic acid
Lauric acid   Myristic acid	CH3(CH2)10COOH CH3(CH2)12COOH	C12:0   C14:0	n-Dodecanoic acid n-Tetradecanoic acid
Palmitic acid	CH3(CH2)14COOH	C16:0	n-Hexadecanoic   acid
Stearic acid	CH3(CH2)16COOH	C18:0	n-Octadecanoic   acid
Arachidic acid	CH3(CH2)18COOH	C20:0	n-Eicosanoic acid
Lignoceric   acid	CH3(CH2)22COOH	C24:0	n-Tetracosanoic   acid
Palmitoleic   acid	CH3(CH2)5CH=CH(CH2)7   COOH	C16:1(∆9)	cis-9-   Hexadecenoic acid
Oleic acid	CH3(CH2)7CH=CH(CH2)7   COOH	C18:1(∆9)	cis-9-Octadecenoic   acid
Linoleic acid	CH3(CH2)4CH=CHCH2CH   =CH(CH)7COOH	C18:2(∆9,12)	cis,cis-9,12-   Octadecadienoic
			acid
Alpha-linoleic	CH3CH2CH=CHCH2CH=	C18:3(∆9,12,15)	cis,cis,cis-9,12,15-

acid	CHCH2CH=CH(CH2)7CO   OH		Octadecatrienoic   acid
Arachidonic	CH3(CH2)4CH=CHCH2C	C20:4(∆5,8,11,1	cis,cis,cis,cis–
acid	H=CHCH2CH=CHCH2CH   =CH(CH2)3COOH	4)	5,8,11,14- Eicosatetraenoic acid

Source: Nelson and Cox, 2008.

Note that the numbering of carbon atoms begins at the carboxyl carbon. The prefix n– indicates  the  “normal”  unbranched  structure.  For  instance,  “dodecanoic”  simply indicates 12 carbon atoms, which could be arranged in a variety of branched forms; “n-dodecanoic” specifies the linear, unbranched form. For unsaturated fatty acids, the configuration  of  each  double  bond  is  indicated;  in  living  organisms  fatty  acids configuration is almost always cis.

Fatty  acids  consist  of  the  elements  carbon  (C),  hydrogen  (H)  and  oxygen  (O) arranged  as a carbon chain skeleton with a carboxyl group (-COOH)  at  one end. Saturated fatty acids (SFAs) have all the hydrogen that the carbon atoms can hold, and therefore, have no double bonds between the carbons.  Monounsaturated  fatty acids (MUFAs) have only one double bond. Polyunsaturated fatty acids (PUFAs) have more than one double bond.

Butyric acid (butanoic acid shown above structurally)  is one of the saturated  short- chain fatty acids responsible for the characteristic flavor of butter. This figure above is a detailed structural formula explicitly showing four bonds for every carbon atom and can also be represented as the equivalent line formulas:

CH3CH2CH2COOH    or    CH3 (CH2)2COOH

The numbers at the beginning  of the scientific names indicate the locations of the double bonds. By convention, the carbon of the carboxyl group is carbon number one. Greek numeric prefixes such as di, tri, tetra, penta, hexa, etc., are used as multipliers and to describe the length of carbon chains containing more than four atoms. Thus, “9,

12-octadecadienoic  acid” indicates that there is an 18-carbon chain (octadeca)  with two double bonds (di en) located at carbons 9 and 12, with carbon 1 constituting a carboxyl group (oic acid). The structural formula corresponds to:

CH3CH2CH2CH2CH2CH=CHCH2CH=CHCH2CH2CH2CH2CH2CH2CH2COOH

9, 12-octadecadienoic acid   (Linoleic Acid) This would be abbreviated as:

CH3 (CH2)4CH=CHCH2CH=CH (CH2)7COOH

Fatty acids are frequently represented by a notation such as C18:2 that indicate that the fatty acid consists of an 18-carbon chain and 2 double bonds. Although this could refer to any of several possible fatty acid isomers with this chemical composition, it implies the naturally-occurring fatty acid with these characteristics, i.e., linoleic acid. Double bonds are said to be “conjugated” when they are separated from each other by one  single  bond,  e.g.,  (–CH=CH-CH=CH-).  The  term “conjugated  linoleic  acid” (CLA) refers to several C18:2 linoleic acid variants such as 9, 11-CLA and 10, 12- CLA which  correspond  to 9,  11-octadecadienoic  acid  and 10,  12-octadecadienoic acid. The principal dietary  isomer of CLA is cis-9, trans-11 CLA, also known as rumenic  acid.  CLA  is  found  naturally  in  meats,  eggs,  cheese,  milk  and  yogurt (Ratnayake and Chen, 1996).

CH3(CH2)5CH=CH-CH=CH(CH2)7COOH

9,11-Conjugated Linoleic Acid

1.4.1    Omega-3 and Omega-6 fatty acids

Omega-3 (ω3) and omega-6 (ω6) fatty acids are unsaturated “Essential Fatty Acids” (EFAs) that need to be included in the diet because the human  metabolism cannot create them from other fatty acids. Since these fatty acids are  polyunsaturated,  the terms n-3 PUFAs and n-6 PUFAs are applied to omega-3 and omega-6 fatty acids, respectively.  These  fatty acids  use the Greek  alphabet  (α,β,γ,…,ω)  to  identify  the location of the double bonds. The “alpha” carbon is the carbon closest to the carboxyl

group (carbon number 2), and the “omega” is the last carbon of the chain  because omega is the last letter of the Greek alphabet. Linoleic acid is an omega-6 fatty acid because it has a double bond six carbons away from the  “omega” carbon. Linoleic acid plays an important role in lowering cholesterol levels. Alpha-linolenic acid is an omega-3 fatty acid because it has a double bond three carbons away from the “omega” carbon (Chan and Cho, 2009). By subtracting the highest double-bond in the scientific name from the number of carbons in the fatty acid we can obtain its classification. For Arachidonic acid, we subtract 14 from 20 to obtain 6; therefore, it is an omega-6 fatty acid. This type of terminology is sometimes applied to oleic acid which is an omega-9 fatty acid.

In  these  simplified   structural  formulas  of  unsaturated   fatty  acids,  each   angle represents  a  carbon  atom.  In  these  formulas,  all the  double  bonds  have  the  cis configuration.

DHA  (docosahexaenoic  acid)  and  AA  (arachidonic  acid)  are  both  crucial  to  the optimal development of the brain and eyes. The importance of DHA and AA in infant nutrition  is  well  established,  and  both  substances  are  routinely  added  to  infant formulas. Excessive amounts of omega-6 polyunsaturated fatty acids and a very high omega-6/omega-3   ratio  have  been  linked  with  pathogenesis  of  many  diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune diseases. The ratio of omega-6 to omega-3  in modern diets is  approximately  15:1, whereas ratios of 2:1 to 4:1 have been associated with reduced mortality from cardiovascular disease, suppressed inflammation in patients with rheumatoid arthritis, and decreased risk of breast cancer. Some researchers have suggested that there is not very strong evidence  for the  benefits  of these ratios, and that it may be better to increase the consumption of omega-3 fatty acids rather than decrease the consumption of omega-6 fatty acids because a reduction of polyunsaturated fats in the diet would increase the incidence of cardiovascular disease (Simpoulos, 2002).

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