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Full Length Research Paper
Nutritional efficacy of avocado seeds
Leonia Ndesiamoo Henry*, Upendo Yonnah Mtaita and Catherine Clemence Kimaro
Department of Science and Laboratory Technology, Dar es Salaam Institute of Technology, P.O BOX 2958, Dar es
Salaam, Tanzania
Accepted 7 August, 2015
Screening of the aqueous extract of Tanzanian avocado seed of Persea specie was done for nutrients
and phytochemical compounds of nutritional importance. The aim of the study was to test for the
presence of nutrients (carbohydrate, protein and vitamin C) and other phytochemical compounds of
nutritional and medicinal values in avocado seeds. Both dry and fresh avocado seeds were tested for
presence of saponnin, flavonoids, tannin, carbohydrates, proteins and vitamin C. Tannins and
flavonoids were indicated only in fresh avocado seeds but none in dry samples. Saponins were found
in both dry and fresh seeds. Proteins, carbohydrates and Vitamin C were indicated in both fresh and dry
seeds. The compounds are reported to be present in the edible part of avocado in different proportions.
Interestingly, Tannin, a widely distributed compound in most unripe fruits, with the main role in
protection of the fruit from predation, and perhaps as pesticides, was tested only in fresh seeds. Tannin
is a water soluble compound and hence making the fresh and unripe fruits well protected against pests
as well as predators. Furthermore, it was noted that the avocado seed is nutritionally valuable based on
the phytochemical and nutrients it constitutes. Tannins that are said to be poisonous are normally
present in fresh seeds and not in the dry seeds, hence recommended to dry the seeds before
processing for consumption.
Key words: Avocado seed, carbohydrates, efficacy, flavonoids, nutrition, proteins, phytochemical compounds,
saponnins, tannins and Vitamin C
INTRODUCTION
Avocados in tropical region and Tanzania in particular
are abundantly available despite the fact that they are
highly underutilized. The low popularity of the fruit
amongst consumers results in a lot of fruits going to
waste every time it is in season. The avocado fruit is
rich in nutrients, high in protein and vitamins. Studies
have shown that avocados are rich in macro nutrients
like carbohydrate, vitamin and proteins (Whitney &
Rolfes, 2005). Tanzanian avocado fruits vary from
round to pear-shaped with a long, slender neck, but
sometimes completely round shapes, and the color
ranges from green to dark purple. Avocados are one of
the great cancer fighting foods, rich in a multiplicity of
nutrients, including many potent anti-oxidants and
phytochemicals as well as vitamins, minerals, fiber and
monounsaturated healthy fats (Chen et al., 2008,
Ensinger, 1994., Kushi, et al., 2006). Dry avocado
seeds are used locally as a relief drink, in treating
diarrhea or dysentery, teeth aches as well as skin
diseases.
*Corresponding author. E-mail: leoniahenry@yahoo.com
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution
License 4.0 International License
ISSN: 2408-5472 Vol. 3 (5), pp. 192-196, August, 2015
Copyright ©2015 Global Journal of Food Science and Technology
Author(s) retain the copyright of this article.
http://www.globalscienceresearchjournals.org/
Glob. J. Food Sci. Technol. 193
Consumption of avocado fruits in Tanzania communities
is very wide. This is due to the availability of avocado
fruits in Tanzania. A good number of people eat avocado
due to its taste, documented medicinal and nutritional
values and its cheap availability in the region. Apparently,
the commonly consumed part of avocado remains to be
the edible part i.e. the soft part, the layer between the
skin and the seed. The seed part of the fruit is commonly
not consumed due to its poor taste, little information on
its medicinal/nutritional value and also difficult processing
to taste. Therefore, different people never prefer the
avocado seeds mainly because they are not informed of
the nutrients and phytochemicals compositions in the
seed part.
The study aimed to establish the baseline on the
nutrients and phytochemical composition in the seed part
and hence recommend on the best exploitation of the
avocado seeds. The main objective of the study is
therefore to test for the presence of nutrients
(carbohydrate, protein, and vitamin C) and other
chemicals of nutritional and medicinal values in fresh and
dry avocado seeds.
MATERIALS AND METHODS
Study Area
The study was conducted in Dar es Salaam in which
avocados were bought from Kariakoo market and the
samples were analyzed at Dar es Salaam Institute of
Technology (DIT) Laboratory. Samples of avocado seeds
both fresh and dry were tested.
Sample Preparation and Analysis
Fresh ripe fruits were taken and then the first and second
layer was peeled (removed) to obtain the central hard
seeds. Ten (10) seeds were grinded fresh while another
ten (10) seeds grinded dry both giving a uniform
powders. Aliquots of 100gm powders were soaked in
200ml distilled water for 12 hours at room temperature to
form the aqueous extract solutions. The extracts were
filtered using filter paper and the filtrates were analysed
in the laboratory.
Phytochemical Screening
Phytochemical screening of the extracts was carried out
to test for the presence of saponnins, tannins and
flavonoids. Chemical tests were carried out on the
aqueous extracts to test for the presence of
phytochemicals in the avocado seeds of both fresh and
dry fruits. Tannins were tested by taking about 2g of the
both fresh and dry powders, boiled in 20 ml of water in a
beaker and then filtered. Few drops of 0.1% ferric
chloride were added. The formation of brownish green or
blue black coloration indicated presence of tannin in the
seeds. A portion of 10ml of the filtrate were mixed with
5ml of distilled water and shaken vigorously for persistent
froth. The froth was mixed with 3 drops of olive oil and
shaken vigorously; the presence of saponins was
indicated by the formation of emulsion. Flavonoids were
tested by adding 5ml of dilute ammonia solution(NH4OH)
to a 5ml of portion of aqueous filtrate, then 1ml of
concentrated sulphuric acid (H2SO4) from which the
formation of yellow coloration indicated presence of
flavonoids.
Nutrients Screening
Carbohydrates
Carbohydrates were tested as both reducing and non
reducing sugars. Benedict‟s solution was used to test for
reducing sugars. A 2.5g of seed powder were soaked in
45ml hot distilled water and cold distilled water added to
make a total of 50ml extract. Additions of cold distilled
water lead to color change to milky color indicating
presence of carbohydrates. Aliquots of 10mls were taken
from each flask into two beakers; 5mls of copper reagent
were added in each beaker, the mixture boiled for two
minutes. The change of colour from blue to brick red
indicated the presence of carbohydrates.
The reaction involves reduction of Cu2+ to Cu+
(precipitated as Cuprous Oxide) indicating the presence
of reducing sugars. Potassium iodide was added followed
with vigorous shaking; again the colour change from brick
red to light blue confirms the presence of carbohydrates
as polysaccharides. Addition of 5ml of normal 0.1M HCl
changed the colour to brick red confirming the presence
of reducing sugars as ketoses.
Proteins
Aliquots of five (5) drops of millon‟s reagents were added
to 1ml of the extract in a test tube followed by 3 drops of
NaOH(aq). White precipitates were observed, which turns
red on heating, indicating presence of proteins.
Vitamin C
Portions of 10ml of the extracts were measured into test
tubes followed by addition of 2-3 drops of starch solution
as an indicator and few drops of iodine solution as
potassium iodide (KI) were added in the test tubes. In the
presence of Vitamin C (C6H8O6), Iodine is oxidized to
Iodide. The more iodine added to the vitamin C solution
more iodide is formed until all vitamin C had reacted to
Henry et al. 194
form dihydroascorbic acid (C6H6O6). Thereafter, more
addition of iodine increased its concentration in the
solution hence changing the starch to blue-black colour.
Therefore, the immediate change of the starch to blue-
black colour when Iodine was added indicates that
Vitamin C is absent.
C6H8O6 + I2 + H2O → 2I- + C6H6O6 + 2H+
Data Analysis
The test results were presented as positive (where the
tested component was indicated in the reaction) and/or
Negative (where the component could not be indicated).
RESULTS
Testing for Nutrients (Protein, Carbohydrate and
Vitamin C) in Avocado Seeds
The three nutrients were found to be present in the seed
extracts of both fresh and dry seeds. It was observed that
fresh seeds of avocado may contain more proteins than
the dry seeds based on the number of drops of the
millons reagent consumed per volume of the extract. The
general test for carbohydrates indicated presence of
carbohydrates in both fresh and dry seeds.
Carbohydrates are sugars that the body uses for energy.
Simple carbohydrates, also called simple sugars, provide
the body with quick energy. Vitamin C was present in
both samples though at small amount. Addition of iodine
solution to 10ml extracts of both fresh and dry seeds
containing starch indicator was performed. Few drops of
iodine were furnished without changing of the colour of
the starch. The end point was shown by a colorless
solution indicating that all ascorbic acid (Vitamin C) had
reacted. More addition of the iodine resulted to change in
colour of the solution to blue-black solution indicating a
complete consumption of the vitamin C (Iodine reacting
with the starch).
Table 1: Screening results for nutrients and
photochemical compounds of both fresh and dry
avocado seeds.
SN.
Component
Fresh seed
Dry seed
1.
Protein
2.
Carbohydrate
3.
Vitamin C
4.
Tannins
X
5.
Saponins
6.
Flavanoids
X
Testing for Tannins, Saponins, Flavanoids in
Avocado Seed.
Phytochemical screening of the seeds showed presence
of saponins in both fresh and dry samples whereas;
tannins were detected in fresh seeds but not in dry seed.
Flavonoids were present in fresh sample but not in dry
seeds.
DISCUSSIONS
The Composition of Nutrients (Carbohydrate, Protein
and Vitamin C) in Avocado Seeds
Proteins, carbohydrates and vitamin C were all present in
both the dry and fresh seed samples. Studies have
shown that avocados are rich in macro nutrients like
carbohydrate, vitamin and proteins (Whitney & Rolfes,
2005). Carbohydrates exist in varying amounts in the
avocado seeds depending on the different activities that
took place in the fruit during storage process before the
analysis. During storage, fruits lose weight, shrivel and
change colour, lose acidity and ascorbic acid but gain
sweetness (Pareek & Dhaka, 2008, Pareek et al., 2009).
Also during this period, the enzyme activity, sugar and
carotenoid contents increase with corresponding
decrease in acidity, pectin and tannin content. To
compare the carbohydrates in both fresh and dry seeds it
needs a test that is specific for a specific type of
carbohydrates. The study by Flitsch & Rein, (2003),
explains the vital functions of carbohydrate found in
avocado seeds as supplying energy for the body process.
Some of the carbohydrates are immediately utilized by
the tissues and the remaining is stored as glycogen in the
liver and muscles and some are stored as adipose
tissues for future energy needs (Flitsch & Rein, 2003).
The proteins were also indicated in avocado seeds
though in varying amounts. Protein is a large biological
molecules consisting of one or more chains of amino
acids. The functions of proteins in the body include
replicating DNA and strengthen the blood vessels
(Gulteridge & Thornton, 2005). Like other biological
macromolecules such as polysaccharides and nucleic
acids, proteins form essential parts of organisms and
participate in virtually every process within cells. Many
proteins found in avocados catalyze biochemical
reactions and are vital to metabolism (Gulteridge &
Thornton, 2005).
Vitamin C constitutes a group of micro nutrients
commonly found in the seeds of certain species like
avocado (Ensminger, 2010). The presence of small
amounts of vitamin C in both fresh and dry samples may
be related to the effect of storage temperature of the
seeds and preservation method. The low storage
temperatures maintain relatively high Vitamin C content
Glob. J. Food Sci. Technol. 195
compared to fruits stored at intermediate and ambient
storage temperatures (Lee and Kader, 2000). Water loss
has also been documented to have a greater effect on
vitamin C levels than temperature (Nunes et al. 1998).
Apparently, Vitamin C is among the micro nutrients those
required in very small amounts for the functions of the
body. Vitamin C (ascorbic acid) is one of the most
important antioxidants. Blood levels of vitamin C are used
to measure nutritional, immune, and cardiovascular
status. Low values occur in scurvy, malabsorption
syndromes, inflammatory bowel disease, alcoholism,
pregnancy, hyperthyroidism, and kidney failure. The
study showed that Vitamin C is obtainable at higher
amounts in the fresh seeds than the dry ones. This is well
in agreement to the argument that higher temperatures of
storage and consequent water losses have an impact in
the stability of Vitamin C (Nunes et al. 1998). Ascorbic
acid is easily oxidised to dehydroascorbic acid in the
Iodine test. Complete reaction is shown by intense blue
colour complex indicating the presence of unreduced
Iodine (I2) in the solution.
O
O
O
OH
HO
HO OH
Dihydroascorbic acid
The Composition of Tannins, Saponins and
Flavonoids in Avocado Seed
The presences of saponin in avocado seed make this
fruit more important because saponins have both
hypertensive and cardiac depressant properties. Saponin
binds to cholesterol to form insoluble complexes; dietary
saponins in the gut of monogastric combine with
endogenous cholesterol excreted via the bile. This
prevents cholesterol reabsorption and resulting to
reduction of serum cholesterol. Tannins are polyphenols
of high molecular weight which are water soluble and
capable of precipitating proteins (Bryant et al., 1992;
Kraus, at al., 2003). Tannin because of their binding
properties, are known to be strongly astringent. This
astringency appears to be major cause of reduced food
intake in mammals. There is some controversy, however,
over whether reduced food intake is the result of the toxic
nature of tannins or not (Hagerman et al, 1992; Silanikore
et al., 2001). This has been very important in protecting
fruits from the attack by insects especially before
ripening. Tannins decreases with the time of ripening and
hence reduced to amounts that are harmless to
mammals. Tannins have high contributions in the
organoleptic properties. In the current study, tannins were
only detected in fresh sample.
The Nutritional Value of Avocado Seeds
The phytochemical compounds in avocado seeds are
responsible for color and organoleptic properties and also
for prevention and treatment of many health conditions,
including cancer, heart disease, diabetes, and high blood
pressure (Kush et al, 2006). There is some evidence that
certain phytochemicals may help prevent the formation of
potential carcinogens (substances that cause cancer),
block the action of carcinogens on their target organs or
tissues, or act on cells to suppress cancer development
(Kush et al, 2006). Tannins were found in fresh seeds
and not in dry ones. This is well indicated even in unripe
fruits causing the bitter taste of the fruits. Tannins protect
fruits from predation, and perhaps also as pesticides, and
in plant growth regulation (Cheeke, et al, 2006). Likewise,
the taste or smell from the tannins is what causes the dry
and the formation of small purse-like gathering (puckery)
feeling in the mouth following the consumption of
unripened fruit of avocado. The seed of the avocado
contains a concentrate of tannins, and these makes the
taste extremely bitter. Tannins is an acid commonly found
in some drinks (e.g. wine, coffee, tea.); but in some cases
it can be the cause for an allergic reaction. In the seeds
tannins were found to concentrate in fresh seeds and
upon drying it disappears. Avocado seeds are high in
tannins, which you may be familiar with from wine, which
give them a somewhat bitter taste and red color. Despite
the taste, tannins are present in seeds at reasonable
levels which are harmless to consumers. The presence of
Tanin
Flavonoid
Saponin
Ascorbic Acid
(Vitamin C)
Henry et al. 196
tannins in the body can improve the appetite and reduce
respiratory problem and circulatory disorder like lowering
blood pressure and reduce of cholesterol in blood
(Cheeke, et al, 2006). Saponins are naturally occurring
compounds that are widely distributed in all cells of
avocado plants. Saponins, which derive their name from
their ability to form stable, soap-like foams in aqueous
solutions, constitute a complex and chemically diverse
group of compounds (Shi et,al., 2004). Saponins affect
the immune system in ways that help to protect the
human body against cancers, and also lower cholesterol
levels (Shi et,al., 2004).
The flavonoids, have diverse beneficial biochemical
and antioxidant effects (Donald & Miranda, 2000). Their
dietary intake is quite high compared to other dietary
antioxidants like vitamins C. The antioxidant activity of
flavonoids depends on their molecular structure.
Flavonoids are different from other phytochemical
compounds especially on its reactivity nature. The other
compounds have the acidic groups that have binding and
nutralizable groups that are lacking in the flavonoids.
Antioxidants are compounds that protect cells against the
damaging effects of reactive oxygen species, such as
singlet oxygen, superoxide, peroxyl radicals, hydroxyl
radicals and peroxynitrite (Donald & Miranda, 2000). An
imbalance between antioxidants and reactive oxygen
species results in oxidative stress, leading to cellular
damage. The flavonoids have aroused considerable
interest recently because of their potential beneficial
effects on human health-they have been reported to have
antiviral, anti-allergic, ant platelet, anti-inflammatory, and
antitumor and antioxidant activities (Donald & Miranda,
2000).
CONCLUSION AND RECOMMENDATIONS
Avocado seed contains a diverse number of nutrients and
phytochemical compounds of nutritional value.
Biologically, the seed part of avocado is meant for
reproduction purposes. Apparently, most of the seeds are
discarded harvazardly compounding the problem of
dangerous wastes especially in the cities. The study
shows that almost all the nutrients and phytochemicals
found in the soft edible part are also found in the seed
part though in varying concentrations. It is learnt that the
seed part is also a potential source of nutrients and
medicinal phytochemical compounds. Avocado seeds
prepared in different ways can be used to keep the body
fit from many diseases and hence reducing expenses for
treatments. The dry seeds are preferred over the fresh
ones for their easy processing and also the reduced
amount of tannins in their product. On the environmental
point of view, utilization of avocado seeds in this way
shall reduce a lot of solid wastes in the environment and
hence keeping our cities cleaner.
The maximum exploitation of the avocado shall require
further studies especially in quantifying the nutrients and
phytochemical compounds in both the seeds and the soft
edible part of the avocado.
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