ABSTRACT
This study evaluated the microbial communities in used and unused vegetable oil. In this study, the predominant microorganisms isolated were Bacillus sp, Staphylococcus aureus, Escherichia coli, Klebsiella sp, Pseudomonas sp, Aspergillus niger, Aspergillus flavus, and Penicillium sp. The total heterotrophic plate count (THPC) of the used vegetable oil ranged from 3.1 × 105cfu/ml to 4.8 × 105cfu/ml, while that of the unused vegetable oil ranged from 1.4 × 105cfu/ml to 3.0 × 105cfu/ml. The total coliform plate count (TCPC) of the used vegetable oil ranged from 3.1 × 105cfu/ml to 4.1 × 105cfu/ml, while that of the unused vegetable oil ranged from 1.1 × 105cfu/ml to 3.2 × 105cfu/ml. The total fungal plate count (TFPC) of the used vegetable oil ranged from 2.4 × 105cfu/ml to 3.9 × 105cfu/ml, while that of the unused vegetable oil ranged from 1.5 × 105cfu/ml to 2.9 × 105cfu/ml. it was observed that Staphylococcus aureus is the most frequently occurring bacteria isolate from the used vegetable oil sample with a percentage occurrence of (37.5%), followed by Bacillus sp with a percentage occurrence of (25.0%), then Escherichia coli, Pseudomonas sp and Klebsiella sp had the least percentage occurrence of (12.5%). In the same sequence, Pseudomonas sp is the most frequently occurring bacteria isolate from the unused vegetable oil sample with a percentage occurrence of (37.5%), followed by Bacillus sp and Staphylococcus aureus with a percentage occurrence of (25.0%) while Escherichia coli has the least percentage occurrence of (12.5%). The regulatory agencies in Nigeria should equally monitor microbial growth in oils meant for human consumption to avoid food poisoning and contamination. Therefore, more improvement is required in the production and distribution of vegetable oils in order to meet the stipulated standards. Statistical analysis showed that there were significant differences in mean count of the used and unused vegetable oil at P< 0.05.
TABLE OF CONTENTS
Title
Page i
Certification iii
Dedication iv
Acknowledgement v
Table
of Contents vi
List
of Tables ix
Abstract x
1.0 CHAPTER ONE 1
1.1 Introduction 1
1.2 Types of Vegetable
Oil 2
1.3 Reasons for the Use
of Vegetable Oil 3
1.4 Vegetable Oils -
General Properties 6
1.5 Industrial
Application of Vegetable Oils 8
1.6 Advantages and
Disadvantages of Vegetable Oil 10
1.7 Benefits of
Vegetable Oil 11
1.8 Factors Affecting
Vegetable Oil 12
1.8.1 Temperature 12
1.8.2 Oxidation 13
1.8.3 Hydrolysis 13
1.8.4 Storage 13
1.9 Aims and Objectives 14
2.0 CHAPTER TWO 15
2.1 Literature Review 15
2.1.1 Extent of Microbial Contamination of
Refined and Unrefined Vegetable
Oils Sold In South-West Nigeria 15
2.1.2 Microbial Safety and
Quality of Edible Oil Examined At Ethiopian
Public Health Institute. 16
2.2 Biodegradation
Characteristics of Vegetable Oils 19
3.0 CHAPTER THREE 22
3.1 Materials and
Method 22
3.2 Study Area 22
3.3 Collection of
Samples 22
3.4 Sterilization of
Materials 22
3.5 Preparation of
Culture Media 23
3.6 Culturing of
Refined and Unrefined Oil Samples 23
3.7 Inoculation and
Isolation 23
3.8 Purification of Isolates 23
3.9 Identification of
Bacterial Isolates 24
3.9.1 Gram Staining 24
3.9.2 Biochemical Test 24
3.9.2.1 Indole test 24
3.9.2.2 Methyl red (MR) 25
3.9.2.3 Voges proskauer (VP) 25
3.9.2.4 Hydrogen sulphide test (H2S) 25
3.9.2.5 Citrate test 25
3.9.2.6 Urease test 25
3.9.2.7 Catalase test 26
3.9.2.8 Coagulase test 26
3.9.2.9 Sugar fermentation test 26
3.9.2.10 Starch test 27
3.10 Identification of
Fungal Isolates 27
3.11 Statistical Analysis 27
4.0 CHAPTER
FOUR
4.1 Results 28
5.0 CHAPTER FIVE
5.1 Discussion,
Conclusion and Recommendation 35
5.1.1 Discussion 35
5.1.2 Conclusion 38
5.1.3 Recommendation 38
References 40
Appendix I 44
Appendix II 50
LIST OF TABLES
|
TABLE
|
TITLE
|
PAGE
|
|
1
|
Total viable microbial
count from the used and unused vegetable oil samples
|
36
|
|
2
|
Morphological identification, Biochemical Identification, Gram
Reaction and Sugar Utilization Profile of bacterial isolates from the used
and unused vegetable oil samples
|
37
|
|
3
|
Cultural Morphology
and Microscopic Characteristics of the Fungal Isolates from the used and
unused vegetable oil samples
|
38
|
|
4
|
Percentage occurrence
of the bacteria isolates from the used and unused vegetable oil samples
|
40
|
|
5
|
Percentage occurrence
of the fungal isolates from the used and unused vegetable oil samples
|
38
|
CHAPTER
ONE
1.1 INTRODUCTION
Vegetable
oils are a group of fats that are derived from some seeds, nuts, cereal grains,
and fruits. It is important to understand that not all of these vegetable oils
are liquid oils at ambient temperatures. In addition, not all of the vegetable
oils are produced in commercial quantities, and of those that are, not all are
considered to be edible as in the sense of being a typical dietary component.
This treatise will cover only edible vegetable oils. The use of fats and oils
by man dates back to antiquity. Their chemical composition and specific
properties have allowed them to find use as foods, fuels and lubricants. Their
sources are numerous, encompassing vegetable, animal, and marine sources. As it
is with all matter, their usefulness to man is determined by their chemical
nature; and all fats and oils have certain characteristics in common.
The biodegradability of vegetable oils is the strongest point in
the case for their industrial use. In the light of more concerns about the
environmental impact of the use of industrial fuels and lubricants, they offer
in theory the most plausible solution to the issue of obtaining renewable and
eco friendly lubricants and fuels. With established biodegradabilities in the
range of 70 – 100%, their eco friendliness is not in doubt. The challenge is
the improvement of their performance in industrial uses; specifically with
reference to their oxidative stabilities and pour points which in general leave
much to be desired. Improvements are inevitable and are already being recorded
with increasing research directed in these areas.
Their established superiority in terms of biodegradability, when
compared with mineral oils, as well as the fact that they are renewable and
generally non toxic has focused attention on technologies that would enhance
their usefulness as bio fuels and industrial lubricants. There are also
concerns as to what to expect in case of vegetable oil spills. This is the
subject of some researchers (Li et al.,
2005) including the process of remediating such spills.
1.2 TYPES OF VEGETABLE OIL
The various types of vegetable oil include;
●
Coconut Oil
Coconut oil helps to prevent hair loss, premature aging and
boosts immunity. The oil can be extracted from the coconut palm meat or from the kernel. It is used for cooking, for
massaging and as carrier oil. The various types of coconut oil are virgin,
pure, refined, fractionated, and organic.
●
Safflower Oil
Extracted from its seeds, this oil contains omega-6 fatty acids,
oleic acid, and linoleic acid which help fight obesity, manage diabetes, prevent symptoms of pre-menstrual
syndrome, boost immunity, and more.
●
Sunflower Oil
A good amount of fatty acids and vitamin E in sunflower oil make it a healthy
option. A non-volatile oil, it is extracted from sunflowers fairly easily.
It helps in boosting energy, improving the health of skin and hair,
preventing heart diseases, reducing the severity of arthritis and asthma, and promoting skin cell regeneration.
●
Soybean Oil
This oil is extracted from soybeans and is rich in fatty acids.
High mineral and vitamin content and the antioxidant properties make this oil a
very healthy choice. Health benefits of soybean oil include better
immunity, eye care, skin care, and reduced risk of heart issues.
●
Olive Oil
Olive oil is fruit oil extracted
from the fruit itself. Most non-vegetarians can get their omega-3 fatty acids
from fish or fish oil, but vegetarians and vegans can receive it from olive oil. It is used for cooking, medicinal purposes,
soaps, and cosmetic products, for pharmaceutical supplements and sometimes as
fuel. Different types can be purchased such as virgin, extra virgin (cold
pressed), pure and lampante.
●
Peanut Oil
This popular cooking oil is extracted from peanuts. With a good
balance of fatty acids, it is also rich in vitamins, minerals, and organic compounds.
It aids in maintaining cholesterol levels, blood pressure, and overall heart
health. It also delays the symptoms of aging such as wrinkles.
●
Sesame Oil
One of the less popular oils, sesame oil is obtained from the
seeds and is a healthy alternative for certain unhealthy vegetable oils. It is
rich in minerals such as zinc, copper, calcium, magnesium; a wide range of
polyunsaturated fats, and tyrosine (amino acid). It helps reduce inflammation,
boosts dental health and metabolism, and reduces age spots. Other types of oil are
corn oil, cottonseed oil, palm oil, canola (rapeseed) oil,
flaxseed oil.
1.3 REASONS FOR THE USE OF VEGETABLE OIL
The various reasons for the use of vegetable oil are;
●
Culinary uses
Many vegetable oils are consumed directly, or indirectly as
ingredients in food – a role that they share with some animal
fats, including butter, ghee, lard, and schmaltz. The oils serve a
number of purposes in this role:
- Shortening – to give the pastry a crumbly
texture.
- Texture – oils can serve to
make other ingredients stick together less.
- Flavor – while less flavorful
oils command premium prices, some oils, such as olive, sesame, or almond oil, may be chosen
specifically for the flavor they impart.
- Flavor base – oils can also
"carry" flavors of other ingredients, since many flavors are due
to chemicals that are soluble in oil.
Oils can be heated to temperatures significantly higher than the
boiling point of water, 100 °C (212 °F), and used to cook foods (frying). Oils for this purpose must have a high flash point. Such oils include the
major cooking oils – soybean, rapeseed, canola, sunflower, safflower, peanut, cottonseed, etc. Tropical oils,
such as coconut, palm, and rice
bran oils, are particularly valued in Asian cultures for
high-temperature cooking, because of their unusually high flash points.
●
Hydrogenated oils
Unsaturated
vegetable oils can be transformed through partial or complete "hydrogenation" into oils of
higher melting point. The hydrogenation process involves "sparging" the oil at high
temperature and pressure with hydrogen in the presence of a catalyst, typically a powdered nickel compound. As each carbon-carbon double-bond is
chemically reduced to a single bond, two hydrogen atoms each form single bonds
with the two carbon atoms. The elimination of double bonds by adding hydrogen
atoms is called saturation; as the degree of
saturation increases, the oil progresses toward being fully hydrogenated. Oil
may be hydrogenated to increase resistance to rancidity (oxidation) or to change its
physical characteristics. As the degree of saturation increases, the oil's
viscosity and melting point increase.
The use of hydrogenated oils in foods has never been completely
satisfactory. Because the center arm of the triglyceride is shielded somewhat by
the end fatty acids, most of the hydrogenation occurs on the end fatty acids,
thus making the resulting fat more brittle. A margarine made from naturally
more saturated oils will be more plastic (more "spreadable") than a
margarine made from hydrogenated soy oil. While full hydrogenation produces largely saturated fatty acids, partial
hydrogenation results in the transformation of unsaturated cis fatty acids to unsaturated trans fatty acids in the oil mixture due
to the heat used in hydrogenation. Partially hydrogenated oils and their trans
fats have been linked to an increased risk of mortality from coronary heart disease, among other increased
health risks.
●
Industrial uses
Vegetable oils are used as an ingredient or component in many
manufactured products. Many vegetable oils are used to make soaps, skin
products, candles, perfumes and other personal care and cosmetic products. Some
oils are particularly suitable as drying
oils, and are used in making paints and other wood treatment products.
Dammar oil (a mixture of linseed oil and dammar resin), for example, is
used almost exclusively in treating the hulls of wooden boats. Vegetable oils
are increasingly being used in the electrical industry as insulators as vegetable oils are
not toxic to the environment, biodegradable if spilled and have
high flash and fire points. However, vegetable oils are
less stable chemically, so they are generally used in systems where they are
not exposed to oxygen, and they are more
expensive than crude oil distillate. Synthetic tetraesters, which are similar
to vegetable oils but with four fatty acid chains compared to the normal three
found in a natural ester, are manufactured by Fischer esterification. Tetraesters generally
have high stability to oxidation and have found use as engine lubricants.
Vegetable oil is being used to produce biodegradable hydraulic
fluid and lubricant.
One limiting factor in industrial uses of vegetable oils is that
all such oils are susceptible to becoming rancid. Oils that are more
stable, such as ben oil or mineral oil, are thus preferred for
industrial uses. Castor
oil has numerous industrial uses, owing to the presence of hydroxyl group on the fatty
acid. Castor oil is a precursor to Nylon.
●
Pet food additive
Vegetable oil is used in the production of some pet foods. AAFCO[12] defines vegetable oil,
in this context, as the product of vegetable origin obtained by extracting the
oil from seeds or fruits which are processed for edible purposes.
●
Fuel
Vegetable oils are also used to make biodiesel, which can be used like
conventional diesel. Some vegetable oil blends are used in unmodified
vehicles but straight vegetable oil, also known as pure
plant oil, needs specially prepared vehicles which have a method of heating the
oil to reduce its viscosity. The use of vegetable oils as alternative energy is growing and the
availability of biodiesel around the world is increasing.
1.4 VEGETABLE OILS - GENERAL PROPERTIES
Vegetable oils are obtained from oil containing seeds, fruits, or
nuts by different pressing methods, solvent extraction or a combination of
these. Crude oils obtained are subjected to a number of refining processes,
both physical and chemical. These are detailed in various texts and articles.
There are numerous vegetable oils derived from various sources. These include
the popular vegetable oils: the foremost oilseed oils - soybean, cottonseed,
pea-nuts and sunflower oils; and others such as palm oil, palm kernel oil,
coconut oil, castor oil, rapeseed oil and others. They also include the less
commonly known oils such as rice bran oil, tiger nut oil, patua oil, kome oil,
niger seed oil, piririma oil and numerous others. Their yields, different
compositions and by extension their physical and chemical properties determine
their usefulness in various applications aside edible uses.
Cottonseed oil was developed over a century ago as a byproduct of
the cotton industry. Its processing includes the use of hydraulic pressing,
screw pressing and solvent extraction. It is classified as polyunsaturated oil,
with palmitic acid consisting 20 – 25%, stearic acid 2 – 7 %, oleic acid 18 –
30% and linoleic acid 40 – 55%. Its primary uses are food related – as salad
oil, for frying, for margarine manufacture and for manufacturing shortenings
used in cakes and biscuits.
Palm
oil, olive oil, cottonseed oil, peanut oil, and sunflower oil amongst others
are classed as Oleic – Linoleic acid oils seeing that they contain a relatively
high proportion of unsaturated fatty acids, such as the monounsaturated oleic
acid and the polyunsaturated linoleic acid (Dunn, 2005). They are characterized
by a high ratio of polyunsaturated fatty acids to saturated fatty acids. They
thus, have relatively low melting points and are liquid at room temperature.
Iodine values, saponification values, specific compositions and melting points
in addition to other physical properties have been determined and are widely
available in the literature. (Oyedeji and Oderinde, 2006).
Other oils fall under various classes such as the erucic acid oils
which are like the oleic linoleic acid oils except that their predominant
unsaturated fatty acid is erucic acid (C22). Rapeseed and mustard seed oil are
important oils in this class. Canola oil is a type of rapeseed oil with reduced
erucic acid content. It is stable oil used in salad dressings, margarine and
shortenings. Soybean oil is important oil with numerous increasing applications
in the modern day world. It is classed as a linolenic acid oil since it
contains the more highly unsaturated linolenic acid. Other oils include castor
oil (a hydroxy-acid oil) which contains glycerides of ricinoleic acid. Also
worthy of note is that coconut oil, which unlike most vegetable oils is solid
at room temperature due to its high proportion of saturated fatty acids (92%)
particularly lauric acid. Due to its almost homogenous composition, coconut oil
has a fairly sharp melting point, unlike other fats and oils which melt over a
range. Oils from several sources are the subject of recent researches. Examples
include corn oil (Sanchez, 2008); camelina
sativa oil (Abramovic and Abram, 2005); Palmarosa oil (Mohanan et al., 2007) and Cineole oil
(Rodriguez, 2006).
1.5 INDUSTRIAL APPLICATION OF VEGETABLE OILS
The application of vegetable oils and animal fats for industrial
purposes and specifically lubrication has been in practice for many years.
Inherent disadvantages and the availability of inexpensive options have however
brought about low utilization of vegetable oils for industrial lubrication
(Mohanan et al., 2007). When applied
in the science of tribology, vegetable oils fall under the class known as fixed
oils. They are so named because they do not volatilize without decomposing.
Prior to recent developments, vegetable and animal oils in tribology have
functioned mainly as additives to mineral lubricating oil formulations,
although in some cases they are applied exclusively, or in blends. For
instance, tallow (acidless) has been used as an emulsifying agent for steam
cylinder oils, while castor, peanut and rapeseed oils have been used in blends
with mineral oils to improve lubrication performance. Palm oil has been used in
isolation as a fluxing dip in the tin plating of steel, while olive oil has
applications as a yarn lubricant.
Reasons for the use of vegetable oils in the science of
lubrication abound. Their superior lubricity and emulsifying characteristics
increase their desirability as additives to the cheaper but less effective
mineral oil based lubricants. Their superior lubricity in industrial and
machinery lubrication sometimes even necessitates the addition of friction
materials in tractor transmissions in order to reduce clutch slippage. Other
advantages that encourage the use of vegetable oils include their relatively low
viscosity temperature variation; that is their high viscosity indices, which
are about twice those of mineral oils (Mohanan et al., 2007).
Additionally, they have low volatilities as manifested by their
high flash points. Significantly, they are environmentally friendly: renewable,
non toxic and biodegradable. In summary, engine lubricants formulated from
vegetable oils have the following advantages deriving from the base stock
chemistry:
i. Higher Lubricity resulting in lower friction losses, and hence
more power and better fuel economy.
ii. Lower volatility resulting in decreased exhaust emissions.
iii. Higher viscosity indices.
iv. Higher shear stability.
v. Higher detergency eliminating the need for detergent additives.
vi. Higher dispersancy.
vii. Rapid biodegradation and hence decreased environmental /
toxicological hazards.
In a comparison of palm oil and mineral based lubricants, palm oil
based lubricants were found to be more effective in reducing the hydrocarbon
and carbon monoxide emission levels, among other things. Vegetable oils have
also been identified as having a lot of potential as alternative diesel engine
fuels (Kayisoglu et al., 2006). This
is supported by an interest in a cleaner environment, as well as the increasing
cost of mineral deposit based energy. Based on availability to meet demand,
soybean, peanut and sunflower oils have been identified as the most promising
fuel sources (Kayisoglu et al.,
2006). When used as a fuel, the term “biodiesel” is applicable. Biodiesel is
defined strictly as “…the mono alkyl ester (usually methyl ester) of renewable
fats and oils. It consists primarily of long chain fatty acid esters, produced
by the trans-esterification reaction of vegetable oils with short chain
alcohols. Distinct advantages of biodiesel include a high flash point of over
100°C, excellent lubricity, a BTU content comparable to that of petro diesel,
and virtually no sulfur or aromatic content. Above all, biodiesel is non-toxic
and biodegradable. Results from investigating performance of vegetable oils in
blends with diesel indicate that blending up to 25% biodiesel (sunflower) with
mineral diesel has no adverse effect on performance. (Kayisoglu et al., 2006). Vegetable oils have also
been applied as transformer coolant oils and have been found to conform to all
industry standards with performances and cost profiles comparable to the
conventional mineral oils applied in transformer cooling. Transformer oil
products have been produced from soybean oils as well as castor oils. The major
disadvantage militating against the use of vegetable oils in industrial
applications is its oxidative stability. This factor has been most researched
particular as biodiesel (Kapilani et al.,
2009). Several proposals on how to tackle this problem have been investigated.
Ways of evaluating the oxidative stability of oils have occupied several
authors (Gertz et al., 2000). Several
oils have been proposed for industrial uses primarily due to their recognized
high oxidative stability compared to other oils. Ghazalia et al. (2006)
investigated the effect of light on the stability of palm olein. Others have
investigated the stability of these oils when anti oxidants are added (Schober
and Mittelbach, 2004).
1.6 ADVANTAGES AND DISADVANTAGES OF VEGETABLE
OIL
The advantages and disadvantages of vegetable oil are;
●
Vegetable Oil Advantages
One of the most important advantages of vegetable oils is their
biodegradability. They are generally renewable and less toxic, reducing the
dependency on imported petroleum oil. Vegetable oil has high flash points at
326 degrees C (610 degrees F) than a flash point of 200 degrees C (392 degrees
F) for most mineral oils. Flash points are the temperature to which a
combustible fluid should be heated to give adequate vapor. This is to form
temporarily a flammable mixture with air when a small flame is applied.
Vegetable oil has very high viscosity index (VI). Viscosity index is a
frequently used measurement for change of fluid’s viscosity with temperature.
The higher the viscosity index, the smaller the change in viscosity with
temperature. A Viscosity index (VI) of 223 is usual for vegetable oil as
compared to 100 Viscosity index (VI) for most mineral oil. In short, high VI
oil changes less with temperature compared to oil with low Viscosity index
(VI).
●
Vegetable Oil
Disadvantages
On the flip side, vegetable oils in their natural form don’t have
enough oxidative stability. Having low oxidative stability means the oil
oxidizes quickly during use if untreated. This becomes thick and polymerizing
into a consistency like that of a plastic. To address this situation, chemical
modification of vegetable oil or using of antioxidants is done. However, this
can increase the price. Apart from that, vegetable oils have high pour point.
This is the lowest temperature at which oil is observed to flow when cooled
under condition. The pour point problem can be solved through winterization in
which chemical additives are added and blended with other fluids that have
lower pour points. To measure the toxicity of vegetable oils, variety of tests
is used that involves other organisms. The toxicity increases once additives
are included as vegetable oils show little toxicity in their natural forms.
1.7 BENEFITS OF VEGETABLE OIL
Some of the benefits of vegetable oils include;
●
Promote Cell Growth
Oils like safflower, cottonseed, sunflower, almond, and wheat germ are all rich in vitamin E which is required in
the body for cell protection and development. This vitamin has a long list of
benefits for our body. From improving the immune system to stimulating the
digestive system, it is vital. It protects body tissues such as skin, eyes, breasts, testes, and liver.
●
Prevent Heart Conditions
Polyunsaturated and monounsaturated fats are the most frequently found forms of fat in vegetable
oils. Polyunsaturated fats help lower bad cholesterol levels and reduce the risk of
cardiovascular diseases. Further, the presence of vitamin E in the oils
helps in preventing heart diseases and eliminating blood clots which are the cause of
heart ailments.
●
Promote Growth
The body requires fatty acids to carry out various functionings,
and vegetable oils provide these in abundance. There are two types of fatty
acids, namely, omega-3 and omega-6. The body doesn’t produce these naturally;
hence, acquiring it from food is essential. Alpha-linolenic, a type of
omega-3 fatty acids, is found in soybean, canola, and flaxseed oil which are very similar
to the fatty acids in fish.
Omega-3 fatty acids are widely known to be anti-inflammatory which
is why they are highly recommended for people suffering from chronic heart,
skin and digestive concerns. On the other hand, omega-6 is pro-inflammatory,
which is also required but long-term use beyond advised quantities can cause
more harm than help. A ratio of 1:1 is ideal to maintain health and avoid
complications. However, many people consume an unhealthy ratio of
16:1, an unbalanced number of omega-6 and omega-3 fatty acids which has been
correlated to various diseases including inflammatory issues, and autoimmune diseases, and chronic diseases.
1.8 FACTORS AFFECTING VEGETABLE OIL
1.8.1 Temperature
Exposure to heat and light creates an environment favorable to
chemical and enzymatic reactions resulting in hydrolysis and oxidation. Oxidative rancidity in oil occurs due to the
oxidation of the double bonds in unsaturated fatty acids present in the
constituent triacylglycerols forming peroxides or hydroperoxides that later
polymerize or decompose producing aldehydes, ketones and low molecular weight
acids. The process of oxidative rancidity or peroxidation and the consequent
rancidification is the major cause of loss of quality of edible oils. Oxidative
rancidity affects flavor, aroma, color, texture, and also decreases the
nutritive value of edible oils via the destruction of fat-soluble vitamins
(especially vitamins A and E) and proteins.
1.8.2 Oxidation
Contact of oils and fats with oxygen, present in the atmosphere,
causes chemical changes in the product which downgrade the quality. Some of the
effects of oxidation may be rectified within an edible oil refinery with some
extra processing and, therefore, extra cost. However, the effects may be so
severe that rectification is not possible. Much can be gained by reducing the
amount of air contact and this principle is the basis of several of the
recommendations. Oxidation proceeds more rapidly as temperature increases, so
each operation should be carried out at the lowest practicable temperature
(Gertz et al., 2000). The rate of
oxidation is greatly increased by the catalytic action of copper or copper alloys,
even when trace amounts are present. Because of this, copper and copper alloys
must be rigorously excluded from the systems. Other metals, such as iron, also
have catalytic effects although less than that of copper.
1.8.3 Hydrolysis
The breakdown of vegetable oil to fatty acids is promoted by the
presence of water particularly at higher temperatures. Hydrolysis is also
promoted by the action of certain micro-organisms. Tanks in which the oil is
being stored or shipped should always be clean and dry before use.
1.8.4 Storage
All oils degrade in response to heat, light, and oxygen. To delay
the onset of rancidity, a blanket of an inert gas , usually nitrogen, is
applied to the vapor space in the storage container immediately after
production a process called tank blanketing (Gertz et al., 2000). In a cool, dry place, oils have greater stability,
but may thicken, although they will soon return to liquid form if they are left
at room temperature. To minimize the degrading effects of heat and light, oils
should be removed from cold storage just long enough for use. Refined oils high
in monounsaturated fats, such as macadamia oil, keep up to a year, while those
high in polyunsaturated fats, such as soybean oil , keep about six months.
Rancidity tests have shown that the shelf life of walnut oil is about 3 months,
a period considerably shorter than the best before date shown on labels. By
contrast, oils high in saturated fats, such as avocado oil , have relatively
long shelf lives and can be safely stored at room temperature , as the low
polyunsaturated fat content facilitates stability.
1.9 AIMS AND OBJECTIVES
This study is therefore, aimed at isolation of some of the
possible species of microorganisms from used and unused vegetable oil.
The objectives are;
- To isolate and characterize
microorganisms present on used and unused vegetable oil.
- To determine the percentage
occurrence of the isolates.
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