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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Over the past several years, extensive research has been done on the microbial production of polyunsaturated fatty acids (PUFA). Regardless, research on the oleaginous microalgae used as feedstock for biofuels production and the overall story about the production of nutraceutical fatty acids from oleaginous microalgae has been very limited. This volume provides an exclusive insight on the production of nutraceutical fatty acids from oleaginous microalgae and their role on human health. Some saturated and monounsaturated fatty acids can be synthesized by humans, whereas long-chain polyunsaturated fatty acids (PUFAs) such as alpha-linolenic acid and linoleic acid cannot and are deemed essential. The products of these acids, such as DHA, which is important for early visual and neurological development, are extremely important to human health. Replacing SFAs with omega-3 and omega-6 fatty acids in the diet reduce the risk of cardiovascular diseases and prevent Alzheimer's, bipolar disorder, and schizophrenia, among other benefits. The ever-rising global demand for omega-3 & 6 PUFAs, however, cannot be met solely by fish oil, due to diminishing fish stocks and pollution of marine ecosystems, which has led to increased interest in alternative sustainable sources. Vegetable oils from genetically engineered plant oilseeds and microorganisms are two potential alternatives to fish oil, even though omega-3 PUFAs are highest in the latter. Although transgenic plants present numerous advantages, their production is dependent on seasonal and climatic conditions and the availability of arable land. Moreover, there are public concerns regarding the cultivation of transgenic crops in open ecosystems. These, together with regulatory issues restrict the large-scale production of genetically modified crops. Microorganisms, however, are known natural producers of microbial oils similar to those obtained from plants and animals and a possible source of nutritionally important omega-3 & 6 PUFAs. This groundbreaking volume presents invaluable new research on essential fatty acids, their production from various oleaginous microorganisms, biochemical and metabolic engineering to improve PUFAs content in oil, extraction and purification of omega 3 fatty acids, and the current market scenario. Whether a veteran engineer or scientist using it as a reference or a professor using it as a textbook, this outstanding new volume is a must-have for any engineer or scientist working in food science.
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Table of Contents
Cover
1 Introduction to Essential Fatty Acids
1.1 Introduction
1.2 Biosynthesis of PUFAs
1.3 Sources of Essential Fatty Acids and Daily Intake Requirement
1.4 Biological Role of Essential Fatty Acids
1.5 Effect of Essential Fatty Acid on Human Health (Disease Prevention and Treatment)
1.6 Concluding Remarks
References
2 Nutraceutical Fatty Acid Production in Marine Microalgae and Cyanobacteria
2.1 Introduction
2.2 Fatty Acid Synthesis
2.3 Glycerolipid Synthesis and Lipid Accumulation
2.4 Current LC-PUFA Sources and the Potential Benefits of Using Marine Microalgae
2.5 Nutraceutical Fatty Acids in Marine Microalgae and Species of Interest
2.6 Autotrophic and Heterotrophic Cultivation
2.8 Optimizing Growth Condition to Promote Lipid Accumulation and Desired FA Profiles
2.9 Genetic Engineering to Promote Lipid Accumulation and Tailoring of Fatty Acid Profiles
2.10 Conclusions
2.11 Acknowledgements
References
3 Production of PUFAs as Dietary and Health Supplements from Oleaginous Microalgae Utilizing Inexpensive Renewable Substrates
3.1 Introduction
3.2 PUFAs as Dietary and Health Supplements
3.3 Microalgae as Source of PUFAs
3.4 Systems for Microalgal Cultivation
3.5 Use of Alternative Substrates for Microalgal Growth
3.6 Factors that Affect the Heterotrophic and/or Mixotrophic Cultures
3.7 Conclusions
3.8 Future Perspectives
3.9 Acknowledgements
References
4 Lipid and Poly-Unsaturated Fatty Acid Production by Oleaginous Microorganisms Cultivated on Hydrophobic Substrates
4.1 Lipid Production (Single Cell Oil)
4.2 Lipid Biodegradation and Synthesis
4.3 Hydrophobic Substrates
4.4 Oleaginous Microorganisms
4.5 Conclusions
References
5 Overview of Microbial Production of Omega-3-Polyunsaturated Fatty Acid
5.1 Introduction
5.2 Microbial Sources of ω-3 PUFA
5.3 ω-3 PUFA Biosynthesis in Microbial Cells
5.4 Factors Affecting ω-3 PUFA Production
5.5 Stabilization of ω-3 PUFA
5.6 Conclusions
References
6 Autotrophic Cultivation of Microalgae for the Production of Polyunsaturated Fatty Acid
6.1 Introduction
6.2 Importance of PUFAs
6.3 Biosynthesis of PUFA in Autotrophic Algae
6.4 Harvesting of Algae and Extraction of Fatty Acids
6.5 Metabolic Engineering Towards Increasing Production of PUFA’s by Algae
6.6 Conclusion
6.7 Acknowledgement
References
7 Production of Omega-3 and Omega-6 PUFA from Food Crops and Fishes
7.1 Introduction
7.2 PUFA as a Dietary Supplement
7.3 Biosynthesis and Metabolism of PUFA
7.4 Potential Commodities for PUFA Production
7.5 Alternate Sources of PUFA
7.6 Future Avenues
7.7 Conclusion
References
8 The Role of Metabolic Engineering for Enhancing PUFA Production in Microalgae
8.1 Introduction
8.2 LC-PUFA Biosynthesis in Microalgae
8.3 Identification and Characterization of Enzymes Involved in PUFA Synthesis
8.4 Metabolic Engineering for Enhancing the LC-PUFA Production in Microalgae
8.5 Conclusion and Future Perspective
References
9 Health Perspective of Nutraceutical Fatty Acids; (Omega-3 and Omega-6 Fatty Acids)
9.1 Introduction
9.2 Health Benefits of PUFA
9.3 Conclusion
References
10 Extraction and Purification of PUFA from Microbial Biomass
10.1 Introduction
10.2 Biochemical Composition of Microalgae
10.3 Microalgae as a Source of Polyunsaturated Fatty Acids
10.4 Composition of PUFAs in Microbial Biomass
10.5 Methods of Lipid Extraction from Microbial Biomass
10.6 Purification and Enrichment of PUFAs
10.7 Concluding Remarks
References
11 Market Perspective of EPA and DHA Production from Microalgae
11.1 Introduction
11.2 Categories of Omega-3 Fatty Acids and Their Health Benefits
11.3 Brain Development
11.4 Cardiovascular Diseases
11.5 Present Sources of Omega-3 PUFAs
11.6 Why Microalgae?
11.7 Factors Affecting Growth and Fatty Acid Composition of Microalgae
11.8 Algal Oil Extraction, Purification and Its Refining Techniques
11.9 Microalgae as a Boon for Long-Chain Omega-3 PUFAs
References
12 Oleaginous Microalgae –A Potential Tool for Biorefinery-Based Industry
12.1 Introduction
12.2 Industrial Applications of Microalgae
12.3 Use of Microalgae as Biofertilizer
12.4 Microalgae as a Food Component
12.5 Microalgae as a Nutraceutical
12.6 Pigments and Carotenoids
12.7 Phycobilins
12.8 Fatty Acids
12.9 Animal Nutrition
12.10 Safety Related Issues Related to Microalgal Nutraceuticals
12.11 Application in Pharmaceutical Industry
12.12 Utilization of Microalgae in Cosmetics Production
12.13 Microalgal Application in Wastewater Treatment
12.14 Factors Affecting Lipid Production in Microalgae
12.15 Application of Microalgae in Biofuel Production
12.16 Biodiesel
12.17 Biogas
12.18 Hydrogen
12.19 Biosyngas
12.20 Ethanol
12.21 Cultivation of Microalgae for Biofuel Production
12.22 Current Research Status in India
12.23 Concluding Remarks and Future Prospectives
12.24 Acknowledgements
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 PUFA content of some fish species [39].
Table 1.2 Omega-3 and omega-6 fatty acids content (% w/w) of plant and vegeta...
Table 1.3 PUFA content of Thraustochytrids species.
Table 1.4 EPA and DHA content of microalgae.
Chapter 3
Table 3.1 Fatty acid composition of lipid from different species of microalga...
Table 3.2 Lipid production (% w/w) of different species of microalgae under h...
Chapter 4
Table 4.1 Intracellular lipid production by microorganisms growing on hydroph...
Table 4.2 Fatty acid composition (%, w/w) of substrate fat (S) and cellular l...
Chapter 5
Table 5.1 Percentage of ω-PUFA in various microorganisms.
Chapter 6
Table 6.1 Various fatty acid molecules derived from algae.
Chapter 7
Table 7.1 PUFA contents in food crops and plants.
Table 7.2 Different sources of PUFA production.
Chapter 8
Table 8.1 List of desaturases and elongases isolated and characterized from d...
Chapter 9
Table 9.1 Commercially significant PUFAs from different microalgal species [6...
Chapter 10
Table 10.1 PUFAs composition of some microbes.
Table 10.2 Extraction and purification methods for enrichment of PUFAs from m...
Chapter 11
Table 11.1 EPA and DHA composition of various marine fishes [1].
Table 11.2 Microalgae metabolites from different microalga species which are ...
Chapter 12
Table 12.1 Utilization of non-edible and edible crops for biofuel production ...
Table 12.2 Lipid content in microalgae [27, 28].
Table 12.3 Microalgae-based nutraceuticals and their application [74].
Table 12.4 Impact of nutrient stress condition on lipid content of microalgae...
Table 12.5 Benefits of using microalgal biofuel [157].
List of Illustrations
Chapter 1
Figure 1.1 The chemical structure of DHA and EPA, representative omega-3 and...
Figure 1.2 Molecular structure of omega-3 fatty acids and omega-6 fatty acid...
Figure 1.3 Synthesis of EPA and DHA from ALA through a series of desaturatio...
Chapter 2
Figure 2.1 Overview of strategy for exploring microalgae for the production ...
Figure 2.2
Nomenclature, structure, and synthesis of FAs.
(a) Chemical struc...
Figure 2.3
A generalized and simplified scheme of acyl lipid synthesis in mi
...
Figure 2.4
Examples of cultivation of Spirulina.
100 L bags in indoors (a) a...
Figure 2.5 Cultivation of
N. gaditana
in closed bioreactors, indoors (a and ...
Figure 2.6 Diatoms grown in biofilms (a) in a circular economy set-up (b).
Chapter 3
Picture 3.1 On the left: Basic Omega-6 PUFAs metabolic pathway, starting fro...
Chapter 4
Figure 4.1 Biosynthesis of intracellular lipids [1].
Figure 4.2 Main principles of aerobic biodegradation of lipids [31, 32].
Figure 4.3 Biosurfactant production and lipid emulsification [27].
Figure 4.4 Hydrolysis of fat substrates (waste butter and waste olive oil) u...
Figure 4.5 Glycerol degradation through biochemical pathways of glycolysis a...
Figure 4.6 Beta oxidation process (http://flipper.diff.org/).
Chapter 5
Figure 5.1 Overview of biosynthesis of ω-3 PUFA in microbial cells.
Chapter 6
Figure 6.1 Various resources of PUFAs biomolecules.
Figure 6.2 Factors affecting autotrophic cultivation for PUFA production.
Figure 6.3 Concept of bio-refinery proposed nowadays for economical sustenan...
Chapter 7
Figure 7.1 Overview of fatty acids.
Figure 7.2 Health benefits of PUFA.
Chapter 8
Figure 8.1 Schematic of aerobic conventional pathway and alternative pathway...
Figure 8.2 Overview of anaerobic biosynthesis of DHA in microalgae. GAP: gly...
Chapter 9
Figure 9.1 Omega-6 PUFA: (a) –Linoleic acid; (b) –γ-Linolenic acid; (c) –Ara...
Figure 9.2 Omega-6 PUFA: (a) α-Linolenic acid; (b) Eicosapentaenoic acid; (c...
Figure 9.3 Biosynthesis of ω-3 and ω-6 polyunsaturated fatty acids by the ac...
Figure 9.4 Structure of cardiolipin.
Figure 9.5 Primary roles of PUFA: Anti-inflammatory, neurological developmen...
Chapter 10
Figure 10.1 Biochemical compositions of microalgae.
Figure 10.2 Classification of microalgae lipid.
Figure 10.3 Chemical structures of polyunsaturated fatty acids.
Figure 10.4 Microalgae as a source of polyunsaturated fatty acids [21].
Figure 10.5 Microalgae cell disruption methods.
Figure 10.6 Schiamatic diagram of proposed solvent extraction mechanism [32]...
Figure 10.7 Solvent lipid extraction processes [32].
Figure 10.8 Green solvents used for lipid extraction.
Figure 10.9 Super critical lipid extraction technique from microalgae, modif...
Chapter 11
Figure 11.1 Chemical structure of EPA and DHA.
Figure 11.2 Different health benefits of EPA and DHA [modified 15].
Figure 11.3 Optimisation of different operational parameters for enhanced EP...
Chapter 12
Figure 12.1 Types of microalgae nutraceuticals [74].
Guide
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Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])
Nutraceutical Fatty Acids from Oleaginous Microalgae
A Human Health Perspective
Edited by
Alok Kumar Patel and Leonidas Matsakas
This edition first published 2020 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2020 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.
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Library of Congress Cataloging-in-Publication Data
ISBN 9781119631712
Cover image: Alok Kumar PatelCover design by Kris Hackerott
1Introduction to Essential Fatty Acids
Alok Patel*, Ulrika Rova, Paul Christakopoulos and Leonidas Matsakas
Biochemical Process Engineering, Division of Chemical Engineering, Department of Civil, Environmental, and Natural Resources Engineering, Luleå University of Technology, Luleå, Sweden
Abstract
Certain omega-3 fatty acids, such as α-linolenic acid (ALA), and omega-6 fatty acids, such as linoleic acid (LA), cannot be synthesized in the human body and are recognized as essential fatty acids. While some long-chain polyunsaturated fatty acids (LC-PUFA) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can be synthesized from the parent omega-3 fatty acids (ALA), this is done at a very low conversion rate, hence it must be taken through diet to fulfill the daily intake requirement. Both EPA and DHA have several vital activities in the human body, such as anti-inflammatory effects and being the structural component of the cell membrane. The fatty acids DHA, arachidonic acid (AA), and LA accumulate most usually in tissues, whereas DHA mostly accumulates in retina and brain gray matters and it is important for proper visual and neurological development during gestation period and postnatal period. Replacement of saturated fatty acids with omega-3 and omega-6 fatty acids in daily diet reduces the risk of cardiovascular disease and prevents diseases such as Alzheimer’s, bipolar disorder, and schizophrenia. Proper EPA and DHA content also help individuals with type 2 diabetes to reduce the elevated serum triacylglycerides. It also facilitates infants to reduce the risks of fatal myocardial infarction and other cardiovascular diseases. Hence, as recommended by the American Heart Association, it is necessary to consume fish, and especially oily fish at least twice per week as it is an excellent source of these fatty acids. Marine fishes of Salmonidae, Scombridae, and Clupeidae families are important sources of omega-3 fatty acids but due to the increasing demand of PUFA and diminishing aquatic ecosystem, fishes are not a sustainable source to serve as a long-term feed-stock for omega-3. Plants can synthesize some of PUFA such as oleic acid, LA, GLA (γ-linolenic acid), ALA, and octadecatetraenoic acid but due to lacking some essential enzymes for PUFA synthesis such as desaturase and elongases, they are incapable of synthesizing EPA and DHA. Oleaginous microalgae and thraustochytrids could be a sustainable option to produce microbial EPA and DHA.
Keywords: Oleaginous microorganisms, lipid accumulation, fatty acid profile, microalgae, nutraceuticals, omega-3 fatty acid, human health
1.1 Introduction
Fatty acids or lipids serve in diverse metabolic functions related to growth and maintenance of cells and tissues, and act as caloric energy molecules involved in various cellular signaling events that accompany several physiological processes after metabolism [1, 2]. Lipids are usually originated from the acetate route and derivatives of polyketides [3]. Chemically lipids are hydrocarbons of C6 to C32 long-chain, containing hydrophilic carboxyl group at one end and methyl group at the terminal end. These hydrocarbon chains are made up of an even number of carbon atoms in naturally occurring fatty acids; however, they can be branched or cyclic that is present in some bacterial strain [3]. The hydrocarbon chain can be saturated, mono-unsaturated or polyunsaturated depending on the presence and numbers of double bond [4, 5]. From the different fatty acid types, polyunsaturated fatty acids (PUFAs) have greater physiological importance because of their medicinal properties [6]. Omega-3 and omega-6 fatty acids belong to a category of PUFAs where the first double bond is located between the 3rd and 4th carbon atom near the methyl end (or omega end) of omega-3 fatty acids (n-3) whereas the first double bond is situated between the 6th and 7th carbon in the case of omega-6 fatty acids (Figure 1.1).
Figure 1.1 The chemical structure of DHA and EPA, representative omega-3 and omega-6 PUFAs.
Figure 1.2 Molecular structure of omega-3 fatty acids and omega-6 fatty acids.
These fatty acids have unique structures due to the presence of the double bond as it introduces the bends in the hydrocarbon chain which affect its physical properties (Figure 1.2) [7]. Mammals can synthesize saturated and unsaturated fatty acids from carbon present in carbohydrates and proteins while they show an inability to synthesize PUFAs due to the lack of certain enzymes that are necessary to introduce the cis double bonds at n-3 and n-6 position [5]. These omega-3 and omega-6 fatty acids are considered as essential fatty acids for human beings and must be taken through diet. α-linoleic acid (ALA, 18:3n-3) and linoleic acid (LA, 18:2n-6) are the parent fatty acids of omega-3 and omega-6 fatty acid series, respectively [4].
Humans can synthesize long-chain PUFA (LC-PUFA) such as eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3), from ALA and dihomo-γ-linolenic acid (DGLA; 20:3n-6) and AA (20:4n-6), from LA. Some investigators showed that only 2 to 10% of ALA can be converted into EPA and DHA [8], while others suggested that 7% of ALA is converted into EPA while low conversion rate (0.013%) is reported for DHA [9]. Hussein et al. (2005) suggested that only 0.3% of EPA and <0.01% of DHA can be converted from ALA [10]. The conversion of ALA to EPA and DHA is too low and cannot meet the daily intake requirement. These fatty acids have several health benefits as they are incorporated in various parts of the body including cell membrane and play a vital role in anti-inflammatory process [11, 12]. Both EPA and DHA are essential for proper aging and fetal development [13], DHA is mainly incorporated in the retina and brain. They are also used to treat and prevent several viral diseases.
1.2 Biosynthesis of PUFAs
Fatty acids are absorbed in intestines after hydrolysis from dietary fats (tri-acylglycerols and phospholipids) by pancreatic enzymes [14]. Micelles are formed in intestines after mixing fatty acids and other fat digestion products in the presence of bile salts. Fats are absorbed to an extent of 85-90% throughout the small intestine from these mixed micelles [14]. Omega-3 fatty acids are considered as essential fatty acids as they cannot be synthesised by humans and animals, due to lack of the Δ-12 and Δ-15 desaturase enzymes [4, 5]. As humans and animals are unable to produce a de novo synthesis of omega-3 fatty acids, these must be taken through their diet from other sources [15]. However, they have the capability to synthesise small amounts of DHA and some intermediate products such as EPA from the parent omega-3 fatty acids such as ALA, and the rest of the required amount is fulfilled from direct consumption of DHA and EPA [16]. The parent ALA intake is done also through our diet from plant sources. The metabolism starts by the action of Δ-6 desaturase on ALA, for the unsaturation in aliphatic carbon chain, followed by the addition of two carbon atoms in the aliphatic carbon chain by the action of elongases. This structure of fatty acids allows the action of Δ-5 desaturase and finally formation of EPA [16]. Some previous studies showed that a desaturation process occurs in endoplasmic reticulum [16]. However, the role of Δ-4 desaturase was established from the microbial pathway for DHA synthesis (22:6ω-3) from 22:5ω-3. This part of the pathway was interpreted after the discovery of 24:5ω-3 from the elongation of 22 carbon chain and further desaturated into 24:6ω-3 in the mammals [17] and there is a reverse pathway of partial oxidation of 24:6ω-3 to synthesize DHA in peroxisomes [18]. This is also evidenced by the treatment of peroxisomal disorders, such as Zellweger syndrome, in infants by dietary supplementation of DHA [19]. The unsaturation and elongation process during synthesis of fatty acids is presented in Figure 1.3.
There is another pathway of fatty acid synthesis that was discovered in the thraustochytrids strain Schizochytrium sp. and is known as polyketide synthesis pathway (PKS). This pathway is distinguished from the conventional Fatty acid synthesis (FAS) pathway in terms of oxygen requirements, as it does not require molecular oxygen for the synthesis of PUFAs [23]. In this microorganism, C14 and C16 fatty acid synthesis follows the FAS system, while the synthesis of LC-PUFA follows the PKS pathway [24]. A major difference between the FAS and PKS pathways is that the elongation of fatty acids is done through dehydration and isomerization of fatty acyl intermediates in the PKS pathway, whereas in the FAS pathway it occurs through elongases and desaturases [25]. Although LC-PUFA synthesis in thraustochytrids is not fully understood yet, the identification of a Δ-4 fatty acid desaturase in thraustochytrids indicated that DHA synthesis might be a result of the FAS pathway [23]. In FAS route of PUFA synthesis, a series of desaturases and elongases works on either the C16:0 or C18:0 to form unsaturated fatty acids and DHA is synthesized from 22:5 by delta-4 desaturase [24]. It has been proved by genome annotation results of thraustochytrids S. limacinum that this microorganism does not have delta-4 desaturase as reported in FAS route of DHA synthesis. DHA is usually synthesized by the PKS pathway present in this microorganism [23, 26, 27] which require a different series of enzymes such as 3-ketoacyl synthase, 3-ketoacyl-ACP reductase, enoyl reductase, and dehydrase/isomerase [28].
Figure 1.3 Synthesis of EPA and DHA from ALA through a series of desaturation and elongation reactions [3, 20–22].
1.3 Sources of Essential Fatty Acids and Daily Intake Requirement
The daily requirement of the parent omega-3 fatty acid LA is 17-20 g for men and 12-13 g for women and can be obtained from vegetable oils such as soybean, corn oil or seeds of various plants [29]. The daily intake of ALA is 1.8-2 g for men and 1.4-1.5 g for women and can be taken through, for example, flaxseeds and canola oil [30]. Animals have the capacity to produce AA from LA, so certain animal products such as meat and eggs are an excellent source of AA [31]. Evening primrose oil and borage seed oil are good sources of γ-linolenic acid (GLA) [32].
The daily intake requirements of EPA and DHA for adults are 200 mg to 1000 mg according to various agencies [30]. The major dietary sources of EPA and DHA are fishes [33] (see Table 1.1). Cod liver oil, for example, is not only enriched with EPA and DHA but also contains vitamins such as vitamin A [34]. Krill oil may be an alternative to fish oils, as it a good source of omega-3 fatty acids and has a high content of EPA and DHA [35]. Nowadays, due to the increasing interest in vegetarian foods, people avoid consuming non-vegetarian sources of DHA and EPA. Moreover, a major concern with consuming certain fishes is the possibility of contamination with several harmful elements such as arsenic, lead and mercury [34]. Some plant and vegetable oils are good source of polyunsaturated fatty acids and are listed in Table 1.2. The only sustainable replacement of non-vegetarian sources of PUFAs is the oils obtained from microbial sources. Microalgae, fungi and bacteria can be sources of microbial oils. These microorganisms are known to be natural producers and the original sources of omega-3 PUFAs [36]. A list of thraustochytrids and microalgae for their omega-3 fatty acid production capabilities are presented in Table 1.3 and Table 1.4, respectively. Despite the high production cost, microorganisms offer certain advantages for the production of omega-3 PUFAs, such as high growth rates, simple nutrient input requirement, controllable culture conditions, easy genetic manipulation and well-annotated genomes and metabolic pathways [37]. Microbial oils usually contain a significant amount of natural antioxidants such as carotenoids and tocopherols, which play a role in protecting omega-3 PUFAs from oxidation. The first microbial oil containing GLA that was produced was from a filamentous fungus, Mucor circinelloides and its commercial production lasted from 1985 to 1990 [38].
Table 1.1 PUFA content of some fish species [39].
Fish species
g DHA per serving
g EPA per serving
Salmon, Atlantic, farmed cooked, 3 ounces
1.24
0.59
Salmon, Atlantic, wild, cooked, 3 ounces
1.24
0.59
Herring, Atlantic, cooked, 3 ounces
0.94
0.77
Tuna, light, canned in water, drained, 3 ounces
0.17
0.02
Table 1.2 Omega-3 and omega-6 fatty acids content (% w/w) of plant and vegetable oils.
Plant or vegetable seeds
PUFA content
Omega-3 fatty acid content
Omega-6 fatty acid content
References
Chia
80.4
NA
NA
[
40
]
Flax
73.6
NA
NA
[
40
]
Hemp
62.8
0.4
62.4
[
41
]
Olive
18.0
1.6
16.4
Sunflower
62.4
0.4
62.2
Sesame
41.2
0.2
40.9
Rapeseed
20.9
1.2
19.6
Canola
30.7
NA
NA
[
42
]
Walnut
65.0
NA
NA
[
43
]
Coconut
1.6
0.0
1.6
[
41
]
Perilla
75.9
NA
NA
[
40
]
Peanut
18.2
0.0
18.2
[
41
]
NA, not available.
1.4 Biological Role of Essential Fatty Acids
1.4.1 Effect on Cell Membrane Structure
Omega-3 and omega-6 fatty acids are important cell membrane structural elements. They affect cellular properties such as membrane fluidity and permeability, and the activities of phospholipids bounded enzymes [65]. Cell membrane composition and molecular structure are totally dependent on the dietary fatty acid consumption as well as endogenous metabolisms and it was evidenced by increased concentration of omega-3 in immune cells, cardiac tissue and other cells throughout the body after intake of omega-3 fatty acids [5, 65–67].
Table 1.3 PUFA content of Thraustochytrids species.
Microorganisms
Cell dry weight (g/L)
DHA concentration (%, total lipid)
References
Aurantiochytrium
sp. ATCC PRA-276
17.0
12.5
[
44
]
11.24
35.76
[
45
]
Aurantiochytrium
sp. KRS101
4.40
14.31
[
46
]
5.50
14.18
Aurantiochytrium
sp. KRS101
9.00
19.88
[
47
]
Schizochytrium limacinum
SR 21
20.10
18.38
[
48
]
Aurantiochytrium
4W-1b
9.01 ± 0.62
27.9
[
49
]
Aurantiochytrium
SW1
19.0
25
[
50
]
Aurantiochytrium
sp. T66
11.24
35.76
[
45
]
Schizochytrium
SR21
21.0
34.9
[
51
]
S. limacinum
SR21
33.24
23.48
[
48
]
A. limacinum
(ATCC MYA-1381)
8.86
15.01
[
52
]
S. limacicum
SR21
10.90 ± 0.30
34
[
53
]
Schizochytrium
sp.
71
48.95
[
54
]
Table 1.4 EPA and DHA content of microalgae.
Microalgal strains
EPA (%)
DHA (%)
References
Phaeodactylum tricornutum
19.87
4.89
[
55
]
P. tricornutum
29
NA
[
56
]
Nannochloropsis sp.
26.7
[
57
]
Nannochloropsis oceanica
23.4
NA
[
58
]
Nannochloropsis salina
28
NA
[
59
]
Pinguiococcus pyrenoidosus
22.03
[
60
]
Chlorella minutissima
39.9
NA
[
61
]
Pavlova viridis
36
[
62
]
Pavlova lutheri
27.7
[
63
]
Isocrysis galbana
28
[
64
]
Pavlova lutheri
41.5
[
63
]
1.4.2 Impact on Vision
DHA is predominantly integrated into the membranes of retinal cells. The retina stores and recycles DHA even if the consumption of omega-3 fatty acids is limited [68–70]. Studies on DHA showed that it regenerates rho-dopsin pigments in retina that usually converts the light from retina to a visual image in the brain [70, 71].
1.4.3 Brain Function
DHA is a structural component of postsynaptic neuronal cell membranes, with the highest amount of DHA and AA to be found in the phospholipids of brain gray matter, representing their importance in central nervous system regulation [72]. DHA starts accumulating in the fetal brain tissue during the last trimester and persists at very high rates until the end of the second year of life [7, 72]. For a proper brain function, DHA should be taken through food, since its endogenous formation is low. Its deficiency showed malfunction of brain, posing a risk of creating a problem of learning deficits [73].
1.4.4 Biosynthesis of Lipid Mediators
Eicosanoids are usually 20 carbon long chain of hydrocarbons and act as bioactive lipid mediators that mainly play an important role in inflammatory and immune response [6]. DGLA, AA and EPA are usually secreted from the cellular membranes after activation by hormones, cytokines and other signals and become substrates to produce eicosanoids [74]. It has been suggested that AA derived eicosanoids are more potent inducers of inflammatory response than the EPA derived eicosanoids [2, 75]. Isoprostanes are produced from free radicals induced oxidation of PUFAs; therefore, they act as markers for oxidative stress and have both pro- and anti-inflammatory effects [74–76].
1.4.5 Effect of Omega Fatty Acids on the Regulation of Gene Expression
Omega-3 and omega-6 fatty acids induce a large number of gene expressions that are involved in inflammation and other immune responses by interrelating through specific transcription factors, such as peroxisome proliferator-activated receptors (PPARs) [77]. In several instances, PUFAs act as steroid hormones to the gene expression by binding with receptors like PPARs and further bind with the promoters of genes that can regulate transcription. They can act as regulators of transcription factors such as NFκB and Sterol Regulatory Element–binding Proteins (SREBP-1) inside the cell’s nucleus [78]. For example, NFκB is suppressed by omega-3 fatty acid to inhibit the production of multiple genes involved in inflammation like eicosanoids and cytokines. SREBP-1 regulates the transcription factor that involves the de novo synthesis of fatty acids, and is also affected by dietary omega-3 fatty acids that suppress the SREBP-1 to further synthesis of omega-3 fatty acids [79].
1.5 Effect of Essential Fatty Acid on Human Health (Disease Prevention and Treatment)
1.5.1 Neonatal Development
DHA is mostly accumulated in the brain and retina during the last trimester of pregnancy and two years from birth [80]. Human breast milk contains approximate 12% of omega-6 and 1.3% of omega-3 fatty acids [81]. Before 2001, infant milk formula contained only ALA as nutritional supplements; however, due to the low conversion of ALA to DHA and EPA, this was not sufficient [82]. Studies on randomized controlled trials testing the visual and neurological development in infants (19 trials, 1,949 infants) with and without DHA supplementation, showed the beneficial effect of DHA supplementation on visual acuity from one month to 12 months after birth [83]. Epidemiological studies showed that omega-3 and omega-6 fatty acid intake from fish and seafood during pregnancy has a positive response on the growth of offspring [84].
1.5.2 Gestation and Pregnancy
The results of randomized controlled trials of omega-3 fatty acids intake during low-risk pregnancy found no positive effect on gestational diabetes, preeclampsia and hypertension but due to high consumption of omega fatty acids, the duration of pregnancy can be increased modestly because of unbalanced prostaglandins production involved in parturition. [85–87]. The fish oil supplementation during last trimester increases the time of pregnancy without affecting foetus growth and on the course of labour [86]. However, according to a meta-analysis of six randomized controlled trials, the gestation period can be increased by 1.6 day in low-risk pregnancies with omega-3 supplementation [88]. According to a 2007 meta-analysis of randomized controlled trials it was evidenced that omega-3 fatty acids do not affect the gestation period in high-risk pregnancies but can reduce early premature birth [89]. It is highly recommended by experts in the US that pregnant and lactating women take at least 200 mg DHA daily for proper development of the foetus and newborn baby [89, 90]. According to the European Food and Safety Authority (EFSA) recommendations, the amount of DHA daily intake should be 100-200 mg along with 250 mg/day EPA as for normal adults.
1.5.3 Cardiovascular Disease
Both omega-3 and omega-6 fatty acids intake are directly corelated with the reduction in risk of cardiovascular diseases [91]. As per observation from randomized controlled trials, the American Heart Association suggested that high intake of omega-6 fatty acids such as LA can reduce the risk of coronary heart disease [91, 92]. The outcomes of 11 cohort studies on 344,696 individuals for the replacement of 5% of energy intake from SFA to PUFAs showed almost 26% less coronary deaths [91].
1.5.4 Cancer Inhibition
Some studies showed that intake of omega-3 fatty acids reduce the risk of cancer due to their potent anti-inflammatory effects and inhibitory effect on cell growth factors [93–96]. Recent studies suggested that increased intake of omega-3 fatty acids or increased blood levels of omega-3 fatty acids reduced the risk of breast and colorectal cancers [97–99]. Opposite to these findings, some studies suggested that high omega-3 intake increases the risk of prostate cancer; however, some scientists have doubts on this findings [100].
1.5.5 Rheumatoid Arthritis
Several metanalysis and randomized controlled trials suggested that intake of PUFAs has positive effects on reducing the risk of rheumatoid arthritis, an autoimmune inflammatory disease of multiple joints that is associated with cardiovascular diseases [101–105]. Intake of PUFAs reduced the leu-kotriene B4 which is a proinflammatory marker and also has a positive effect on blood profile levels, with the triacylglycerol level found to be reduced [106].
1.5.6 Effect on Suicide Risk in Mood Disorders
The deficiency of PUFAs and the ratio of omega-3 to omega-6 fatty acids leads to unipolar and dipolar disorders and is further associated with suicidal behaviour that was evidenced after recent epidemiological studies [107, 108]. After treating patients with mental disorders by PUFAs intake, the results showed reduced depression but no statistically significant changes were observed on omega-3 fatty acids depletion in both control and the patient with mental illness or with suicidal behaviour [109].
1.6 Concluding Remarks
The long-chain omega-3 fatty acids EPA and DHA can be synthesized from ALA, but it is recommended that both should be derived through diet. The most common PUFAs that accumulate in tissues are LA, AA and DHA. Fish oil alone cannot satisfy the ever-increasing global demands for omega-3 omega-6 PUFAs due to declining fish stocks and marine ecosystem pollution, which has led to increased interest in sustainable alternative sources. Two possible alternatives to fish oil are vegetable oils from genetically engineered plant oils and microbial oils, with the omega-3 PUFAs content to be higher in the latter. Several examples of genetically engineered plant species with the ability to produce omega-3 PUFAs are Brassica juncea, Arabidopsis thaliana, and Camelina sativa. Although there are numerous advantages for transgenic plants, their production depends on seasonal and climatic conditions and arable land availability. However, microorganisms are natural sources of microbial oils and can serve as an excellent source of omega-3 and omega-6 PUFAs of nutritional significance.
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