VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULITY OF CHEMISTRY Topic ANTIOXIDANT ACTIVITIES OF ESSENTIAL OIL Supervisor Dr Nguyen Hoang Yen Performed of students Tran Thi Thuy Van Hanoi – 2021 ACKNOWLEDGEMENT First of all, I would like to express my gratitude and sincere thanks to Dr Nguyen Hoang Yen were helpful, oriented way of thinking and way of doing science for children Those are very valuable suggestions not only in the process of making this thesis but also a step.
VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULITY OF CHEMISTRY *** Topic: ANTIOXIDANT ACTIVITIES OF ESSENTIAL OIL Supervisor: Dr Nguyen Hoang Yen Performed of students: Tran Thi Thuy Van Hanoi – 2021 ACKNOWLEDGEMENT First of all, I would like to express my gratitude and sincere thanks to Dr Nguyen Hoang Yen were helpful, oriented way of thinking and way of doing science for children Those are very valuable suggestions not only in the process of making this thesis but also a stepping stone for me in the process of studying and setting up a career in the future And finally, thank you to family and friends who are always willing to share and help in study and life Hopefully, we will stick together forever Wish the best will always accompany everyone Hanoi, May 20, 2021 Student Tran Thi Thuy Van CONTENT ACKNOWLEDGEMENT CONTENT LIST OF ABBREVIATIONS LIST OF FIGURES LIST OF TABLES INTRODUCTION CHAPTER 1: OVERVIEW 1.Essential oils and their antioxidant activity 1.1 Overview of essential oils 1.2 Antioxidants 11 1.3 Antioxidant activity of essential oils 15 1.4 Plants rich in antioxidants 18 Methods used for analysis 19 2.1 Determination of antioxidant activity by DPPH method 19 2.2 Test methods inhibitory activity radical NO[12] 20 2.3 TBARS method 21 Study on extracting and evaluating antioxidant effects of garlic essential oil from garlic bulbs (Allium sativum L.) [16] 21 3.1 Brief about garlic 21 3.2 Resources 22 3.3 Device 22 3.4 Research Methods 22 CHAPTER 2: FURUTE RESEARCH DIRECTIONS 25 REFERENCES 26 LIST OF ABBREVIATIONS Notion Meaning EO Essential Oils BHA Butylated hydroxyanisole BHT Butylhydroxytoluene TBHQ Tertbutyl hydroquinone PG Propyl galat AIBN 2,2′-azobis(isobutyronitrile) LIST OF FIGURES Scheme Simplified Mechanism of Hydrocarbon Autoxidation and Antioxidant Protection………………………………………………………12 Scheme Some Common Phenolic EO Components…………………… 18 Scheme 3: Effect of antioxidant concentration on initial reaction rate with DPPH…………………………………………………………… ………….21 LIST OF TABLES Table 1: Some foods rich in antioxidant……………………………………20 INTRODUCTION Plant essential oils are used for many different purposes such as flavoring foods, additives in cosmetics , etc In particular, essential oils have very good antioxidant properties that can replace antioxidants synthetic oxidation Realizing the great application of the antioxidant activity of essential oils and to familiarize and improve knowledge and skills, I have chosen this topic for my thesis CHAPTER 1: OVERVIEW 1.Essential oils and their antioxidant activity 1.1 Overview of essential oils 1.1.1 What is essential oils? Essential oils is a form of liquid containing aromatic compounds volatile extracted from the leaves; trunk; flower; roots; or other plant parts There are many methods to extract essential oils such as steam distillation, solvent extraction method, pressing method, etc Essential oils are likened to the resin of a tree, so they bring the vitality and purest energy of herbs from nature and are 50-100 times stronger than dried herbs (herbs) Most essential oils are clear, with the exception of a few essential oils like patchouli, orange oil , and lemongrass , which are yellow or amber in color Essential oils are used in the production of perfumes, cosmetics, shower gels, soaps, flavoring drinks and foods, or adding scents to incense/agarwood and other household cleaning products In particular, essential oils have been and are one of the most important ingredients in cosmetic products such as perfumes and lotions About 3000 essential oils have been discovered and nearly 300 are commercially produced such as jasmine, rose, lavender, etc Essential oils are also used as a therapeutic agent for various problems digestive problems, muscle pain, insomnia In addition, the antioxidant activity of essential oils has also been paid special attention by researchers [2, 3] Essential oils have also historically been used in the field of medicine Medicinal applications range from skin beautification to cancer treatment and are often purely based on historical accounts of the use of essential oils for these purposes Claims about the effectiveness of essential oil medical treatments, in particular as a cancer treatment, are currently subject to regulatory regulations in many countries 1.1.2 Classification of essential oils There are two types of essential oils: Pure Essential Oils and Nonpure Essential Oils Pure essential oils are essential oils that have not been mixed with other chemical components, which are very good and safe for health Non-pure essential oils are essential oils that are mixed from pure essential oils with other chemicals but still retain the aroma of the essential oil 1.1.3 Structure of the components in the essential oil They can be divided into four main groups [2] : • Monoterpenes derivatives For example: Non-oxygen derivatives: Oxygen-containing derivatives : Myrcen Nerol • Sesquiterpenes derivatives For example: Famescen Farnesol • Aromatic derivatives For example: Vanilin Thymol • Compounds containing nitrogen (N) and sulfur (S) Isothiocyanate derivatives, Alicin For example: Methylalranilat 1.1.4 Physical properties of essential oils At room temperature, most essential oils are liquid Usually colorless or pale yellow, the longer it is left over due to oxidation, the color may darken Essential oils have a pleasant aroma , some are pungent Essential oils are volatile at room temperature, have a density less than Insoluble in water, soluble in organic solvents and alcohols The boiling point depends on the composition, so fractional distillation can be used to separate each component in the essential oil The refractive index of essential oils is from 1,450 to 1,560 [2] 1.1.5 Chemical composition of essential oils Essential oils are usually extracted by steam distillation from leaves, stems, flowers, bark, roots or other plant components The hydrocarbons commonly found in essential oils are terpenes (C10H16 )n open-chain or cyclic Any essential oil has the following ingredients [ 5-10 ] : • Monoterpenes: Found in almost all essential oils, Monoterpenes have the molecular formula C10 H16 open-chain Effective in disinfecting and as a tonic in nature They also have the ability to filter the air, making leaves protect cells, such as miaxene and oximene found in bay flower essential oil • Sesquiterpenes: Although not as volatile as monoterpenes, linear and cyclic sesquiterpenes, notably Farnesene These substances have about 15 carbon atoms They have soothing, anti-infective, and antiinflammatory effects • Phenol: most of the essential oils are antiseptic, stimulating the body when used in small doses When used in high doses, it is a poison to the nervous system and causes skin irritation Some phenols such as Thymol, Estragol , • Alcohols: There are many types of alcohols contained in essential oils Typically, Menthol, α- Terpincol, Geraniol, etc They work as antiseptic, antibacterial, antifungal and antibiotic drugs, very good tonics for the nervous system and stimulate immune responses fluid in the body • Esters: The esters evaporate quickly and give flavor to the fragrance Some esters are present in essential oils: ethyl anthranilate, benzyl acetate, In addition to the use of aromatherapy for essential oils, these esters have antispasmodic, antibacterial and anti-inflammatory effects, especially non-irritating skin • Aldehytes: There are many aldehydes in essential oils, but now all aldehydes are obtained through chemical synthesis Only aldehydes such as Cuminic Aldehydes, Citral and Citronellal are extracted directly from natural materials Aldehytes have anti-inflammatory effects, with properties similar to ketones and alcohols However, high amounts of aldehydes can cause severe skin irritation and mucous membrane formation • Other compounds: In addition to the compounds mentioned above, essential oils also contain oxide group compounds such as: amino acids (antranilic acid), lactones (coumarin, ambretolite), compounds containing sulfur such as: (anlylisosulfocyannat), nitrogenous compounds (methyl antranilate) 1.1.6 The role of essential oils for plants to form species that not propagate the oxidation chain Because preventive antioxidants are completely inactive once the process begins, chain-breaking antioxidants are by far the most important direct antioxidant The fact that a compound can react with several radicals does not mean it is an antioxidant, unless it is a peroxyl radical; reacts much faster than the radical reaction with the material to be protected, for example, unsaturated lipids; and the products of the reaction are species that are not capable of propagating a chain reaction Phenol is an antioxidant that breaks the prototype chain Some compounds that are not supplied to related antioxidant systems or food products, still increase antioxidant defenses in living systems, for example, by inducing expression or enhance the activity of antioxidant enzymes These compounds are referred to as indirect antioxidants with related examples among natural products [12] 1.2.3 Types of antioxidants in foods 1.2.3.1 Natural antioxidants Substances unsaturated fatty in biological tissues are relatively stable The reason is because biological tissues contain antioxidants as well as enzymes that prevent oxidation • Ascorbic Acid (Vitamin C): Vitamin C or ascorbic acid is a major nutrient for higher animals and other species The presence of ascorbate is important for the metabolic reactions of animals, plants and the internal functioning of human organs It is known as vitamin whose deficiency is the cause of scurvy (due to lack of vitamin C in daily life) Vitamin C has antioxidant activity when it reduces oxidizing chemicals such as hydrogen peroxide In addition, it will also reduce metal ions that generate free radicals through Fenton reactions 2Fe3 + + ascorbate → 2Fe2 + + Dehidroascorbate 2Fe2 + + 2H2O2 → 2Fe3 + + 2OH- • Tocopherol (Vitamin E) : Vitamin E is the collective name for a set of eight related tocopherols and is a fat-soluble vitamin with antioxidant properties Among them, the αtocopherol form is the most important fat-soluble antioxidant, which has the ability to protect cell membranes from oxidation by reacting with lipid radicals produced in the reaction transmission line Thereby eliminating intermediate free radicals and preventing continuous propagation reactions Vitamin E is separated during the oil refining process Vitamin E is abundant in soybean oil, cereals • Carctenoids: also exhibit antioxidant activity Among them, carotene showed the strongest antioxidant activity Flavanone and flavonol: are substances with high antioxidant activity that can be found in plants such as green tea leaves, herbs, wood • Vanillin: external role flavor, it also acts as a chemical ng oxidation good In addition, the reactions formed in the Maillard reaction are also antioxidants that form in foods 1.2.3.2 Synthetic antioxidants Antioxidants in total foods must satisfy the following requirements: Non-toxic, have high oxidizing activity at low concentrations, can be concentrated on the surface of the oil phase, stable under the technical conditions of the process food processing Commonly used synthetic oxidizing agents are: BTH (Butylated hydroxyltoluene), BHA (Butylate hydroxyanisole), synthetic tocopherol, TBHQ (Tertbutyl hydroquinone), dodecyl gallate, propyl gallate, ascorbyl palmitate… • BHT (Butylated Hydroxytoluene) BHT is also known as 2,6-bis(1,1-dimethylethyl)-4-methylphenol; 2,6di-tert-butyl-p-cresol; 2,6-di-tert-butyl-4-methylpheno BHT is formed by the reaction of para-cresol (4-methylphenol) with isobutylene (2-methylpropene) catalyzed by sulfuric acid, with the molecular formula C15H24O This substance acts similarly to a synthetic vitamin E, primarily acting as an inhibitor of oxidation, an unsaturated process in which (usually) organic compounds are attacked by oxygen in the atmosphere The antioxidant BHT catalyzes the reaction by converting the peroxide free radicals in the bound hydroperoxides This affects the antioxidant function by donating a hydrogen atom: RO2 + ArOH → ROOH + ArO RO2 + ArO → nonradical R is alkyl or aryl, and where ArOH is the phenolic of BHT or is related to antioxidants It was found that BHT binds to two peroxy radicals In addition, it is also an effective antioxidant and is widely used in high-fat products Therefore, it has the effect of preserving food, preventing spoilage and rancidity of flavors In addition, it also has a stabilizing and emulsifying effect for shortening Used alone or in combination with BHA, Propyl gallate (PG) and citric acid, used in shortening, vegetable oil, animal food, lard, cereals, widely used in industry because of its low cost money • BHA (Butylated Hydroxyanisole) BHA is a mixture of 3-Tetiary-butyl-4-hydroxyanisole or 3-and 2tertiary-buty-4-hydroxyanisole, also known as BOA In which, the first isomer is more dominant (>= 90%) Has the molecular formula C11H16O2 The mechanism of action is similar to that of BHT, which prevents the chain reaction of fat oxidation BHT works by electron donor mechanism to control the free R radical BHA is absorbed through the small intestine wall, participates in metabolism, is suspected to cause allergies or cancer Due to exist in cell tissues and participate in a number of metabolic processes It is an effective antioxidant for animal fats and baked goods, stabilizes the end product, and is commonly used in shortening, vegetable oils, potato products, soups, chewing gum, cereals, which are most widely used in high-fat products, not work with unsaturated vegetable oils Often used in combination with other antioxidants 1.3 Antioxidant activity of essential oils Essential oils have been used for millennia for their health benefits, well documented in ancient documents Several health-promoting properties, for example, antiseptic, antioxidant and anti-poisoning properties, have been supported by recent scientific investigation Hundreds of compounds (secondary metabolites) with relatively low boiling points have been identified in EOs, and the large chemical diversity of their components confers the oxidative stability of EOs On the other hand, some essential oils are believed to have good antioxidant properties, which can be exploited to protect other materials , such as protecting foods from going rancid The antioxidant properties also play an important role in several biological activities of EOs, which is evidenced by the involvement of oxidative stress in the pathology aerobic oxidation of organic matter, although the process by which the oil is obtained from the raw material (distillation) limits the phenol content in the final substrate because many such compounds are non-volatile However, there are phenol-free EOs that exhibit antioxidant properties due to the basicity of some terpenoids and other volatile components (eg, the sulfur-containing component of garlic) The search for natural antioxidants with the advantage of being nontoxic has led to a large number of studies on the antioxidant potential of EOs This is particularly relevant since most common synthetic antioxidants (such as butylated hydroxyanisole (BHA) or butylhydroxytoluene (BHT)) are suspected to be potentially harmful to human health [12] Different fields or from different laboratories are sometimes at odds with each other, often due to diverse experimental settings, making it difficult for any comparison between results to be made Several methods used to evaluate the antioxidant performance of EOs avoid limitations that, if not satisfactorily addressed, can affect the results significantly To rationalize the mechanism of antioxidant activity exhibited by essential oils, it is necessary to briefly address the composition Despite the large chemical diversity observed the major constituents of essential oils can generally be classified in two structural families related to the hydrocarbon skeleton: terpenoids, formed by the union of two (monerpene), three (sesquiterpene), or four (diterpene) isoprene units, and phenylpropanoide Both terpenoids and phenylpropanoids include phenolic compounds, which are sometimes counted among the major components of some EOs Scheme Some Common Phenolic EO Components In general, phenolic compounds, both natural (eg, α-tocopherol) or synthetic (eg, BHA), act as antioxidants due to their high reactivity with peroxyl radicals Other terpenoid components of essential oils can react rapidly with peroxyl radicals; however, the reaction produces a reactive alkyl radical (from the terpene hydrocarbon skeleton) which, in the presence of oxygen, forms a peroxyl radical that propagates the oxidation chain In other words, phenol unsaturated terpenoids , especially unsaturated ones, will selfoxidize in the same way as unsaturated fats When α-pinene or similar EO components are mixed with a readily oxidizing material such as an unsaturated lipid, both the lipid and the EO components will undergo autooxidation, and will undergo similar degradation In other words, the substrate to be protected (lipid) and the potential antioxidant (EO components) will co-oxidize When auto-oxidation is forcibly initiated by some controlled source (eg, AIBN), no true inhibitory phase is observed for the immediate enhanced end-antioxidants both at high concentrations and there was no linear (or even non-monotonic) dependence between antioxidant performance and antioxidant concentrations 1.4 Plants rich in antioxidants STT Antioxidants Plants Content Quote Anthocyanin Blueberry [17] Vitamin C, Anthocyanin Strawberry 9,2 mmol/ 100 gram 5,4 mmol/ 100 gram Axit chlorogenic Artichoke [17] Lycium barbarum polysaccharides Goji berries 4,7 mmol/ 100 gram 4,3 mmol/ 100 gram Vitamin C, Anthocyanin Raspberries mmol/ 100 gram [17] Vitamin C, Anthocyanin Kale 2,7 mmol/ 100 gram [17] Table 1: Some foods rich in antioxidant [17] [17] Methods used for analysis 2.1 Determination of antioxidant activity by DPPH method DPPH is compound , - diphenyl- - picrylhydrazyl, a dark crystalline powder includes molecules stabilize free radicals [13] This method is not applicable to matrices with high oil and fat content (> 50 % fat) Reagents: Antioxidants with purity >99%, high purity DPPH, gallic acid and some other chemicals Principle: This method determines the antioxidant activity of foods by reaction with stable radical DPPH The free DPPH radicals have a strong maximum absorbance at 517 nm and have a burgundy color The burgundy to yellow transition corresponding to the molar absorptivity of the DPPH radical at 517 nm decreases from 9660 μM-1 cm-1 to 1640 μM-1 cm-1 when the free electron of the DPPH radical is coupled with an electron from the antioxidant and a hydrogen atom (the hydride equivalent) to form reduced DPPH-H The resulting decolorization is proportional to the equivalent amount of hydride retained Antioxidant compounds can be water-soluble , lipid- soluble, insoluble, or bound to cell walls Thus, extraction efficiency is an important factor in quantifying the antioxidant activities of foods Maximize extraction efficiency by adding the DPPH standard solution directly to the sample, without the need for separate extraction Antioxidant compounds were continuously extracted from the samples and immediately reacted with DPPH until extraction and reaction were complete The sample is then filtered and the change in absorbance is determined Calibration was performed as described below by comparison with solutions with known concentrations of trolox Samples and Trolox, a vitamin E analogue used as a control standard, react with methanol-water DPPH solution for hour at 35o C in a ring shaker rack and measure the absorbance absorbed at 517 nm The amount of sample required to react with the DPPH moiety is expressed as the relative amount of Trolox reacted The antioxidant activity of the sample was expressed as the number of micromoles of Trolox equivalent per 100g of sample [14] Scheme 3: Effect of antioxidant concentration on initial reaction rate with DPPH [15] 2.2 Test methods inhibitory activity radical NO[12] In the central and peripheral nervous system , the role of NO is very important: Play a role in neurotransmitters, carry signals anywhere in the body, control brain vascular homeostasis, regulate harmonize pain perception, control thought processes and memory NO e u reachable organization born from NOS (nNOS and eNOS) will affect the muscle tone of cerebral vessels and contribute conditioned vasomotor being stimulated Therefore, NO disorder will lead to a number of brain diseases such as Alzheimer's disease, cerebral ischemia, stroke NO has an extremely important role for the body as a contributor to blood pressure regulation, in addition, NO is also a factor causing endogenous vasodilation If too much NO is produced, the dilation of blood vessels will lead to a drop in blood pressure, and if too little NO is produced, it will lead to an increase in blood pressure The human disorders e u wall metabolism L-arginine - NO alter NO levels generated These disorders nà y th U pipes to some diseases nh u : hypertension, diabetes, obesity, heart failure, cirrhosis atherosclerosis, aging, injury th u wer blood vessels Also, when l u owe the output too much, the substance itself becomes endotoxin and NO then react with ROS also harmful to the body, free radicals ONOOexample, is the root cause nitrite harmful to the body Principle NO reacts with oxygen to produce stable products, nitrite and nitrate, NO inhibitors will react competitively with oxygen, resulting in a decrease in nitrite products formed in aqueous solution and nitrite concentration in aqueous solution were determined photometrically using Greiss reagent In which, nitrite reacts with Greiss reagent to form a stable diazo colored compound with a maximum absorption wavelength at 540 nm Based on the decrease in nitrite concentration, the active ingredient's ability to block NO free radicals (in % inhibition) was calculated 2.3 TBARS method The TBARS method (thiobarbituric acid reaction type) is based on the spectroscopic measurement of the pink addition product of 2-thiobarbituric acid (λmax≈532 nm) with malondialdehyde, which is one of the end products formed by the process oxidation and further degradation of polyunsaturated lipid hydroperoxides However, this method has limitations due to the reaction of TBA with other compounds that are not involved in lipid peroxidation [12] Study on extracting and evaluating antioxidant effects of garlic essential oil from garlic bulbs (Allium sativum L.) [16] Based on experimental suggestions, garlic contains many antioxidant compounds, especially sulfur-containing compounds such as diallyl sulfide, diallyl disulfide, 3-vinyl-1,2-dithiacyclohex-4-en, 3-vinyl -1,2-dithiacyclohex5-en and diallyl trisulfide, so the selected object is garlic 3.1 Brief about garlic Garlic (Allium sativumL.) is a species of plant in the onion family (Allium) that is consumed worldwide The allicin (diallyl disulfide, diallyl trisulfid) present in garlic essential oil exhibits good antibacterial and antioxidant effects Garlic essential oil contains diallyl trisulfid, diallyl disulfide, propyl disulfide and many other compounds with strong antibacterial and antioxidant effects and is extracted from garlic bulbs by various extraction methods such as steam distillation, extraction with organic solvents, extracted with supercritical solvents 3.2 Resources Garlic, 1,1-diphenyl-2-picrylhydrazyl; sodium sulfate, methanol, nhexane, ascorbic acid, pure water, CO2 cleaning Excipients and chemicals are of pharmaceutical grade or of analytical purity 3.3 Device Spectrophotometer UV-2600, balanced distribution of technical, analytical balance, the system extracts CO2 supercritical SFE500, electric stoves, systems gas chromatography coupling mass spectrometry GC-MS, securing system turned Rovapor R-210 3.4 Research Methods 3.4.1 Material handling Fresh garlic samples were peeled, minced with a blender to prepare for extraction 3.4.2 Methods of extracting garlic essential oil • Extraction of garlic essential oil by supercritical CO2 solvent (SCO2 ): Factors affecting the extraction of the raw material, extraction pressure, extraction temperature, the ratio of pharmaceutical / solvent, flow rate of CO2, and extraction time In which the factors of temperature and pressure greatly affect the solubility of substances in supercritical CO2 solvents Conducted by solvent extraction garlic 200g CO2 supercritical in the conditions as follows: - Pressure: 100 -300 bar - Temperature: 35 -50o C - Flow rate CO : 10 gram/ - Extraction time: -150 minutes - The extracted essential oil was stored in a refrigerator at o C • Extraction of essential oils by steam distillation : 200 g of garlic is added to a pot with 1000 mL of water and then installed in a steam distillation system After a period of hours, turn off the stove to cool, because the essential oil is lighter than the water at the top, so drain the valve to let the water flow out first, then the essential oil will be obtained Use Na2SO4 salt to anhydrous the remaining water mixed in the essential oil to obtain pure essential oil Essential oils are stored in the refrigerator at 4o C • Extraction of essential oils by Soxhlet extraction method with n-hexane solvent: 200 g of garlic was put into filter paper, wrapped and then placed in the extraction flask, 200 mL of n-hexane was added to the flask and then installed in the Soxhlet extraction system After hours, turn off the stove to cool, the whole extract revenue brought her to turn under reduced pressure to remove the n-hexane at a temperature of 40o C Bring the weight and oil content is obtained Essential oils are stored in a refrigerator at ° C 3.4.3 Method to determine the extraction efficiency of garlic essential oil The extraction yield of garlic essential oil was calculated according to the following formula: Extraction efficiency (%)=(Essential oil weight/Sample weight) x 100 Where: Essential oil weight: mass of extract (g) Sample weight: the mass of garlic extracted (g) Methods of evaluating essential oils: Appearance: determines the color, clarity and smell of the essential oil Method to determine the main chemical components of essential oils: The chemical composition of garlic essential oil was determined by gas chromatography coupled to mass probes (GC-MS) : DPPH antioxidant effect: 1,1-diphenyl-2-picrylhyd razyl (DPPH) is a free radical scavenger used to screen for the antioxidant effect of the investigated substances The antioxidant activity was demonstrated by reducing the color of DPPH, as determined by photometric measurement at λ = 517 nm Prepare DPPH solution with a concentration of 0.24 mg/ml in methanol (MeOH) The test sample is diluted in MeOH in a concentration range of 50 μg/ml; 37.5 μg/ml; 25 μg/ml; 12.5 μg/ml; 3.125 μg/ml (garlic essential oil obtained by SCO2 method); and in a concentration range of 500 μg/ml; 300 μg/ml; 250 μg/ml; 150 μg/ml; 125 μg/ml (garlic oil obtained by steam distillation) Get 450 μl DPPH 0.24 mg/ml mix with 2550 μl MeOH and 100 μ/ml of diluted sample was mixed, wrap foil, incubated in the dark Response time to 20 minutes at 25°C, read absorbance density tubers a DPPH not made n stasis ng pr ng machine read the UV-2600 spectrophotometer at 517 nm wavelength The percentage DPPH free radical scavenging of the test sample was calculated according to the following formula: % antioxidant= ( Ac-As )/ Ac×100 Where: Ac is the optical absorbance of the standard sample As is the optical absorbance of the test Ascorbic acid standards were performed in the same way as the test samples with concentrations t of μg/ml, respectively; μg/ml; 0.5μg/ml; 0.25μg/ml; 0.125μg/ml ; 0.0625μg/ml IC50 is calculated according to the % antioxidant value correlated with different concentrations of the reagent, the experiment was repeated with n = CHAPTER 2: FURUTE RESEARCH DIRECTIONS Essential oils have a great role in human life, especially beneficial to our health as antiseptics, anti-poisoning agents On the other hand, some essential oils also have good antioxidant properties, which can be exploited to protect foods from going rancid These properties are due to the inherent ability of some components in essential oils such as phenols, terpenoids and more volatile components Although the potential and usefulness of essential oils have been explored, the methods used to evaluate their antioxidant performance need to be reviewed and the most appropriate methods selected, as they have not yet been shown to be effective maximum performance The antioxidant activity of some essential oils has potential for practical applications in food systems, and the use of essential oils as natural antioxidants is an area of increasing interest But there needs to be a more rational and standardized approach in experimental design to create the highest efficiency and practical application to create products for food protection and human health REFERENCES Vietnamese: Nguyễn Văn Đàn, Ngô Ngọc Khuyến (1999), Hợp chất thiên nhiên dùng làm thuốc, Nhà xuất Y học, Hà Nội Phạm Thanh Kỳ (2015), Dược liệu học Tập 2, Nhà xuất Y học, Hà Nội English: J Agric (2007), “Antioxidant Activities and Volatile Constituents of Various Essential Oils”, Journal of Agricultural and Food Chemistry J Agric (2010), “Antioxidant/Lipoxygenase Inhibitory Activities and Chemical Compositions of Selected Essential Oilsils”, Journal of Agricultural and Food Chemistry Abdel-Kader MS (2001), "Phenolic constituents of Ononis vaginalis roots", Planta Med, 67(4), tr.388-90 Abouelela M E1, Abdelhamid RA1, Orabi MAA1,2 (2019), "Species of Pterocarpus", A Review: International Journal of Pharmacognosy and Phytochemical Research, 11(4), tr.264-281 Hai LQ, Liang H, Zhao YY, Du NS (2002), "Studies on chemical constituents in the root of Hedysarum polybotrys", Zhongguo Zhong Yao Za Zhi, 27(11), tr.843-5 Maria José C Falcão 1, Yvone Brígido M Pouliquem, Mary Anne S Lima (2005), "Cytotoxic flavonoids from Platymiscium floribundum", Journal of natural products, 68(3), tr.423-6 Palazzino G, Rasoanaivo P, Federici E, Nicoletti M, Galeffi C (2003), "Prenylated isoflavonoids from Millettia pervilleana", Phytochemistry, 63(4), tr.471-4 10 Yin H, Zhang S, Wu J (2004), "Study on flavonoids from stem bark of Pongamia pinnata", Zhong Yao Cai, 27(7), tr.493-5 11 Werner Dabelstein, Arno Reglitzky, Andrea Schutze and Klau Reders (2007), “Automotive Fuels”, Ullmann’s Encyclopedia of Industrial Chemistry 12 J Agric (2013), “Antioxidant Activities of Essential Oils”, Journal of Agricultural and Food Chemistry 13 Om P Sharma Tej K Bhat (2019), “DPPH antioxidant assay revisited”, Food Chemistry 15 J Xie K M Schaich (2014), “Re-evaluation of the 2,2Diphenyl-1-picrylhydrazyl Free Radical (DPPH) Assay for Antioxidant Activity”, Department of Food Science 16 Nguyễn Văn Khanh, Đỗ Thị Nhài, Bùi Thanh Tùng, Nguyễn Thanh Hải (2020), “The Effect of Different Extraction Procedures on Antioxidant Activity of Garlic (Allium sativumL.)Essential Oil”, VNU Journal of Science: Medical and Pharmaceutical Sciences 17 Ryan Raman, MS, RD (2018), “12 Healthy Foods High in Antioxidants”, https://www.healthline.com/ ... countries 1.1.2 Classification of essential oils There are two types of essential oils: Pure Essential Oils and Nonpure Essential Oils Pure essential oils are essential oils that have not been mixed... thesis CHAPTER 1: OVERVIEW 1 .Essential oils and their antioxidant activity 1.1 Overview of essential oils 1.1.1 What is essential oils? Essential oils is a form of liquid containing aromatic... Non-pure essential oils are essential oils that are mixed from pure essential oils with other chemicals but still retain the aroma of the essential oil 1.1.3 Structure of the components in the essential