ABSTRACT
The objective of the study is to produce oregano flavoured extra virgin olive oil, soybean oil and rosemary flavoured extra virgin olive and soybean oil. The study was also carried out to evaluate the physio-chemical characteristics and the antioxidant capacities of the oil samples. Flavoured oil samples were produced using dry herbs to prevent water from getting into the oil. The method employed was the hot infusion method. The chemical and physical properties were analysed. From the results obtained it was detected that; the oregano, rosemary extra virgin olive oil samples had higher PV (4.44 to 3.96 meqO2/kg), compared to the oregano, rosemary soybean oil samples (1.20 to 1.17 meq O2/kg. The acid value obtained showed significant difference (p<0.05) among the oil samples with values ranging from (16.73 to 0.28 mg KOH/g). Flavoured oregano, rosemary flavoured soybean oil samples had higher acid value. Rosemary flavoured olive sample had higher iodine value (87.09g iodine/100g) compared to the reference olive oil sample (84.97g iodine/100g). Rosemary flavoured extra virgin olive oil and soybean oil had higher saponification value 297 .13 to 188.83KOH/g compared to the control oil samples 194.85 to 124.53KOH/g which suggested the dominance presence of shorter chains that favour stability. Flavoured olive oil samples had higher FFA value (8.34 to 8.21 %). Higher value of smoke point was recorded in oregano flavoured olive oil. Oregano and rosemary flavoured extra virgin olive oil had higher flash point compared to other flavoured oil samples (370.00˚C to 313.50˚C). The fire point of the oregano and rosemary flavoured extra virgin olive oil and soybean oil ranged from 386˚C to 325 ˚C which implied that the oils were suitable for high temperature heating. GC-MS analysis was carried out and, a total of 15 compounds were identified in the rosemary flavoured olive oil, 23 compounds in the oregano flavoured olive oil, 25 compounds in the oregano flavoured soybean oil, and 14 compounds in the rosemary flavoured soybean oil. The flavoured olive oil samples contained notable concentrations of gamma tocopherol, delta tocopherol, vitamin E, Beta-sitosterol, gamma sitosterol and squalene.
TABLE OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table of contents vi
List of Tables ix
List of Figures x
List of Plates xi
Abstract xii
CHAPTER 1: INTRODUCTION 1
1.1 Background of the study 1-2
1.2 Statement of S problem 2
1.3 Justification of the study 2
1.4 Objectives of the study 2-3
CHAPTER 2 LITERATURE REVIEW 4
2.1 Olive Oil 4-6
2.1.1 Flavouring olive oil 6-8
2.2 Soybean Oil 9
2.2.1 Oxidative stability 9
2.2.2 Flavour Reversion 9
2.3 Bioactive Compounds 11
2.3.1 Plant Stanols& Sterols 11-12
2.4 Oregano 12-13
2.5 Rosemary 13
CHAPTER 3: MATERIALS AND METHODS 14
3.1 Material procurement 14
3.1.2 Sample preparation 14
3.2 Determination of the chemical compositions 18
3.2.1 Determination of Peroxide Value 18
3.2.2 Determination of Acid Value 18
3.2.3 Determination of Iodine Value 19
3.2.4 Determination of Saponification Value 19
3.2.5 Determination of Thiobarbituric Acid Value 20
3.2.6 Determination of Free Fatty Acid 21
3.2.7 Determination of Smoke point, Flash point and Fire point. 21
3.3.8 Sample Extraction 21-22
3.2.9 Gas Chromatography – Mass Spectrometry (GC-MS) Analysis 22
3.3.0 Experimental Design/ Statistical Analysis 23
CHAPTER 4 RESULTS AND DISCUSSION 24
4.1 Characterization of the oil samples 24
4.1.1 Chemical composition of oregano and rosemary flavoured soybean and olive oil 24
4.1.2 Peroxide value 24
4.1.3 Acid Value 26
4.1.4 Iodine Value 26
4.1.5 Saponification Value 27
4.1.6 Thiobarbituric Value 27-28
4.1.7 Free fatty acid Value 28
4.2 Physical properties of oil samples 28
4.2.1 Smoke Point 29
4.2.2 Flash Point 31
4.2.3 Fire Point 31
4.3 Antioxidant Compounds 31-32
4.4 Compounds identified in the oregano and rosemary flavoured extra virgin olive oil and soybean oil samples 39-41
CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 42
5.1 Conclusion 42
5.2 Recommendations 43
REFERENCES 44
LIST OF TABLES
Table 4.1 Chemical properties of the oil samples 25
Table 4.2 Physical properties of the oil samples 30
Table 4.3 Compounds identified in Rosemary flavoured extra virgin olive oil 33
Table 4.3.1 Compounds identified in Oregano flavoured extra virgin olive oil 34
Table 4.3.2 Compounds identified in Oregano flavoured soybean oil 35
Table 4.3.3 Compounds identified in Rosemary flavoured soybean oil 36
Table 4.3.4 Compounds identified in Extra virgin olive oil 37
Table 4.3.5 Compounds identified in Soybean olive oil 38
LIST OF FIGURES
Figure 3.1 Flow chart for the production of Oregano Flavoured oil 15
Figure 3.2 Flow chart for the production of Rosemary Flavoured oil 16
LIST OF PLATES
Plate 3.1 Dried Rosemary 17
Plate 3.2 Dried Oregano 17
Plate 3.3 Infused rosemary and oregano flavoured extra virgin and soybean oils 17
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Flavoured oil is a vegetable oil that contains aromatic molecules of a plant or flower that has been steeped in and contain essential oils of the plants. They are not the same as carrier oils (Geoff, 2003).
Oregano (Origanum Vulgare), Greek oregano throughout the world is the most recognized herbs as being authentic or original “oregano” (Mastro et al., 2017). The benefits of oregano on human health have been associated and attributed to the phytochemicals found therein (Oniga et al.,2018). This perennial herb has been suggested to have variety of health promoting properties ranging from antioxidant, anti-inflammatory, analgesic and anti-microbial and enhances food stability (Gracia- Diez et al., 2017).
Rosemary (Rosimarinus Officinalis) is an aromatic plant from Lamiacae family originated from the Mediterranean region. It may be used as a spice in cooking or as a natural preservation in the food industry (De oliveira et al., 2019).
Extra virgin olive oil (EVOO), is a typical ingredient in a Mediterranean diet ingredient and its protective role is as a result of its specific components, including high proportions of mono-unsaturated fatty acids (oleic acid) and balanced presence of poly unsaturated fatty acids, and other minor components which guarantee its high antioxidant potential. (Moura et al 2017).
Soybean oil, is a vegetable oil extracted from the seeds of the soybean (Glycine Max), it has an oil content accounting for around 22% of the dry seed (Hammond et al 2005). It is one of the most widely consumed cooking oils. Soybean is a complex mixture of five fatty acids (palmitic, stearic, oleic, linoleic and linolenic acids), all of which have different melting points, oxidative stabilities and chemical functionalities (Cahoon, 2003).
1.2 STATEMENT OF PROBLEM
In Nigeria, the use of flavoured oils is not popular among the locals excepts to the “fine diners” these are those exposed to modern and high classed restaurants where continental and intercontinental meals are prepared as well as chefs who are culinary experts. This is because knowledge of these products and their benefits are not widely spread. Vegetable oils undergo several unit operations that rid them of their original properties, flavouring oils increase their nutritional value.
1.3 JUSTIFICATION OF THE STUDY
Flavoured oil is a good source of energy, fat, acids, and vitamins. Given its nutritional and culinary potential, it is necessary to evaluate its composition as this will encourage its usage. Extra virgin olive oil, represents one of the most studied antioxidant food sources. (Saleh and Saleh 2011). Extra virgin olive oil has been shown to more resistant to oxidation due to its high contents in monounsaturated fatty acids and antioxidants (Condelli et al., 2015). The use of green herbs in cooking either for their medicinal benefits or flavour benefits is one that cannot be done without as they not only provide us with the flavour but with health benefits that enhance healthy living. Most Nigerians restrict their cooking oils to groundnut vegetable oil while there are other vegetable oils have better flavour and benefits.
1.4 OBJECTIVES OF THE STUDY
The main objective of the study was the production and evaluation of flavoured extra virgin and soybean oil using dried oregano and rosemary
Specific objectives included to;
i. produce oregano and rosemary extra virgin flavoured oil, oregano and rosemary soybean flavoured oil.
ii. evaluate the physio - chemical properties of flavoured oil samples
iii. determine the anti-oxidant activities/ capacities of the oil samples
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