The Extra-Virgin Olive Oil Handbook E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
According to European legislation, extra virgin is the top grade of olive oils. It has a superior level of health properties and flavour compared to virgin and refined olive oils. Mediterranean countries still produce more than 85% of olive oil globally, but the constant increase of demand for extra virgin olive oil has led to new cultivation and production in other areas of the world, including California, Australia, China, South Africa and South America. At the same time, olive oil’s sensory properties and health benefits are increasingly attracting the attention and interest of nutritionists, food processors, manufacturers and food services. Progress and innovation in olive cultivation, harvesting and milling technologies as well as in oil handling, storage and selling conditions make it possible to achieve even higher quality levels than those stipulated for extra virgin oils. As a consequence, a new segment – excellent extra virgin olive oils – is increasingly attracting the attention of the market and earning consumers’ preference.
The Extra-Virgin Olive Oil Handbook provides a complete account of olive oil’s composition, health properties, quality, and the legal standards surrounding its production. The book is divided into convenient sections focusing on extra virgin olive oil as a product, the process by which it is made, and the process control system through which its quality is assured. An appendix presents a series of tables and graphs with useful data, including conversion factors, and the chemical and physical characteristics of olive oil.
This book is aimed at people involved in the industrial production as well as in the marketing and use of extra virgin olive oil who are looking for practical information, which avoids overly academic language, but which is still scientifically and technically sound. The main purpose of the handbook is to guide operators involved in the extra virgin olive oil chain in making the most appropriate decisions about product quality and operating conditions in the production and distribution processes. To these groups, the most important questions are practical ones of why, how, how often, how much will it cost, and so on. The Extra-Virgin Olive Oil Handbook will provide the right answers to these key practical considerations, in a simple, clear yet precise and up-to-date way.
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Veröffentlichungsjahr: 2014
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Table of Contents
Title Page
Copyright
List of Contributors
Acknowledgements
Introduction
Part I: The product
Chapter 1: The extra-virgin olive oil chain
1.1 The legal classification and denomination of olive oils
1.2 The subject of this handbook
1.3 The extra-virgin olive oil chain
1.4 Yield and quality
Reference
Chapter 2: Virgin olive oil: definition and standards
2.1 The legal definition of virgin olive oil
2.2 Quality standards of virgin olive oil
2.3 Authenticity standards of virgin olive oil
Reference
Chapter 3: The composition and nutritional properties of extra-virgin olive oil
3.1 Triglycerides and fatty acids
3.2 The nutritional role of olive oil triglycerides and fatty acids
3.3 Minor components and antioxidants in extra-virgin olive oil
3.4 The colour and odour components of extra-virgin olive oil
3.5 Conclusion
References
Chapter 4: The sensory quality of extra-virgin olive oil
4.1 Introduction
4.2 The official evaluation of defects and positive sensory attributes
4.3 The sensory profile
4.4 Sensory performance of extra-virgin olive oil-food pairing
Annex 4.1: The method for evaluating extra-virgin olive oil sensory profiles
References
Chapter 5: Olive tree cultivars
5.1 Introduction
5.2 Cultivars
5.3 The cultivar's relationship to productivity
5.4 The cultivar's relationship to oil quality
5.5 Common-sense recommendations
References
Chapter 6: The role of oxygen and water in the extra-virgin olive oil process
6.1 The conflicting roles of oxygen
6.2 The role of water in the transformation of phenolic compounds
References
Further reading
Chapter 7: Extra-virgin olive oil contaminants
7.1 Introduction
7.2 Contaminants of virgin olive oil
References
Part II: The process
Chapter 8: Olive harvesting
8.1 Introduction
8.2 Olive ripening
8.3 Harvesting systems
Annex 8.1: Methods for olive maturity assessment
References
Chapter 9: Olive handling, storage and transportation
9.1 The autocatalytic nature of olives and oil degradation
9.2 Avoid mechanical damage to the olives
9.3 Control the time-temperature relationship
9.4 Management of the harvesting-milling link
References
Chapter 10: Olive cleaning
10.1 Introduction
10.2 The separation section
10.3 The washing section
10.4 Control points
Chapter 11: Olive milling and pitting
11.1 Introduction
11.2 Milling machines
11.3 Pitting machines
References
Chapter 12: Olive paste malaxation
12.1 Basic phenomena in malaxation
12.2 Malaxers
References
Chapter 13: Centrifugal separation
13.1 Introduction
13.2 The three-phase process
13.3 The two-phase process
13.4 Decanters
13.5 Disc centrifuges
13.6 Final comments and remarks
Further reading
Chapter 14: Filtration of extra-virgin olive oil
14.1 Introduction
14.2 Filtration principles
14.3 The filter media
14.4 Filtration equipment
14.5 Filtration systems
14.6 Conclusion
Further reading
Chapter 15: Extra-virgin olive oil storage and handling
15.1 Introduction
15.2 Prevention of temperature abuse
15.3 Prevention of exposure to air (oxygen)
15.4 Prevention of exposure to light
15.5 Prevention of water and organic residues in the oil
15.6 Prevention of exposure to contaminated atmosphere and poor hygienic standards
15.7 Prevention of mechanical stress
Annex 15.1: Pumps, tanks and piping
Reference
Further reading
Chapter 16: Extra-virgin olive oil packaging
16.1 Introduction
16.2 The packaging process
16.3 The packaging materials
16.4 The packaging operation
References
Further reading
Chapter 17: The olive oil refining process
17.1 Introduction
17.2 The process of extraction of crude pomace oil
17.3 The refining process
17.4 The physical refining process
17.5 The quality and uses of refined olive oil
Reference
Further reading
Part III: The process control system
Chapter 18: Process management system (PMS)
18.1 Introduction
18.2 The structure of a PMS
18.3 Control of critical points
18.4 Risk analysis: a blanket rule for management decisions
Annex 18.1: Excellence in extra-virgin olive oil
References
Further reading
Chapter 19: Extra-virgin olive oil traceability
19.1 Introduction
19.2 Four basic steps
19.3 Comments and conclusion
References
Further reading
Chapter 20: Product and process certification
20.1 Aims and approaches
20.2 Product and process certification
20.3 The selection of a certification system
20.4 The certification procedure
Reference
Further reading
Chapter 21: The hygiene of the olive oil factory
21.1 Introduction
21.2 Hygiene of the external environment and buildings
21.3 Hygiene of the plant
21.4 Hygiene of the personnel
21.5 Hygiene management system (HMS) and HACCP
Annex 21.1: Hygienic design
Reference
Further reading
Chapter 22: Olive mill waste and by-products
22.1 Introduction
22.2 Composition, treatment and uses of olive mill wastewater
22.3 Composition, treatment and uses of olive mill pomace
Annex 22.1: Mass balance of the extra-virgin olive oil process
Reference
Further reading
Chapter 23: The production cost of extra-virgin olive oil
23.1 Introduction
23.2 Concepts, terms and definitions
23.3 Hypotheses for the cost analysis
23.4 Cost calculation
Further reading
Chapter 24: The culinary uses of extra-virgin olive oil
24.1 A brief history of the olive
24.2 Old versus new: expanded culinary possibilities offered by excellent extra-virgin olive oil
24.3 Excellent extra-virgin olive oil as a condiment at the table and in the kitchen
24.4 Putting excellent extra-virgin olive oils to work
24.5 Education and communication: revolutionizing the perception of olive oil one drop at a time
References
Chapter 25: An introduction to life-cycle assessment (LCA)
25.1 Introduction
25.2 Methodological approach
25.3 Limits and advantages of the carbon footprint
25.4 Environmental communication strategies
25.5 The food sector
References
Appendix
A.1 Conversion table of physical parameters
A.2 Weight-to-volume conversion of oil quantities
A.3 Density
A.4 Concentration
A.5 Yield
A.6 Viscosity
A.7 Water activity
A.8 Temperature
A.9 Specific heat
A.10 Boiling and smoke point
A.11 Fatty acids of olive oil
A.12 Minor components of extra-virgin olive oil
References
Further reading
Index
This edition first published 2014 © 2014 by John Wiley & Sons, Ltd
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Library of Congress Cataloging-in-Publication Data
The extra-virgin olive oil handbook / [edited by] Claudio Peri.
pages cm
Includes bibliographical references and index.
ISBN 978-1-118-46045-0 (cloth)
1. Olive oil—Handbooks, manuals, etc. I. Peri, C. (Claudio), editor of compilation.
TP683.E98 2014
664′.362—dc23
2013039742
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.
Cover image: Noam Armonn www.shutterstock.com
Cover design by www.hisandhersdesign.co.uk
List of Contributors
Acknowledgements
I would like to express my deep gratitude to Sr. Mary Frances Traynor, teacher of English at the University of Perugia (Italy), for her care in correcting, improving and sometimes reshaping the English text. Her knowledge and experience in the food chemistry and technology field made her contribution much more valuable than simple language editing. She has been a precious collaborator in detecting mistakes and inconsistencies.
I am also indebted to Valérie Ganio Vecchiolino, a student at the University of Gastronomic Sciences in Pollenzo (Italy), who drew plant and designs with great care, precision and patience.
Introduction
This handbook deals with the basic science and technical aspects of extra-virgin olive oil, from harvesting the olives to processing, storing and using the oil at the consumer's table. It is divided into three parts: the product, the process and the process control system. One chapter gives some fundamental information about the best culinary uses of olive oils. Some important physical and physical-chemical parameters are summarized in the appendix and a detailed subject index indicates where major topics can be found in the handbook.
The main purpose of the handbook is to guide those involved in the extra-virgin olive oil chain in making the most appropriate decisions about product quality and operating conditions in the production and distribution processes. The approach of the handbook is mainly educational, providing guidelines for good extra-virgin olive oil practice. Basic information about various phenomena is presented in an easy-to-understand form, while systematic methods for choosing the most appropriate operating conditions are suggested. The instructive approach is evident in many parts of the text: (i) in the presentation of the principles, methods and examples of quality and safety management; (ii) in the presentation of methods to calculate mass and cost balances because they are considered as important as evaluating the chemical and sensory characteristics of the oil; (iii) in the choice of time–temperature relationships in olive storage, in olive paste malaxation and in olive oil storage. The semi-log plots in Chapters 9, 12 and 15 are a contribution to critical points management based on sound scientific principles; (iv) in the presentation of the health-promoting properties of extra-virgin olive oils and in the choice of the analytical parameters for their evaluation; (v) in the discussion and presentation of sensory profiles as essential tools of product style and differentiation.
The second purpose of the handbook relates to quality as the guiding factor of managerial and operating strategies. A producer of olive oil has different options. The first is to put aside quality and focus on yield increase and cost reduction. Overripe olives are harvested by letting them drop to the ground and then collected mechanically; in this case ‘lampante’ oil is produced and sold to refineries to produce refined olive oil. This approach has proven profitable in some cases and is sometimes unavoidable due to olive spoilage, pest attack or lack of appropriate harvesting equipment. The handbook describes the olive oil refining process and explains why refined olive oil should be considered as a good, reliable and useful product among the vegetable oils.
Another option is to produce an olive oil that meets extra-virgin standards. This requires considerable care to ensure that the olives are healthy and undamaged and that proper operating conditions are used in the milling and handling operations. With this choice, the quality of the olive oil reaches a high level.
The handbook points out that the standards of extra-virgin olive oil can be further improved beyond the present legal requirements and levels of excellence can be achieved. Attention is focused on neglected but critical issues such as: (i) residence time distribution in olive paste malaxation; (ii) hygienic design of plants and equipment and, most of all, (iii) in Chapter 15 on olive oil storage and handling, where the principles of the quality-proximity matrix are presented and thoroughly discussed.
It can be said that producing a ‘lampante’ olive oil does not require special care and skill. Producing an extra-virgin olive oil is a much more challenging and demanding task. Finally, only excellent operators can make excellent extra-virgin olive oils available to the final consumer. The goal of this handbook is to guide the operators in the olive oil chain towards excellence, all the way from the olive grower to the restaurant chef. With a chapter on the culinary uses of extra-virgin olive oil, we would like to activate a new alliance between excellent producers, retailers and chefs for the production and use of excellent extra-virgin olive oil. We hope to contribute to spreading a new consumer culture about this exceptionally good, healthy and natural product, which is so old in its millenarian tradition, so young in present-day processing technologies and so well tailored to the health, taste and dietary needs of new and traditional consumers around the world.
Part I
The product
Chapter 1
The extra-virgin olive oil chain
Claudio Peri
University of Milan, Milan, Italy
Abstract
This chapter presents the classification and commercial denomination of six olive oil categories recognized in international law (two virgin and four refined). Extra-virgin olive oil is the highest quality olive oil. The extra-virgin olive oil chain, is presented as a sequence of five processes: (i) olive tree cultivation, (ii) olive harvesting and processing, (iii) oil storage, bottling and distribution, (iv) selling bottled oil and (v) oil use in culinary preparations. Processes (ii) and (iii), the subject matter of this handbook, are further presented as a sequence of unit operations. The main steps and conditions determining oil quality and yield are outlined.
1.1 The legal classification and denomination of olive oils
When talking or reading about olive oil, the first point to be clarified is the category of olive oil that is being discussed. Ignoring the category that the oil belongs to can be a source of confusion and misunderstanding and can lead to mistakes in buying, tasting or using it. Figure 1.1 is a flow-chart of the classification and denomination of the various categories of virgin and refined olive oils as globally agreed (see Council Regulation (EC) No. 1234/2007 of 22 October 2007, (Single CMO Regulation), consolidated version 2013-01-26, Annex XVI).
Figure 1.1 The flow-chart of virgin and refined olive oils.
The six categories highlighted by the grey background are suitable for human consumption.
The flow-chart starts with the olive milling process, whose products are the ‘virgin’ olive oils. Two of them, namely extra-virgin and virgin, are allowed for consumption. The third category, lampante, becomes edible only after a physical-chemical refining process and it is called ‘refined olive oil’.
On the other hand, the pomace, which is the solid residue from the milling process, still contains a small amount of olive oil that is impossible to extract by mechanical means. It can be extracted with solvents; the raw oil from this extraction is refined with a process very similar to that applied to lampante oil. The refined oil derived from pomace is called ‘refined olive-pomace oil’.
Both the ‘refined olive oil’ and the ‘refined olive-pomace oil’ can be mixed with extra-virgin or virgin olive oil in various undefined proportions in order to improve their flavour. These are called, respectively, ‘olive oil composed of refined and virgin olive oil’ and ‘olive-pomace oil’.
Chapter 17 gives a short presentation of the refining process. It is important that olive oil producers, retailers and consumers know the difference in technological and compositional terms between a virgin oil and a refined oil.
Regarding quality, extra-virgin olive oil is higher in quality than virgin olive oil and refined olive oil is higher in quality than refined olive-pomace oil. Refined olive oil is very mild and almost neutral in taste: it is very good for cooking, frying and for preserving canned vegetables or meat or fish. Extra-virgin olive oil is flavourful and tasty. A picture of the culinary uses of olive oil and especially excellent extra-virgin olive oils is given in Chapter 24.
1.2 The subject of this handbook
Focusing on extra-virgin olive oil opens a wide panorama because the oil varies depending on cultivar, climate and soil, and the conditions of the production-extraction-storage-and-distribution process. Extra-virgin olive oils can be of common or good or excellent quality. The purpose of this handbook is to discuss the technological and management conditions that allow an operator of the extra-virgin olive oil chain to improve the quality of the product, which is finally served at the consumer's table.
1.3 The extra-virgin olive oil chain
The extra-virgin olive oil chain can be divided into a series of five processes: (i) olive tree cultivation, (ii) olive harvesting and milling, (iii) oil storage, bottling and distribution, (iv) oil selling and (v) oil use in culinary preparations (Table 1.1).
Table 1.1 The processes of the extra-virgin olive oil chain.
These five processes have different structural and operational requirements, different marketing policies and different economies of scale. They are therefore usually managed and owned by different companies.
Processes (ii) and (iii) represent the core content of this handbook. There is some discussion about process (i) in Chapters 5 (olive tree cultivars) and 7 (olive harvesting), whereas Chapter 24 gives some general indications about the use of extra-virgin olive oil in culinary preparations.
1.3.1 Compact versus complex chain organization
The most compact organization of an extra-virgin olive oil chain entails a direct connection between only two parts (or modules): the first is represented by the producer and the second by the final consumer. In this case, which is very common in olive oil producing regions, a producer who is responsible for the chain from the field to the package, sells his oil directly to the final consumer, either a family or a restaurant. This organization is typical of traditional markets in a narrow area close to production, but sometimes it is also implemented in a global market and across continents. It is common to find commercial agreements between a restaurant in Los Angeles or Tokyo and a producer in Andalusia or Tuscany.
On the other hand, very complex chain organizations are implemented in large-scale and global businesses with multiple inputs and outputs connecting the five processes listed in Table 1.1.
Traceability of product origin and identity is easy in the case of the compact chain, whereas it may be very difficult or impossible in complex chain organizations.
1.3.2 The extra-virgin olive oil processes
As chains can be considered sequences of processes, processes can similarly be considered as sequences of unit operations. Processes are interconnected in series in a chain, so unit operations are interconnected in series in a process with the output of a unit operation being the input of the following one (Peri et al. 2004). Table 1.2 presents the unit operations of processes (ii) and (iii).
Table 1.2 The unit operations of extra-virgin olive oil processes.
Preliminary activities
Unit operation
Ancillary activities
Monitoring of olive maturity. Supply and maintenance of harvesting nets, crates and equipment
Harvesting
Storage and transportation of olives
Mill plant maintenance, cleaning, and start trial
Olive reception at the mill plant
Standards agreed upon between the olive grower and the milling company
Visual inspection, control of origin and olive integrity
Decisions in case of nonconformity to standards
Milling batches, identification and weighing
Record of milling batches
Deleafing at the olive grove site. Supply of potable water
Olive cleaning and washing
Disposal of solid residues and dirty water
Olive milling or pitting
In case of pitting: discharge and use of olive stones
Olive-paste malaxation
Monitoring and control of the time-temperature relationship
Solid-liquid and liquid-liquid separation
Pomace to treatment and use. Wastewater to disposal
Supply of filter aids or filter pads
Oil filtration
Disposal of exhausted filtering material
Agreed upon standards of oil quality and yield
Oil weighing, chemical and sensory evaluation
Decisions in case of nonconformity
Maintenance of storage facilities
Storage batches formation and identification
Standard documentation of storage batches
Oil storage
Waste disposal
Customers' orders and requirements
Oil blending, packaging batches formation
Chemical and sensory evaluation of packaging batches. Record of packaging batches
Maintenance and supply of packaging material
Packaging
Waste disposal
Shipment of consignment to customers
1.4 Yield and quality
The primary objective of an extra-virgin olive oil company is to maximize oil yield and quality. Obtaining the largest quantity of oil with a high level of quality is the ultimate measure of process effectiveness and efficiency.
Contrary to the situation with other agricultural products, yield and quality are not competitive in extra-virgin olive oil production, but independent or concurrent parameters. Conditions determining quality losses also determine yield losses. Figure 1.2 represents the critical steps and conditions determining extra-virgin olive oil yield and quality.
Figure 1.2 Critical steps and conditions for yield and quality of extra-virgin olive oil.
The extra-virgin olive oil chain is divided into two parts. In the first part, corresponding to olive tree cultivation, the basic condition for success is olive integrity. If, due to climatic conditions or pest attack, olives are seriously damaged, the unavoidable consequence is an irreversible loss of yield and quality.
If, on the other hand, olives are undamaged and healthy, the final result is determined by three factors of similar importance: (i) the cultivar and the environment (climate and soil); (ii) the ripeness of olives at harvesting; (iii) the oil processing and storage conditions.
Processing of the olives and storage of the oil are the last and hence the decisive steps affecting oil quality. The product of the best, healthy and undamaged olives can be a very common oil or even a bad oil, as a consequence of errors and carelessness in the processing and distribution steps.
A point that should be kept in mind is that the loss of quality of virgin olive oil is irreversible. Feedback control is not possible and amplification instead of slowdown of the negative effects takes place: spoiled olives produce spoiled oil and spoiled oil tends to spoil further at a much faster rate than good oil. Process control should be based on prevention. The only corrective action available in the case of a spoiled oil is downgrading and refining it.
Reference
Peri, C., Lavelli, V. and Marjani, A. (2006) Sistemi di gestione per la qualità nei processi e nelle filiere agro-alimentari, Hoepli, Milan.
Chapter 2
Virgin olive oil: definition and standards
Manuela Mariotti
Department of Food, Environmental and Nutritional Sciences,University of Milan, Milan, Italy
Abstract
Basic information is given about virgin olive oil standards according to European legislation. Standards are divided into two groups: (i) quality standards aimed at classifying extra-virgin, virgin and inedible ‘lampante’ olive oil and (ii) authenticity standards aimed at identifying oil adulteration by mixing virgin olive oil with refined olive oil or oil of other kinds. The importance and meaning of free acidity, peroxide value, UV absorption values and sensory defects are discussed.
2.1 The legal definition of virgin olive oil
Definitions and standards for virgin olive oil are primarily based on European legislation, especially Commission Regulation (EC) No. 1019/2002 of 13 June 2002, on marketing standards for olive oil, and Commission Regulation (EC) No. 702/2007 of 21 June 2007, on the characteristics of olive oil and on the relevant methods of analysis. Other standardization organizations, such as the International Olive Council (IOC; www.internationaloliveoil.org/) and The Codex Alimentarius Commission (www.codexalimentarius.org/), take part in defining olive oil standards, but European legislation is the first and main reference worldwide. The European Community recognizes several categories of olive oil, each with its particular qualities and market value.
Virgin olive oil is defined by EC Regulation No 1019/2002 (Art. 3) as follows: ‘Virgin olive oil is the olive oil obtained directly from olives and solely by mechanical means.’ Conformity with this definition is the basic authenticity requirement for virgin olive oil.
Three categories of virgin olive oil are further defined, based on quality criteria, as: ‘extra-virgin olive oil’, ‘virgin olive oil’ and ‘lampante olive oil’. Lampante (literally ‘lamp oil’ according to its use in ancient times) is a virgin olive oil obtained from bad fruit or careless processing and it is of such a low quality that it cannot be used for human consumption and must be refined in order to become edible.
Regulation (EU) No 29/2012, dated 13 January 2012, codifies the substantial amendments that have taken place since regulation No 1019 on olive oil marketing standards was introduced in 2002. One of those, Council Regulation (EC) No 1234/2007 of 22 October 2007, establishes a common organization of agricultural markets and specific provisions for certain agricultural products, olive oil included. According to this regulation, ‘virgin olive oils’ are defined as:
“oils obtained from the fruit of the olive tree solely by mechanical or other physical means under conditions that do not lead to alterations in the oil, which have not undergone any treatment other than washing, decantation, centrifugation or filtration, to the exclusion of oils obtained using solvents or adjuvants having a chemical or biochemical action, or by re-esterification processes and any mixture with oils of other kinds.”
Commission Regulation (EC) No 702/2007 of 21 June 2007 defines the analytical and sensory standards of all the categories of olive oils, virgin or refined. Only the standards related to the three categories of virgin olive oil are presented here. These standards have been established by law as indicators of oil quality and authenticity.
Quality standards are analytical parameters that allow virgin olive oils to be classified according to a scale of quality. In general, these parameters indicate oil spoilage. Therefore, it is assumed that the lower their values, the higher the quality of the oil.
Authenticity standards are analytical parameters that allow an oil to be declared as ‘virgin’, in compliance with the definition reported above. In general, these parameters indicate the presence of refined olive oil (violation of the condition of ‘solely by mechanical means’) or other vegetable oils (violation of the condition of being obtained ‘directly from olives’).
2.2 Quality standards of virgin olive oil
Quality standards of virgin olive oil can be divided into two groups: chemical and sensory standards.
2.2.1 Chemical quality standards
The chemical standards that must be evaluated for classifying the quality levels of virgin olive oils are reported in Table 2.1. Quality standards are useful to verify hydrolytic and oxidative degradation that takes place in the olives and the oil during processing and storage. Olive oil producers should concentrate on the quality standards presented in Table 2.1, making a coherent decision about the processing procedure and conditions according to the level of quality they want to achieve.
Table 2.1 Chemical standards of virgin olive oil.
Free acidity
Hydrolysis of triglycerides due to lipolytic enzymes (lipases) causes free fatty acids and monoglycerides or diglycerides to be released from the triglycerides. The products of the lipolytic reaction are tasteless and odourless and therefore no sensory defects can be perceived. Hence, it is not correct to refer to ‘acidity’ as a flavour sensation of an olive oil. Sometimes, the sensation of pungency is mistakenly interpreted as ‘acidity’.
The lipolytic reaction is due to the endogenous lipases that are naturally present in the olive. When the integrity of the olive is lost due to mechanical action, lipases that are present in the pulp or in the seed cells come into contact with the oil, originally contained in specialized vacuoles. At this point, lipolysis starts and free fatty acids are produced. The reaction accelerates with increase in temperature and is a function of the time of contact between the lipases and the oil. Lipases are hydrophilic and they are active only in the presence of an aqueous phase. When water is separated, by decanting and centrifugation, lipolysis slows down or is totally stopped if the water and cell residues are completely separated from the oil. This is the reason why filtering the oil, removing the suspended materials and partially reducing the amount of water, is important.
In any case, the lipolytic reaction due to the endogenous lipases in the olives is relatively slow. Oil obtained from healthy fruit, regardless of the cultivar and processed just after harvesting, have very low values of free acidity. Free acidity rapidly increases in the presence of moulds and micro-organisms, which produce large quantities of very active lipases (exogenous lipases). In broken, dirty, unhealthy olives, lipase activity causes a rapid increase in free acidity beyond the limits for extra-virgin or virgin olive oils, with an obvious loss in quality and value. A further and very rapid acceleration of this reaction takes place due to olive fly attacks. The intestines of the olive flies and their excrement, in fact, contain very high concentrations of lipases that cause a very rapid increase in free acidity. It is most unfortunate that this happens when the fruit is still on the tree. Thus at harvesting time, the damage has been irreversibly done. Other factors affecting the integrity of olives are attacks by parasites, mechanical crushing and bruising, extended contact with soil, delayed harvesting (over-ripeness), prolonged heaping and storage before processing.
Free acidity is expressed as the percentage of free fatty acids on the basis of oleic acid, which is the main fatty acid of olive oil. Each producer should be able to determine free acidity at the milling site, not only to verify the quality of the oil, but also to avoid mixing good and bad oil.
The legal limit of 0.8% for extra-virgin olive oil is not very demanding. A good oil should have a free acidity value less than 0.5% and an excellent oil less than 0.3%.
Peroxide value and spectrophotometric absorption in the UV
The two main spoiling reactions of olive oil are lipolysis and lipid oxidation. Lipolysis can be easily estimated as free acidity, but oxidation is more difficult and complex to evaluate.
Assessment of the degree of olive oil oxidation is based on determinations of both the primary and secondary products of oxidation. The primary stage of oxidation is the formation of hydroperoxides from polyunsaturated fatty acids, through a radical mechanism (see Chapter 6).
Peroxides are primary oxidation products and they are used as indicators of oil quality and stability. Their value increases, reaches a maximum and then decreases because of their further degradation into secondary products of oxidation such as aldehydes, ketones and conjugated dienes. These substances, that are formed at an advanced stage of oxidation, are responsible for the rancid flavour of the oil.
Thus, the peroxide value is a measure of the degree of oxidation of the oil at an early stage of oxidative spoilage, long before a rancid smell or taste becomes perceivable. An increase in the peroxide value should be considered as a warning signal that oxidation is taking place.
Spectrophotometric values:
Specific absorbances (conventionally indicated as K) are measured in the UV region, at the wavelengths corresponding to the maximum absorption (about 232 and 270 nm) of secondary products formed in the autoxidation process. An increase in absorption at K232 and K270, may also be due to the presence of conjugated dienes and trienes, which are formed in oils that have been heated during the refining process. Conjugated dienes contain two double bonds that alternate with single bonds. A conjugated triene contains three alternating double bonds. Therefore, a high spectrometric value can be considered an indicator of oxidation or of adulteration of the oil.
Peroxide and spectrophotometric values are not easy to evaluate (see framed note below). However, they are so important that a good producer seeking high quality must have one or both of the analyses carried out as an essential tool of process control.
Lipid oxidation is greatly accelerated by lipolysis because free fatty acids are more easily oxidizable than fatty acids linked in a triglyceride molecule. This means that there is a synergy between lipid hydrolysis and oxidation in accelerating oil spoilage. Oil oxidation is also greatly accelerated by the presence of oxidative enzymes (lipoxidases, lipoxygenases) that are naturally present in the olive pulp and seed cells, and much more in case of moulds and fly spoilage. The removal of water may prevent or eliminate enzymatic oxidizing activity. However, unlike lipolysis, oxidation can also take place in the absence of water by a purely chemical, autocatalytic mechanism.
The legal limit of the peroxide value is 20 meqO2/kg for extra-virgin oil, which is a very poor standard, as a good oil must have a peroxide value of less than 12, and an excellent oil less than 8. The same can be said for K232, the most reliable spectrophotometric indicator of oil oxidation. The limit of 2.50 is not very selective; it should be lower than 2.10 for a good extra-virgin olive oil and lower than 1.90 for an excellent extra-virgin olive oil.
2.2.2 Sensory quality standards
The sensory analysis as a method for the legal recognition and classification of virgin olive oil was proposed by the International Olive Council in June 1987, and recognized by the European Commission in July 1991 (Commission Regulation (EEC) No 702/2007 amending Commission Regulation (EEC) No 2568/91 on characteristics of olive oil and olive-residue oil and on relevant methods of analysis, 21 June 2007). The method was further modified and replaced by subsequent amendments and finally updated by Commission Regulation (EC) No 640/2008 of 4 July 2008 amending Regulation (EEC) No 2568/91 on sensory characteristics of olive oil and the relevant methods of analysis. The sensory standards for classifying the various levels of quality of virgin olive oil are reported in Table 2.2 (see Chapter 4).
Table 2.2 Sensory standards of virgin olive oil.
Nonconformity with the requirement of a fruitiness note greater than zero is rare, as it is almost impossible to have a virgin olive oil without any odour and taste. Therefore, conformity to this requirement is very easy to achieve. Nonconformity to the prescription of zero defects, on the other hand, is frequent and may be the consequence of minor mistakes in processing. Therefore, conformity to this requirement is difficult to achieve. In addition, due to some difficulties in standardizing and obtaining reproducible results from different panels of tasters, sensory standards are difficult to be universally defined. The inclusion of sensory requirements among the legal standards for virgin olive oil was a ‘daring’ decision because sensory analysis can detect very low concentrations of good or bad oil components and because it is difficult to obtain reproducible results of positive and negative sensory attributes.
Probably, when establishing the sensory standards, the legislators did not take enough care in considering the difference between this requirement and the others. In fact, while the chemical standards measure concentrations of negative components at the level of per cent or per thousand, sensory defects are easily detected by human odour and taste receptors at concentrations that may be in the range of ppm (parts per million) or even ppb (parts per billion). It has been found that when mixing 1 mL of rancid oil with 10 L of a perfect oil (1:10 000 dilution), a defect is easily perceived by trained sensory assessors, while no significant change occurs in the values of the chemical indices. In addition, a variation in free acidity or peroxide value or K232 requires a massive evolution of spoilage reactions; on the contrary, the presence of a smell or flavour of staleness or rancidity may be due to a very minor contamination of a good oil. Thus, it is not surprising that some oils that have very good chemical standards may fail to be classified as extra-virgin olive oil because of the presence of sensory defects. These defects often arise from the presence of dead spots in the milling plant (for example, improper plant design) or to uneven distribution of residence times at critical temperature conditions (see the hygienic design in Annex 21.1 in Chapter 21). Small quantities of olive paste or oil undergoing intense spoilage, in fact, may act as sensory contaminants of large quantities of good oil.
The identification of olive oil defects through sensory analysis has the disadvantage of being a lengthy and expensive methodology, whose final result depends on many factors, especially the training and experience of the panelists. In recent years, instrumental methods have been proposed, based on the analysis of volatile compounds by dynamic headspace high-resolution gas chromatography. This is a more precise and reliable technique, but has two critical limitations: in the first place it requires the use of complex and expensive analytical instruments by highly skilled analysts; in the second place, establishing a reliable relationship between the instrumental response and the perceived sensations of a panelist or a consumer is still a matter of research and long-term experience. An interesting alternative for rapid, in-line evaluation of both negative and positive odour notes is the use of sensors to detect the volatile compounds present in the headspace of an oil container (the electronic nose). An interesting review on the different techniques applied to olive oil aroma analysis, with their advantages and disadvantages, has been published by Escuderos et al. (2007).
2.3 Authenticity standards of virgin olive oil
Authenticity standards are used to detect frauds that may derive from: (i) the use of prohibited additives or technological adjuvants; (ii) the use of prohibited technological operations as, for example, deacidifying and deodorizing by vacuum evaporation and steam stripping, or (iii) mixing with refined olive oil or other vegetable oils.
The main chemical standards that are evaluated for detecting extra-virgin olive oil adulteration are reported in Tables 2.3 and 2.4.
Table 2.3 Authenticity standards of virgin olive oil: fraudulent mixing with refined olive oil.
Table 2.4 Authenticity standards of virgin olive oil: fraudulent mixing with other vegetable oils.
Reference
Escuderos, M.E., Uceda, M., Sánchez, S. and Jiménez, A. (2007) Olive oil sensory analysis techniques evolution. European Journal of Lipid Science and Technology109, 536–546.
Chapter 3
The composition and nutritional properties of extra-virgin olive oil
Manuela Mariotti1 and Claudio Peri2
1Department of Food, Environmental and Nutritional Sciences,
University of Milan, Milan, Italy
3University of Milan, Milan, Italy
Abstract
Chapter 3 gives basic information about the composition and nutritional properties of extra-virgin olive oil. As triglycerides make up 97 to 99% of extra-virgin olive oil, the main chemical-physical characteristics of the oil depend on the composition of the triglyceride moiety. However, the minor components give an invaluable contribution to sensory and health-promoting properties. It is mainly the presence of these components that differentiates extra-virgin olive oil from all other edible oils.
3.1 Triglycerides and fatty acids
Extra-virgin olive oil essentially includes two groups of chemical compounds:
triglycerides: 97–99% wt
minor components: 1–3% wt
Triglycerides mainly contain a monounsaturated fatty acid (oleic acid), a fair amount of polyunsaturated fatty acids (linoleic and α-linolenic) and a slight amount of saturated fatty acids (palmitic and stearic).
The minor components are a complex mixture of polar, nonpolar and amphiphilic substances: hydrocarbons, tocopherols, phenolic compounds, sterols, chlorophyll, carotenoids, terpenic acids, monoglycerides and diglycerides, free fatty acids, esters and other volatiles. They contribute in a particular way to the sensory and health-promoting properties of extra-virgin olive oil.
Extra-virgin olive oil is separated from an aqueous medium so it still contains a very small, but essential amount of water. The water saturation threshold of extra-virgin olive oils is 300–400 mg per kg of oil, but they often have higher amounts, ranging from 300 to 1200 mg per kg of oil. Water is present in micro-droplets, less than one-tenth of a µm in diameter, impossible to separate by centrifugation. These microdroplets are associated with and stabilized by water-compatible, polar or amphiphilic substances of the minor components group.
Triglycerides belong to lipids, organic compounds that do not mix with water. They derive from the combination of three fatty acid molecules with one molecule of glycerol. Glycerol is a short 3-carbon chain alcohol that serves as the frame to which the three fatty acids can attach themselves with an ‘ester’ link. Fatty acids consist of chains 4 to 30 carbons long, with an acidic group at one end: it is this group that binds to glycerol to make a glyceride. Natural fatty acids usually have an even number of carbon atoms, as their synthesis in vivo is based on the assembly of a variable number of acetyl-CoA, a 2-carbon molecule (O'Keefe 2008).
Figure 3.1 shows the structural formula of a fatty acid molecule (stearic acid). It consists of a long chain of 18 carbon atoms (C) with their four valence bonds. Two bonds create the basic connection of the chain, whereas the other two are saturated by hydrogen atoms (H). At one end of the molecule there is a special group in which the carbon atom is linked to an oxygen atom (O) and to a hydroxyl group (OH). The resulting COOH group is called the ‘acidic group’. At the other end, the carbon atom is linked to three hydrogen atoms forming a ‘methyl group’ (CH3).
Figure 3.1 The structural formula of stearic acid.
The position of carbon atoms is usually identified by a number in the sequence that starts from the acidic group and ends at the methyl group. The acidic group is also called α (alpha), the first letter of the Greek alphabet. The methyl group is called ω (omega), the last letter of the Greek alphabet.
Figure 3.2 represents the same molecule of Figure 3.1 but with a different graphical convention, which is called the ‘skeletal’ formula. Carbon atoms are represented as black dots and hydrogen atoms, directly connected to the carbon atoms, are not indicated: each carbon atom is understood to be associated with enough hydrogen atoms to give the carbon atom four bonds. An even simpler representation is the skeletal formula without the black dots. In this type of representation, it is implied that the carbon atoms are located at the corners and ends of the line segments.
Figure 3.2 The skeletal formula of stearic acid.
Figure 3.3 shows how a molecule of glycerol combines with three molecules of the fatty acid (in this case stearic acid), giving a triglyceride molecule (in this case ‘tristearin’) and three molecules of water.
Figure 3.3 The triglyceride of stearic acid (tristearin).
In some fatty acids there are double bonds that derive from the elimination of two hydrogen atoms from two adjacent carbon atoms. Figure 3.4 shows a fatty acid derived from the stearic acid of Figure 3.2, by removing two hydrogen atoms from carbons 9 and 10, in the middle of the stearic molecule.
Figure 3.4 The skeletal formula of oleic acid.
When double bonds are present, fatty acids are defined as ‘unsaturated’. The unsaturated fatty acid represented in Figure 3.4 is the most important fatty acid of olive oil and it is called ‘oleic acid’. It represents from 65 to 85% of all fatty acids in olive oil.
A very particular structural change that takes place in the presence of double bonds is the bending of the fatty acid molecule, as shown in Figure 3.4.
The same fatty acid molecule can have several double bonds, as illustrated in Figure 3.5, in which four fatty acids are shown, all with 18 carbon atoms but with a different number of double bonds:
stearic acid is a saturated fatty acid
oleic acid is a monounsaturated fatty acid (acronym: MUFA)
linoleic and α-linolenic acids are polyunsaturated fatty acids (acronym: PUFA) with two and three double bonds, respectively.
Figure 3.5 The molecules of stearic acid (a), cis-oleic acid (b), cis-linoleic acid (c) and cis-α-linolenic acid (d).
Double bonds are the most reactive position in a fatty acid molecule, especially if multiple double bonds are ‘conjugated’, which means ‘separated by a single CH2 group’, which is the case with both linoleic and α-linolenic acid. Double bonds can react with oxygen, thus spurring the oxidative spoilage of oil, or they can react with hydrogen, thus re-establishing a saturated condition.
If one double bond of a natural PUFA is saturated by chemical reaction with two hydrogen atoms, the resulting unsaturated fatty acid has a linear structure. Therefore, if a double bond of α-linolenic acid is transformed into linoleic acid by saturation of a double bond, the resulting linoleic acid has a linear structure. Similarly, if a natural linoleic acid is transformed into oleic acid by saturation of a double bond, the resulting molecule of oleic acid has a linear structure (Figure 3.6). In order to distinguish these forms, all natural forms of unsaturated (and bended) fatty acids are identified with the prefix cis-, while all trans-formed, artificial, unsaturated fatty acids are identified with the prefix trans-.
Figure 3.6 Transformation from cis-linoleic (a) to trans-oleic acid (b) by hydrogenation.
However having an equal number of carbon atoms and the same number of double bonds, trans-isomers have physical, chemical and biological characteristics that are more similar to saturated fatty acids than to unsaturated fatty acids. Thus, trans-oleic acid is more similar to stearic acid than to cis-oleic acid.
Trans oils increase the risk of coronary heart disease by raising the level of LDL cholesterol and lowering the level of ‘good’ HDL cholesterol. The presence of trans-isomers in an extra-virgin olive oil is a clear sign of fraud and can be easily detected through analytical methods that are common practice nowadays.
Due to the bending of the molecule, the ‘cis’ structure makes it more difficult for these fatty acids to solidify into compact crystals, so at a given temperature unsaturated fatty acids are softer than saturated fatty acids. In other words, unsaturated fatty acids have lower melting points in comparison to saturated fatty acids. Table 3.1 shows the four C18 fatty acids that are present in olive oil. Despite the fact that they have very similar molecular formulas and molar masses, they have different degrees of unsaturation and very different melting points. It is especially worth noting that stearic acid, a saturated fatty acid, has a melting point that is much higher than the human body temperature (37 °C or 98.5 °F) and therefore is solid in the body, whereas all the others are unsaturated fatty acids and have a melting point lower than the body temperature and therefore are liquid in the body.
Table 3.1 Melting points of C18 fatty acids.
Lipid oxidation is influenced by many factors: the presence and concentration of oxygen, temperature, light and metal catalysts, but, most of all by the degree of unsaturation and the presence of conjugated double bonds.
The velocity of oxidative reactions is more than proportional to the number of double bonds as is evident by comparing the data in Table 3.2.
Table 3.2 Relative velocity of oxidative degradation.
Fatty acid
The relative velocity of oxidative reactions
Stearic acid
0
Oleic acid
1
Linoleic acid
64
α-linolenic acid
100
3.2 The nutritional role of olive oil triglycerides and fatty acids
Oils and fats are the nutrients with the highest caloric value (9 kcal/g). Excess fat in the diet results in accumulation of fat in the adipose tissue. This aspect of their nutritional contribution, however, is only partial. In fact, they have essential structural roles in the skin, retina, nervous system (the brain is the body's organ with the highest concentration of lipids), and biological membranes. They are precursors of hormones and the vehicle for the absorption of liposoluble vitamins (Kritchevsky 2008).
It is interesting to observe the percentage distribution of fatty acids in olive oil in Table 3.3. Polyunsaturated fatty acids with 18 carbon atoms (linoleic and α-linolenic acid) play crucial roles in cell structure and function. They cannot be synthesized by the body and therefore must be part of our diet; hence, they are referred to as ‘essential fatty acids’ (EFA). Nutritional studies have shown that they have preventive effects on cardiovascular diseases and nutritionists have identified them as ω-6 (linoleic acid) and ω-3 (α-linolenic acid) depending on the position of the first double bond in their molecule, counting from the ω end (Figure 3.5). However, these two important fatty acids are metabolically and functionally distinct, and often have opposing physiological functions in cell membranes. In some cases it has been found that their high reactivity and susceptibility to oxidation may represent a health risk. Therefore, a suitable balance of these essential fatty acids is important for good health and normal development. The ratio of monounsaturated to polyunsaturated fatty acids, and in particular ω-6 to ω-3 fatty acids in olive oil, is close to the optimal ratio recommended by nutritionists.
Table 3.3 Distribution (%) of the fatty acids in the triglycerides in olive oils.
Fatty acids
Percentage of total fatty acids in olive oil
Monounsaturated fatty acids, oleic acid
65–83
Saturated fatty acids
8–14
Polyunsaturated (ω-6), linoleic acid
6–15
Polyunsaturated (ω-3), α-linolenic acid
0.2–1.5
Most of all, the profile of olive oil fatty acids is characterized by the abundant presence of oleic acid, whose characteristics and functions are summarized in the box below.
3.3 Minor components and antioxidants in extra-virgin olive oil
Free radicals are highly reactive oxygen species. They are formed in the body during normal metabolism and, at a higher rate, upon exposure to environmental factors such as cigarette smoke and pollutants, or as a consequence of disease and traumatic events.
If free radicals are not intercepted and neutralized, they can cause serious damage to essential molecules such as DNA, protein, polyunsaturated fatty acids, especially those in the phospholipids of cell membranes, and lipoprotein. As a consequence, free radicals are closely associated with a range of disorders including cancer, arthritis, atherosclerosis, Alzheimer's disease, diabetes, and aging. The body reacts to oxidative threat with internal defence mechanisms and with molecules derived from food (tocopherols, carotenoids, phenolic compounds).
Since the discovery of the health benefits of the Mediterranean diet (Willet et al. 1995), interest in health protection from the daily consumption of extra-virgin olive oil has increased enormously (Visioli et al. 2002; Covas et al. 2006; Cicerale et al. 2009; Viola and Viola 2009; Pelucchi et al. 2010). This has also stimulated studies on the relationship between the health-promoting properties and quality of extra-virgin olive oils (Lavelli 2002; Servili and Montedoro 2002).
3.3.1 Hydrocarbons
Hydrocarbons are organic compounds that contain only carbon and hydrogen atoms. The major hydrocarbon in olive oil is squalene (skeletal formula in Figure 3.7); its name derives from the fact that it is extracted from the liver oil of sharks (in Latin squalus).
Figure 3.7 Squalene.
Squalene is a triterpene hydrocarbon that exerts antioxidant activity by reacting with oxygen radicals and oxygen-reactive species, thus protecting the skin against UV rays (something like a biological filter). Squalene has also been cited for its immune-stimulating properties and for its antineoplastic effects on colon, breast and prostate cancers.
Olive oil is a major source of squalene in the diet. Extra-virgin olive oil contains 200–700 mg of squalene per 100 g of oil, while refined olive oil contains about 25% less. Other useful hydrocarbons are present in extra-virgin olive oil, as for example β-carotene (pro-vitamin A), even if in small quantities.
3.3.2 Tocopherols
Tocopherols are fat-soluble alcohols that function as vitamin E, especially α-tocopherol (spacial formula in Figure 3.8), a very important antioxidant. Alpha-tocopherol is uniquely able to intercept free radicals and prevent chain reactions of lipid destruction at the cell membrane level. It also protects low-density lipoprotein (LDL) from oxidation. Oxidized LDL is implicated in the development of cardiovascular diseases. Extra-virgin olive oil contains 150 to 250 mg/kg of α-tocopherol with an optimal vitamin E-to-polyunsaturated fatty acid ratio of 1.5–2.0.
Figure 3.8 α-tocopherol.
3.3.3 Phytosterols
Sterols are unsaturated alcohols present in the fatty tissues of plants (phytosterols) and animals. Although these compounds represent a minor part of lipids in vegetable oils, their quantification can be useful to establish the origin of an oil and to reveal intentional adulterations. The amount in extra-virgin olive oil varies from 100 to 250 mg/100 g of oil, of which 90–95% is β-sitosterol (spacial formula in Figure 3.9). Cholesterol is absent.
Figure 3.9 β-sitosterol.
In addition to their cholesterol-lowering actions, mounting evidence suggests that phytosterols act against cancer of the lung, stomach, ovary and estrogen-dependent human breast cancer. In vitro studies using cell culture models have shown that β-sitosterol may have anticarcinogenic effects with regard to cancer of the prostate, colon, breast and stomach.
The total sterol content and determination of the amount of individual sterols (cholesterol, brassicasterol, campesterol, stigmasterol, Δ-7-stigmastenol, and β-sitosterol) gives an indication of authenticity (see Table 2.4 in Chapter 2).
3.3.4 Phenolic compounds
These compounds are increasingly attracting the attention of researchers. The most important are the 5-hydroxytyrosol and its elenoic acid ester, oleuropein (Figure 3.10), the latter being an exclusive constituent of olive leaves and olive oil.
Figure 3.10 5-hydroxytyrosol (a) and oleuropein (b).
The sugar part of the oleuropein molecule is removed by enzymatic digestion during the malaxing operation, thus producing oleuropein aglycones. These compounds are partially soluble in oil and therefore they pass from the olive paste to the oil. This is a critical step for olive oil quality because these compounds have a high antioxidant potential and a bitter taste, which is a typical and positive sensory attribute of extra-virgin olive oils.
Oleuropein and its metabolite hydroxytyrosol have powerful antioxidant activity in vitro and in vivo associated with anti-inflammatory action. Oleuropein, in particular, has several pharmacological properties. Other simpler phenolic compounds present in lower amounts, such as caffeic acid, vanillic acid and ferulic acid have a protective effect on α-tocopherol and lignans, a class of phenols with protective effects against colon and breast cancer.
In summary, from the recent and extensive scientific literature, the following biological activities have been attributed to the phenolic compounds of extra-virgin olive oil: (i) direct antioxidant activity; (ii) protection of α-tocopherol antioxidant activity; (iii) binding of metal ions that favours radical formation; (iv) inhibition of platelet aggregation; (v) reduction of plasma cholesterol levels; (vi) inhibition of LDL oxidation; (vii) increased immune activity; (viii) anti-inflammatory activity; (ix) decreased cancer growth; (x) anti-allergic activity; (xi) skin protection.
Evaluation of the phenolic fraction and its composition provides important information in terms of oil quality, stability and nutritional value. The most reliable method is based on high-performance liquid chromatography (HPLC) (Servili et al. 1999). Interesting information can be obtained from chemical or enzymatic methods for assessing antioxidant potential (Lavelli 2002). These are, however, complex and time-consuming methods, also requiring sophisticated analytical equipment and therefore they cannot be used as process control tools. In fact, evaluation of the phenolic content of extra-virgin olive oil can be used to characterize milling batches or to establish blending proportions, or to correlate an olive maturity index to the quality profile of the oil. A very commonly used method is based on the Folin–Ciocalteau colorimetric assay of total phenolics, which is simple but necessitates a well-equipped laboratory. Recently, the use of portable, easy-to-use, rapid analytical apparatuses has spread with success for online control duties among olive oil producers and millers. However, the problem of setting up a rapid and precise method of phenolic compounds analysis of olive oil that is in good agreement with the more reliable HPLC method, is still open (Garcia et al. 2013).
3.4 The colour and odour components of extra-virgin olive oil
The colour of extra-virgin olive oil ranges from green to yellow due to the prevalence of chlorophyll or carotenoids, respectively. The green colour of early-harvested olive oil, which is particularly intense in oil from some cultivars (e.g. Correggiolo), is very appealing to many consumers. Chlorophyll is a molecule very sensitive to light, and careful storage to protect the oil from oxygen and light helps maintain the green colour for a longer time. A rapid loss of the green colour is a sensitive indicator of poor storage conditions.
The odour of extra-virgin olive oil is a much more complex subject. Over a hundred volatile compounds have been identified by gas chromatography and mass spectrometry in extra-virgin olive oil: aldehydes, alcohols, esters, hydrocarbons, ketones, furans and others. Only a few of them have a real impact on the perceived odour, like, for example, those derived from hexanal (green, grassy), trans
