Zahra Mohammed

8/13/2019 Zahra Mohammed

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Olive oil volatile compounds, flavor developments and quality

Zahra Mohammad


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Overview

1. Introduction

2. Olive oil quality

3. Volatile compounds

4. Formation of volatile compounds5. Enzyme action in volatile compounds

6. Processing condition and volatile compounds

7. Volatile compounds and olive oil flavor

8. Oxidation of volatile compounds

9. Conclusion


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Introduction

Olive oil is known to possess a highly distinctive taste and

flavor. The quality and flavor of olive oil is attributed to the

formation of volatile compounds that are formed as a result of

oxidation of fatty acids. A number of factors influence the

formation of these compounds and the quality of olive oil.

Thus, an understanding of the formation stages of volatile

compounds can be used to control the volatile composition and

enhance the quality of olive oil.


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Olive oil quality

The International Olive Oil Council(IOOC) have defined

the quality of olive oil based on the free fatty acid which is

an important factor for classifying olive oil into

commercial grades. The olive oil with high quality is

called extra- virgin. The quality of olive oil is affected by

many parameters such as cultivar, climatic conditions

,agronomic practices and presence or absence of certain

volatile compounds.


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Olive oil quality

The stability and sensory characteristics of olive oil

also can be affected by phenolic content and may

serve as a good indicator of olive oil. Olive oil is

susceptible to both hydrolytic and oxidative reactionsthat can change the quality of olive oil.


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What is Volatile Compounds

Volatile compounds are low molecular weights which vaporize at

room temperature, it is formed during and after olive oil extraction

due to the oxidation of fatty acids (triglycerides), and it is responsible

for Olive oil aroma and quality . Reported that the major volatilecompounds that responsible for positive aroma are the aldehydes,

alcohols, esters, hydrocarbons, ketones, and furans that are involved

C6 and the C5 volatile compounds .


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What is Volatile Compounds

The Volatile compounds are influenced by a number of factors such

as cultivar, geographic region, fruit maturity, processing methods and

parameters.

- Fruit from different cultivars grown under the same environmental

conditions produce oils with different volatile compounds.

- fruit of the same cultivar grown in different geographic regions alsoproduce oils with different volatile compounds.

- Different volatile compounds and different aroma are produced with

different degree of olive fruit maturity.

-Different volatile compounds are produced with different with

different Extraction methods and condition , and processingtemperature and time.


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Formation of Volatile Compounds

Volatile compounds formed as a result of oxidation of olive fatty acid.

During the climacteric phase (earlier) fruits produce ethylene, oil from

this phase has a high quality and rich in aromatic volatile

compounds. The formation of volatile compounds include different

pathways , these pathways involve chemical and enzymatic

oxidation. However, the volatile compounds from chemical pathways

are responsible for the off- flavor due to the oxidative rancidity. And

the volatile compounds that give a high oil quality and aroma are

those formed through enzymatic pathways especially through the

lipoxygenase pathway.


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Lipoxygenase pathway include two pathways, one pathway is

enzymatic cleavage of linoleic and linolenic acid into C6 and C9

aldeydes and C9 and C12 oxo acids. Another pathway is through

fatty acid metabolism, producing acids, alcohols, esters and ketones.

Volatile compounds can be formed by other enzymatic pathways,such as amino acids, but this pathway has been paid less attention.

However, an understanding of the various pathways can improve the

production and storage of premium quality olive oil.



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Lipoxygenase

Olive Lipids

Linoleic

acid

Linolenic acid

9-

hydroperoxide

13- hydroperoxide 13-

hydroperoxide9-

hydroperoxide

Hexanal Cis-3-hexenal

Trans-2-

hexenal

Hexanol Cis-3-hexenol

trans-2-

hexenol

Hexyl

acetate

Cis-3- hexenyl

acetate

Trans-2-hexenyl

acetate

Hydroperoxide lyase

Alcohol dehydrogenase

Alcohol acetyl transferase

Acyl hydrolase

Cis-3: trans-2-enal isomerase


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Enzyme action in volatile compounds

The formation of volatile compounds throughlipoxygenase pathway involves a series of enzymes.

The volatile compounds start with enzyme acyl hydrolase(AH) and

hydrolyses triglycerides and phospholipids to release free fatty acids.

Then fatty acids are oxidized by the action of enzyme

lipoxygenase(LOX) to produce hydroperoxides , this enzyme is moreactive with linolenic acid than linoleic acid and produce more C6

unsaturated volatile compounds that is contributed to virgin olive oil

aroma. And it is more active with alkaline range than acidic

conditions.


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Enzyme action in volatile compounds Fatty acid hydroperoxides are cleavage by enzyme hydroperoxide

lyase (HPL) to produce volatile C6 aldehydes and C12 oxoacids

from 13-hydroperoxides of linolenic or linoleic acid which are

responsible for olive aroma or produce C9 aldehyde and C9

oxoacids from 9- hydroperoxide which are responsible for cucumber

like odour. Then, aliphatic aldehydes catalyses to alcohols by

enzyme alcohol dehydrogenase (ADH) which is abundant in the

plant kingdom and is responsible for the formation of volatile

compounds that responsible for the aroma of vegetable products.


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Enzyme action in volatile compounds The activity of enzyme ADH decreases when the olive fruit color

changes to purple during the ripening process which leads to

decrease of C6 alcohols in the aroma of olive oils. Then, from

alcohols that are produced by ADH, volatile esters and acetate esters

such as (hexyl acetate) which are important compounds of sweet,

fruity note produced by the action of enzyme Alcohol acetyl

transferase (AAT). This enzyme is more active with long chains.

Thus, increasing the AAT activity can increase the production of

volatile esters responsible for the fruity and sweet aroma in olive oil.


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Processing conditions and volatile formation

Processing conditions of olive fruit can affect both quality and

quantity of olive oil because the formation of volatile compounds is

dependent on the action of enzymes, which have different optimum

temperature for activity. Thus, Malaxation temperature and time canbe controlled to produce high quality and quantity of olive oil.

However, different processing parameters may be required in

different geographic growth regions to produce high quality olive oil.


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Volatile compounds and olive oil flavor

More than 120 volatile compounds that contribute both positive and

negative flavor and sensory of olive oil has been identified. The

evaluation of the flavor and quality of olive oil depend on the volatile

compounds that are formed during the processing of olive fruit. The

IOOC provides some standards flavor to evaluate virgin olive oil

sensory quality.

The positive attribute

Fruity: the flavor of the oil from unripe olives, and it is grassy or leafy

attributes. Whereas, ripe olives has aromatic flavor.

Bitter: it is characteristic taste of olive oil from green or turning colorolive.

Pungent: it is characteristic taste of olives that are unripe


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Volatile compounds and olive oil flavor The negative attribute of olive oil

Fusty: a characteristic flavor of oil from olives stored in piles of

notable thickness or in jute sacks for long time before extraction due

to anaerobic.

Musty- humid: a characteristic flavor of oil from fruit infested withfungi and yeast that stored in low temperature and high humidity.

Muddy sediment: a characteristic flavor of oil that has been left in

contact with the sediment for a long time.


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Volatile compounds and olive oil flavor Winey-vinegary: a flavor due to the fermentation that lead to the

formation of acetic acid, ethyl acetate and ethanol that has a flavor

reminiscent of wine or vinegar.

Metallic: a flavor, reminiscent of metals due to the long contact with

metallic surfaces during process or storage. Rancid: a flavor of oils that have undergone oxidation of unsaturated

aldhydes.

The flavor sensory is due to the interaction of several volatile

compounds, but not single volatile. The positive aroma have been

associated with volatile C6 aldehyde , alcohols, and C5 aldehydes ,alcoholes and esters.


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Oxidation of volatile compounds

Oxidization of the triglycerides of virgin olive oil causes significant

changes in the chemical, sensory and nutritional properties of oil thataffect the quality. The oxidation is influenced by external factors,

such as storage condition like temperature, light and oxygen

concentration. At low temperature ketones and aldehydes dominate

the volatile compounds in oil, whereas oil stored at high oxygen

concentration carboxylic acids dominate the volatile compounds inoil, and at high temperature the polymeric volatile compounds are

produced.

It has been reported that the absence of C6 aldehyde, C6 alcoholes

and esters from the lipoxtgenase pathway and presence of many

C7-C12 aldehydes and other volatile cause off-flavors of olive oil. Nonanal and the ratio of hexanal/nonanal used as indicator of

oxidation. However, most studies have been used nonanal as a

primary indicator of rancidity that has focused on the volatile

compound that causes the rancid off-flavor.


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Conclusion

It is important to understand the formation of volatile compounds and

their pathways in order to be able to enhance the desirable flavor

and the quality of olive oil. However, producing the high quality of

olive oil remains challenge since the quality of olive oil depends on

the rate of volatile compounds in oil. Volatile compounds and the

quality of olive oil are influenced by a number of factors such ascultivars, agronomic practices, geographic region, fruit maturity,

processing condition, and storage condition of fruits. However,producing olive fruit with high properties and positive attributes with

controlling the processing parameters are essential to produce high

quality olive oil. More studies should be done in post harvest fruithandling technologies that enhance production of positive volatile

compounds.


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Zahra Mohammed