The effect of storage on olive oil quality

Jamie Ayton, Rod Mailer and Kerrie Graham Wagga Wagga Agriculture Institute

2012 AOA National Olive Industry Conference – 31st October/1st November 2012 – Adelaide

Introduction

Considerable time, effort and money is required to produce high quality extra virgin olive oil (EVOO).

EVOO quality deteriorates over time, however the rate of deterioration depends on:

– Composition of the oil – Storage conditions

Research to determine the rate of deterioration based on

initial oil composition and storage conditions (temperature, oxygen, light exposure and storage container type).

Introduction – RIRDC projects

Project 1 – Effect of storage conditions on olive oil quality.

– Investigation of a number of different types of olive oil stored in

bottles under variable conditions. » Temperature » Oxygen » Light

Project 2 – Effect of storage in bulk containers on olive oil quality.

» One oil stored in different container types

Project 1– Effect of storage conditions

LOW OXIDATIVE STABILITY Low polyphenols High linolenic acid

Low PP Mid C18:2

Low PP Low C18:2

Mid PP High C18:2

MEDIUM OXIDATIVE STABILITY Mid polyphenols Mid linolenic acid

Mid PP Low C18:2

High PP High C18:2

High PP Mid C18:2

HIGH OXIDATIVE STABILITY High polyphenols Low linolenic acid

Least stable

Most stable

Typical Australian olive oil types PP = total polyphenols

C18:2 = linoleic acid

Initial oil composition

Least stable Most stable

Storage conditions

Nine oils stored for 3 years – analysed at regular intervals

Temperature (stored in dark, closed) • 15°C • 22°C • 37°C

Oxygen (stored at room temp, in the dark)

• Open • Closed

Light (stored at room temp, closed)

• Clear bottle, exposed to light • Dark bottle, stored in darkness

Temperature Factory

Warehouse

Supermarket Home

Temperature - Peroxide value

Least stable (LP,HL) Most stable (HP,LL)

AS-5264-2011 – <20 mEq O2/kg oil

Temperature - Free fatty acids

AS-5264-2011 – < 0.8%

Least stable (LP,HL) Most stable (HP,LL)

Temperature - DAGs

AS-5264-2011 – >35%

Least stable (LP,HL) Most stable (HP,LL)

Temperature - Pyropheophytin a

AS-5264-2011 – < 17%

Least stable (LP,HL) Most stable (HP,LL)

Temperature Sensory analysis – low stability oil

15°C, dark, closed 22°C, dark, closed 37°C, dark, closed

•Results shown are for low stability oil (LP,HL)

•Similar results for other oils

•High stability oils – less likely to be rancid at low temperature

Oxygen

Oxygen - Peroxide value

AS-5264-2011 – <20 mEq O2/kg oil

Least stable (LP,HL) Most stable (HP,LL)

Oxygen - UV absorbance - K232

AS-5264-2011 – < 2.50

Least stable (LP,HL) Most stable (HP,LL) Least stable (LP,HL) Most stable (HP,LL)

•Similar results for K268

Oxygen - Polyphenols Least stable (LP,HL) Most stable (HP,LL)

Oxygen - α-tocopherol

Least stable Most stable Least stable (LP,HL) Most stable (HP,LL)

Oxygen - Sensory analysis

Closed Open

Leas

t sta

ble

Mos

t sta

ble

Not affected by oxygen

FFA PPP DAGs

•FFA slight increase

•PPP - increase 8-10% per year

•DAGs decrease – 25-35% per year then reaches equilibrium

Light

Light - α-tocopherol

Least stable Most stable

Least stable (LP,HL) Most stable (HP,LL)

Light - Chlorophyll •Significant decrease in oils exposed to light

•Same response in all oils

•Antioxidant in dark, pro-oxidant in light

Green

Brown/golden

•Pyropheophytin a – breakdown product of chlorophyll

•No chlorophyll = no PPP. Undetectable after initial analysis

Light – Sensory analysis

Dark Light

Leas

t sta

ble

Mos

t sta

ble

Compliance with AS5264-2011

PV FFA Pyro DAG SensoryK232 K268

15°C 12 1822°C 24 18 6 1237°C 6 3 3 6

Closed 24 18 6 12Open 6 6 24 24 18 6 3

Dark 24 18 6 12Exposed 24 18 *ND 6 12

UV Absorbance

Storage Temperature

Oxygen

Light

Least stable

*ND: Not detected after 3 months storage

Within AS5264-2011 limit after 36 months

Exceeds AS5264-2011 limit

Number = months before exceeding limit

Compliance with AS5264-2011

PV FFA Pyro DAG SensoryK232 K268

15°C22°C 18 1837°C 36 30 3 3 6

Closed 18 18Open 18 12 24 18 18 18

Dark 18 18Exposed 6 *ND 18 18

UV Absorbance

Storage Temperature

Oxygen

Light

Most stable

*ND: Not detected after 3 months storage

Within AS5264-2011 limit after 36 months

Exceeds AS5264-2011 limit

Number = months before exceeding limit

Project 2 - Bulk storage

One oil stored for 1 year

Bulk storage containers

» Polyethylene » Nylon » Metallised polyester » Silver foil » HDPE

Storage conditions » 22°C » closed » dark

Bulk storage - Peroxide value

•Container type had significant effect

•Oxygen permeability

•Oil in polyethylene container increased significantly – outside limit after 12 months storage.

AS-5264-2011 – <20 mEq O2/kg oil

Bulk storage - UV absorbance - K232

•Container type had significant effect

•UV absorbance of oil in PE container increased significantly – outside limit after approx 6 months storage.

AS-5264-2011 – < 2.50

Bulk storage - Total polyphenols

•Container type had significant effect

•Oxygen permeability of PE – polyphenols consumed in oxidation process

Bulk storage - DAGs

•Same as results from previous project eg presence of oxygen had no effect, identical for all containers

•30% decrease in DAGS over 12 months

AS-5264-2011 – >35%

Conclusions – storage conditions Storage conditions - significant influence on the quality of olive oil.

– Higher storage temperature

– More rapid increase %FFA and PPP, decrease in DAGs and sensory quality

– Oxygen exposure – More rapid increase PV and UV absorbance, decrease in antioxidants and

sensory quality

– Light exposure – More rapid decrease in tocopherols, chlorophyll, sensory quality

PPPs and DAGs

– Good indicators of freshness of oil – initial quality and storage conditions important

Keep olive oil in dark, cool areas and ensure exposure to oxygen is kept minimal to

maintain EVOO quality

Conclusions - Bulk storage

Bulk storage containers can have a significant effect on olive oil quality

– be aware of the type of material used – oxygen permeability – ensure storage temperature is kept as low as

possible and exposure to light is limited.

Acknowledgements

NSW DPI Staff

• Veronica Woodbury

• Francisca Boshuizen

• Donna Seberry

• Chris Wallace

• Helen Taylor

•Janelle Rowland

Special thanks to all members of the Wagga Wagga Olive Oil Sensory Panel (WWOOSP)