the effect of storage on olive oil quality...st november 2012 – adelaide introduction considerable...
TRANSCRIPT
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)