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 – 31 st October/1 st 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 Typical Australian olive oil types PP = total polyphenols C18:2 = linoleic acid Least stable LOW OXIDATIVE Low PP Low PP STABILITY Mid C18:2 Low C18:2 Low polyphenols High linolenic acid MEDIUM OXIDATIVE Mid PP Mid PP STABILITY High C18:2 Low C18:2 Mid polyphenols Mid linolenic acid HIGH OXIDATIVE High PP High PP STABILITY High C18:2 Mid C18:2 High polyphenols Low linolenic acid Most stable
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 O 2 /kg oil
Temperature - Free fatty acids Least stable (LP,HL) Most stable (HP,LL) AS-5264-2011 – < 0.8%
Temperature - DAGs Least stable (LP,HL) Most stable (HP,LL) AS-5264-2011 – >35%
Temperature - Pyropheophytin a Least stable (LP,HL) Most stable (HP,LL) AS-5264-2011 – < 17%
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 Least stable (LP,HL) Most stable (HP,LL) AS-5264-2011 – <20 mEq O 2 /kg oil
Oxygen - UV absorbance - K 232 Least stable (LP,HL) Most stable (HP,LL) Least stable (LP,HL) Most stable (HP,LL) • Similar results for K 268 AS-5264-2011 – < 2.50
Oxygen - Polyphenols Least stable (LP,HL) Most stable (HP,LL)
Oxygen - α -tocopherol Least stable (LP,HL) Most stable (HP,LL) Least stable Most stable
Oxygen - Sensory analysis Closed Open Least stable Most stable
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 (LP,HL) Most stable (HP,LL) Least stable Most stable
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 Least stable Most stable
Compliance with AS5264-2011 Least stable PV UV Absorbance FFA Pyro DAG Sensory K232 K268 Storage 15°C 12 18 Temperature 22°C 24 18 6 12 37°C 6 3 3 6 Closed 24 18 6 12 Oxygen Open 6 6 24 24 18 6 3 Dark 24 18 6 12 Light Exposed 24 18 *ND 6 12 Within AS5264-2011 limit after 36 months Exceeds AS5264-2011 limit Number = months before exceeding limit *ND: Not detected after 3 months storage
Compliance with AS5264-2011 Most stable PV UV Absorbance FFA Pyro DAG Sensory K232 K268 Storage 15°C Temperature 22°C 18 18 37°C 36 30 3 3 6 Closed 18 18 Oxygen Open 18 12 24 18 18 18 Dark 18 18 Light Exposed 6 *ND 18 18 Within AS5264-2011 limit after 36 months Exceeds AS5264-2011 limit Number = months before exceeding limit *ND: Not detected after 3 months storage
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 O 2 /kg oil
Bulk storage - UV absorbance - K 232 • 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)
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