PREDICTING SHELF
LIFE IN FOODS
THROUGH OXIDATIVE
STABILITY
LINDSAY WARD
APRIL 9, 2015
WHAT DETERMINES
SHELF LIFE?
The time period within which the food is safe to
consume or has an acceptable quality to consumers
When conducting a shelf life study, it is best to do so
based upon the food product’s limiting factor
• Microbial activity
• Chemical or enzymatic activity
• Lipid oxidation, browning
• Moisture migration
ACCELERATED SHELF
LIFE STUDIES
Used for practical purposes to shorten the
process of determining shelf life
• Deliberately increase the rate of deterioration
• Especially useful when the product is shelf
stable
Most studies pertain to chemical deterioration
PREDICTING SHELF LIFE THROUGH
EXTRAPOLATION
Select the kinetic factor for accelerating the
deterioration process
• Addition of heat, enzymes, metals, etc.
Use product deterioration data to
extrapolate the kinetic model to predict
shelf-life at actual storage conditions
Source: Understanding and Measuring the Shelf-Life of Foods
PREDICTING SHELF LIFE USING THE
Q10 VALUE
Ratio of the shelf life of a product at temperatures
10oC apart
Shelf-life at T (°C)
Q10 = --------------------------Shelf-life at (T (°C) + 10°C)
LIPID
OXIDATION…WHAT IS
IT?
Lipid oxidation occurs due to a catalytic event
• Free Radicals
• Lipoxygenase
• Light
• Heat
Leads to the formation of radicals and peroxides
• off flavors and odors
• Rancidity of the product
L.O. AS IT RELATES
TO SHELF LIFE
Lipid oxidation (chemical deterioration) is one of
the most common limiting factors in a food
product’s shelf life
Monitoring lipid oxidation is a primary method to
predict food product shelf life in accelerated
studies
• elevated temperatures
ASLT METHODS FOR
PREDICTING SHELF LIFE
OXIDATIVE STABILITY
Schaal Oven Test
Active Oxygen Method
Oxygen Bomb
SCHAAL OVEN TEST
METHOD
Accelerates oxidation by increasing temperature
Samples placed in oven (~60oC)
• Loosely capped test tubes
Oxidation level commonly measured using the
peroxide value
• Sensory (rancidity), G.C. to measure volatile
compounds
ACTIVE OXYGEN
METHOD
Accelerates oxidation by increasing temperature
and addition of air
Sample placed in a test tube and incubated at
~98oC oil bath
Dry air bubbled into the sample continuously
Peroxide values measured at different time points
to determine oxidation
OXYGEN BOMB
METHOD
Oxidation accelerated by increasing temperature and
the addition of oxygen and pressure
Samples placed in a pressure vessel (“bomb”)
Oxygen is pressurized into the vessel
Vessel in incubated in an oil-bath (~99oC)
Lipid oxidation is determined by the decrease in
oxygen pressure over time
DOWNSIDES TO ASLT
METHODS
Lipid oxidation reaction mechanism changes at
high temperatures
• Physical and chemical changes in food system
• Extrapolations of the reaction to determine actual
shelf life may not be as accurate
Volatile antioxidants may be removed from food
product due to addition of heat and oxygen
FREE RADICAL
GENERATION ASSAYS
Chemically induced radical generation through the addition
of azo-initiators (R-N=N-R)
• 2,2′-azobis-(2,4-dimethylvaleronitrile) (AMVN)
Balili and Pintauer, 2010
• Allows for the use of lower acceleration
temperatures
• More accurate actual shelf life predictions
FREE RADICAL
GENERATION ASSAYS….
Induction point (inflection point in curve) without
free radical addition is >20 days
Van Dyck, et al., 2005
…APPLICABLE FOR
SHELF LIFE TESTING?
Slopes of the curves calculated from the FRG-OB
assay used to predict TBA max
• Used to indicate shelf life
• Results compared to non-accelerated shelf life
study evaluated with TBARS
Van Dyck, et al., 2005
REFERENCES
ASTM D 942-02. Standard test method for oxidation stability of lubricating greases by the oxygen
pressure vessel method. In Annual Book of ASTM Standards; ASTM International: West
Conshohocken, PA, 2002.
Balili, M. N. C.; Pintauer, T. 2010. Kinetic Studies of the Initiation Step in Copper Catalyzed Atom
Transfer Radical Addition (ATRA) in the Presence of Free Radical Diazo Initiators as Reducing Agents.
Inorganic Chemistry. 49(12): 5642-5649.
Frankel, E. N.; Meyer, A. S. 2000. Review: The problems of Using One-Dimensional Methods to
Evaluate Multifunctional Food and Biological Antioxidants. Journal fo the Science of Food and
Agriculture. 80: 1925-1941.
Li, H; Fa, Y.; Li, J.; Tang, L.; Hu, J.; Deng, Z. 2013. Evaluating and Predicting the Oxidative Stability of
Vegetable Oils with Different Fatty Acid Compositions. Journal of Food Science. 78: 633- 641.
Quinchia, L. A.; Delgado, M. A.; Valencia, C.; Franco, J. M.; Gallegos, C. 2011. Natural and Synthetic
Antioxidant additives for Improving the Performance of New Biolubricant Formulations. Journal of
Agricultural and Food Chemistry. 59: 12917-12924.
Ragnarsson, J. O.; Labuza, T. P. 1977. Accelerated Shelf-life Testing for Oxidative Rancidity in Foods –
A Review. Food Chemistry. 2: 291-308.
Steele, Robert. 2004. Understanding and Measuring the Shelf-life of Food.
Subramaniam, A.; Veazey, R. L.; Schober, A.; Rada, A.; Rong, Y.; van Sleeuwen, M. T.; Golding, R.;
Zhang, S. 2013. Orange Oil Stability in Spray Dry Delivery Systems. Carbohydrate Polymers. 97: 352357.
Van Dyck, S. M. O.; Verleyen, T.; Dooghe, W.; Teunckens, A.; Adams, C. A. 2005. Free Radical
Generation Assays: New Methodology for accelerated Oxidation Studies at Low Temperature in
Complex Food Matrices. Journal of Agricultural and Food Chemistry. 53: 887-892.
QUESTIONS?