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 STUDIESUsed 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 METHODAccelerates 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 METHODOxidation 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)

• Allows for the use of lower acceleration temperatures

• More accurate actual shelf life predictions

Balili and Pintauer, 2010

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

REFERENCESASTM 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: 352-357.

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?