Accelerated Oxidation Studies

1. Accelerated Oxidation Studies DERRICK BRIAN AMOAKO APRIL 8, 2014

2. Introduction • Oxidation is an important quality parameter mostly used as predictor of the quality or shelf stability of a food product • Foods containing fats and oils such as edible oils, emulsifiers, meats, cookies etc • Common routine tests used as indicators of lipid oxidation include peroxide value, Free Fatty Acid levels, TBARS etc

3. Conducting oxidation studies • Keep food product at typical storage conditions and monitor markers of oxidation over time, complemented with sensory data (rancidity). • Oxidation rate at room temperature is relatively slow, and rancidity may only be evident after several weeks or even months • The need for faster methods of measuring oxidative stability to predict shelf life of food products or antioxidant capacity of new compounds Dyck et al., (2005). Free Radical Generating Assays

4. Accelerated oxidation studies • The objective of AOS is to offer quick and efficient evaluation of the oxidative stability and antioxidant properties of food products and compounds • AOS basically changing conditions in the food environment to levels that initiate and accelerate oxidation rate • Eg: temperature (60-1400 C), oxygen pressure (3-165 psia), Added metals (25-100 ppm in lipid) • Complemented by measuring oxidation parameters, and values are matched with extended oxidation studies for correlation and extrapolation Labuza and Ragnarsson (1976). Accelerated Shelf-life testing for oxidative rancidity in foods – A Review

5. Accelerated oxidation studies http://www.floratech.com/fileMgr/upload/files/ARTICLES/REPRINTS/M013.pdf

6. Methods for Accelerated oxidation studies • Active Oxygen Method • Oxidative Stability Instrument/Rancimat • Oxygen bomb • Free radical generating assays Dyck et al., (2005). Free Radical Generating Assays; Warner et al., (1995). Methods to Assess Quality and Stability of Oils and Fat Containing Foods

7. Active Oxygen Method (AOM) • About 20mL of oil sample is placed in a glass tube and aerated continuously at 97.80 C. • Samples are withdrawn periodically and analyzed for peroxide value • The time (in hours) elapsed to reach a peroxide value of 100mEq/kg is reported as the AOM hours for the oil Warner et al., (1995). Methods to Assess Quality and Stability of Oils and Fat Containing Foods

8. Pros and Cons of AOM Pros • Most extensively used (an established AOCS official method) Cons • Can be used on a few products such as lard and oil • Time consuming (periodic titration) Blakenship et al., (1973). Comparison of Oxygen Bomb Method to Other Methods for Measuring Oxidative Stability of Peanuts and Peanut Products

9. Oxidation Stability Instrument • Air is bubbled through small amount of oil to initiate and accelerate oxidation • Organic acids (secondary oxidation products) are transported in the stream of air to the second vessel containing distilled water detected by an increase in conductivity • The time which elapses for the until the increase in conductivity is the induction time (an index of oxidative stability) (Dyck et al., 2005; http://www.floratech.com/fileMgr/upload/files/ARTICLES/REPRINTS/M013.pdf)

10. Pros and Cons of OSI Pros • Good correlation with AOM • Faster than the AOM Cons • Requires extraction of fat from some fat-containing foods for analysis Warner et al., (1995). Methods to Assess Quality and Stability of Oils and Fat Containing Foods

11. Oxygen Bomb equipment • The OB continuously measures the change in pressure in the headspace over a food matrix under pure oxygen environment in a sealed system at pressure, 345kPa and temperature, 1350C. • When oxygen is incorporated in the lipid molecules of the food matrix due to oxidation, there is a corresponding decrease in the headspace pressure. • A two psi drop in pressure is considered the induction time (related to the time where the product begins to absorb oxygen) • A plot of oxygen absorbed against time is used as a measure of the oxidative stability of the food matrix Dyck et al., 2005; Warner et al., (1995). Methods to Assess Quality and Stability of Oils and Fat Containing Foods

12. Oxygen Bomb equipment Stable products exhibit a slower rate of oxygen absorption with a delayed induction period Dyck et al., (2005). Free Radical Generating Assays; Warner et al., (1995). Methods to Assess Quality and Stability of Oils and Fat Containing Foods

13. Pros and Cons of Oxygen Bomb method Pros • An accurate tool for measuring the oxidative stability of diverse materials (from pure fats to finished products) • About 2-10 times faster than the AOM test • Good correlation with shelf-life and other oxidative tests Cons • Special attention may be required for maintaining temperature and oxygen pressure Warner et al., (1995). Methods to Assess Quality and Stability of Oils and Fat Containing Foods

14. Bottleneck with methods that utilize high temperatures as accelerators • A major disadvantage of OSI,OB,AOM is the use of high temperatures as initiators and accelerators of oxidation • The reaction mechanism of oxidation typically changes at high temperatures (different activation energy) • Certain properties of the food product can change be altered at high temperatures (eg. Aw) • A clear correlation between tests at high temperatures and actual shelf life is controversial. Dyck et al., (2005). Free Radical Generating Assays; Warner et al., (1995). Methods to Assess Quality and Stability of Oils and Fat Containing Foods

15. Bottleneck with methods that utilize high temperatures as accelerators Dyck et al., (2005). Free Radical Generating Assays

16. Free radical generating assays • Free radical generating assays combine lipid oxidation initiators (diazo initiators such as 2.4-dimethylvaleonitrile, isobutyronitrile, 2,4-methylbutyronitrile) with OSI and OB methods at low temperatures (35-600C) • The azo compounds generate the free radicals for oxidation • This method is thus more closely related to the natural oxidation process and improves the correlation between the accelerated screening of food products and real shelf life of food products. Dyck et al., (2005). Free Radical Generating Assays

17. Conclusions • Accelerated oxidation studies which utilize high temperatures as initiators and accelerators of oxidation do not model well the natural process of oxidation • Use of free radical generation assays have a potential of producing a better model of natural oxidation, as well as stronger correlation with actual food product shelf life

18. Questions?