Oxidation 101

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Editor: Dr Matt Miller www.plantandfood.com Oxidation of food grade oils What is oil oxidation? Oil oxidation is an undesirable series of chemical reactions involving oxygen that degrades the quality of an oil. Oxidation eventually produces rancidity in oil, with accompanying off flavours and smells. All oil is in a state of oxidation - you cannot stop it completely - but there are ways to reduce it. Attempts should therefore be made to reduce oxidation at each stage of oil manufacture. Oxidat
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  www.plantandood.com What is oil oxidation? Oil oxidation is an undesirable series o chemical reactionsinvolving oxygen that degrades the quality o an oil. Oxidationeventually produces rancidity in oil, with accompanying oavours and smells. All oil is in a state o oxidation - you cannotstop it completely - but there are ways to reduce it. Attemptsshould thereore be made to reduce oxidation at each stage ooil manuacture.Oxidation is not one single reaction, but a complex series oreactions. When oil oxidises it produces a series o breakdownproducts in stages, starting with primary oxidation products(peroxides, dienes, ree atty acids), then secondary products(carbonyls, aldehydes, trienes) and fnally tertiary products.Oxidation progresses at dierent rates depending on actorssuch as temperature, light, availability o oxygen, and thepresence o moisture and metals (such as iron). The type ooil also inuences the rate o oxidation. Marine oils (includingfsh, mussel) are highly susceptible to oxidation due to the largenumber o polyunsaturated atty acids (PUFA) they contain.These unsaturated atty acids have reactive double bondsbetween their carbon atoms, whereas saturated ats have nodouble bonds so they oxidise more slowly. How do we measure oxidation? Measuring oxidation involves testing or the primary andsecondary breakdown products. The most common test isperoxide value (PV). However, very rancid oils can have areduced PV thereore the anisidine value (AV) and a Totox valueare used to show the whole oxidation story (see Figure 1). Othermeasurements o oxidation are the acid value (ree atty acidFFA), thiobarbituric acid value (TBA) and iodine value (IV). Headspace volatiles (smell) can also be tested using artifcial nosetechnologies. Peroxide value (PV) Primary oxidation processes in oil mainly orm hydroperoxides,which are measured by the PV. In general, the lower the PV, thebetter the quality o the oil. However PV decreases as secondaryoxidation products appear (Figure 1). Most customers willrequire a PV o less than 10 in marine oils, but PV may need tobe as low as 2, depending on the market. Oxidation oood grade oils Editor: Dr Matt Miller The PV test is a good way to measure the amount o primaryoxidation products in resh oils. Oils with signifcant levels operoxides may still be odourless i secondary oxidation has notbegun. I oxidation is more advanced, the PV may be relativelylow but the oil will be obviously rancid. Anisidine value (AV) The secondary stage o oxidation occurs when the hydro-peroxides decompose to orm carbonyls and other compounds,in particular aldehydes. These are what gives the oil a rancidsmell, and they are measured by the AV. The lower the AV, thebetter the quality o the oil. Most customers will require an AVo less than 30 in marine oils but AV may need to be as low as10, depending on the market.The AV test is a good way to measure secondary oxidation productsand should be used together with a primary test like PV. Totox value The Totox value is calculated by the ormula AV + 2PV to indicatean oil’s overall oxidation state. The lower the Totox value, thebetter the quality o oil. Figure 1 : The oxidation o oil over time as measured by peroxide value(PV), anisidine value (AV) and Totox value. Note: PV can decrease overtime so AV and/or Totox calculation is needed to appreciate the wholeoxidation story. PV AV Totox Time  2 FURTHER INFORMATION // Dr Matt Miller Plant & Food Research300 Wakefeld QuayPort NelsonNelson 7010, New Zealandtel: +64-3-539 1833ax: +64-3-356 7049 millerm@crop.cri.nz Acid value The acid value (which is twice the ree atty acid (FFA) value)measures how many atty acids (a component o oil) are cleavedrom their parent molecules (triglycerides or phospholipids).Cleavage o a ree atty acid rom a parent molecule showshydrolytic breakdown and is oten used in whole biologicalsystems as an indication o stress. The test reveals enzymaticactivity due to microorganisms in the raw material. Thiobarbituric acid (TBA) value The TBA value is a method to investigate secondary oxidativealdehyde products, usually in PUFA. The TBA test is unsuitableor complex ood and biological systems. The test is not specifcand can interact with other non-oil minor components (DNA,sugars). Iodine value (IV) The IV (“iodine adsorption value” or “iodine number” or “iodineindex”) measures the number o reactive double bonds presentin an oil. A higher IV number indicates more double bonds inthe sample and thereore that greater care will be needed toslow down oxidation. IV can range rom 10 or coconut oil, 94-120 or rapeseed oil, and 117-143 or soybean oil, up to 185 orfsh oil. IV is not a measure o quality but is an indicator o oilcomposition. Preventing oxidation Several dierent actors can be controlled to reduce the amounto oxidation that occurs in your oil. These include: Temperature - the number one contributing actor o oxidationin oil. I possible reduce the temperature to the lowest possiblethroughout processing, shipping and manuacture. Oxygen exposure (in the air) will be a catalyst or productiono ree radicals. To reduce oxidation, seal all containers withthe smallest possible headspace, reduce the area o the oilin contact with air and/or cover the oil with an inert gas (likenitrogen) at all possible points. Light (UV) can trigger the oxidative degenerative cascade.Reduce the exposure o the oil to direct light by using brownglass/plastic containers or black plastic bags. Moisture in combination with these other actors can accelerateoxidation. I possible limit the amount o water in the oil to lessthan 0.2%. Transition metals , in particular transition metals like iron andcopper, can act as pro-oxidants. I possible, you may need tochange equipment (e.g. no brass valves), limit time in contactwith and/or remove transition metals rom the oil to reduceoxidation. Antioxidants (AOX) terminate the oxidation chain reactions andinhibit other oxidation reactions by being oxidised themselves.AOX do not stop oxidation, but do slow down the rate at whichoxidation occurs.There are many dierent ways AOX can reduce oxidation, so it isimportant to choose the right AOX or your application/product.AOX can be synthetic or extracted rom natural plant sources.Common AOX are: ã Tocopherols (vitamin E) ã Carotenoids β -carotene ã SyntheticBHT- butylated hydroxytolueneBHA - butylated hydroxyanisoleTBHQ - tert-ButylhydroquinonePropyl gallateEthoxyquin ã Natural extractsFlavonoidsRosemary and spice extractsTea catechinsSeaweed ã Phospholipids ã Retinol (vitamin A) ã Preventive AOXCitric acid, phosphoric acid, ascorbic acid (vitamin C),ethylene diamine tetraacetic acid (EDTA), uric acid
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