Ingredients, foods and supplements can undergo deteriorative changes during their shelf life that can impact on their chemical, sensory and nutritional properties (texture, appearance, flavour, nutritional value, beneficial oxidation of oils and fats has a critical influence on ingredients and finished products. However, there are several strategies available to improve stability, as Dr Robert Griffiths, Technical Specialist at RSSL, explains health effects).
The factors that can cause these changes are varied and include moisture loss/gain, fat degradation or migration, alterations in colour, and reactions such as hydrolysis and oxidation that impact flavour compounds.
Often products are considered unacceptable and rejected by consumers due to changes in flavour, with one of the most pronounced effects being the generation of rancid off-flavours/notes caused by the oxidation of oils and fats (and other food components). This chemical decomposition can result in the product being unpalatable. It must also be remembered, however, that some of these flavours caused by degradation of fats can be desirable in products such as aged cheese.
Oxidation of fats or oils is a complex process initiated by free radical reactions at the double bonds of unsaturated fatty acids. Therefore, the greater the number of double bonds or degree of unsaturation of the fatty acids, the greater the susceptibility to oxidation. The process of oxidation is affected by many factors including atmospheric oxygen, heat, heavy metals, exposure to light, and other chemical components that promote initiation of the oxidation process.
These factors can promote the formation of free radicals which lead to the formation of peroxide radicals, hydroperoxides and subsequent chain reactions leading to the formation of secondary oxidation products, including aldehydes and ketones. It is these secondary oxidation products that often produce the distinctive and generally undesirable rancid off flavours/notes, and the accumulation of these components over time increases the likelihood of the product being rejected.
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