The study, published in LWT - Food Science and Technology, measured the oxidative stability of whole grain bread by monitoring levels of antioxidants, oxidation products, and using a sensory analysis. The researchers found that small, but significant changes occur in bread during storage, that may lead to the development of off flavours and odours – and that these changes may be avoidable through a reduction in or prevention of lipid oxidation.
“The ability to delay or even prevent lipid oxidation in bread with extended shelf life would entail an improvement in flavour stability and an enhancement in consumer satisfaction,” wrote the researchers, led by Sidsel Jensen a PhD student at the University of Copenhagen and Aarhus University, Denmark.
“Moreover a product with a higher oxidative stability could contribute to a reduction in the amount of bread returns.
“Use of antioxidants constitute possible strategies for postponing lipid oxidation and reduce flavour deteriorations that ought to be explored,” they added.
Volatile compounds
The oxidation of unsaturated fatty acids yields a complex mixture of volatile compounds that significantly affects sensory properties of foods even when present in low quantities.
Previous research has shown such compounds lead to changes in aroma, flavour and taste occur during storage of whole wheat bread. Specific changes include the development of aroma and flavour attributes such as ‘acidic’, ‘off’, ‘rancid’ and ‘dust’, together with the taste attributes ‘sweet’ and ‘bitter’.
The stability of whole wheat flour and bread is affected by the balance between lipid composition and the presence of different antioxidants.
The researchers stated that the characterisation of early oxidative changes occurring during storage should be valuable for the understanding of quality changes for such products, and may provide a tool for shelf life prediction of bread products.
However, they noted that a thorough study of the oxidative stability of bread during extended storage has, until now, not been reported.
Oxidative changes
The researchers reported that oxidative changes occur in both crumb and crust during extended storage.
The oxidative changes in the whole wheat bread were found to be relatively minor, however were significant enough to cause changes to flavour and odour, with attributes characterising the stored bread reported as ‘aged’, ‘dusty’, ‘rancid’, ‘sickly sweet’, and ‘bitter’.
The content of lipid hydroperoxides – a primary oxidation product – was found to be significantly higher in stored bread crumb compared to bread crust, and reached a maximum peak after 2-3 weeks of storage.
Subsequently, the researchers found a decrease in lipid hydroperoxides after 4 and 5 weeks of storage, which they said indicates that the formation of secondary oxidation products was larger than the production of primary oxidation products.
“Bread can be regarded as a product with a relatively high oxidative stability. Despite the high stability the present study clearly showed that oxidative changes occurred in both crumb and crust of whole wheat bread as a consequence of extended storage at room temperature,” wrote Jensen and co-workers.
“A decrease in the anti-oxidative capacity as a consequence of storage reflects a progress in the oxidative reactions depleting antioxidants … [The] quality of bread with extended shelf life may accordingly be improved by minimising oxidation,” they added.
Source: LWT - Food Science and Technology
Published online ahead of print, doi: 10.1016/j.lwt.2010.10.011
“Oxidative stability of whole wheat bread during storage”
Authors: S. Jensen, H. Oestdal, M.R. Clausen, M.L. Andersen, L.H. Skibsted