The introduction of new processing techniques is increasing the amounts of proteins and polypeptides in edible oils. The purpose of this project is to develop specific analytical methodologies to characterise proteins in oils (chiral amino acid analysis and protein mass-spectrometry); none currently exist. Published protein contents vary widely, depending on the type and source of the oil and analytical strategy (Fig 1). When more sophisticated (HPLC based) analysis is used yields are significantly higher than was previously supposed, even in refined oils[i].
The disparity in studies attests to the need for improved protein quantitation. However an even greater need is protein identification. Proteins should enhance oil stability due to their anti-oxidant properties[ii], but Hidalgo et al.,[iii] observed a negative correlation between stability and protein content. Lipoxygenase and polyphenol oxidase catalytic activity has been reported[iv], the former are in part responsible for differences in the aroma of in different cultivars of extra virgin olive oil[v].
Refining-resistant proteins are selectively enriched during production of both peanut and soya oils and are responsible for many IgE-mediated food allergies. The increased concentration proteins as a result of modern oil processing may enhance allergenicity[vi],[vii],[viii]. Polypeptides (4.6kDa) derived from the mesocarp of olive drupes are reported been reported to persist even in refined oils[ix].
Mass-spectrometric techniques will be developed to identify peptides from oil. These peptides may prove to be useful markers of authentication or adulteration. Transformations of these proteins may occur as a result of refining, long-term storage or processing in complex food matrixes thereby providing further clues to sample history. Robust, persistent peptides may also prove useful in unravelling the archaeology of ancient oil production and distribution.
The is a joint project with Food Safety and Quality, Central Science Laboratory
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[i] Hidalgo, F. J., Alaiz, M., & Zamora, R. (2001). Determination of peptides and proteins in fats and oils. Analytical Chemistry, 73, 698–702.
[ii] Pokorny, J., Yanishlieva, N., & Gordon, M. (2001). Antioxidants in food: Practical applications. Cambridge, UK: Woodhead Publishing.
[iii] Hidalgo, F. J., Alaiz, M., & Zamora, R. (2002). Low molecular weight polypeptides in virgin and refined olive oils. Journal of the American Oil Chemists’ Society, 79, 685–689.
[iv] Georgalaki, M. D., Sotiroudis, T. G., & Xenakis, A. (1998). The presence of oxidizing enzyme activities in virgin olive oil. Journal of the American Oil Chemists’ Society, 75, 155–159.
[v] Ridolfi, M., Terenzani, S., Patumi, M. & Fontanazza G. (2002). Characterization of the Lipoxygenases in Some Olive Cultivars and Determination of Their Role in Volatile Compounds Formation. J. Agric. Food Chem. 50, 835-839.
[vi] Besler, M., Steinhart, H., & Paschke, A. (2001). Stability of food allergens and allergenicity of processed foods. Journal of Chromatography B, Biomedical Sciences and Applications, 756, 207–228.
[vii] Crevel, R. W. R., Kerkhoff, M. A. T., & Koning, M. M. G. (2000). Allergenicity of refined vegetable oils. Food and Chemical Toxicology, 38, 385–393.
[viii] Hefle, S. L., & Taylor, S. L. (1999). Allergenicity of edible oils. Food Technology, 53, 62–70.
[ix] Zamora, R., Alaiz, M., & Hidalgo, F. J. (2001). Influence of cultivar and fruit ripening on olive (Olea europaea) fruit content, composition, and antioxidant activity. Journal of Agricultural and Food Chemistry, 49, 4267–4270.
