Effect of Cyclolinopeptides on the Oxidative Stability of Flaxseed Oil

January 1, 2014 Human Health and Nutrition Data 0 Comments

Effect of Cyclolinopeptides on the Oxidative Stability of Flaxseed Oil

Year: 2014
Authors: Sharav, O. Shim, Y.Y. Okinyo-Owiti, D.P Sammynaiken, R. Reaney, M.J.T.
Publication Name: J. Agric. Food Chem.
Publication Details: Volume 62; Pages 88 – 96


Polar compounds present in flaxseed oil increase its oxidative stability. Flaxseed oil becomes less stable to oxidation when filtered with silica. This observation may be linked to antioxidant compounds present in flaxseed oil. Flaxseed oil was passed over a silica adsorbent column to remove polar compounds. The polar compounds were then eluted from the silica absorbant using a series of increasingly polar solvents. The polar fractions from flaxseed oil were then added back to silica treated flaxseed oil to determine the impact of fractions containing polar compounds on oxidative stability (induction time) at 100  degrees C. A polar fraction containing mainly cyclolinopeptide A (CLA, 1), but also containing beta, gamma and delta tocopherol increased the induction time of silica-treated flaxseed oil from 2.36  plus and minus  0.28 to 3.20  plus and minus  0.41 h. When oxidative stability was determined immediately after addition of the polar fractions other flaxseed fractions and solvent controls did not affect oil stability. However, when the oxidative stability index (OSI) test was delayed for three days and oil samples were held at room temperature after the addition of the polar fractions to the flaxseed oil, it was observed that the control oil treated with silica had become highly sensitive to oxidation. A polar fraction containing a mixture of CLs, improved the oxidative stability of peptide free oil with respect to the control when the OSI measurement was made three days after adding the fraction. In addition, effects of 1 on the oxidative stability of peptide free oil containing divalent metal cations was investigated.
Despite its distinctive unstable oil content, flaxseed produces antioxidants that protect the meal in storage.  Flaxseed contains several known bioactive compounds, including lignans, phenolic acids, anthocyanin pigments, flavonols, flavones, and phytic acid, all of which may contribute to the seed’s antioxidant capacity.  The concentration of these antioxidants in flaxseed oil depends on the extraction procedure and the treatment of the oil. Moreover, refining may also reduce minor compounds that have an effect on oil shelf life. The unrefined oil may have higher nutritional value and longer shelf life than refined flaxseed oil. On the other hand, coldpressing procedures do not involve heat or chemical treatments and the oil is extracted under mild conditions.  It has been reported several antioxidant compounds in cold pressed flaxseed oil, including flavonoids, phenolic acids tocopherols and plastochromanol. It is possible that other minor oil soluble compounds play a role in slowing the oxidation of flaxseed oil.  Cyclolinopeptides (CLs) are hydrophobic compounds present in flaxseed oil with polarity comparable to known natural antioxidants, but the antioxidant activity of these compounds has not been studied. The purpose of this study was to isolate polar fractions present in flaxseed oil, including CLs, to determine if these fractions increased the oxidative stability of flaxseed oil that has been treated to remove polar compounds. The effect of CL containing fractions obtained from crude flaxseed oil were tested for their effects on the oxidative stability of peptide free flaxseed oil. Subsequently the effects of enriched CLs on the oxidative stability of flaxseed oil in the presence of metal cations were determined.  Crude flaxseed oil had higher oxidative stability than silica-treated flaxseed oil, indicating that some of the chemical constituents that were removed by silica gel play a significant role in reducing the rate of flaxseed oil oxidation.
 According to the study, cold-pressed flaxseed oil purchased in New Zealand, including locally produced and imported oil, contained 76.8 to 307.3 mg/100 g phenolic acid, 12.7 to 25.6mg/100 g flavonoids, 3.4 to 5.5 mg/100 g plastochromanol8, and 11.1 to 24.5 mg/100 g tocopherols. In addition, cold-pressed flaxseed oil may contain up to 150 mg/100 g CLs.  Therefore, reduced oxidative stability observed with silica treatment may be related to the removal of any or all of these polar compounds. This study revealed that the antioxidant activity of the fractions increased with the polarity of the solvent used to elute that fraction from the silica. Phenolic compounds are also reported in fractions exhibiting the strongest antioxidant activity.
Fractions containing 1 and tocopherols (fraction D), and a mixture of CLs (fraction E), improved the oxidative stability of peptide free oil, suggesting the significant role played by these compounds in protecting oil from oxidation.  CLs have their own role in the strong antioxidant system of flaxseed oil. They may behave as antioxidants or pro oxidants depending on concentration and environment. Dose- and time dependent antioxidant properties of these peptides were observed. CL 1 is able to interact with metals selectively. (Editors comments)

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