Squalene oxidation products: Monitoring the formation, characterisation and pro‐oxidant activity

Abstract

Squalene (SQ), a precursor of sterols and terpenoids is a functional lipid of high importance in the food and pharmaceutical sectors. SQ oxidation studies are rather limited compared with those for other olefins. The aim of the present study was to monitor the formation of SQ oxidation products under different conditions (temperature, air supply), to characterise the most abundant of them by spectroscopic techniques and then examine their pro-oxidant activity in a model lipid substrate. Squalane (SQA), the saturated analogue of SQ, was used as a reference compound. FT-MIR analysis indicated the presence of alcohols, epoxides, aldehydes, and ketones. GC-MS was used to characterise SQ primary oxidation and scission products. The presence of epoxides was further confirmed by means of 1 H NMR and 13 C NMR spectroscopy. It could be argued that SQ stability is due to its stereochemistry and specifically to the presence of methyl groups next to the double bonds. The pro-oxidant activity of SQ oxidation products was evident at 62 and 40°C and suppressed only in the presence of primary antioxidants, not of SQ. The present work adds to the characterisation of SQ oxidised products. To our knowledge their pro-oxidant activity has never been examined before.Practical applications: Characterisation of squalene oxidation products and assessment of their activity as pro-oxidants present both scientific interest regarding the kinetics and product identity as well as a practical impact in case this bioactive lipid is provided for consumption as a functional product. In the past, cholesterol oxidation products and more recently phytosterol ones attracted the interest of researchers, who studied the stability of the respective parent compounds for food safety reasons.

Plant Sources, Extraction Methods, and Uses of Squalene

“…After 80 years, with advanced techniques ( 1 H·NMR and 13 C·NMR), it was found that oxidation mechanisms and chemical structures of epoxy and alcohol are formed after a prolonged oxidation to 55-150°C [14][15][16][17].…”

“…Naziri et al [17] studied squalene oxidation at di erent temperatures and air conditions, nding the formation of epoxy with prooxidant activity in the oil at 40°C and 62°C. On the other hand, Psomiadou and Tsimidou [18] reported the antioxidant e ect of SQ in olive oil, where the antioxidant activity was weak in presence of other fatty acids, possibly due to a competitive oxidation between the same lipids of the extract.…”

“…Finally, two molecules of farnesyldiphosphate are reduced via enzymatic reaction to form the SQ which continues its path to the biosynthesis of phytosterols [1,10,22,29]. Phytosterols are the products of cascade cyclization of SQ; these mechanisms are activated from ionic species by deprotonation, hydration (Figure 4), or from oxidesqualene activated by the action of triterpene enzymes such as squalene cyclase (SQs) and oxide-squalene cyclase (OSQ) [17,30].…”

Effects of oil-droplet diameter on the stability of squalene oil in spray-dried powder

“…Yeo and Shibamoto [36] reported that squalene undergoes photooxidation to produce malonaldehyde, formaldehyde, acetone, and acetaldehyde. Naziri et al [37] investigated squalene oxidation compounds. Squalene is a suitable model compound to investigate the oxidation stability of emulsified fish oil in spray-dried powder because squalene can be analyzed using gas chromatography.…”

Advantages of supercritical fluid extraction for recovery of squalene from wine lees

“…Considering that these products, mainly hydroxy-and epoxy-derivatives of SQ and aldehydes (e.g. and b-citral, farnesal, farnesyl acetaldehyde, 4,9,13,17-tetra-11 methyl -4,8,12,16- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 14 expected to have a pro-oxidant activity in the lipid extract [38], a more oxidative stable extract is obtained via SCCO 2 . When complete separation of SQ from other glyceride and non-glyceride components is required, post-extraction fractionation is a prerequisite [32].…”