Occurrence of Conjugated Linolenic Acids in Purified Soybean Oil

Abstract

A high performance liquid chromatographic (HPLC) method is described for the determination of conjugated linoleic acids (CLA) and conjugated linolenic acids (CLN). Methyl esters prepared from purified lipid fractions of soybean oil were analyzed using HPLC system equipped with photodiode-array detector to detect peaks having maximum absorption around 233 nm and 275 nm. These peaks were concentrated by AgNO 3 -silicic acid column chromatography and reversed-phase HPLC.The structural analysis, of dimethyloxazoline (DMOX) derivatized methyl esters, using GC-MS showed the occurrence of 9,11-and 10,12-conjugated linoleic acids (CLA) and 8,10,13-, 8,10,12-and 9,11,13-conjugated linolenic acids (CLN). The comparison of these conjugated fatty acids with authentic isomers by HPLC revealed the presence of isomeric mixtures of CLA (cis(c),trans(t) or t,c and t,t) and CLN (c,t,t or t,t,c and t,t,t).Traces of 9,11-and 10,12-CLA (c,t or t,c) was found in crude oil. CLN isomers (8,10,12-18:3 and 9,11,13-18:3) were found to be forming during bleaching of soybean oil processing. 8,10,13-CLN and 9,11-and 10,12-CLA (t,t) were only found in soybean oil after deodrization step. CLN contents in commercial soybean oil varied from 387 mg/kg oil to 1316 mg/kg oil. Decreased level of bleaching earth and temperature resulted in reduced CLN content. Possibly, CLN would be derived from linoleate hydroperoxides formed during processing and storage of soybean oil.KEY WORDS: HPLC, CLA, CLN, soybean oil, lipid oxidation. 2Conjugated fatty acids have evoked increased interest due to the beneficial effects they afford in terms of human health. Among them, conjugated linoleic acid (CLA) has been researched and reviewed extensively in relation to its occurrence (1), metabolism and physiological effects (1-4). On the other hand, several researchers have reported the occurrence of various conjugated fatty acids including trienes, tetraenes and pentaenes in different plant resources from both terrestrial and aquatic enviroments.Conjugated linolenic acids (CLN) have been reported to occur in terrestrial plant lipids, especially seed oils. Important CLN from plant sources include α-eleostearic acid (9cis(c),11trans(t),13t-18:3), catalpic acid (9t,11t,13c-18:3), punicic acid (9c,11t,13c-18:3), calendic acid (8t,10t,12c-18:3) and jacaric acid (8c,10t,12c-18:3) (5).On another hand, Yurawecz et al. (6) only could find traces (up to 0.2%) of CLN in vegetable oils in their study of 27 oils for CLN content by UV measurement. The isomers were identified as α-eleostearic acid (9c,11t,13t-18:3), β-eleostearic acid (9t,11t,13t-18:3), and 8t,10t,12t-18:3. The possible mechanism for the formation of these CLN isomers involves linoleate oxidation, reduction of hydroperoxide to hydroxide, and dehydration (7,8). CLN exhibits less oxidative stability as reported by our previous study (9), indicating that CLN may influence oxidative deterioration of vegetable oils, in spite of being present in trace.Crude oil is refined by a series of processes to remove impu...

Characterization of constituents, quality and stability of pomegranate seed oil (Punica granatum L.)

“…Stability of CLnA geometric isomers in each group was also found to be dependent on the position of the three conjugated double bonds. The presence of CLnAs can contribute to oxidative deterioration of vegetable oils (Kinami et al, 2007). However, PSD met all standards of quality, and most of the indices evaluated were below those of soybean oil, rich in unconjugated fatty acids, reported by Kinami et al (2007).…”

Chromatographic analyses of fatty acid methyl esters by HPLC-UV and GC-FID

“…These trans isomers of 18:3 and 18:2 may be formed in their refinement during the oil separation process involving heating or isomerization in the course of the hydrogenation reactions. 23 The calibration curve for each fatty acid ester is described in Table 2 and Figure 3. Table 2 reports the parameters a, b, r 2 and s y of the calibration curves, range of concentration and retention time.…”

Chemical and physiological aspects of isomers of conjugated fatty acids

“…This result was expected since the PA and the LNA have greater degree of unsaturation in their structure which makes them more susceptible to oxidation (MELO et al, 2010). These results indicated that CLNAs may influence the oxidative deterioration of vegetable oils despite their presence (KINAMI et al, 2007).…”

“…Like CLAs, CLNAs can be also formed during the processing of vegetable oils as a result of the isomerization or dehydration of secondary oxidation products of LA and LNA (KINAMI et al, 2007;CAO et al, 2009;YANG et al, 2009). Although alkaline isomerization is effective for mass-production of CLNAs, identification of the detailed profiles of the synthetic CLNAs is difficult because the resultant mixture is composed of many different CLNA isomers.…”

“…The three double bonds present in CLNAs are primarily in positions Δ9,11,13 and Δ8,10,12 and exist in both cis and trans geometrical isomer forms (SASSANO et al, 2009). CLNAs have been reported to occur in terrestrial plant lipids, especially seed oils (KINAMI et al, 2007), present in high amounts accounting for 40-80% of total fatty acids (YANG et al, 2005;ARAO et al, 2004b). Five CLNA isomers occur as components of major seed oils of several plants: α-eleostearic acid cis9,trans11,, punicic acid (PA,cis9,trans11,calendic acid (trans8,trans10,jacaric acid (cis8,trans10,, and catalpic acid (trans9, trans11, cis13-18:3) (IWABUCHI; KOHNO-MURASE; IMAMURA, 2003; further studies are needed to provide a clearer understanding of this mechanism of CLNAs metabolism (YUAN, G. F.; YUAN, J. Q.; LI, 2009).…”