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Synthesis of conjugated linoleic acid by microwave‐assisted alkali isomerization using propylene glycol as solvent
Author(s) -
SilvaRamírez Ana Sonia,
RochaUribe Alejandro,
GonzálezChávez Marco Martín,
González Carmen
Publication year - 2017
Publication title -
european journal of lipid science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.614
H-Index - 94
eISSN - 1438-9312
pISSN - 1438-7697
DOI - 10.1002/ejlt.201600079
Subject(s) - conjugated linoleic acid , isomerization , chemistry , catalysis , conjugated system , solvent , organic chemistry , linoleic acid , nuclear chemistry , fatty acid , polymer
Conjugated linoleic acid (CLA) is a group of isomers of linoleic acid (LA) with a conjugated double‐bond system that occurs in trace amounts in natural oils. As result of the beneficial properties on the health, bioactive isomers of CLA ( cis 9, trans 11‐CLA and trans 10, cis 12‐CLA) have been industrially produced by alkali isomerization of LA. A large amount of studies regarding the CLA production might be found; however, new approaches as the use of microwave irradiation have been recently suggested. Here, we develop an efficient and sustainable method to selectively produce bioactive CLA by microwave‐assisted isomerization of LA using propylene glycol as solvent. The investigated reaction variables were solvent/LA mass ratio (1:1–6:1), catalyst/LA mass ratio (0.25:1–0.6:1), temperature (160–180°C), catalyst type (KOH or NaOH), and reaction time. The results showed that: (i) KOH increased the production of conjugated trans ‐ trans isomers; (ii) a considerable reduction of propylene glycol on the reaction was possible using NaOH; and (iii) the reaction time was drastically reduced in comparison to conventional heating. Thus, the optimum conditions for the cis 9, trans 11‐CLA and trans 10, cis 12‐CLA production (91.21% in equimolar ratio) were: NaOH at a catalyst/LA mass ratio of 0.5:1 and solvent/LA mass ratio of 1:1 at 160°C during 4 min. Practical applications: CLA has been subject of growing interest in nutrition and the food industry due to its wide range of biological activities including anti‐carcinogenic and anti‐atherogenic properties. Here, the chemical synthesis of CLA by microwave‐assisted alkali isomerization was studied in order to lower the production costs by decreasing both, the propylene glycol content (the most expensive solvent used for this kind of reaction) and the reaction time. In comparison to conventional heating, reaction time was drastically reduced by employing microwave heating while the selective synthesis of cis 9, trans 11‐CLA and trans 10, cis 12‐CLA was achieved at low solvent conditions when the reaction conditions were optimized. In this sense, the methodology developed in this work could be used in order to obtain more efficiently and sustainably the bioactive forms of CLA, which in turn could be used in the manufacture of functional foods or dietary supplements. cis 9, trans 11‐CLA and trans 10, cis 12‐CLA were selectively synthetized through basic catalysis of linoleic acid in propylene glycol under microwave irradiation.