Synthesis of conjugated linoleic acid by microwave-assisted alkali isomerization using propylene glycol as solvent

卷:119

Sonia Silva-Ramirez, Ana ; Rocha-Uribe, Alejandro ; Martin Gonzalez-Chavez, Marco ; Gonzalez, Carmen

Univ Autonoma San Luis Potosi

关键词: Alkali isomerization;    Conjugated linoleic acid;    Microwave irradiation;    Propylene glycol;    Synthesis;   

DOI  :  10.1002/ejlt.201600079

学科分类：食品科学和技术

【 摘 要 】

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 (cis9, trans11-CLA and trans10, cis12-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 degrees 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 cis9, trans11-CLA and trans10, cis12-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 degrees 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 cis9, trans11-CLA and trans10, cis12-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.