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Food and Nutrition Sciences, 2017, 8, 658-677

http://www.scirp.org/journal/fns

ISSN Online: 2157-9458

ISSN Print: 2157-944X

DOI: 10.4236/fns.2017.86047

June 28, 2017

Response Surface Optimization of a Solvent

Free Production of cis-9, trans-11 and trans-10,

cis-12 Isomers of Conjugated Linoleic Acid

Using High Linoleic Sunflower Oil

Sara Koohikamali

1,2

Department of Food Science and Technology, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran

Young Researchers Club, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran

Abstract

The most dominant and beneficial conjugated linoleic

acids isomers (CLAs)

with miscellaneous biological tasks are 9c11t-C18:2 and 10t12c-

C18:2. The

problem with most of the commercial CLA produced by non-optimized co

ventional approaches is the heterogeneity of their isomers and undesirable

toxic by-products

. In this study, optimization of the isomerization of the fatty

acid methyl esters of the high linoleic sunflower oil was investigated through

response surface methodology (RSM). The reaction temperature, the conce

tration of PEG400 and NaOCH

had positive

influence on the total conjugated

linoleic acid methyl esters (CLAME) production as response. However, the

effect of the polyethylene glycol 400 (PEG400) concentration was more signi

ficant on response than those of other factors (p < 0.05). The reaction

time

and the interactions between the factors had no significant effect on response

(p ≥ 0.05). The optimum point for the maximum response of 72.90% (

i.e

based on the mass percentage of total fatty acid

methyl esters mixture) was at

5% w/w NaOCH

, 1.06% w/w PEG400 and temperature of 140˚C.

Keywords

CLA Methyl Esters, Isomerization, Commercial CLA, RSM, Phase

Transfer Catalyst, PEG400

1. Introduction

Conjugated linoleic acid (CLA) has been found to be an extraordinary essential

fatty acid with miscellaneous functional effects on the human body. The most

beneficial CLA isomers participate with biological performance are 9c11t-C18:2

How to cite this paper:

Koohikamali, S.

(201

Response Surface Optimization of a

Solvent Free Production of

cis

-9,

trans

-11

and

trans

-10,

cis

-12

Isomers of Conjugated

Linoleic Acid Using High Linoleic Su

flower Oil

Food and Nutrition Sciences

658

-677.

https:

//doi.org/10.4236/fns.2017.86047

Received:

May 9, 2017

Accepted:

June 25, 2017

Published:

June 28, 2017

7 by author and

Scientific

Research Publishing Inc.

This work is licensed under the Creative

Commons Attribution International

License (CC BY

4.0).

http://creativecommons.org/licenses/by/4.0/

Open Access

S. Koohikamali

659

and 10t12c-C18:2 [1] [2].

Despite CLA exists at levels of 0.3% - 0.8% (w/w) of the fat in beef and dairy

products of the ruminants, this negligible level cannot provide the recommen-

ded 3 - 3.4 g of CLA per day that is necessary to produce the desired physiologi-

cal effects [1]. Furthermore, the high consumption of such natural resources is

not recommended due to intake of undesirable amounts of saturated fats and

cholesterol. For this reason, an alternative source that contains high amounts of

CLA that is low in saturated fat and cholesterol would be recommended for the

human diet [3]. CLA commercialization has been highly studied through various

methods and with regard to CLA insufficient daily intake by the natural source.

The most common way to produce CLA is base-catalyzed isomerization [4] [5].

However, the severe conditions (e.g., high temperature, solvents and large

amount of alkalis) which are usually required for the routine isomerization were

to lead to the formation of unwanted trans isomers, polymerization and cycliza-

tion reactions and thus, the reduction of theoretically expected yield [6].

In order to produce commercial CLA with less unwanted isomers, Abney and

Anderson (2002) applied linoleic acid methyl esters (LAMEs) as the substrate of

isomerization which was found to result in the production of a high yield of

conjugated linoleic acid methyl esters (CLAMEs). They proposed the isomeriza-

tion of LAMEs by using negligible amounts of alkali catalyst, at a low tempera-

ture and in the presence of phase transfer catalyst (PTC) instead of solvents.

Their technique resulted in increasing the degree of the isomerization from 6%

without PTC to 90% [4]. Despite this improvement, its limitation is that it was

based on the traditional 1-factor-at-a-time approach; and thus, time-consuming

and also the fact that it was almost impossible to achieve real optimal condition.

Furthermore, it has been demonstrated that the results of one-factor-at-a-time

experiments, often ignore the interactions between factors that are present con-

currently [7]. In this research, high linoleic sunflower oil which contains more

than 65% linoleic acid (LA), a fatty acid with the potential to be isomerized to

CLA, and could therefore be utilized to produce CLA-rich oil was applied as the

isomerization substrate. A detailed study is conducted on the optimization of the

isomerization using response surface methodology (RSM) with the aim of im-

proving the degree of isomerization and thus the process yield compared to pre-

vious researches.

2. Experimental Procedure

2.1. Materials

High linoleic sunflower oil (>65% linoleic acid) fatty acid methyl esters (FAMEs)

were prepared as described previously [8]. PEG400, NaOCH

, H

(85%;

w/w), urea, the standard mixture of 37 fatty acid methyl esters (external stan-

dard, dissolved in hexane), CLA methyl ester standard mixture

cis

-9,

trans

-11

and

trans

-10,

cis

-12 isomers (>98% pure), methyl-heptadecanoate (17:0, internal

standard) and micro-membrane syringe filters and Whatman No.2 qualitative

filter papers (Whatman Intl. Limited, Kent, UK) were purchased from Sigma

S. Koohikamali

660

Chemical Co. (St. Louis, MO, USA). Methanol, ethanol, n-hexane (GC grade),

isooctane (GC grade), HCl (6 N), NaOH, anhydrous sodium sulfate and other

chemicals were obtained from Fisher Scientific (Pittsburgh, PA, USA).

2.2. Methods

2.2.1. Experimental Procedure

The first phase of the experiments was the optimization of the isomerization or

conversion of LAMEs from sunflower oil into CLAMEs. The second stage in-

volves the production of enriched CLA via four sequential steps including the

saponification, hydrolysis, phase separation and purification through the two-

step urea inclusion crystallization. All stages were performed using a 2 litre

double-walled stainless steel pressure laboratory reactor (IKA, LR 2000 P, Ger-

many) equipped with the pressure gauge, a mechanical stirrer, water condenser,

temperature regulator, sampling outlet, and an adjustable water bath providing

the desired temperatures.

2.2.2. Experimental Design for RSM Study

The design of experiment (DOE), data analysis and optimization procedures

were performed using the Minitab v.14 statistical package (Minitab Inc., 2000,

State College, PA, USA). RSM was applied to determine the effect of four inde-

pendent variables (

i.e

., reaction time, the temperature, the amounts of NaOCH

and PEG400) or their interactions and on the mass of percentage of total

CLAMEs (% w/w) as a response. Thirty isomerization treatments were designed

based on a central composite design (CCD) considering five levels for each fac-

tor. The experimental matrix of isomerization is indicated in

Table 1. The expe-

riments randomized to minimize the effects of any extraneous factors on the actual

response and method repeatability was assessed by repeating the centre point six

times [9]. Isomerization was performed according to the DOE obtained from RSM

(

Table 1). Approximately, 500 g of distilled FAMEs of sunflower oil, NaOCH

the form of a paste with negligible amounts of methanol and the PEG400 were

placed into the reactor. The reactor was then sealed and nitrogen was introduced

as an inert gas to prevent FAMEs from oxidation (at 1.5 bar). The nitrogen was

discontinued and the agitation (300 rpm) started to proceed up to the desired

temperatures and based on the reaction times defined in the DOE matrix.

The reaction was then terminated with the addition of 1 mL of H

, during

which phosphate salts were precipitated. The reactor was cooled to 80˚C, the

precipitates were removed and the contents were transferred into a separatory

funnel for the phase separation [10]. The conjugated fatty acid methyl esters

(CFAMEs) mixture was then washed twice with deionized water (dH

O) (80˚C -

90˚C) to separate the residues of NaOCH

, soaps and PEG400. H

was added

and further washing was repeated until the pH of the drain reached to the neu-

tral value of 7 to remove PEG400 from the fatty acid layer [11]. The layers al-

lowed to be separated for 20 min and aqueous bottom layer was decanted. The

CFAMEs from the upper layer mainly consist of CLAMEs transferred into a rotary

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