Lipozyme RM IM-Catalyzed Acidolysis of Cinnamomum camphora

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Lipozyme RM IM-catalyzed acidolysis of Cinnamomum camphora seed oil with oleic acid to produce human milk fat substitutes enriched in medium-chain fatty acids Xian-Guo Zou, Jiang-Ning Hu, Man-Li Zhao, Xue-Mei Zhu, Hong-Yan Li, Xiao-Ru Liu, Rong Liu, and Ze-yuan Deng J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/jf503691p • Publication Date (Web): 09 Oct 2014 Downloaded from http://pubs.acs.org on October 10, 2014

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Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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Journal of Agricultural and Food Chemistry

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Lipozyme RM IM-catalyzed acidolysis of Cinnamomum

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camphora seed oil with oleic acid to produce human milk fat

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substitutes enriched in medium-chain fatty acids

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Xian-Guo Zou1, Jiang-Ning Hu1,2*, Man-Li Zhao1, Xue-Mei Zhu, Hong-Yan Li1,

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Xiao-Ru Liu1, Rong Liu1, Ze-Yuan Deng1*

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1

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Nanchang University, Nanchang, Jiangxi 330047, China

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2

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State Key Laboratory of Food Science and Technology, Institute for Advanced Study,

College of Food Science & Technology, Nanchang University, Nanchang, Jiangxi

330047, China

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Running title: HMFS synthesized from CCSO and oleic acid

13 14 15

* To Corresponding authors:

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Telephone No: +86 88304449-8226, E-mail address: [email protected] (J-N Hu);

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Telephone/ Fax No: +86 791 88304402, E-mail address: [email protected] (Z-Y Deng)

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ABSTRACT

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In the present study, a human milk fat substitute (HMFS) enriched in

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medium-chain fatty acids (MCFAs) were synthesized through acidolysis reaction

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from Cinnamomum camphora seed oil (CCSO) with oleic acid in a solvent-free

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system. A commercial immobilized lipase, Lipozyme RM IM, from Rhizomucor

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miehei, was facilitated as a biocatalyst. Effects of different reaction conditions,

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including substrate molar ratio, enzyme concentration, reaction temperature and

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reaction time were investigated using response surface methodology (RSM) to

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obtain the optimal oleic acid incorporation. After optimization, results showed that

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the maximal incorporation of oleic acid into HMFS was 59.68%. And compared with

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CCSO, medium-chain fatty acids at sn-2 position of HMFS possessed more than

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70%, whereas oleic acid was occupied predominantly at the sn-1,3 position (78.69%).

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Meanwhile, triacylglycerol (TAG) components of OCO (23.93%), CCO (14.94%),

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LaCO (13.58%), OLaO (12.66%) and OOO (11.13%) were determined as the major

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TAG species in HMFS. The final optimal reaction conditions were carried out as

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follows: substrate molar ratio (oleic acid: CCSO), 5:1; enzyme concentration, 12.5%

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(w/w total reactants); reaction temperature, 60℃; and reaction time, 28 h. The

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reusability of Lipozyme RM IM in the acidolysis reaction was also detected, which

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could be reused up to 9 times without significant loss of activities. Urea inclusion

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method was used to separate and purify the synthetic product. As the ratio of

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HMFS/urea increased up to 1:2, the acid value lowered to the minimum. In a

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scale-up experiment, the contents of TAG and total tocopherols in HMFS (modified 2

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CCSO) were 77.28% and 12.27 mg/100g, respectively. And all the physicochemical

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indexes of purified product were within food standard. Therefore, such

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MCFAs-enriched HMFS produced by acidolysis method might have a potential

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application in infant formula industry.

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KEYWORDS: Human milk fat substitutes (HMFS), Response surface methodology

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(RSM), Lipozyme RM IM, Cinnamomum camphora seed oil (CCSO)

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INTRODUCTION

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As a naturally important subsistence source for newborn infants, human milk fat

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(HMF) provides a vital source of energy and nutrients to support infant growth.

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Unlike the triacylglycerol (TAG) composition of vegetable oils and cow milk fat,

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HMF has a unique structure of the TAG, where the major saturated fatty acid, palmitic

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acid (16:0), locates at sn-2 position (approximately 70%), while unsaturated fatty acid,

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such as oleic acid (30-35%), and linoleic acid (7-14%) are presented at sn-1,3

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positions.1,2 Researches showed that such unique TAG profile of HMF facilitates the

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absorption of nutrients.3 The long chain saturated fatty acid palmic acid at sn-2

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position is not hydrolyzed by pancreatic lipase, and as 2-monopalmitin it forms a

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mixed micelle with bile salt, which is efficiently absorbed.4 In contrast, mostly

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traditional powdered infant formulas have a non-specific fatty acid position in their

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TAG structures, where saturated fatty acids at sn-1,3 positions are hydrolyzed by

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pancreatic lipase, producing free saturated fatty acids, then further form poorly

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absorbed calcium soap in the intestine, and result in constipation symptoms.2,5

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Considering the drawbacks of traditional infant formula and the absorption

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advantages of HMF, in recent ten years, preference for imitating the similar structure

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of HMF to produce infant formula has gained a great number of attentions.6,7

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Nowadays, “BetapolTM”, a commercial structured lipid made of vegetable oils through

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position-specific enzymatic interesterification, has been approved as HMFS by many

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European countries as well as South Korea and China. Compared to interesterification,

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many reports recently prefer to use acidolysis reaction to produce HMFS which 4

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contained palmitic, oleic, stearic, and linoleic acids,8 essential fatty acids,9

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gamma-linolenic acid,10 and omega-3 polyunsaturated fatty acids.11 Acidolysis

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reaction has the advantages of positional selectivity and specificity, low cost and less

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side products which is caused by the inevitable existence of acyl migration and can be

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minimized by the control of reaction conditions, such as water content, enzyme load,

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reaction time, substrate ratio and mainly reaction temperature.12 The acidolysis

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mechanisms include two steps:12 at initial stage, the hydrolysis of an ester bond

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between the fatty acid residue and the glycerol moiety of the triglyceride resulted in

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the release of the free fatty acid and generation of a glyceride containing at least one

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hydroxyl group, and then, a new ester bond is formed by the reaction between the

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newly created hydroxyl group and the incoming new free fatty acid.

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Besides that the fatty acids at different position of TAG affect the absorption

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efficiency, different length of fatty acids also have different absorption rates and

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different functions. Clinical experiments reveal that long-chain fatty acids (LCFAs,

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C14-C22) were more slowly absorbed than medium-chain fatty acids (MCFAs,

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C6-C12).13 An increase in change length of saturated fatty acids reduced the

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absorbability of them as well increased the loss of energy intake and calcium. MCFAs

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were absorbed more efficiently than LCFAs in gastrointestinal tract via the portal

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system, and rapidly provide energy for the body.14 It has also been reported that

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MCFAs had more antiviral and antibacterial activity than LCFAs.15 Due to the

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predominantly LCFAs in infant formula and human milk fats, the incorporation of

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MCFAs into HMFS has been suggested to provide a concentrated source of energy by 5

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many clinical nutrition experts.16 Recently, a commercial product named Neobee

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consists of MCFAs (caprylic and capric acids) has been developed as a functional

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food for patients. To our knowledge, in the literature, few data can be found regarding

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the enrichment of human milk fat substitutes with MCFAs.17

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Lipozyme RM IM, which is a immobilized lipase from Rhizomucor miehei, is

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widely used as a catalyst in pharmaceuticals and drugs production and lipid

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modifications. It has the characteristics of substrate specificity, stereospecificity, and

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regioselectivity.18 In recent study, different strategies of lipase immobilization were

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investigated to improve enzyme properties by positive alterations of structure, which

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may enhance enzyme activity, specificity or selectivity and increase its mechanical

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strength, hydrophobic or hydrophilic character and regeneration.19

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Cinnamomum camphora (lauraceae), known as an evergreen tree, is largely

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distributed in south area of the Yangtze River in China. In previous study, it has been

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reported that the oil from Cinnamomum camphora (lauraceae) seeds has a unique

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fatty acid profile that mainly contains MCFAs (capric acid, C10:0, 53.27%; lauric acid,

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C12:0, 39.93%).20 Liu et al.21 have also confirmed that Cinnamomum camphora seed

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oil (CCSO) is nontoxic with no side effects, which could be used as woody edible oil

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for its further development and utilization. Recently, our research group has managed

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to use CCSO for the production of medium-chain triacylglycerol (MCT) enriched

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plastic fats.22-24

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The aim of this work was to synthesize HMFS enriched with MCFAs through

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enzymatic acidolysis of CCSO and oleic acid using immobilized Lipozyme RM IM 6

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lipase as a catalyst. The effects of reaction conditions (time, temperature, enzyme

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concentration, and substrate mole ratio) on oleic acid incorporation were optimized

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by response surface methodology (RSM). Subsequently, scale-up trials were

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conducted to determine the feasibility of enzymatic modification of CCSO for the

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production of HMFS and the reusability of Lipozyme RM IM.

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MATERIALS AND METHODS

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Materials and chemicals. Oleic acid (≥85%) was purchased from local oil market

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(Nanchang, China). CCSO was extracted from Cinnamomum camphora seeds by the

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CO2 supercritical fluid method as described in Hu et al.20 Lipozyme RM IM, a

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commercial immobilized 1,3-specific lipase from Rhizomucor miehei, was purchased

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from Novozymes A/S (Bagsvaerd, Den-mark). The specific activity of Lipozyme

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RM IM was 150 IU/g, having 0.35-0.45 g/mL bulk density and 0.3-0.6 mm particle

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diameter. Carbon dioxide (99.9%) was provided by Wanli Gas Corp (Nanchang,

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China). #463 of standard fatty acid methyl esters (FAMEs) containing methyl esters

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C8-C20 saturated fatty acid, methyl myristate, methyl palmitoleate, methyl oleate,

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methyl linoleate, methyl linolenate and four positional conjugated linoleic acid

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isomers were purchased from Nu-Chek Prep Inc. (Elysian, MN). Tocopherol (α, γ,

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and δ) standards were acquired from Sigma Chemical Co. (St. Louis, MO). All other

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chemicals used were of analytical or chromatographic grade.

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Acidolysis reaction of small-scale sample. CCSO (1 g each) was blended with

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oleic acid at substrate mole ratios of 1:2, 1:4 and 1:6. Lipozyme RM IM of 6, 10,

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14% (w/w total reactants) was added to the blend in 50 ml screw-capped flask. The 7

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acidolysis was performed under 200 rpm orbital shaking water bath and temperature

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was set at 55, 60 and 65℃ for 20, 24 and 28 h incubation. After reaction, RM IM

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lipases were separated from the mixture through a 0.45-µm polytetrafluoroethylene

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(PTFE) syringe membrane filter. The filtrate was stored at -18℃ until analysis.

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Experimental design for RSM study. Enzyme-catalyzed acidolysis was

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influenced by reaction conditions such as water content, substrate mole ratio,

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enzyme concentration, temperature and reaction time.12 Before models were set up

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by RSM, single factor experiments were carried out to detect the effects of these five

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conditions on the oleic acid incorporation. Then, four of the five factors were

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selected as independent variables, and the optimal reaction conditions for the

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acidolysis reaction were established via RSM. RSM, a useful mathematical tool, has

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been widely applied to the optimization of reaction conditions for the production of

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HMFS in several studies.25,26 In our experiment, a four-factor and three-level full

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factorial design called Box-Behnken design (BBD) were employed to generate factor

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combinations by using Design Expert 7.1 software (Stat-Ease Inc., Minneapolis, MN,

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USA). The four selected factors were substrate mole ratio (A), enzyme concentration

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(B), temperature (C) and reaction time (D) and three levels were substrate mole

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ratios of 1:2, 1:4 and 1:6, Lipozyme RM IM of 6, 10, 14% (w/w total reactants),

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temperature of 55, 60 and 65℃ and reaction time of 20, 24 and 28 h. To avoid bias,

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29 runs including 16 factorial points, 8 axial points and 5 center points were

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performed in a random order. Oleic acid incorporation was acted as response value.

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The independent variables (A, B, C, D) and exact experimental model are presented 8

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in Table 1. Experiments were run randomly, and duplicate reactions were performed

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at all design points.

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Fatty acid profile. The fatty acid compositions of substrates and products were

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determined. Thin-layer chromatography (TLC) analysis was carried out for the

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separation of newly-synthesized product. About fifty microliters of product was

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applied to TLC plates coated with silica gel G. The developing solvent was

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hexane/diethyl ether/acetic acid (50:50:1, v/v/v). Then, The bands were sprayed with

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0.2% 2,7- dichlorofluorescein in methanol and visualized under UV light. Finally,

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the TAG band was scraped off into a screw-capped test tube and dissolved in 2 mL

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hexane for fatty acid composition analysis. The TAG sample was converted to fatty

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acid methyl esters (FAMEs) following the procedure of Zhu et al.27 and then

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analyzed by a gas-liquid chromatograph (GLC) (model 6890N, Agilent Technologies,

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USA) equipped with an auto injector, a fused-silica capillary column (CP-Sil 88, 100

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m × 0.25 mm × 0.2 µ m i.d.) and a flame ionization detector (FID) and operated in

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splitless mode. The injector and detector temperatures were maintained at 250 and

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260℃, respectively. The column temperature was held at 45℃ for 3 min, then

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programmed to 175℃ for 27 min at the rate of 13℃/min. The temperature was then

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further increased to 215℃ at at the rate of 4℃/min and held for 35 min. The carrier

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gas was nitrogen, and the total gas flow rate was 52 mL/min. The injecting sample

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volume was 0.3 uL.

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Sn-2 positional analysis. Composition of sn-2 FAs was analyzed by the

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pancreatic hydrolysis method as previously described.28 Likewise, TLC was used to 9

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separate 2-monoacylglycerol (2-MAG) from the hydrolysate. The 2-MAG band was

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scrapped off, methylated and analysed by GLC as also described above.

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The identification of TAGs species. The different species of TAGs of CCSO and

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HMFS were separated by reversed-phase high-performance liquid chromatograph

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(HPLC) with a Nova-Pak C18 column (150 × 3.9 mm, Waters, Milford, MA) and an

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evaporative light-scattering detector (Alltech 2000ES, USA) operating at 55℃ and a

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gas flow rate of 1.5 L/min. Samples were dissolved in methanol and filtered by

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0.45-µm PTFE syringe membrane filter. Twenty microliters of filtered sample were

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injected and eluted by acetonitrile (solvent A) and 2-propanol/n-hexane (1:1, v/v)

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(solvent B) at a flow rate of 1.8 mL/min with the following profile: 0 to 20 min, 30%

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B; 21 to 36 min, 60% B; 37 to 40 min, 100% B, and then back to the initial flow rate.

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Last, the separated TAGs were identified by comparing the retention time and

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equivalent carbon number (ECN). ECN = CN-2DB, used to predict the elution order,

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where CN is the total carbon number except three carbons of glycerol in the TAG

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and DB is the total number of double bonds on the fatty acids.

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Urea inclusion for separation and purification of HMFS. The mechanism of

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urea inclusion is traditionally explained as follows: separation of mixed fatty acids

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by urea inclusion occurs in terms of different saturation degrees and carbon-chain

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lengths of the fatty acids.29 Urea/HMFS mixed with 50 mL 95% (v/v) ethanol were

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put into a round-bottomed flask. Under the nitrogen gas flow, the mixture was

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refluxed at 60℃ in a water bath till the solution became clear. Then, the product was

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cooled at room temperature for 1 h and placed at -4℃ for 24 h. The mixture was 10

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separated by suction filtration using Buchner funnel to obtain urea inclusion

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compounds and non-urea inclusion compounds. The non-urea inclusion compounds

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contained PUFA and acylglycerol were transferred to a round-bottomed flask and

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ethanol was evaporated as much as possible. Acylglycerol was separated and

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analyzed by HPLC.

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Tocopherol analysis. About 1g of CCSO or HMFS sample were weighted into a

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flask and fully dissolved in 10 mL of hexane. After filtering with 0.45-µm PTFE

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syringe filter, three microliters sample were injected into the Agilent 1100 series

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HPLC. Then, the contents of tocopherol in prepared sample were determined by

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reversed-phase HPLC equipped with Hypersil ODS2 column (5μm, 4.6 × 150 mm,

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Agilent Technologies, USA) and a fluorescence detector (FLD). The mobile phase

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was methanol/water (98/2, v/v) with a flow rate of 0.8 mL/min. Standards of α-,γ

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-, and δ -tocopherol dissolved in hexane were used for identification and

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quantification.30

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Physicochemical characteristics. The determination of CCSO and HMFS on

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chemical properties, such as acid value, peroxide value, saponification value and

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iodine value, were conducted following AOAC (1990) standard analytical

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methods.31

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Scale-up trial. Model verification was carried out from RSM design. To verify the

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feasibility of the scaled-up acidolysis, a batch reaction (50 times scaling-up) in 500

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-mL flask was carried out at optimum conditions. The incorporation of oleic acid and

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productivity of TAG were determined to evaluate the feasibility of scale-up trial. 11

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Statistical analysis. The effects of different substrate mole ratio, enzyme

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concentration, temperature and reaction time studied in this work and their

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interactions were analyzed by using Design Expert 7.1 software. Mean values and

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standard deviation of single-factor experiment, contents of tocopherol and

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physicochemical characteristics were analyzed by using the Statistical Analysis

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System software (SAS 2000, Cary, NC, USA).

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RESULTS AND DISCUSSION

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Effect of water content. The water content in any quantity cannot be neglected

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because lipases were activated by a small amount of water32 and it is required to a

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first breaking of the triglyceride,12 however, too much water can make the lipase

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unstable and have an adverse impact on their activity, leading to a higher amount of

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byproducts.33 Some authors reported that the optimum water contents were generally

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in the range of 0.2-3%,34-36 however, for a given enzymatic reaction, it depends on

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many factors (the selected enzyme, support, solvent and quantities of substrates).

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Thus, there is a necessity to optimize the water content in the reaction system. With

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enzyme of 10% (w/w total reactants), 4/1 substrate mole ratio (oleic aid: CCSO),

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reaction temperature of 60℃ and time of 24 h, the effects of water contents in the

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range of 1% to 20% (w/w total reactants) on the incorporation of oleic acid were

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studied (Figure 1(a)). It showed that the incorporation increased from 55.72±0.31%

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to a maximum level of 57.44±0.25% when water content increased from 1% to 5%.

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And then, a decrease till to 52.81±0.19% was observed when water content increased

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from 5% to 20%. Hence we chosed 5% water content for the ongoing study. 12

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Effect of enzyme concentration. The effect of enzyme load, by varying from 1%

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to 25% (w/w total reactants) with constant substrate mole ratio of 4:1 and 60∘C

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reaction temperature after 24 h incubation, on the oleic acid incorporation was also

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observed (Figure 1(b)). An increase in the catalyst percentage from 1% to 10% led to

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a incorporation increase from 38.41±0.54% to 57.26±0.75%. Further increase in the

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enzyme load from 10 to 25%, however, did not lead to further incorporation increase.

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This is possibly due to the saturation of the enzyme at the interface between CCSO

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and aqueous phase, in which an increase in enzyme concentration provided no

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significant changes on the incorporation.37 Our results are similar to these reported

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by Rooney et al.37 and Djéssica et al.38 Considering the incorporation of oleic acid

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and cost of Lipozyme RM IM, 10% (w/w total reactants) enzyme concentration was

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chosen for optimization in following optimization.

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Effect of reaction temperature. Temperatures from 40 to 70℃ were evaluated

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in the present study. Substrate mole ratio (oleic acid: CCSO), water content, enzyme

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load and reaction time were 4:1, 5%, 10% and 24 h, respectively. Results are shown

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in Figure 1(c). It can be noted that the increasing temperature in the range of 40 to

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60 ℃ increased oleic acid incorporation from 42.11±0.54% to 57.63±0.83%.

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However, when the temperature further increased to 70 ℃ , the incorporation

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decreased to 57.19±0.92%. This result is in good agreement with the results of

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Phuah et al.39 who investigated the effect of temperature on the hydrolysis of partial

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palm oil. And it has been stated that enzyme activity and acyl migration are both

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increased by an increase in temperature until reaching the maximal rate.40 Therefore, 13

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a higher temperature was not suggested. Temperature of 60℃ was suitable for

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further study.

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Effect of reaction time. The reaction time was set from 1 to 36 h to investigate its

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influence on the incorporation. And substrate mole ratio (oleic acid: CCSO), water

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content, enzyme load and reaction temperature were 4:1, 5%, 10% and 60℃,

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respectively. As shown in Figure 1(d), the incorporation of oleic acid increased from

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42.51±0.43% to 57.48±0.94% when reaction time increased from 1 h to 24 h. In 36 h,

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the oleic acid incorporation was 58.62±0.90%. In similar study the optimal reaction

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time was different depending on the use of enzyme and substrate.41 Fourty hours as

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the optimal reaction time was reported by Akoh et al. for the incorporation of EPA

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and capric acid into borage oil.41

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Effect of substrate mole ratio (oleic acid: CCSO). The effect of molar ratio of

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oleic acid to CCSO on oleic acid incorporation was studied from 1:1 to 8:1 at a

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constant enzyme concentration (10%, w/w total reactants) and temperature of 60℃

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for 24 h (Figure 1(e)). It showed that the incorporation increased from 32.75±0.24%

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to 58.73±0.13% as the substrate mole ratio changed from 1:1 to 4:1. And then, from

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4:1 to 8:1, the incorporation increase till to 59.84±0.26% was found. It was reported

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that the appropriate substrate molar ratio was in favor of the reaction equilibrium and

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increased the ratio of the collision between substrates and catalyst,42 but higher

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substrate ratios were not desirable on this account that a large amount of FFAs

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containing high levels of free or ionized carboxylic acid groups acidify the enzyme

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layer, leading to absorption of water from the interface which may decrease the 14

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activity of the enzyme.43 Considering the stability of enzyme and cost of materials,

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substrate mole ratio of 4:1 was chosen for further investigation.

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Experimental design for RSM. To find the optimal condition of the greatest

293

incorporation and also to see whether the reaction parameters have interactions on

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each other, RSM was used. According to the results of single-fator experiment

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discussed above (Figure 1), the water content was set at constant 5% (w/w total

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reactants), the substrate mole ratio (A, oleic acid: CCSO), enzyme load (B, w/w total

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reactants), temperature (C, ℃) and reaction time (D, in hours) were chosed as the

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four optimizing factors. Experimental model is shown in Table 1.

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Model fitting and variance analysis. Quadratic models were well established by

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multiple regression and backward elimination using Design Expert 7.1 software. The

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model equation for the responses (% oleic acid incorporated) catalyzed by Lipozyme

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RM IM can therefore be written as:

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Y=57.60+3.8A+2.36B+0.81C+1.65D+1.31AB-0.82AC+0.097AD-0.012BC-0.80BD

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-0.54CD-4.80A2-1.80B2-1.54C2-0.51D2.

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Where Y is the oleic acid incorporation, A is substrate mole ratio, B is enzyme load,

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C is temperature, and D is reaction time.

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The analysis of variance (ANOVA) of models for response variables is listed in

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Table 2. The very small P values (