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<ul><li><p>Research ArticleUltrasound-Assisted, Base-Catalyzed, Homogeneous Reaction forFerulic Acid Production from -Oryzanol</p><p>Hoa Thi Truong ,1 Manh Van Do,1 Long Duc Huynh,1 Linh Thi Nguyen,1 Anh Tuan Do,1</p><p>Thao Thanh Xuan Le,1 Hung Phuoc Duong,2 Norimichi Takenaka,3</p><p>Kiyoshi Imamura,4 and Yasuaki Maeda4</p><p>1Danang Environmental Technology Center, Institute of Environmental Technology, Vietnam Academy of Scienceand Technology, Tran Dai Nghia Road, Ngu Hanh Son Dist., Da Nang 550000, Vietnam2International Cooperation Department, Ministry of Natural Resources and Environment, 10 Ton &amp;at &amp;uyet St.,Hanoi 100000, Vietnam3Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho,Nakaku, Sakai, Osaka 599-8531, Japan4Research Organization for UniversityCommunity Collaborations, Osaka Prefecture University, 1-1 Gakuen-cho,Nakaku, Sakai, Osaka 599-8531, Japan</p><p>Correspondence should be addressed to Hoa i Truong; hoa.danetc@gmail.com</p><p>Received 8 September 2017; Accepted 11 April 2018; Published 13 May 2018</p><p>Academic Editor: Sevgi Kolayl</p><p>Copyright 2018 Hoa i Truong et al. is is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.</p><p>A method for producing ferulic acid by ultrasound-assisted, homogeneous, base-catalyzed hydrolysis of c-oryzanol was de-veloped. Experiments were conducted using various reaction temperatures and ratios of c-oryzanol to base catalyst in bothhomogeneous and heterogeneous systems. e reaction performed without ultrasound under the homogeneous conditions ofpotassium hydroxide/c-oryzanol ratio (wt/wt) 20 :1 and 75C gave a ferulic acid yield of 83.3% in 3 h. Acceleration of thehomogeneous reaction using ultrasound irradiation at 20 (horn type) and 200 kHz (planar type) was explored by evaluating thekinetic parameters. At 30C, the ratios of ultrasonic irradiation at low (20 kHz, 50W) and high (200 kHz, 50W) frequencies versusthose of the heating method increased by 2.0- and 1.4-fold in comparison with those at 60C, respectively. e contribution ofultrasonic irradiation (50W) to the hydrolysis reaction decreased with increase of temperature. However, irradiation at 20 kHzand a power of 180W gave a 94% ferulic acid yield at 60C in 3 h. ese results indicate that the use of low frequency (horn typeand high-power irradiation) enabled yields higher than 90% to be obtained.</p><p>1. Introduction</p><p>Ferulic acid (FA) is one of the most promising biomass ofphenolic acid derivatives with its antioxidant properties suchas UV protectant in cosmetics, food additive, and being usedin various medical applications. FA also helps to preventcardiovascular disease, diabetes, Alzheimers disease, andcolon cancer [18]. Nitrites, usually sodium nitrite, are usedin the food industry as preservatives to maintain color andprevent pathogen growth. In acidic conditions in thestomach, nitrites can react with many other compounds toproduce nitrosamines, which are known carcinogens. e</p><p>use of FA to block nitrosamine formation from nitrites hasbeen investigated in the literature [9].</p><p>FA can be synthesized by the condensation of vanillinwith malonic acid. e reaction gives a high yield ofa mixture of trans- and cis-FA [10]; trans-FA, which can becrystallized, is commercially important because of its bi-ological activities. Alkaline hydrolysis has been used toproduce FA from natural sources, and various proceduresfor extraction of FA have been applied depending on theproperties of the raw material [1, 1113]. FA cannot beextracted directly from their matrix in the rice bran [14]because of existence of conjugated forms and/or its ester</p><p>HindawiJournal of ChemistryVolume 2018, Article ID 3132747, 9 pageshttps://doi.org/10.1155/2018/3132747</p><p>mailto:hoa.danetc@gmail.comhttp://orcid.org/0000-0003-0829-6806https://doi.org/10.1155/2018/3132747</p></li><li><p>form of c-oryzanol. However, FA can be produced fromc-oryzanol-containing by-products by hydrolysis reaction,for example, soapstock from rice bran oil processing [15, 16].</p><p>Ultrasound irradiation has recently been evaluated asan effective method for accelerating hydrolysis reactions[1727]. However, a few experiments on the hydrolysis ofthe hydrophobic compounds of c-oryzanol consisting ofbulky steroid groups and para-orientated hydroxyl grouphave been conducted. In our previous study, the ultrasoundirradiation (78 kHz, 130 kHz, 50W, and planar type) wasexplored, and the reaction was accelerated by around 10%[16] at the temperature of 60 and 75C in comparison withthe conventional heating method.</p><p>In this study, we examined the ferulic acid productionfrom c-oryzanol by various kinds of binary solvent systems:two kinds of homogeneous and one kind of heterogeneoussystems. e experiments were performed using variousratios of c-oryzanol/base catalyst and reaction tempera-tures. For accelerating the reaction, ultrasound irradiationsof two kinds of frequency, for example, 20 kHz (horn type)and 200 kHz (planar type) with power of 50W and 180Wwere applied.e kinetic parameters of ultrasound-assistedhomogeneous reaction systems were also estimated.</p><p>2. Materials and Methods</p><p>2.1. Chemicals and Equipment. e purities of trans-FA,c-oryzanol, and ethyl ferulate (EF) standards (Sigma-Aldrich, USA) were over 99%. Inorganic compounds (po-tassium hydroxide (KOH), sulfuric acid, and phosphoricacid) and organic reagents and solvents (acetic acid, ethanol,and ethyl acetate) were of analytical grade and purchasedfrom Merck (Germany). Acetonitrile, methanol, and waterused as mobile phases were of HPLC grade and were alsopurchased from Merck.</p><p>A solution of c-oryzanol (48mg/mL) was prepared bydissolving c-oryzanol (4.8 g) in ethyl acetate (100mL). KOHsolutions of concentrations 192, 240, 384, and 480mg/mLwere prepared by dissolving 48, 60, 96, or 120 g of KOH inwater (250mL). For comparison, KOH solutions of con-centrations 96, 120, 192, and 240mg/mL, that is, half theconcentrations of the aqueous solutions, were prepared inmethanol. e mass ratio of KOH/c-oryzanol, denoted byKO, was varied from 8 :1 to 20 :1.</p><p>A low-frequency (20 kHz) horn-type ultrasonicator(Sonifier 450, Ti horn of diameter 1.1 cm, maximum power400W, Branson Co., Tokyo, Japan) and a high-frequency(200 kHz) planar-type ultrasonicator (Kaijo Corporation,Tokyo, Japan) were used to accelerate the hydrolysis re-action. e dissipation powers were 50 and 180W.</p><p>2.2. Hydrolysis of c-Oryzanol. In our previous study, theexperiment of c-oryzanol hydrolysis was evaluated withthe initial concentration of 12mg/mL of c-oryzanol under thereaction temperature of 6075C to prevent the precipitates inthe homogeneous systems [16]. In this study, the initialconcentration of c-oryzanol was adjusted by 6mg/mL, and</p><p>the reaction temperature was varied in the range of 3075Cto avoid precipitation during the reaction.</p><p>2.2.1. Composition of Homogeneous Type A Solvent (EthylAcetate/Water/Ethanol). e homogeneous reaction systemdesignated as Type A was prepared as follows. A c-oryzanolsolution (48mg/mL, 4mL) was added to ethanol (20mL) ina 100mL glass flask with a screw cap. e flask was placedin a water bath controlled at temperatures from 30 to 75Cusing a temperature controller (ermal Robo TR-2A, AsOne, Osaka, Japan). KOH solutions of various concentra-tions (192, 240, 384, and 480mg/mL, 8mL) were added tothe mixture to prepare solutions with KO ratios of 8, 10, 16,and 20. e initial concentration of c-oryzanol was6mg/mL. After closing the flask with the cap, the mixturewas shaken by hand to form a uniform dispersion and thenheld in the water bath, without stirring or acceleration byultrasound irradiation (hereinafter called the heatingmethod). e reaction temperature was varied from 30 to75C. An aliquot (100 L) was removed every 30min, and thereaction products and amount of c-oryzanol were de-termined using HPLC. e reaction was monitored for 4 h.</p><p>2.2.2. Composition of Homogeneous Type B Solvent (EthylAcetate/Methanol/Ethanol). e procedure for preparationof the homogeneous reaction system designated as Type Bwas as follows. A c-oryzanol solution (48mg/mL, 4mL) wasadded to ethanol (12mL) in a 100mL glass flask with a screwcap. Methanolic KOH solutions of concentrations 96, 120,192, and 240mg/mL (16mL), corresponding to KO ratios of8, 10, 16, and 20, were added. e subsequent process wasthe same as that described in Section 2.2.1.</p><p>2.2.3. Composition of Heterogeneous Type C Solvent (EthylAcetate/Water). eheterogeneous system designated as TypeC consisted of a c-oryzanol in ethyl acetate solution andaqueous KOH solution. e preparation procedure was thesame as that described in Section 2.2.1, except for the addition ofethanol as a cosolvent and the volume of ethyl acetate (20mL).</p><p>2.3. Hydrolysis Using Ultrasound Irradiation. e effects ofultrasound irradiation on the reaction were examined usinga homogeneous aqueous organic phase (Type A) at 30 to60C.e procedure was as follows. A solution of c-oryzanol(48mg/mL, 16mL) in ethyl acetate was added to ethanol(80mL) in a 250mL glass flask with a screw cap. is flaskwas placed in a water bath at a specified temperature,controlled by a Robo TR-2A thermal controller (As One Co.,Osaka, Japan), and then KOH solution (32mL) was quicklyadded. e flask was shaken by hand. For low-frequency(20 kHz) irradiation with a horn-type sonicator, the horn tipwas immersed in the middle of the mixed solution. e flaskwas covered with paraffin film, and the dissipation powerwas 50 or 180W. e reaction products were monitored for4 h. For high-frequency (200 kHz) irradiation with a planar-type sonicator, the flask containing the reaction mixture was</p><p>2 Journal of Chemistry</p></li><li><p>closed with the screw cap and placed on the transducer, andthen irradiation was started.</p><p>2.4. HPLC Determination of c-Oryzanol, FA, and EF. FA,c-oryzanol, and EF were determined as follows: Concentratedacetic acid (100L) was added to the reactionmixture (100L)to terminate the reaction. e mixed solution was diluted to1.5mL with ethanol, and an aliquot (10L) was subjected tohigh-performance liquid chromatograph (HPLC) analysis.e GL-7480 HPLC system (GL Science Inc., Tokyo, Japan)was equipped with a photodiode array detector (GL-7452, GLScience Inc., Tokyo, Japan) and an autosampler (GL-7420, GLScience Inc., Tokyo, Japan). A reverse-phase Inertsil ODS-3C18 (4.6mm 250mm, lm thickness 5m; GL Science,Tokyo, Japan) column was used. e analytical parameterswere described in our previous study [16]. e FA, EF, andc-oryzanol contents were determined using a direct calibra-tion method with a coecient of determination (R2) greaterthan 0.9990 in the concentration ranges of 10250, 10100,and 1001200g/mL, respectively. Because c-oryzanol isa mixture of four main components, the calibration curve forc-oryzanol was based on the sum of the areas of the four peaksversus the concentration of FA.e yield of FA (%) and that ofEF (%) were calculated as</p><p>yield of FA (EF) FAc (EFc)</p><p>FAc + EFc +Orc 100%, (1)</p><p>where FAc is themolar concentration of FA, EFc is themolarconcentration of EF, and Orc is the molar concentration ofc-oryzanol. e obtained values were the averages of trip-licate measurements.</p><p>2.5. Kinetic Calculation. e base-catalyzed hydrolysis ofester is expressed as the second-order reaction as the reaction</p><p>rate depends on both concentrations of ester and hydroxideion as follows:</p><p>rate k OH[ ][ester]. (2)</p><p>Usually, large amount of reagent [OH] versus ester isadded to the reaction system, and then the rate can beabbreviated and converted to pseudo-rst-order reaction bydependency of ester concentration [28] as follows:</p><p>kt lnCtC0( ), (3)</p><p>where C0 is the initial concentration (mg/mL) of c-oryzanolandCt is the concentration of c-oryzanol (mg/mL) at reactiontime t (min). e activation energy (Ea, J/mol) for c-oryzanolhydrolysis was estimated using the following equations:</p><p>k A expEaRT( ), (4)</p><p>ln k EaRT</p><p>+ lnA, (5)</p><p>where k is the rate constant, T is the Kelvin temperature, R isthe molar gas constant (8.3415103 kJ/(mol/K)), and A isthe pre-exponential factor.</p><p>3. Results and Discussion</p><p>3.1. HPLC Analysis of c-Oryzanol, FA, and EF. e HPLCchromatogram (photodiode array detection at 325 nm) ofc-oryzanol and its hydrolysis products of homogeneoussystem of Type A is shown in Figure 1. e peaks eluted inthe range of 3245min were assigned to c-oryzanol bycomparing with authentic standards (Figure 1(a)). As hy-drolysis proceeded, peaks for trans-FA and the intermediatesethyl ferulate (EF) appeared at retention times of 9.3 and14.4min, respectively (Figure 1(b)).</p><p>500</p><p>450</p><p>400</p><p>300</p><p>350</p><p>250</p><p>200</p><p>150</p><p>100</p><p>50</p><p>0</p><p>500</p><p>450</p><p>400</p><p>300</p><p>350</p><p>250</p><p>200</p><p>150</p><p>100</p><p>50</p><p>0</p><p>5 10 15 20 30 35 40 45 5025(Min)</p><p>(mAu</p><p>)</p><p>Trans-ferulic acid</p><p>Ethyl ferulate</p><p>-Oryzanol</p><p>32.1</p><p>73</p><p>38.1</p><p>9336</p><p>.313</p><p>44.6</p><p>B</p><p>A</p><p>Figure 1: HPLC chromatogram (UV235 nm) of c-oryzanol standards (A) and hydrolysis products (B).</p><p>Journal of Chemistry 3</p></li><li><p>3.2. Hydrolyses Using Homogeneous and HeterogeneousSystems. Two homogeneous solvent systems, that is, binarysolvents consisting of ethanol/ethyl acetate combined withwater (Type A) or methanol (Type B), and heterogeneousone (Type C, KOH/water) were investigated. e yields ofFA were evaluated using various KO ratios and reactiontemperatures as shown in Table 1. Under aqueous het-erogeneous conditions (Type C), the maximum yield of FAwas 12.3% even at 75C. As in the case of esters containingacidic protons, such as methyl p-hydroxybenzoate andmethyl salicylate, hydrolysis was sluggish because of theformation of stable anions [29]. c-oryzanol contains anacidic proton on the para-substituted hydroxyl group of anaromatic skeleton. Furthermore, the alcoholic portions ofc-oryzanol consist of bulky steroidal groups, which couldprevent reactant molecules attacking c-oryzanol. Hydro-lysis, therefore, hardly occurred in the Type C solventsystem.</p><p>e yields of FA obtained using the Type A systemcontained with solvent of water were in the range of37.383.3%, but the yields obtained using the Type B systemcontained with solvent of methanol were only 0.71.8%, andnone of peaks corresponding to ferulic acid esters wereobserved. Hydrolysis and/or transesterification proceedrapidly under homogeneous conditions [30]. However, theseresults indicate that the presence of water as a solvent in thereaction system is important in the hydrolysis reaction.Hydrolysis is an equilibrium reaction; therefore, the FAproduced dissolved in water as the potassium salt, and thenthe forward reaction proceeded to form FA.</p><p>e yields of FA using Type A were investigated byvarying the reaction temperature from 30 to 75C and theKO ratio from 8 to 20 at 75C. e FA yield increased with</p><p>increasing reaction temperature and KO ratios. When theKO ratio was greater than 16, the FA yield reached greaterthan 80% at 75C in 3 h (Table 1). Experimentally, a KO ratioof 20 (A20) was the maximum value for maintaining ho-mogeneous conditions of system, and then, the FA yield of83.3% was obtained wi...</p></li></ul>

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