Journal of Oleo Science Copyright ©2017 by Japan Oil Chemists’ Society doi : 10.5650/jos.ess16224 J. Oleo Sci. 66, (9) 951-961 (2017) Characterization of Coconut Oil Fractions Obtained from Solvent Fractionation Using Acetone Sopark Sonwai＊ , Poonyawee Rungprasertphol, Nantinee Nantipipat, Satinee Tungvongcharoan and Nantikan Laiyangkoon Department of Food Technology, Faculty of Engineering and Industrial Technology, Silpakorn University, THAILAND Abstract: This work was aimed to study the solvent fraction of coconut oil (CNO). The fatty acid and triacylglycerol compositions, solid fat content (SFC) and the crystallization properties of CNO and its solid and liquid fractions obtained from fractionation at different conditions were investigated using various techniques. CNO was dissolved in acetone (1:1 w/v) and left to crystallize isothermally at 10℃ for 0.5, 1 and 2 h and at 12℃ for 2, 3 and 6 h. The solid fractions contained significantly lower contents of saturated fatty acids of ≤ 10 carbon atoms but considerably higher contents of saturated fatty acids with > 12 carbon atoms with respect to those of CNO and the liquid fractions. They also contained higher contents of high-melting triacylglycerol species with carbon number ≥ 38. Because of this, the DSC crystallization onset temperatures and the crystallization peak temperatures of the solid fractions were higher than CNO and the liquid fractions. The SFC values of the solid fractions were significantly higher than CNO at all measuring temperatures before reaching 0% just below the body temperature with the fraction obtained at 12℃ for 2 h exhibiting the highest SFC. On the contrary, the SFC values of the liquid fractions were lower than CNO. The crystallization duration exhibited strong influence on the solid fractions. There was no effect on the crystal polymorphic structure possibly because CNO has β’-2 as a stable polymorph. The enhanced SFC of the solid fractions would allow them to find use in food applications where a specific melting temperature is desired such as sophisticated confectionery fats, and the decreased SFC of the liquid fractions would provide them with a higher cold stability which would be useful during extended storage time. Key words: coconut oil, fractionation, crystallization, solid fat content, polymorphism 1 Introduction food industry5）. Therefore, these fats are usually modified Coconut oil（CNO）is one of the most important oil crops via processes such as fractionation and hydrogenation to in tropical regions. It is an edible oil obtained from matured improve their quality. Due to its low melting temperature coconuts. CNO is thought to be beneficial to health and lack of plasticity and hardness, CNO cannot be used in because it contains high amount of medium-chain triacylg- food products such as margarines, chocolate coatings and lycerols （TAGs）, which are composed mainly of saturated coffee whiteners without modification. fatty acids with chain length from 6 to 12 carbon atoms1）. Fractionation or fractional crystallization is a common The main fatty acid components in CNO are lauric acid technique for fat and oil modification that allows the sepa- （42.6％）and myristic acid（21％）2）. Medium-chain TAGs ration of TAGs in fractions with different melting ranges are hydrolyzed faster and more completely than long-chain and physical properties that are suitable for a variety of TAGs3）, hence, they are used immediately as energy food products6）. Fractionation consists of a controlled crys- sources in the body and avoid being stored in the adipose tallization in bulk crystallizers followed by a physical sepa- tissue2）. Moreover, it has been shown that medium-chain ration of the liquid fraction（olein）from the crystalline TAGs may reduce the incorporation and storage of dietary fraction（stearin）7）. For the fractionation of natural fats and fats and oil in adipose tissue4）. However, fats rich in satu- oils, which are complex mixtures of numerous TAG rated fatty acids usually contain a wider variety of TAG species, olein fraction is enriched in triunsaturated and species that are associated with broader melting ranges monosaturated TAGs hence exhibiting a higher cold stabili- and which are not appropriate for many applications in the ty. On the other hand, disaturated and trisaturated TAGs ＊Correspondence to: Sopark Sonwai, Department of Food Technology, Faculty of Engineering and Industrial Technology, Silpakorn University, THAILAND E-mail: [email protected] Accepted April 21, 2017 (received for review December 1, 2016) Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online http://www.jstage.jst.go.jp/browse/jos/ http://mc.manusriptcentral.com/jjocs 951 S. Sonwai, P. Rungprasertphol, N. Nantipipat et al. concentrate in the stearin fraction giving it a specific controlled double jacket crystallizer. Fractionation was melting behavior suitable for a specific application. The carried out at 10℃ for 0.5, 1 and 2 h and at 12℃ for 2, 3 basis of such fractionation resides in the solubility of the and 6 h with a constant agitation rate of 25 rpm. After frac- TAG species in the liquid phase at controlled temperatures, tionation, samples were separated by vacuum filtration which is dependent on the molecular weight and degree of using a Whatman No.1 filter paper to obtain the liquid and unsaturation8）. Industrial-scale fractionation is classified solid fractions of CNO. Acetone was removed from the into three main groups, such as dry, detergent, and solvent liquid fractions using a rotary vacuum evaporator with fractionation9）. The main advantage of solvent fractionation moderate heating. Then, remaining solvent in all fractions is the great separation efficiency and the enhanced yield of was further removed using nitrogen flushing. All samples the targeted phase compared to the other methods10）. were kept at －18℃ prior to analysis. Different abbrevia- The aim of this study was to characterize TAG and fatty tions were designated to all solid and liquid fractions ac- acid compositions, solid fat content and crystallization cording to their crystallization temperature and duration as properties of the solid and liquid fractions of CNO obtained shown in Table 1. The yields of the solid fractions obtained from solvent-fractionation with different conditions（crys- at different fractionation conditions are also given in Table tallization temperature and cluration）. This was hoped to 1. create different fractions of CNO that would meet specific requirements for different food applications. 2.3 Fatty acid compositions CNO and its solid and liquid fractions were converted into fatty acid methyl esters using AOAC official method 969.3311）. The fatty acid methyl esters analysis was per- 2 Materials and Methods formed in a Shimadzu GC with flame ionization detector 2.1 Materials （GC-FID）. The system had an VertiBondTM wax capillary Refined, bleached and deodorized CNO was purchased column（50 m long, 0.25 mm internal diameter and 0.20 μm from Katevanich Industry Co., Ltd.（Nakhonpathom, Thai- film thickness）. Compound identification was carried out land）and used without further treatment. Its free fatty acid using external standards of fatty acids methyl esters. content（as oleic acid）was ＜0.02％. The standard fatty Helium was used as a carrier gas with a flow rate of 1 mL/ acid methyl esters for fatty acid analysis using gas chroma- min and with a controlled initial pressure of 93.2 kPa at tography（GC）were purchased from AccuStandard, Inc. 120℃. N2 and air were makeup gases. The injection tem- （USA）. The standards for TAG analysis using high perfor- perature was 210℃, and the oven temperature program mance liquid chromatography（HPLC）were purchased from was holding at 120℃ for 3 min before increasing at a rate Sigma Chemical Co.（St. Louis, MO, USA）. Acetone and of 10℃/min to 220℃, holding at this temperature for 30 acetonitrile were of HPLC grade from Burdick and Jackson min, increasing at a rate of 5℃/min to 240℃, followed by （Muskegon, MI, USA）. All other chemicals and solvents holding at 240℃ for 30 min. The split ratio was 100:1, the used were obtained commercially and were of the highest injection volume was 1 μL, and the detector temperature purity available. was 280℃. After the samples were analyzed, their chro- matograms were acquired and the fatty acid contents were 2.2 Fractionation of coconut oil calculated based on percentage of peak area. A mass of 100 g of CNO was melted at 80℃ for 10 min and cooled to 50℃ before being mixed with 100 ml of 2.4 Triacylglycerol compositions warm acetone（50℃）and transferred to a temperature- The TAG compositions of the mixtures were determined Table 1 Abbreviations for all solid and liquid fractions and the yield of all solid fractions obtained from fractionation at different conditions. Abbreviations Fractionation conditions Yield of solid fractions Solid fractions Liquid fractions ℃ Temperature ( ) Duration (h) (％ wt.) S10C0.5h L10C0.5h 0.5 17.9±1.9 S10C1h L10C1h 10 1 33.1±3.5 S10C2h L10C2h 2 47.2±3.7 S12C2h L12C2h 2 11.0±0.7 S12C3h L12C3h 12 3 13.6±0.8 S12C6h L12C6h 6 18.4±1.7 952 J. Oleo Sci. 66, (9) 951-961 (2017) Solvent fractionation of coconut oil by HPLC（Shimadzu LC-20 AD, Shimadzu Corp, Kyoto, tinuously recorded for 6 h. Japan）with system controller CBM-20A and diode array detector SPD-M20A. Two C-18 columns（Inertsil ODS-3; 4.6 2.8 Crystal morphology ×250 mm; 5 μm particle size; by GL Sciences Inc., Japan） Crystal network microstructure of the all samples was were used in series. The mobile phase consisted of acetone observed by polarized light microscopy（PLM）（ Olympus and acetonitrile（70:30, v/v）with a flow rate of 0.72 mL/min. BX51, Olympus Optical Co., Ltd., Tokyo, Japan）equipped The column temperature was set at 35℃ with a column with a digital camera（Olympus C- 7070, Olympus Optical heater（Shimadzu CTO-10AS column oven）.