Change in glyceride composition of olive pomace oil during enzymatic esterification Fahrettin Gög ˇüs ˛ , Sibel Fadılog ˇ lu and Ozan Nazım Þiftçi 1 Introduction Olive pomace is the pulpy material remaining after remov- ing most of the oil from the olive paste. The commercial value of the olive pomace depends mainly on its oil and water con- tent which in turn depends on the process applied and on the operating conditions [1]. Olive pomace contains about 8% oil. The recovery of oil from olive pomace is carried out by extrac- tion with solvent [2]. The raw, unrefined oil extracted from the pomace is dark green and has a medium to high free acidity. The oil in olive pomace undergoes rapid deterioration due to the moisture content which favors triacylglycerol hydrolysis [1]. Carola [3] reported that the acidity of olive pomace oil may increases from 5 to 60% in a short time. Olive pomace oils with high acidity were mostly used for the production of household soaps, before detergents appeared on the market. Refined olive pomace oil is an acceptable edible oil. Its chemi- cal composition does not differ from refined olive oil [1]. In the last few years, olive pomace oil has an increasing demand to be used as edible oils for frying or similar purposes. After refining, this oil may be used for edible purposes [4]. In order to make the oil edible, it has to be deacidified, bleached, and deodorized [2]. However, its high free fatty acid (FFA) content makes it difficult to process by neutralization. The yield of product is also low and it increases the cost of unit product pro- duced. So it is necessary to reduce the FFA content before refining process [5]. Oneway to reduce the FFA content is to convert the FFAs to glycerides [6]. Ester synthesis has a good potential for indus- trial applications. Nonenzymatic processes for glyceride pro- duction are based either on direct esterification of glycerol with fatty acids or on the interesterification of triglycerides with glycerol (glycerolysis) in the presence of inorganic cata- lysts at high temperatures such as 200–300 8C. These reactions are nonselective and consume large amounts of energy [7]. Lipases are known to be useful catalysts for producing a num- ber of commercially important esters. The application of lipase for esterification reactions in organic solvents has increased significantly during the last decade [8]. In fact, although lipases were designed by nature to cleave ester bonds of tri- acylglycerols with the concomitant consumption of water molecules (hydrolysis), lipases are also able to catalyze the reverse reaction under microaqueous conditions results in the formation of ester bonds between alcohol and carboxylic acid moieties (ester synthesis) [9]. The substrates for enzymatic glycerolysis are triglyceride and glycerol in contrast to enzymatic ester synthesis where the substrates are fatty acids and glycerol [10]. The potential use of vegetable oils as a substrate for the production of added- value compounds such as monoglyceride (MG) and diglyceride (DG) is an attractive way to valorize the olive oil industry [4]. Enzymatic esterification has been investigated for the produc- tion of MG and/or DG by several authors [11, 12]. The work reported here describes the application of enzy- matic esterification process of glycerol and FFAs for the synth- esis of triglycerides in olive pomace oil. Experiments were car- ried out with and without glycerol. Effects of glycerol contents on the change in FFAs, MG, DG, and triglyceride (TG) compo- sition of olive pomace oil were investigated. Instead of a model system with only one type of glycerides [7], a natural product, olive pomace oil, was used to observe the nature of exact reac- tion system. 2 Materials and methods 2.1 Materials Olive pomace oil and immobilized lipase from Candida ant- arctica (Novozym 435, activity 7000 PLU/g) were kindly pro- vided by Güvenal Sabun Pirina Yag ˇ San. ve Tic. A.S ˛ . (Gazian- tep, Turkey) and Novo Nordisk A/S (Bagsvaerd, Denmark), respectively. Glycerol and molecular sieve (particle size of 5 ) were purchased from Sigma Chemical (St. Louis, MO, USA), hexane, acetone, and acetonitrile were high-perform- ance liquid chromatography (HPLC)-grade and purchased from Merck Chemical (Darmstadt, Germany). Standards for fatty acids (stearic, palmitic, oleic) and triglyceride mixtures were also supplied from Sigma Chemical. 2.2 Glycerolysis reactions Glycerolysis reactions were carried out in the absence and presence of different amounts of glycerol. Limiting amount of glycerol (glycerol to FFA molar ratio of 1/3) and half of limit- ing amount of glycerol (glycerol to FFA molar ratio of 1/6) were used in glycerolysis reactions. The limiting glycerol con- i 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/food.200300396 Nahrung/Food 48 (2004) No. 3, pp. 205 – 208 205 Enzymatic esterification of free fatty acids of olive pomace oil with glycerol was investigated. The esterification reaction was carried out in the absence and presence of glycerol (glycerol to free fatty acids (FFA) molar ratio of 1/3 and 1/6). In the absence of glycerol, the FFA concen- tration decreased from 32 to 21% while the triglyceride concentration increased from 33 to 40% after of 8 h of reaction time. The most signifi- cant decrease in FFAs and increase in triglycerides was observed at the limiting concentration of glycerol (glycerol to FFA molar ratio of 1/3). The FFA concentration decreased to 2.5% and the triglyceride concen- tration increased up to 78%. The change in both FFA and triglyceride concentrations was found to be statistically significant (P a 0.05). Correspondence: Prof. Dr. Sibel Fadılog ˇlu, University of Gaziantep, Faculty of Engineering, Food Engineering Department, TK-27310 Gaziantep, Turkey E-mail: fadiloglu@gantep.edu.tr Fax: +90-342-3601105 Abbreviations: DG, diglyderide; FFA, free fatty acid; MG, monogly- ceride; RI, refractive index; TG, triglyceride Keywords: Enzymatic esterification / Lipase / Olive pomace oil /