ABSTRACT: The effects of enzymatic transesterification on the melting behavior of palm stearin and palm olein, each blended separately with flaxseed oil in the ratio of 90:10 and catalyzed by various types of lipases, were studied. The commercial li- pases used were Lipozyme IM, Novozyme 435, and mycelium- bound lipases of Aspergillus flavus and A. oryzae. The slip melt- ing point (SMP) of the palm stearin/flaxseed oil (PS/FS) mixture transesterified with lipases decreased, with the highest drop noted for the mixture transesterified with Lipozyme IM. How- ever, when palm stearin was replaced with palm olein, the SMP of the palm olein/flaxseed oil (PO/FS) mixture increased, with the commercial lipases causing an increase of 41 to 48% com- pared to the nontransesterified material. As expected, the solid fat content (SFC) of the transesterified PS/FS was lower at all temperatures than that of the nontransesterified PS/FS sample. In contrast, all transesterified PO/FS increased in SFC, particu- larly at 10°C. Results from DSC and HPLC analyses showed that the high-melting glycerides, especially the tripalmitin of palm stearin, were hydrolyzed. Consequently, 1,3-dipalmitoylglyc- erol was found to accumulate in the mixture. There was no dif- ference in the FA compositions between the transesterified and nontransesterified mixtures. Paper no. J10267 in JAOCS 80, 133–137 (February 2003). KEY WORDS: DSC analysis, high-melting glyceride, palm olein, palm stearin, slip melting points, solid fat content. Varying fat properties tailored to suit the requirements of a product can expand the application of vegetable oils. These changes can be brought about either through simple blending or by enzymatic transesterification. Palm olein or palm stearin, when blended with flaxseed oil, is a unique mixture because it contains the EFA α-linolenic acid, an n-3 FA, and linoleic acid, an n-6 FA, in appreciable amounts. Palm olein and palm stearin blends are used in numerous food and non- food applications. Graille et al. (1) reported that the transes- terification of a palm stearin/palm kernel oil (30:70) mixture for 30 min produced a firm margarine, whereas a soft mar- garine was produced after 3.5 h of treatment. Transesterifica- tion with fluid oils could also give fats that are virtually fluid at 20°C and that could be used as salad oils in tropical countries. By utilizing the specific properties of lipolytic enzymes, one can effect a selective transesterification reaction that is not possible in transesterification using traditional chemical catalysts. Under the right conditions, “tailor-made” glycerides with desired configurations and characteristics can be ob- tained. For example, lipase from Rhizomucor miehei was used by Zainal and Yusoff (2) as a catalyst in the enzymatic inter- esterification of palm stearin and palm kernel olein to achieve the physical properties of margarine fats. A commercial im- mobilized 1,3-specific R. miehei lipase also has been reported to reduce the m.p. of a tallow/rapeseed oil mixture (3). Lai et al. (4) reported using nonspecific (Pseudomonas sp.) and 1,3- specific (R. miehei) lipases for the transesterification of palm stearin and sunflower oil, resulting in melting properties ap- propriate for use as table margarine. The present study deals with the solid fat content (SFC) and the melting and crystal- lization behavior of palm stearin/flaxseed oil (PS/FS) and palm olein/flaxseed oil (PO/FS) mixtures, at a 90:10 (w/w) mass ratio, following tranesterification using commercial and mycelium-bound lipases. MATERIALS AND METHODS Materials. Refined, bleached, and deodorized palm stearin and palm olein were obtained from Golden Jomalina Indus- tries Sdn. Bhd. (Kuala Langat, Selangor, Malaysia), and flaxseed oil was obtained from Waihi Bush Ltd. (Woodbury, Geraldine, New Zealand). Commercial lipases, Lipozyme IM, and Novozyme 435 were obtained from Novo Nordisk Indus- try A/S (Copenhagen, Denmark), and mycelium-bound li- pases of Aspergillus flavus and A. oryzae were prepared ac- cording to the method of Long et al. (5). All other chemicals and solvents used were of the highest purity available. Transesterification reaction. PS/FS and PO/FS mixtures were formulated in the mass ratio of 90:10 (w/w). The enzy- matic reaction was carried out by mixing 50 g of oil blends with 1.5 g of lipase and agitating in an orbital shaker at 45°C, 200 rpm. After a 2-h reaction, 6 g of molecular sieve was added (to adsorb water) and the reaction was allowed to proceed for an- other 4 h. Sample was then filtered to separate the enzyme and Copyright © 2003 by AOCS Press 133 JAOCS, Vol. 80, no. 2 (2003) *To whom correspondence should be addressed at Food Technology Centre, Malaysia Agricultural Research and Development Institute, P.O. Box 12301, 50774 Kuala Lumpur, Malaysia. E-mail: amai@mardi.my Effect of Enzymatic Transesterification with Flaxseed Oil on the High-Melting Glycerides of Palm Stearin and Palm Olein K. Long a, *, I. Zubir a , A.B. Hussin a , N. Idris b , H.M. Ghazali c , and O.M. Lai c a Food Technology Centre, Malaysia Agricultural Research and Development Institute, 50774 Kuala Lumpur, Malaysia, b Palm Oil Research Institute of Malaysia, Bandar Baru Bangi, 43650 Selangor, Malaysia, and c Department of Biotechnology, Faculty of Food Science and Biotechnology, Universiti Putra Malaysia, UPM 43400 Serdang, Selangor, Malaysia