Volume 61, No. 1, 1996—JOURNAL OF FOOD SCIENCE—97 Optimization of Sucrose Polyester Synthesis Using Response Surface Methodology CHWEN-JEN SHIEH, PHILIP E. KOEHLER, and CASIMIR C. AKOH ABSTRACT Response Surface Methodology (RSM) was used to evaluate the effects of synthetic variables such as reaction time (6–12 hr), temperature (130– 150°C), and substrate molar ratio of fatty acid methyl esters (FAME) of peanut oil to sucrose (10:1 to 14:1) on the % molar conversion to sucrose polyester, utilizing 10g of free sucrose as the reactant. Optimization of the synthetic reaction was performed by canonical analysis to derive the stationary point. Based on contour plots and canonical analysis, optimum conditions were: reaction time 11.5 hr, synthetic temperature 144°C, and substrate molar ratio 11.4:1. Predicted molar conversion was 43.39% (10g sucrose synthesized 29.4g sucrose polyester) at the optimum point. Experimental data indicated up to 48.4% yield based on theoretical % molar conversion. Key Words: sucrose polyester, contour plot, optimization, response sur- face INTRODUCTION THE FOOD INDUSTRY has introduced the use of sucrose polyes- ters (SPE) in foods as reduced or zero calorie fat and oil sub- stitutes. SPE, a fat substitute consisting of a sucrose molecule with 4–8 fatty acids attached to the hydroxyl group (developed under the trade name of olestra) has potential uses in many food items, especially cooked and fried foods. In addition to having no food calories, SPE has also shown promise in reducing blood cholesterol and body weight of obese individuals (Jandacek et al., 1990). An optimized process for high yield synthesis of SPE would benefit food manufacturers and processors (Akoh and Swanson, 1990). The use of sodium metal as a catalyst in directed interester- ification was reported with yields 99% weight conversion based on sucrose octaacetate (Akoh and Swanson, 1990). Mc- Coy et al. (1989) employed the soap method wherein the syn- thesis of SPE with free sucrose was catalyzed by potassium hydroxide and potassium carbonate. Several patents have been based on the reaction process for making sucrose polyester (Gib- son, 1990; Gibson et al., 1990; Van Der Plank, 1990; Van Der Plank and Rozendaal, 1991; Van Lookeren; 1991; Wagner et al., 1990). Boutte and Swanson (1994) modified the soap method using a rotary evaporator in a laboratory scale experi- ment and suggested approximate reaction parameters. The syn- thesis of SPE was carried out at 135–140°C for 10–12 hr with a fatty acid methyl ester (FAME) to sucrose ratio of 14:1. How- ever, there were no advanced combined effects of reaction pa- rameters nor any detailed optimum conditions specified. Response Surface Methodology (RSM) is a useful statistical technique for investigation of complex processes and has been widely adopted in food science research. The original concept was developed by Box and Wilson (1951) to study relationships between a response and several related factors. The basic the- oretical and fundamental aspects of RSM have been reviewed (Cochran and Cox, 1957; Johnson and Leone, 1964; Hill and Hunter, 1966; Myers, 1971; Box et al., 1978 and 1987; Thomp- son, 1982). The review of RSM and its applications in different Authors Shieh, Koehler, and Akoh are with the Dept. of Food Sci- ence & Technology, Food Science Bldg., The Univ. of Georgia, Athens, GA 30602-7610. Address inquiries to Dr. C.C. Akoh. processing areas was presented by Hill and Hunter (1966), and biological applications were described by Mead and Pike (1975). Myers et al. (1989) reviewed the evolution of RSM from 1966 to 1988 including progress in experimental design, data analysis, and applications. RSM has been successfully applied for optimizing conditions in food research (Mudahar et al., 1989; Crisanta et al., 1990; Batistuti et al., 1991; Mouguet et al., 1992; Abdullah et al., 1993; Shieh et al., 1995), but has not been reported for optimizing the synthesis of sucrose polyester. Our objectives were to better understand the relationships be- tween the factors (reaction time, synthetic temperature, substrate molar ratio) and the response (synthetic yield); and to determine optimum synthetic conditions for SPE production, using RSM and canonical analysis. MATERIALS & METHODS Materials Peanut oil was purchased locally (Athens, GA). Sucrose, potassium hydroxide, sodium hydroxide, molecular sieve 4A ˚ and hydrochloric acid were purchased from J.T. Baker Co. (Phillipsburg, NJ). Naphthoresor- cinol (1,3-naphthalenediol) was purchased from Eastman Kodak Co. (Rochester, NY). Supelco Redi-coats G silica gel 20  20  0.25 cm TLC plates were purchased from Supelco, Inc. (Bellefonte, PA). All organic solvents, potassium carbonate and decolorizing carbon (Norit) were from Fisher Scientific (Norcross, GA). Synthesis and purification SPE was synthesized using FAME derived from peanut oil by the procedure of Akoh and Swanson (1988). The average molecular weight of peanut oil FAME was assumed to be 294.3 based on fatty acid com- position as determined by gas liquid chromatography (GLC). The pro- cedure for synthesis of SPE was according to the patent of McCoy et al. (1989), as modified by Boutte and Swanson (1994). In a typical synthesis, 10g sucrose (0.029 mole) and 102.42g FAME (0.348 mole) were reacted in a 2L round bottom flask attached to a Bu ¨chi rotary evaporator (Bu ¨chi, Switzerland) as the reactor at a speed 200 rpm. The amount of KOH was 2.5% and methanol was 40% by weight of FAME and sucrose. Potassium hydroxide was dissolved in methanol first and FAME was added and stirred at room temperature for 30 min, after which sucrose was added. Reactants were heated to 85°C for 15 min at atmospheric pressure to form a soap and to remove most of the methanol. Remaining methanol was removed by applying intermittent vacuum until foaming subsided, then full vacuum was applied and the mixture was heated to an experimental temperature (130, 140, and 150°C) for the transesterification (ester exchange) reaction. After 2 hr, 0.5% (w/w) po- tassium carbonate was added to catalyze the SPE reaction. At the end of the experimental time (6, 9, and 12 hr), the reaction was cooled to 80°C and neutralized with 2–3 mL of concentrated acetic acid. The crude product was washed five times with 1.5L water (70°C), and five times with 300 mL 95% ethanol at 80°C. Then, SPE was dissolved in hexane, stirred and bleached with decolorizing carbon (30%, w/w) twice. Char- coal particles were removed by filtering SPE solution through a 0.5 μm filter. A KDL-4 short-path distillation apparatus (UIC, Joliet, IL) was used to remove excess FAME and sucrose esters of lower degree of substitution following the method of Boutte and Swanson (1994) with the exception that full vacuum was used. SPE was not steam deodorized. SPE confirmation and analysis Thin layer chromatographic (TLC) analysis of SPE was conducted according to the method of Akoh and Swanson (1987). The solvent