Solvent-free enzymatic synthesis of structured lipids from peanut oil and caprylic acid in a stirred tank batch reactor

Structured lipids were synthesized by transesterification of peanut oil and caprylic acid in a stirred-batch reactor. Different substrate molar ratios (1:1 to 1:4, peanut oil/caprylic acid) were used. The reaction was perform ed for 72 h at 50 degrees C catalyzed by IM60 lipase from Rhizomucor miehei (10 g, 2% w/w substrate) in the absence of organic solvent. The highest in corporation of caprylic acid was obtained with a 1:2 molar ratio (peanut oi l/caprylic acid) after 72 h reaction. With a 1:2 molar ratio, the incorpora tion increased by 28% from 1:1. On the other hand, a 1:4 molar ratio gave t he lowest incorporation during the reaction. The effect of different mixing speeds (200, 640, or 750 rpm) on reaction was studied with a 1:2 substrate molar ratio for 24 h. A high incorporation of caprylic acid (14.3 mol%) wa s obtained at 640 rpm, while 200 rpm gave the lowest incorporation (2.2 mol %), suggesting that good mixing is essential in a stirred-batch reactor. Af ter 24 h of reaction at different rpm, IM60 lipase was recovered, washed wi th hexane, and reacted with substrates to study its stability after reactio n at different mixing speeds. The results showed that caprylic acid incorpo ration was similar (24.9, 24.3, 24.2 mol%) at 200, 640, and 750 rpm, respec tively. When 20 g of IM60 lipase (4% w/w substrate) instead of 10 g was use d in a 1:1 substrate molar ratio reaction, the incorporation of caprylic ac id increased by 26% after 72 h. To study enzyme reuse, 10 g of IM60 lipase was used in a 1:1 substrate molar ratio for 24 h at 640 rpm. The incorporat ion of caprylic acid gradually decreased with increased number of reuses. D uring five times of reuse, 15, 13.9, 9.6, 6.7, and 9.7 mol% of caprylic aci d were incorporated into peanut oil, respectively.