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 performed for 72 h at 50°C catalyzed by IM60 lipase from Rhizomucor miehei (10 g, 2% w/w substrate) in the absence of organic solvent. The highest incorporation of caprylic acid was obtained with a 1:2 molar ratio (peanut oil/caprylic acid) after 72 h reaction. With a 1:2 molar ratio, the incorporation increased by 28% from 1:1. On the other hand, a 1:4 molar ratio gave the 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%) was 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. After 24 h of reaction at different rpm, IM60 lipase was recovered, washed with hexane, and reacted with substrates to study its stability after reaction at different mixing speeds. The results showed that caprylic acid incorporation was similar (24.9, 24.3, 24.2 mol%) at 200, 640, and 750 rpm, respectively. When 20 g of IM60 lipase (4% w/w substrate) instead of 10 g was used in a 1:1 substrate molar ratio reaction, the incorporation of caprylic acid 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 incorporation of caprylic acid gradually decreased with increased number of reuses. During five times of reuse, 15, 13.9, 9.6, 6.7, and 9.7 mol% of caprylic acid were incorporated into peanut oil, respectively.