Lipase - catalyzed Modification of Rice Bran Oil Solid Fat Fraction

This study used a rice bran oil solid fat fraction (RBOSF) to produce cocoa butter alternatives via interesterification reaction catalyzed by immobilized lipase (Lipozyme® RM IM) in hexane. Effects of reaction time (6, 12, and 18 h), temperature (55, 60, and 65°C), mole ratios of 3 substrates [RBOSF:palm olein:C18:0 donors (1:1:2, 1:2:3, and 1:2:6)] were determined. The substrate system was dissolved in 3 mL of hexane and 10% of lipase was added. Two sources of C18:0 donors, stearic acid (SAd) and ethyl stearate (ESd) were used. Pancreatic lipase - catalyzed sn-2 positional analysis was also performed on both substrates and structured lipids (interesterification products). Structured lipids (SL) were analyzed by gas - liquid chromatography (G40.35LC) for fatty acid composition. Major fatty acids of RBOSF were C18:1, oleic acid (OA, 41.15±0.01%), C18:2, linoleic acid (LA, 30.05±0.01%) and C16:0, palmitic acid (PA, 22.64±0.01%), respectively. A commercial raw cocoa butter (CB) contained C18:0, stearic acid (SA, 33.13±0.04%), OA (32.52±0.03%), and PA (28.90±0.01%), respectively. Fatty acids at sn-2 position of RBOSF were OA (46.52±0.63%) and LA (42.98±1.1%), while major fatty acid at sn-2 position of CB was OA (85.24±1.22%). The RBOSF had low SA (2.40±0.01%) compared to CB (33.13±0.04%). The content of OA (46.52±0.63%) at sn-2 position in RBOSF was half of that found in CB (85.24±1.22%). Optimal reaction was 1:2:6 mole ratio of the substrate (RBOSF:PO:SAd), at 65°C for 12 h. Fatty acid compositions of the SL were 31.72±0.99% SA, 30.91±0.53% LA, 23.18±0.32% OA, and 13.26±0.34% PA, respectively. Fatty acids at sn-2 position of the SL were 53.72±4.21% OA, 25.11±3.69% LA, 14.18±1.58% PA, and 6.99±0.02% SA, respectively. DSC curves showed the melting point of CB at 20.94°C, while those of the SL were 14.15 and 40.35°C, respectively. The melting completion temperature (Tmc) of CB was 25.5°C while that of SL was 43.9°C, respectively.