The objective of this research was to study the kinetics of synthesis of a commercially important ester - Isopropyl Palmitate (IPP) using immobilized lipase (Lipozyme IM). It was studied in a packed bed differential reactor. In order to establish the kinetics of the reaction, parameters such as linear velocity of the fluid through the reactor, particle size, substrate concentration, substrate molar ratio, temperature and water activity were studied. Operational and storage stability of the enzyme were also assessed. The reaction followed Michaelis-Menton kinetics as observed from the relationship of initial rate of the reaction as a function of substrate concentration. It was found that the optimum substrate concentration was 0.15M palmitic acid and isopropyl alcohol in 1:1 stoichiometric ratio. Inhibition by excess of isopropyl alcohol has been identified. The optimum temperature for the esterification reaction was found to be around 50 degrees C. The activation energy of this process was determined to be 43.67 kJ/mol. The optimum water content was 0.50%. The reaction rates were measured in the absence of any significant external diffusional limitations. Since internal diffusional limitations could not be eliminated, the kinetics observed is only apparent.
Several human clinical trials have now evaluated palm oil's effects on blood lipids and lipoproteins. These studies suggest that palm oil and palm olein diets do not raise plasma TC and LDL-cholesterol levels to the extent expected from its fatty acid composition. With maximum substitution of palm oil in a Western type diet some coronary heart disease risk factors were beneficially modulated: HDL2-cholesterol was significantly increased while the apolipoprotein B/A1 ratio was beneficially lowered by palm oil. Comparison of palm olein with a variety of monounsaturated edible oils including rapeseed, canola, and olive oils has shown that plasma and LDL-cholesterol were not elevated by palm olein. To focus these findings, specific fatty acid effects have been evaluated. Myristic acid may be the most potent cholesterol raising saturated fatty acid. Palmitic acid effects were largely comparable to the monounsaturated oleic acid in normolipidaemic subjects while trans fatty acids detrimentally increased plasma cholesterol, LDL-cholesterol, lipoprotein Lp(a) and lowered the beneficial HDL-cholesterol. Apart from these fatty acids there is evidence that the tocotrienols in palm oil products may have a hypocholesterolaemic effect. This is mediated by the ability of the tocotrienols to suppress HMG-CoA reductase. These new findings on palm oil merit a scientific reexamination of the classical saturated fat-lipid hypothesis and its role in lipoprotein regulation.
To compare the effects of dietary palmitic acid (16:0) vs oleic acid (18:1) on serum lipids, lipoproteins, and plasma eicosanoids, 33 normocholesterolemic subjects (20 males, 13 females; ages 22-41 years) were challenged with a coconut oil-rich diet for 4 weeks. Subsequently they were assigned to either a palm olein-rich or olive oil-rich diet followed by a dietary crossover during two consecutive 6-week periods. Each test oil served as the sole cooking oil and contributed 23% of dietary energy or two-thirds of the total daily fat intake. Dietary myristic acid (14:0) and lauric acid (12:0) from coconut oil significantly raised all the serum lipid and lipoprotein parameters measured. Subsequent one-to-one exchange of 7% energy between 16:0 (palm olein diet) and 18:1 (olive oil diet) resulted in identical serum total cholesterol (192, 193 mg/dl), low-density lipoprotein cholesterol (LDL-C) (130, 131 mg/dl), high-density lipoprotein cholesterol (HDL-C) (41, 42 mg/dl), and triglyceride (TG) (108, 106 mg/dl) concentrations. Effects attributed to gender included higher HDL in females and higher TG in males associated with the tendency for higher LDL and LDL/HDL ratios in men. However, both sexes were equally responsive to changes in dietary fat saturation. The results indicate that in healthy, normocholesterolemic humans, dietary 16:0 can be exchanged for 18:1 within the range of these fatty acids normally present in typical diets without affecting the serum lipoprotein cholesterol concentration or distribution. In addition, replacement of 12:0 + 14:0 by 16:0 + 18:1, but especially 16:0 or some component of palm olein, appeared to have a beneficial impact on an important index of thrombogenesis, i.e., the thromboxane/prostacyclin ratio in plasma.