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Abstract
Structured lipids (SLs) were synthesized from roasted sesame oil and caprylic acid by Rhizomucor miehei lipase-catalyzed acidolysis and phytosteryl esters (PEs) were synthesized from phytosterols and oleic acid by Candida rugosa lipase-catalyzed esterification. The reactions were modeled by response surface methodology, respectively, and their optimal reaction conditions were established using the models, respectively. For SLs, the substrate molar ratio (caprylic acid/sesame oil) should be kept as high as possible (6.0) and relatively low temperature (45.0 C) was required to maximize total incorporation and minimize acyl migration. Furthermore, total incorporation should be kept below 55 mol% caprylic acid to prevent decrease in quality and yield of targeted SLs. The optimal reaction conditions for PEs were: temperature, 51.3 C; reaction time, 17.0 h; substrate molar ratio (oleic acid/phytosterols), 2.1; enzyme amount, 7.2%; and degree of esterification was 97.0 mol% under these conditions. The SLs were produced in a bench-scale continuous packed bed reactor under the optimal reaction conditions established above. Total incorporation and acyl migration of caprylic acid in the SLs were 42.5 mol% and 3.1 mol%, respectively. The SLs displayed different physicochemical properties: lower viscosity, lower melting and crystallization temperature ranges, higher melting and crystallization enthalpies, higher smoke point, higher saponification value, and lower iodine value, in comparison to unmodified sesame oil. There was no difference in the contents of tocopherols and phytosterols. However, total sesame lignans content was decreased in SLs due to the loss of sesamol and most volatiles were removed from SLs during short-path distillation of SL. The dietary effects of SLs and PEs on the blood lipid profiles and cardiovascular parameters were investigated in spontaneously hypertensive rats. Rats fed sesame oil fortified with PEs or SLs fortified with PEs showed higher plasma high density lipoprotein (HDL) cholesterol levels and higher plasma HDL/total cholesterol ratios than those fed lard, sesame oil or SLs. There was no notable difference in plasma lipid profiles of rats fed SLs compared to those fed lard or sesame oil. Resting arterial blood pressures in the rats fed high-fat diets including SLs or PEs were not different from controls (rats fed normal diet); however, resting heart rates in the rats fed high-fat diets were higher than the controls.