Effect of moisture content on immobilized lipase‐catalyzed triacylglycerol hydrolysis under supercritical carbon dioxide flow in a tubular fixed‐bed reactor

Abstract

Surplus fats and oils were reacted with several lipases under supercritical fluid conditions for the purpose of obtaining value-added products. Lipases, however, require sufficient moisture content to act as effective biocatalysts. An immobilized lipase from Candida antarctica was chosen to examine the rate of enzyme moisture loss under laboratory ambient conditions and also under supercritical fluid conditions. A more important aspect was to determine the effect of lipase moisture content on the hydrolysis of triacylglycerols under the same supercritical fluid conditions. Under ambient conditions at constant air flow, the immobilized lipase lost water at the rate of 4 to 5%/h, from 48.3% moisture to a final moisture content of 0.2%. Water is known not to be very soluble in supercritical carbon dioxide (SC-CO 2 ). Nevertheless, under supercritical fluid conditions of 60°C, 4000 psi, and carbon dioxide flow rates of 0.5 or 1 L/min measured as expanded gas, the enzyme moisture loss was approximately 2 to 6%/h. To determine the effect of moisture loss on enzymatic hydrolysis, lipase beds in a tubular reactor with moisture contents of 1.5 to 23.5% were reacted with tripalmitin under supercritical conditions. A lipase with an initial moisture content of 1.5% gave little evidence of hydrolysis whereas those containing 5.4 to 23.5% moisture content resulted in products that contained only palmitic acid and unreacted tripalmitin. Thus, optimal parameters for continuous lipase hydrolysis of tripalmitin require: enough enzyme moisture to compensate for complete substrate hydrolysis; sufficient enzyme moisture for losses due to water solubility in SC-CO 2 ; temperature and pressure sufficient to solubilize the tripalmitin; high carbon dioxide total flow to solubilize all the tripalmitin; and a relatively large enzyme bed volume to increase the solubilized substrate contact time with the enzyme.

Effects of Water on Enzyme Performance with an Emphasis on the Reactions in Supercritical Fluids

“…They showed that the optimum water content was dependent on glycerol content, which was about 6% (w/w) of the glycerol at 0.10 g glycerol/mL substrate solution. In agreement with most of the studies above, Hampson and Foglia (1999) reported that for the hydrolysis of tripalmitin in SCCO 2 at 27 MPa and 60 • C, the immobilized lipase from Candida antarctica with 1.5% moisture content did not cause hydrolysis.…”

“…In the above study, Hampson and Foglia (1999) reported that the enzyme with 5.4-23.5% initial moisture content led to the products with palmitic acid and unreacted tripalmitin only. This indicates a full hydrolysis of the reacted tripalmitin without any intermediate products, mono-and dipalmitin.…”

Lipase‐catalyzed esterification of stearic acid with ethanol, and hydrolysis of ethyl stearate, near the critical point in supercritical carbon dioxide

“…Thus, lipase-catalyzed reactions in SCCO 2 have been carried out for such reactions as hydrolysis of tripalmitin (5) and canola oil (6); alcoholysis of cod liver oil (7) and palm kernel oil (8); glycerolysis of soybean oil (9); synthesis of oleoyloleate from oleic acid (10)(11)(12); acylation of glucose with lauric acid (13); thioesterification between oleic acid and butanethiol (14); transesterifications of milk fat with canola oil (15); tristearin with palm oil (16); palm oil with stearic acid (SA) (17); triolein with ethyl behenate and behenic acid (18,19); triolein with SA (20) and propyl acetate with geraniol (21); and randomization of fat and oils (22).…”

Synthesis and Characterization of Phenolic Lipids

“…Furthermore, lipase catalyzed hydrolysis reactions only in the presence of amount of water. This is due to the fact that water molecules participate in the breaking of covalent bond in the substrate as well as subsequent incorporation of their elements into these bonds to form reaction products [66].…”