Effects of Particle Size of Sucrose Suspensions and Pre‐incubation of Enzymes on Lipase‐Catalyzed Synthesis of Sucrose Oleic Acid Esters

Abstract

The effects of high‐speed homogenization, high‐intensity ultrasound, and their combination were evaluated for the reduction of the particle size of sucrose crystals to enhance solvent‐free lipase‐catalyzed synthesis of sucrose oleate at 65 °C. The combination of homogenization and ultrasound greatly decreased the particle size of suspended sucrose crystals in mixtures of oleic acid/sucrose oleate (86 wt% monoester and 14 wt% diester at a ratio of 90/10 w/w) from 88 to 18 μm. The suspension‐based medium was charged to a stirred tank bioreactor that also contained immobilized lipase from Rhizomucor miehei or Candida antarctica (Lipozyme®IM and Novozym® 435, respectively; Novozymes, Franklinton, NC, USA), that was pre‐incubated in oleic acid for several different temperatures (23–60 °C), durations (4–24 h), and stir rates (50–400 rpm, radius of 3 cm), prior to use. The optimal performance was achieved using C. antarctica lipase (83.3 wt% ester, consisting of 46 wt% monoester) in the presence of molecular sieves (18 wt%). The low water concentration (~0.12 wt%) did not affect the activity of C. antarctica lipase.

Solvent-Free Lipase-Catalyzed Synthesis of Technical-Grade Sugar Esters and Evaluation of Their Physicochemical and Bioactive Properties

“…The saccharide concentration in the liquid phase of the reaction medium decreased during the time course of reaction due to its consumption by the reaction; however, saccharide was not completely consumed ( Figure 1C). It appears that the ultra-low water concentration did not negatively affect CALB activity, in agreement with the results in literature [20,24]. As shown in Figure 1D, the proportion of monoester decreased during the time course of both reactions, from 90% to 60%-70%.…”

“…HPH reduced the particle sizes of saccharide crystals in the solvent-free suspension media from 91.5˘2.8 µm to 2.1˘0.6 µm for fructose oleate and 98.7˘2.1 µm to 3.3˘0.8 µm for sucrose oleate (data not shown), a 6-7-fold reduction in particle size than that produced by high-speed homogenation plus ultrasound [20]. Figure 1 depicts the time course of sucrose and fructose-oleic acid esterification after implementation of the three strategies.…”

“…Sucrose laurate was purchased from Modernist Pantry (purity > 99%, Portsmouth, NH, USA). Tween ® 80, polyoxyethylene (20) sorbitan monooleate, was obtained from Sigma-Aldrich (St. Louis, MO, USA). Deionized water was used throughout and all materials were used without further purification.…”

“…The decrease is attributable to differences in the inherent regioselectivity between CALB and RML [25,26], the latter used to prepare the initial reaction medium. An additional factor is the lower water concentration for CALB due to its more hydrophobic immobilization matrix, which results in the more hydrophobic microenvironment for the enzyme, thereby enhancing the transformation of monoester into diester [20,27]. Upon completion of the biochemical reactions, the only purification enacted was the removal of CALB by sedimentation.…”

“…When reaching approximately 60 wt % ester, a stronger water removal method was introduced to increase the yield, e.g., the combination of N 2 bubbling and vacuum pressure or molecular sieves, which decreased the water concentration in the liquid phase from~0.8 wt % to~0.4 wt %. This approach generated a yield 69~92 wt % esters within 132 h. Recently, the combination of high-speed homogenization and high-intensity ultrasound was utilized to reduce the particle size of sucrose crystals five-fold, enhancing the rate and extent of reaction [20].…”