A comparison of lipase‐catalysed ester and lactone synthesis in low‐water systems: Analysis of optimum water activity

Abstract

We investigated the effects of the lyophilisation medium (enzyme plus buffer salt and additives) and of water activity (a(w)) on the catalytic properties of lipase from Chromobacterium viscosum (lipase CV) in organic solvents; catalysis of ester and lactone synthesis were compared and, despite the similarities of the reactive groups involved in these reactions, some interesting differences were observed. Including 2-[N-morpholino]ethanesulfonic acid (MES) buffer in the lyophilisation medium of lipase CV increased its catalytic activity in transesterification and lactonisation, although the buffer salt requirement for maximal activity differed between the two reactions. Sorbitol, glucose, lactose, 18-crown-6 (crown ether 18-C-6), beta-cyclodextrin and bovine serum albumin were employed as alternative additives in the transesterification reaction, but were not as effective as MES buffer. Salt hydrates were used to investigate the effect of a(w) on esterification and lactonisation reactions catalysed by lipase CV. The maximum rate of hexadecanolide synthesis in toluene occurred at a(w) = 0.48. The optimum a(w) for the transesterification reaction in heptane/alcohol mixtures depended on the alcohol substrate employed (1-heptanol, 2-heptanol, or 3-methyl-3-hexanol) but not on the acyl donor (p-NP acetate or caprylate). The optimum a(w) values for both reactions were unchanged when a common solvent system (toluene/1-heptanol) was employed, indicating that the dependence of enzyme activity on a(w) is an intrinsic property of the enzyme-catalysed reaction and not a function of the solvent or other additives.

Characterization of the volatile organic compounds of Italian ‘Fossa’ cheese by solid‐phase microextraction gas chromatography/mass spectrometry

“…Esters were the most abundant compounds isolated in the headspace of Fossa cheese. Esters can be assigned to enzymatic activity, most frequently by lipases 36, 37. The microorganisms involved in ester formation are mainly yeasts;38 however, some lactic acid bacteria, as well as chemical reactions, can also be responsible for their formation 39.…”

Lipase‐Catalyzed Cellulose Acetylation in Aqueous and Organic Media

“…For example, modification of the enzyme by surfactant or lipid coating may protect the enzyme from denaturation or inactivation from its direct contact with solvents such as DMSO (51 − 53). Proper adjustment of the water content or activity in organic media in terms of the partition of water between the enzyme and organic solvents may satisfy the varied requirement for water by the enzyme in its contact with solvents of different polarity (16, 28, 54, 55). Work is in progress using these as well as other strategies with the aim of optimizing enzymatic synthesis of cellulose esters in organic media.…”

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“…The 2 wt % cellulose solution and vinyl acetate were equilibrated separately in sealed flasks in a shaking incubator at 30°C for 4 days. The reactions were initiated by mixing the preequilibrated phases (11 mL vinyl acetate/g cellulose) and adding lipase A12 (8000 units/g cellulose), followed by adding the corresponding salt hydrates or molecular sieves (10 mg/mL reaction mixture) to maintain the a w throughout the reactions (13,30). In the case of water-saturated condition, the cellulose solution and vinyl acetate were equilibrated in separate sealed desiccators with saturated water vapor in the presence of liquid pure DI water for 4 days.…”

“…A preliminary screening of various salt hydrates was done in the absence of enzyme to test for the compatibility of salts with reaction components (13,26,30). The screening excluded the use of some salt hydrates, for example, those consisting of divalent metal ions such as Figure 5 at a fixed irradiation time of 60 min.…”