Green Process for the Enzymatic Synthesis of Aroma Compounds Mediated by Lipases Entrapped in Tailored Sol–Gel Matrices

Abstract

We report a simple enzymatic procedure for the synthesis of short-chained flavor esters by direct esterification of natural acids with short-chain primary alcohols mediated by lipase B from Candida antarctica entrapped in a tailored sol–gel matrix in the presence of three additives, using vacuum for water removal. Maximal immobilization yields (100%) were obtained for all three biocatalysts, while the enzyme loading and the synthetic activity depend on the used additive (6.7, 7.6, and 7.7 μg enzyme/mg biocatalyst for β-cyclodextrin, polyvinyl alcohol, and glycerol, respectively, and 76–110% recovered activity as compared with free lipase). The process was optimized using the reaction of hexan-1-ol with butyric acid as the model with significant conversion improvements (from <40% to >94%) reducing the alcohol/enzyme ratio (from 100:1 to 25:1 weight ratio) for all novel biocatalysts. Other short-chain flavor esters were prepared with excellent yields (>90%) under the previously established optimal conditions. Atom economy (90.53), E-factor (17.22), atom efficiency (88.36), mass intensity (18.58), and reaction mass efficiency (60.07) as relevant sustainability metrics were calculated for the preparative scale model reaction with glycerol as the additive. Based on our results, this green and sustainable new approach can be used for the synthesis of many flavor esters.

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

“…17–21 Nevertheless, it is still quite a utilized enzyme immobilization strategy today. 22–24 Here the enzyme is coated with a silicate that is formed by polymerization of different polymers, that require a curing step usually coupled to UV irritation or heat, the immobilization is trapped and require the formation of small pores, that generate high diffusional restrictions. Due to the hydrophobicity of these systems, results in terms of activity recovery and stability use to be not very high, in fact some authors propose to previously immobilize the enzyme in a porous support before trapping on the sol–gel matrix.…”

Deep eutectic solvents – a new additive in the encapsulation of lipase B from Candida antarctica: biocatalytic applications

“…The sol-gel entrapment of CaL-B was performed using a previously reported protocol: 31 the mixture of 0.5 mL CaL-B solution (8.2 mg mL −1 ), 100 μL 1 M NaF, 200 μL isopropyl alcohol and 200 μL of different additives (4% aqueous solution, additives presented in Table 1) was shaken (500 rpm) in a 4 mL glass vial for 30 minutes at room temperature. After completing the homogenization, 3 mmol silane precursors were added (OTEOS/n-PTMOS/TMOS in a 1.6 : 0.4 : 1 molar ratio).…”

“…Popular additives described in the recent literature are ILs 30 and polyhydroxy compounds such as glycerol, β-cyclodextrin and polyvinyl alcohol. 31 Sol-gel entrapped CaL-B can be classified as a nanostructure due to the fact that the median size of sol-gel particles is in the nano range, of course depending on the mixture of organosilane precursors used in the immobilization. Nanosupports present several advantages such as: a larger surface-to-volume ratio, high porosity and high mass transfer.…”

Producing Natural Flavours from Isoamyl Alcohol and Fusel Oil by Using Immobilised Rhizopus oryzae Lipase

“…The typically poor selectivity of chemically catalysed processes can result in unwanted side reactions yielding racemic mixtures, rather than pure substances, and even by-products. Besides, the processes usually require harsh conditions that are scarcely compatible with Green Chemistry, a positive industrial trend to face the present environmental crisis and comply with increasingly stringent public policies [6][7][8]. Also, European Legislation (EC 1334/2008, EC 32/2009) precludes labelling chemically produced esters as natural, which has placed them at a loss on the growing market for natural products [9].…”