# Solid/Gas Synthesis of Isobutyl Propionate Catalyzed by Packed-Bed CalB Cross-Linked Enzyme Aggregates (CLEA)

## TL;DR

Researchers developed a green method using an enzyme-based catalyst to efficiently produce isobutyl propionate, a chemical compound, under sustainable conditions.

## Contribution

The study introduces a novel CalB cross-linked enzyme aggregate (CLEA) formulation for solid/gas synthesis of isobutyl propionate with improved sustainability and efficiency.

## Key findings

- CalB-CLEA achieved 91.71% yield of isobutyl propionate in a solid/gas bioreactor under optimized conditions.
- CalB-CLEA outperformed commercial CalB ImmoPlus in terms of total turnover number and specific space–time yield.
- The CalB-CLEA system is more sustainable and cost-effective for industrial-scale production.

## Abstract

This research examines the viability and effectiveness
of cross-linked
enzyme aggregates (CLEA) ofCandida antarctica lipase B (CalB)/bovine serum albumin (BSA) for the green synthesis
of isobutyl propionate (isoPro) from propionic acid (aciP) and isobutyl
alcohol (isoB). Solid/gas (S/G) biocatalysis is proposed as a more
sustainable alternative to chemical synthesis, which involves toxic
catalysts and harsh conditions, or plant extraction compounds, which
are economically unfeasible for bulk production. A formulation containing
10 mg mL–1 BSA and 3% glutaraldehyde (GA) was selected
based on CalB-CLEA’s demonstrated catalytic efficiency in n-heptane as solvent, along with its thermal and operational
stability. Using 600 mg of the selected CalB-CLEA in the S/G bioreactor
yielded 91.71% isoPro at a water activity (a
w) of 0.52, with a nitrogen flow rate of 62 mL min–1 and a 1:4 acid/alcohol molar ratio, operating at 55 °C and
585 mmHg. Although 1.0 g of commercial CalB ImmoPlus achieved a higher
yield (98.9%), its total turnover number (TTN) (mol product mol–1 enzyme) and specific space–time yield (STYspe) (g product L–1 h–1 mg–1 CalB) under steady-state conditions were
6- and 4-fold lower, respectively, than those of CalB-CLEA. Additionally,
CalB-CLEA eliminates resin disposal costs, yielding similar outputs
with lower enzyme loads while achieving comparable productivity. Ultimately,
the S/G system incorporating CalB-CLEA outperforms both CalB ImmoPlus
(in S/G) and CalB-CLEA (in n-heptane) in green, mass-based
sustainability metrics, underscoring its strong potential for industrial-scale
applications.