Integrating kinetics with thermodynamics to study the alkaline extraction of protein from Caragana korshinskii Kom.

Extraction and recovery of protein from abundant plant biomass is one potential way to improve the economic feasibility of biorefineries. However, valorization of the protein fraction is challenging due to its low yield (kg protein extraction/kg biomass). In order to reveal the limiting operation parameters, the alkaline extraction process of protein from Caragana korshinskii Kom. was investigated by an integrative analysis of kinetics and thermodynamics. Both a two-site kinetic extraction model and a second-order model indicated that particle size is the most pivotal factor affecting protein extraction yield. In a two-site model, most proteins are extracted quickly from broken cells, while protein removal from the intact cells takes much longer; these are the faster and slower processes, respectively. A decrease of particle size from 20-40 to 60-80 mesh resulted in a decrease of C2 (protein yield in the slower process) from 14.02 to 7.32 mg g(-1), but a great increase of C1 (protein yield in the faster process) from 20.61 to 59.07 mg g(-1) . However, the protein yield was dominated by the faster process when the average particle size is under 80 mesh. The maximum initial extraction rate was 72.20 mg g(-1) min(-1) with the particle size of 60-80 mesh, almost ninefold of that with 20-40 mesh. Thermodynamic analysis revealed that the enthalpy change (ΔH) and entropy change (ΔS) in the protein extraction process were calculated as 21.08 kJ mol(-1) and 84.76 J K(-1), respectively. The standard free energy (ΔG) had a magnitude from -3.77 to -5.46, suggesting that the extraction process was spontaneous and physically feasible.