Effect of oxygen transfer rate in stirred tank and air-lift bioreactors for Theobroma cacao cell culture

Plant cell cultures for metabolite production have been performed in stirred tank bioreactor (STB) and air-lift bioreactor (AB). However, to optimize plant cell cultures and evaluate their perspectives for scale-up it is necessary to study the effect of the oxygen transfer rate (OTR) as a function of the volumetric oxygen transfer coefficient (k_La). The aim of this work was to evaluate the effect of the k_La in 7.5L STB and AB of Theobroma cacao cell cultures for polyphenol production. For this purpose, four empirical models of k_La for different impeller-gas sparger configurations were obtained in STB. The results evidenced that pitched-blade–microbubbles (PB-Mi) configuration reached k_La values from 17.92 to 53.89 h^‑1. On the other hand, pitched blade – perforated ring (PB-PR) configuration reached k_La values from 2.41 to 32.18 h^‑1. In the AB, two empirical models of k_La for two types of gas spargers were obtained. The results showed that the stainless-steel mesh reached k_La values between 7.16 to 31.36 h^‑1. An optimal k_La value of 27.13±0.25 h^‑1 in STB for T. cacao cell culture a volumetric productivity of 0.835±0.034 g L^‑1 day^‑1 and a cell viability of 79.2±3.0% after 14 days of culture. Additionally, the total polyphenol content (TPC) was 34.193±2.739 mg GAE g^‑1, in which the content of (+)-catechin and (-)-epicatechin was 0.55±0.07 and 3.23±0.44 mg g^‑1, respectively. For AB the optimal k_La value was 28.38±1.15 h^‑1 with a low volumetric productivity of 0.351±0.007 g L^‑1 day^‑1, a cell viability of 55.0±4.2% after 14 days of culture, and a low TPC.