BACKGROUND Process variability in bioprocess systems involving genetically engineered strains is a common bottleneck and a real-time insight of the on-going process is crucial to achieve the desired product and its quality. In this study, a process analytical technology (PAT) platform was developed for the monitoring and control of specific growth rate during methanol induction phase (mu(met)) of glycoengineered Pichia pastoris fermentation for human interferon alpha 2b (huIFN alpha 2b) production. RESULTS The PAT guided approach involves real-time monitoring of capacitance (Delta C) facilitating online estimation of specific growth rate (mu(est)), which serves as a process input during controller application. Fed-batch experiments using pulsed-feeding of methanol at different dosage (20 g and 30 g) did not significantly influence mu(met). Exponential methanol feeding was achieved using a modified proportional, integral and derivative (PID) controller for different predefined specific growth rate set point (mu(sp)) values, namely 0.015, 0.03, 0.04 and 0.06 h(-1). Exponential feeding strategy during the induction phase resulted in two crucial outcomes: (i) controlled methanol feeding rate (regulated by the developed PID controller) balanced the methanol consumption rate (q(s, met)) of the P. pastoris; (ii) significant improvement in huIFN alpha 2b titer (1483 mg L-1) and specific productivity(>0.4 mg g(-1). h) was achieved by the robust control of mu(met) at optimal (0.04 h(-1)) value. The purified huIFN alpha 2b was found to exhibit antiproliferative effect against human breast cancer cell lines. CONCLUSIONS Efficient control of mu(met) at a very low narrow range was achieved with a long-term controller stability (>10 h) and the highest titer reported to date for huIFN alpha 2b (at optimal mu(met)) in the yeast expression platform. (c) 2019 Society of Chemical Industry