In this study, experimental power input curves were obtained in a four-phase system. Sauter mean diameter of air and oil dispersions obtained in a four-phase Trichoderma harzianum fermentation model (aqueous salt solution, castor oil, air and T. harzianum mycelia) are presented. Experiments allowed to analyze the effect of varying amounts of surfactant (mixture of proteins coming from the biomass and bovine serum albumin) and solid concentration (mycelial biomass) on gassed power input, mean drop and bubble size distributions. Experimental power input measurements showed that the different mixtures of biomass and protein, keeping constant the agitation rate, affected the gassed power consumption by approximately +/- 10%. By keeping the gassed power input fixed during the dispersion experiments, it was possible to rule out the effects of the power consumption variation and to discern and analyze the impact of the amount of protein and biomass on the dispersion of air bubbles and oil drops. The protein, due to its surface-active properties, caused a considerable decrease in the Sauter mean diameter of air bubbles compared to the system without protein, regardless of the concentration. Protein did not have an effect on oil drops, which maintained a constant Sauter diameter through the studied concentration range (0-1.36 g/L). It was shown that, for comparable biomass concentrations, the gassed power input is the parameter determining the Sauter diameter of air bubbles as well as for the oil drops. It was found that, even by keeping the power input constant, the addition of biomass to the mixtures has additional interactions with the dispersions, decreasing the Sauter mean diameter of bubbles and increasing the value in oil drops. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.