The cellulase-inhibitor binding constant (beta) for chlorogenic, ferulic, caffeic and sinapic acids, when these compounds were present in the range of concentrations found during the aqueous extraction of sunflower oil, was calculated. Chlorogenic acid presented a weak inhibiting power (beta = 0.14 L/mmol), whereas sinapic acid conducted as the strongest inhibitor (beta = 14.60 L/mmol). The inhibition effects were not additive, since in the presence of mixtures the enzyme retained 75-85% of its activity.