Mathematical modeling of the effect of pH on 4-ethylphenol formation during two-phase olive pomace storage

Abstract

Typically, two-phase olive pomace is stored during the peak of olive harvesting period, leading to the formation of malodorous compounds like 4-ethylphenol that are then released to the atmosphere during olive pomace drying prior to kernel oil extraction. The acidification of pomace prior to storage is an effective way of preventing the enzymatic process that leads to 4-ethylphenol formation from p-coumaric acid. In this work, experimental data were used to train a mathematical model that simulates the three-step process of 4-ethylphenol formation. The process includes the release of p-coumaric acid from the lignocellulosic material, p-coumaric acid decarboxylation to 4-vinylphenol, and finally, 4-vinylphenol reduction to 4-ethylphenol. Michaelis-Menten kinetics were used to describe the concentrations of the compounds with the addition of enzyme concentration inducibility and activity inhibition from pH. The trained model was able to predict the concentration of 4-ethylphenol as a function of time and storage pH, using only the initial concentrations of p-coumaric acid, 4-vinylphenol (intermediary product) and 4-ethylphenol. Such a model can be used to optimize an acidification scheme, adjusted to the expected storage duration at kernel oil extraction facilities and a set limit in the final 4-ethylphenol concentration.