Hydroxytyrosol and tyrosol as the main compounds found in the phenolic fraction of steam-exploded olive stones

The lignocellulosic by-products, whole stones, and seed husks obtained from processing pitted table olives and oil olives were pretreated under various conditions of steam explosion, with and without previous acid impregnation. The various water-soluble noncarbohydrate compounds generated during steam explosion, such as sugar degradation compounds (furfural and hydroxymethylfurfural), lignin degradation compounds (vanillic acid, syringic acid, vanillin, and syringaldehyde) and the simple phenolic compounds characteristic of olive fruit (tyrosol and hydroxytyrosol), were identified. The amount of hydroxytyrosol solubilized was higher than that of the other compounds, and increased with increasing steaming temperature and time. This suggests its presence as a structural component of the olive stone.