Demethyloleuropein and β-glucosidase activity in olive fruits

Demethyloleuropein plays a major role in the defense mechanism of olive fruits. To understand how this molecule is metabolized during different stages of maturation of olive fruits, a biomolecular approach to identify the demethyloleuropein chemistry was employed. The β‐glucosidase activity in crude extracts was assayed spectrophotometrically using the chromogenic substrate p‐nitrophenyl‐β‐D‐glucopyranoside. Demethyloleuropein was extracted and identified by HPLC‐MS from both infected and uninfected olive fruits at different physiological stages. The release of more functionally relevant dialdehydes in uninfected fruits was investigated using ESIMS/ MS. In fruits harvested in October, the activity of β‐glucosidase was significantly enhanced in uninfected fruits when compared to the infected fruits. Quantitative differences in the demethyloleuropein content from uninfected fruits showed the highest values (5.09 mg/g) in October, whereas lower levels (4.44 mg/g) were found in infected fruits. The results demonstrated that demethyloleuropein derivatives could be influenced by β‐glucosidase activity to improve the quality of the olive products with the best dialdehyde nutraceutical content.