Naturally fermented black olives: Effect on cell wall polysaccharides and on enzyme activities of Taggiasca and Conservolea varieties

Black olives of Taggiasca (Ta) and Conservolea (Co) varieties were processed according to the Greek style method in order to investigate the effect of this type of table olive processing on cell wall composition. Naturally black processing involves the storage in brine of fully ripe olives for several months, allowing a spontaneous fermentation by a mixed flora followed by fermentation by the lactic acid bacteria and yeasts. The smaller fruits of Ta variety are richer in pectic polysaccharides, accounting for half of total cell wall polysaccharides (12 mg/fruit), whereas in Co they accounted for one third (23 mg/fruit). Fresh Co olives had higher proportion of glucuronoxylans and xyloglucans (33%), whereas these polysaccharides accounted for 22% in Ta. The processing did not cause significant variations in the cell wall polysaccharide composition of Ta fruits, although pectic polysaccharides became more soluble in aqueous solutions. Conversely, processed Co olives had slightly higher amounts of galacturonan-rich pectic polysaccharides than the unprocessed fruits, suggesting that the long stage in brine might have contributed to the stabilisation and/or the biosynthesis of new polysaccharides. The changes caused by processing on cell wall polysaccharides appear to be closely related to the activity and availability of cell wall degrading enzymes.