Effect of selected microbial starters on polyphenols composition, antioxidant activities and bioaccessibility of Apulian table olives

Table olives are a typical food of the Mediterranean diet and an important source of phenolic compoundswith high biological potential for human health. Their concentrations (?1-2% of FW) confer to table olives antioxidant, anti-inflammatory, and antitumoral properties. The polyphenols content and composition in table olives can be affected by several factors, such as cultivars, climate, fruits ripeness, and, mainly, the processing methods. Among the de-bittering processes, the Greek method represents a spontaneous fermentation procedure that is driven by a mixed population of microorganisms, mainly consisting of yeasts and lactic acid bacteria (LAB). In this work, the effects of fermentation by autochthonous yeast and LAB starters on phenolics composition of Apulian table olives, Bella di Cerignola (BDC), Termite di Bitetto (TDB) and Cellina di Nardò (CEL) were studied in comparison with the commercial products. The samples were characterized by HPLC-DAD for their polyphenols composition; 18 compounds were identified and the cultivar related effect was highlighted. The main identified phenolics were hydroxytyrosol, tyrosol, verbascoside and luteolin, followed by hydroxytyrosol-acetate detected in BDC and cyanidine-3-glucoside and quercetin in CEL. Further, the fermentation using selected LAB and yeasts influenced differently the composition and amount of polyphenols of the three cultivars, in particular the BDC amount was doubled compared with the commercial sample. Instead, for TDB and CEL, the treatment did not influence the polyphenols composition. It is noteworthy that the use autochthonous microbial starter to drive table olives fermentation process allows to maintain stable or increases polyphenols concentration in fermented table olives, significantly reducing the time necessary for de-bittering and improving organoleptic and sensory characteristics of the final product. Scavenger capacity in both DPPH and CAA assays, assessed the highest antioxidant effect for CEL with starters (21.7 mg Trolox eq/g FW; 8.5 ?mol hydroxytyrosol eq/100g FW). Moreover, the polyphenols were highly in vitro bioaccessible (>60%), although modifications in their profile, probably for combined effect of environment and microorganisms, were noted. Finally, fermented table olives are excellent source of health promoting compounds. Indeed, hydroxytyrosol and tyrosol are almost 8 times more than in olive oil for which a nutritional EU claim (No 433/2012 of 23 May 2012) that attributes the protective effect from oxidative stress by polyphenols on blood lipids, has been established.