Abstract
Nocellara Etnea is one of the main Sicilian cultivars traditionally used to produce both olive oil and naturally fermented table olives. In the present study, the effect of different salt concentrations on physico-chemical, microbiological, sensorial, and volatile organic compounds (VOCs) formation was evaluated in order to obtain functional Nocellara Etnea table olives. The experimental design consisted of 8 treatments as follow: fermentations at 4, 5, 6, and 8% of salt with (E1-E4 samples) and without (C1-C4 samples) the addition of starters. All the trials were carried out at room temperature (18 ± 2°C) and monitored for an overall period of 120 d. In addition, the persistence of the potential probiotic Lactobacillus paracasei N24 at the end of the process was investigated. Microbiological data revealed the dominance of lactic acid bacteria (LAB), starting from the 7th d of fermentation, and the reduction of yeasts and enterobacteria in the final product inoculated with starters. VOCs profile highlighted a high amount of aldehydes at the beginning of fermentation, which significantly decreased through the process and a concomitant increase of alcohols, acids, esters, and phenols. In particular, esters showed an occurrence percentage higher in experimental samples rather than in control ones, contributing to more pleasant flavors. Moreover, acetic acid, ethanol, and phenols, which often generate off-flavors, were negatively correlated with mesophilic bacteria and LAB. It is interesting to note that salt content did not affect the performances of starter cultures and slightly influenced the metabolome of table olives. Sensory data demonstrated significant differences among samples registering the highest overall acceptability in the experimental sample at 5% of NaCl. The persistence of the L. paracasei N24 strain in experimental samples, at the end of the process, revealed its promising perspectives as starter culture for the production of functional table olives with reduced salt content.
Highlights
The greater consumer’s attention for healthy food is confirmed by the growing trend in fermented vegetables consumption, such as table olives (International Olive Council (IOC), 2016)
It is well established that Lactobacillus plantarum and Lactobacillus pentosus are the main detected species, due to their versatile adaptation to the brine environment (Ruiz-Barba et al, 1994; GAlegria et al, 2004; Bautista-Gallego et al, 2010; Randazzo et al, 2011, 2012; Hurtado et al, 2012; Cocolin et al, 2013; Tofalo et al, 2014), and different strains are widely used as starter cultures in several table olive fermentations (Arroyo-López et al, 2012; Hurtado et al, 2012; Randazzo et al, 2014)
Based on our previous reported data (Randazzo et al, 2017), with the aim to set up functional table olives from Nocellara Etnea cultivar, in the present study the fermentation was carried out at different salt contents (4, 5, 6, and 8%), by using starter cultures constituting of the promising probiotic strain L. paracasei N24 and by the strain L. plantarum UT2.1
Summary
The greater consumer’s attention for healthy food is confirmed by the growing trend in fermented vegetables consumption, such as table olives (International Olive Council (IOC), 2016). The relationship between core and pulp is very high and this character makes this cultivar one of the best for the production of green table olives. The latter are mostly obtained by a spontaneous process in which the hydrolysis of oleuropein is relied on enzymatic activities of indigenous microorganisms, and on the plasmolytic effect of salt. This process is mainly dominated by lactic acid bacteria (LAB) and yeasts, which form a natural consortium (Randazzo et al, 2010). It is well established that Lactobacillus plantarum and Lactobacillus pentosus are the main detected species, due to their versatile adaptation to the brine environment (Ruiz-Barba et al, 1994; GAlegria et al, 2004; Bautista-Gallego et al, 2010; Randazzo et al, 2011, 2012; Hurtado et al, 2012; Cocolin et al, 2013; Tofalo et al, 2014), and different strains are widely used as starter cultures in several table olive fermentations (Arroyo-López et al, 2012; Hurtado et al, 2012; Randazzo et al, 2014)
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