Physico-chemical and microbiological characterization of spontaneous fermentation of Cellina di Nardò and Leccino table olives

Abstract

Table olives are one of the most important traditional fermented vegetables in Europe and their world consumption is constantly increasing. In the Greek style, table olives are obtained by spontaneous fermentations, without any chemical debittering treatment. Evolution of sugars, organic acids, alcohols, mono, and polyphenol compounds and volatile compounds associated with the fermentative metabolism of yeasts and bacteria throughout the natural fermentation process of the two Italian olive cultivars Cellina di Nardò and Leccino were determined. A protocol was developed and applied aimed at the technological characterization of lactic acid bacteria (LAB) and yeast strains as possible candidate autochthonous starters for table olive fermentation from Cellina di Nardò and Leccino cultivars. The study of the main physic-chemical parameters and volatile compounds during fermentation helped to determine chemical descriptors that may be suitable for monitoring olive fermentation. In both the analyzed table olive cultivars, aldehydes proved to be closely related to the first stage of fermentation (30 days), while higher alcohols (2-methyl-1-propanol; 3-methyl-1-butanol), styrene, and o-cymene were associated with the middle stage of fermentation (90 days) and acetate esters with the final step of olive fermentation (180 days).

Keywords: fermented food; lactic acid bacteria; table olives; volatile compounds; yeast.

Figure 1

Yeast (A) and LAB (B) total counts (Log CFU/ml) of Cellina di Nardò and Leccino naturally fermented table olives. Detection limit ± 10 cfu/ml. LAB were not detected during the period of time between 15 and 120 days of fermentation.

Figure 2

Temperature (A) and pH (B) of Cellina di Nardò and Leccino naturally fermented table olives.

Figure 3

Sugar, organic acid and alcohol evolution in Cellina di Nardò (A,B) and Leccino (C,D) brines during natural fermentation process.

Figure 4

Mono and polyphenol compound concentrations in Cellina di Nardò (A) and Leccino (B) brines during natural fermentation process.

Figure 5

PCA of volatile compounds associated with Cellina di Nardò fermented table olives. PCA variables were the data obtained from the analysis of concentration and presence of volatile compounds at three different fermentation times. The figure displays the sample scores and variable loadings in the planes formed by PC1–PC2.

Figure 6

PCA of volatile compounds associated with Leccino fermented table olives. Score plot of variables (concentration of volatile molecules) and three different fermentation times in the plane formed by the first two principal components (PC1 against PC2).