Abstract
The use of β-glucosidase positive strains, as tailored-starter cultures for table olives fermentation, is a useful biotechnological tool applied to accelerate the debittering process. Nowadays, strains belonging to Lactiplantibacillus plantarum species are selected for their high versatility and tolerance to stress conditions. The present study investigated the effect of different stress factors (pH, temperature and NaCl) on growth and on oleuropein-degrading abilities of selected L. plantarum strains. In addition, the presence of the beta-glucosidase gene was investigated by applying a PCR based approach. Results revealed that, overall, the performances of the tested strains appeared to be robust toward the different stressors. However, the temperature of 16 °C significantly affected the growth performance of the strains both singularly and in combination with other stressing factors since it prolongs the latency phase and reduces the maximum growth rate of strains. Similarly, the oleuropein degradation was mainly affected by the low temperature, especially in presence of low salt content. Despite all strains displayed the ability to reduce the oleuropein content, the beta-glucosidase gene was detected in five out of the nine selected strains, demonstrating that the ability to hydrolyze the oleuropein is not closely related to the presence of beta-glucosidase. Data of the present study suggest that is extremely important to test the technological performances of strains at process conditions in order to achieve a good selection of tailored starter cultures for table olives.
Highlights
Table olives are the most widespread fermented vegetables in the Mediterranean area and their production and consumption are expanding worldwide, thanks to the nutritional and functional components of drupes, such as polyphenols, vitamins, fiber, minerals, and short chain fatty acids
The ladders are mainly represented by oleuropein, which is responsible for the bitterness taste [3] and for inhibiting a range of bacteria, especially lactic acid bacteria (LAB) [4,5,6,7]
In Sicilian style green table olives, the debittering process is exclusively relied on microorganisms naturally present on the drupes, through the activity of two enzymes, the beta-glucosidase, which leads to the release of two intermediates, which are completely degraded by an esterase into tasteless phenols [9]
Summary
Table olives are the most widespread fermented vegetables in the Mediterranean area and their production and consumption are expanding worldwide, thanks to the nutritional and functional components of drupes, such as polyphenols, vitamins, fiber, minerals, and short chain fatty acids. Olive drupe contains low concentrations of sugar (2.6–6.0%) and high oil (12–30%) and polyphenols content [1,2]. In Sicilian style green table olives, the debittering process is exclusively relied on microorganisms naturally present on the drupes, through the activity of two enzymes, the beta-glucosidase, which leads to the release of two intermediates (glucose and aglycone), which are completely degraded by an esterase into tasteless phenols (hydroxytyrosol and elenolic acid) [9]. In order to shorten the debittering step in naturally fermented table olives, tailored-starter cultures, with enhanced debittering ability, are required [10]
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