Lactiplantibacillus strains (n. 77) were screened for technological properties (e.g., xylose fermentation, EPS production, antimicrobial activity, tolerance to NaCl and phenolic compounds, oleuropein degradation and hydroxytyrosol formation) relevant for the production of fermented table olives. Survival to olive mill wastewater (OMW) and to simulated gastro-intestinal tract (GIT), the capability to grow at different combinations of NaCl and pH values, radical scavenging activities and biofilm formation were further investigated in 15 selected strains. The screening step revealed high diversity among Lactiplantibacillus strains. Most of the strains were able to ferment xylose, while only a few strains produced EPS and had inhibitory activity against Y. lipolytica. Resistance to phenolic compounds (gallic, protocatechuic, hydroxybenzoic and syringic acids), as well as the ability to release hydroxytyrosol from oleuropein, was strain-specific. OMWs impaired the survival of selected strains, while combinations of NaCl ≤ 6% and pH ≥ 4.0 were well tolerated. DPPH and hydroxyl radical degradation were strain-dependent, while the capability to form biofilm was affected by incubation time. Strains were very tolerant to the GIT. The genome of Lpb. pentosus O17 was sequenced and analysed to verify the presence of genes involved in the degradation and metabolism of phenolic compounds. O17 lacks carboxylesterase and gallate decarboxylase (subunits B and D) sequences, and its gene profile differs from that of other publicly available Lpb. pentosus genomes.

Table olives are widely produced and consumed in the Mediterranean area. The production of table olives is mainly based on spontaneous fermentations, which may have several drawbacks (e.g., the development of undesirable microorganisms; organoleptic defects) compared to fermentative processes driven by starter cultures (typically lactic acid bacteria, yeasts, or their combinations). Studies on the effect of starter cultures have been mainly focused on some technological traits (e.g., acidifying capability, the degradation of phenolic compounds, metabolite production) and, to a lesser extent, on the dynamics of olive microbiota during fermentation. Recently, the application of Amplicon Targeted—High-Throughput Sequencing (AT–HTS) has enabled improvement of the knowledge on the composition and evolution of microbial communities during fermentations, including the role of starter cultures. The AT–HTS approaches used so far, however, have several constraints (e.g., poor investigation of mycobiota and metabolically active microorganisms) that do not allow a full understanding of the complex microbial interactions occurring in fermented olives. The aim of this review is to provide insights into the role of starter cultures in fermented olives and highlight the need to apply, as for other fermented foods, integrated “omics” approaches to predict and exploit their metabolic potential to improve the final properties of products.

Leuconostoc mesenteroides includes strains used as starter and/or adjunct cultures for the production of several fermented foods. In this study, the effect of anaerobic and respiratory cultivations, as well as of citrate supplementation and different pH values, was evaluated on growth, biomass, metabolite, and enzymatic activities (pyruvate oxidase, POX; NADH-dependent oxidase, NOX; NADH-dependent peroxidase, NPR) of Leuconostoc mesenteroides subsp. cremoris E30. We compared the respiration-increased growth rate and biomass production of Leuc. mesenteroides E30 to anaerobic cultivation. A supplementation of citrate impaired the growth rate of the respiratory cells. As expected, anaerobic cultures did not consume oxygen, and a similar trend in oxygen uptake was observed in respiratory cultures. The aerobic incubation caused changes in the metabolic pattern, reducing the production of ethanol in favour of acetic acid. Citrate was already exhausted in the exponential phase and did not affect the yields in acetic acid and ethanol. NOX activity increased in the presence of oxygen, while catalase was also detected in the absence of hemin. The absence of H₂O₂ suggested its degradation by NPR and catalase. Respiratory cultivation provided benefits (increase in growth rate, biomass, and activity in antioxidant enzymes) for Leuc. mesenteroides E30. Therefore, the exploitation of respiratory phenotypes may be useful for the formulation of competitive starter or adjunct cultures.

γ-aminobutyric acid (GABA) has several beneficial effects on human health. GABA may be produced via chemical synthesis or through microbial metabolism, and Levilactobacillus brevis is recognized as a GABA-producing species. In this study, 11 Lvb. brevis strains were screened for GABA production, and the best producers were selected to verify the effect of aerobic (AE) and respiratory (RS) cultivations on growth parameters, biomass, and GABA accumulation. Lvb. brevis LB12 was then used to evaluate the combined effect of the incubation atmosphere (anaerobiosis vs. aerobiosis), cell protection (free vs. immobilized cells), and cell recycling (fresh vs. starved cells) on GABA production. Glutamate (GLU) consumption and GABA accumulation were detected by Thin-layer Chromatography (TLC) and RP-HPLC analyses. The ability to produce GABA was widespread among the strains. AE and RS growth improved biomass production, but oxygen availability impaired GLU to GABA conversion, and the anaerobically growing cells had the highest GABA productivity. Immobilized strains had lower efficiency in both GLU uptake and conversion compared to free cells, probably due to the poor diffusion in alginate beads. The use of resting cells allowed further GABA production without the cultivation step, but cell activity was exhausted after three cycles of reutilization. Lvb. brevis LB12 is an excellent GABA producer, and AE cultivation can be exploited to improve the final cell density; however, the conditions for boosting GLU to GABA conversion and cell regeneration need to be further investigated.

The Protected Designation of Origin (PDO) “Oliva di Gaeta” is a type of Italian fermented table olive obtained through a spontaneous fermentative process (“Itrana” method) driven by the indigenous olives microbiota. Although the use of starter cultures may improve the fermentative process and the quality of the final product, this has been poorly investigated for PDO Gaeta olives. In this study, we evaluated the use of Lactiplantibacillus pentosus O17 as a starter culture for the production of Gaeta-like olives. Three fermentations were performed: a spontaneous process (according to PDO regulation, trial A), fermentation driven by Lpb. pentosus O17 (trial B), and O17-driven fermentation combined with different brine formulation (trial C). Physicochemical properties (i.e., pH, titratable acidity, salt, and total phenolic content) and microbial population (plate counting and metataxonomy) were monitored up to 180 days. Sensory and texture profiles were evaluated in the final product. Driven fermentations (trials B and C) led faster acidification and enhanced the microbial quality of table olives without altering the organoleptic features of Gaeta-like olives. Our study suggests that the use of a starter culture and a different brining method could improve the microbiological quality of Gaeta-like olives, while preserving the traditional identity and the sensory attributes related to this PDO product.

Members of the family Lactobacillaceae , which now includes species formerly belonging to the genera Lactobacillus and Pediococcus , but also Leuconostocaceae , are of foremost importance in food fermentations and spoilage, but also as components of animal and human microbiota and as potentially pathogenic microorganisms. Knowledge of the ecological distribution of a given species and genus is important, among other things, for the inclusion in lists of microorganisms with a Qualified Presumption of Safety or with beneficial use. The objective of this work is to use the data in FoodMicrobionet database to obtain quantitative insights (in terms of both abundance and prevalence) on the distribution of these bacteria in foods and food environments. We first explored the reliability of taxonomic assignments using the SILVA v138.1 reference database with full length and partial sequences of the 16S rRNA gene for type strain sequences. Full length 16S rRNA gene sequences allow a reasonably good classification at the genus and species level in phylogenetic trees but shorter sequences (V1-V3, V3-V4, V4) perform much worse, with type strains of many species sharing identical V4 and V3-V4 sequences. Taxonomic assignment at the genus level of 16S rRNA genes sequences and the SILVA v138.1 reference database can be done for almost all genera of the family Lactobacillaceae with a high degree of confidence for full length sequences, and with a satisfactory level of accuracy for the V1-V3 regions. Results for the V3-V4 and V4 region are still acceptable but significantly worse. Taxonomic assignment at the species level for sequences for the V1-V3, V3-V4, V4 regions of the 16S rRNA gene of members of the family Lactobacillaceae is hardly possible and, even for full length sequences, and only 49.9% of the type strain sequences can be unambiguously assigned to species. We then used the FoodMicrobionet database to evaluate the prevalence and abundance of Lactobacillaceae in food samples and in food related environments. Generalist and specialist genera were clearly evident. The ecological distribution of several genera was confirmed and insights on the distribution and potential origin of rare genera ( Dellaglioa, Holzapfelia, Schleiferilactobacillus ) were obtained. We also found that combining Amplicon Sequence Variants from different studies is indeed possible, but provides little additional information, even when strict criteria are used for the filtering of sequences.