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.

Table olives are produced from a large number of olive varieties subjected to different trade preparations, resulting in a highly heterogeneous family of fermented foods. To characterise the diversity of bacterial and fungal communities and its relationship with variety, ripeness, and trade preparation, we surveyed 363 samples from 40 producers across 6 countries, combining physicochemical measurements, viable counts, and amplicon-based metagenomics. This is the largest survey of table olive microbial communities to date and includes the first culture-independent characterisation of microbial communities for several Italian PDO and non-PDO varieties, most notably Oliva di Gaeta. The contrast between alkali-treated and naturally fermented olives was the dominant structuring factor, with HALAB (Halophilic and Alkalophilic Lactic Acid Bacteria) and other halophiles enriched in alkali-treated varieties and a diverse array of Lactobacillaceae and Pseudomonadota characterising naturally fermented olives. Despite these consistent signals, striking variability was observed within the same variety and even within the same producer, driven by stochastic colonization events, house microbiota, and the widespread use of small fermentation vessels. This variability obscured variety-specific microbial signatures and prevented reliable discrimination of Italian PDO varieties from similar non-PDO counterparts using amplicon-based approaches. The ecological and taxonomic complexity documented here, encompassing bacterial and fungal genera with largely untapped starter and flavour potential, provides the foundation for the development of variety-specific microbiome-based starter cultures. Highlights: We report a metataxonomic survey of microbial communities in 363 table olive samples Alkali treatment and natural fermentation drive distinct microbial community structures House microbiota and stochastic colonization generate high within-variety variability Microbiome data provide ecological foundations for olive microbiome-based starters

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.

Levilactobacillus brevis is able to produce ɣ-aminobutyric acid (GABA), a non-proteogenic amino acid that provides several benefits to human health. In this study, we investigated the effect of glutamate (Glu) and oxygen (O₂) on biomass yield, GABA production and regulation of the gad operon in Lvb. brevis LB12. A change in incubation atmosphere from anaerobiosis (AN) to aerobiosis (AE) was applied to elucidate if AE pre-adaptation and cultivation could be exploited to improve cell density, as well as to determine the role of O₂ on the expression of the gad operon. AE increased biomass yield, but impaired Glu to GABA conversion, in both the cultivation and the adaptation phases. The gad operon (gadR, gadC, gadB, gltX) was up-regulated in the presence of Glu, while O₂ strongly reduced the transcription of gadC and gadB. Switching the incubation atmosphere (AE vs. AN) and Glu supplementation did not restore the gene functionality, suggesting that the negative effect of O₂ was persistent and more prolonged adaptation to AN would be required. This study provides additional data on the regulation of the gad operon, but further insight on the effect of O₂ upon GABA production by Lvb. brevis must be expanded to understand the possible mechanisms involved.

Phlorizin is a naturally occurring dihydrochalcone predominantly found in apple trees (Malus domestica), where it is one of the species’ characteristic phenolic compounds. Its accumulation varies according to genotype, tissue type, developmental stage, environmental conditions, and cultivation practices. While these factors are fundamental for understanding phlorizin biosynthesis and distribution, growing attention has focused on its biological activities and potential health applications. This review provides an integrated overview of phlorizin, from its occurrence in apple plants to its emerging nutraceutical and biomedical relevance. Particular emphasis is placed on the molecular mechanisms underlying its antioxidant, anti-inflammatory, antimicrobial, antiviral, and metabolic effects. Phlorizin is best known for inhibiting sodium–glucose co-transporters (SGLT1 and SGLT2), a mechanism that inspired the development of synthetic SGLT inhibitors for metabolic diseases. Beyond glucose regulation, increasing evidence highlights its broader effects on lipid metabolism, gut microbiota modulation, neuroprotection, cardioprotection, hepatoprotection, anti-aging pathways, and tissue regeneration. Advances in extraction, purification, encapsulation, and delivery technologies are expanding its applications in functional foods, dietary supplements, and biomaterials. However, limited bioavailability and scarce clinical evidence remain key challenges. Overall, phlorizin represents a promising apple-derived phytochemical with significant potential for future health-oriented applications.