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Review

Starter Cultures for the Production of Fermented Table Olives: Current Status and Future Perspectives

by
Marilisa Giavalisco
,
Emanuela Lavanga
,
Annamaria Ricciardi
and
Teresa Zotta
*
Scuola di Scienze Agrarie, Forestali, Alimentari ed Ambientali (SAFE), Università degli Studi della Basilicata, Via dell’Ateneo Lucano n. 10, 85100 Potenza, Italy
*
Author to whom correspondence should be addressed.
Fermentation 2024, 10(7), 351; https://doi.org/10.3390/fermentation10070351
Submission received: 11 June 2024 / Revised: 28 June 2024 / Accepted: 2 July 2024 / Published: 12 July 2024
(This article belongs to the Special Issue Development and Application of Starter Cultures, 2nd Edition)
Browse Figure
Versions Notes

Abstract

:
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.

1. Introduction

Fermented table olives are a traditional food widely consumed in the Mediterranean area, with a significant economic impact. The worldwide production of table olives for the season 2023/24 was about 2.65 million tons, 23% of which was produced and consumed in several European countries, such as Spain, Greece, Italy, and Portugal, with an average per capita consumption in the EU of approximately 2.0 kg/year [1].
According to trade standards [2], table olives can be processed and classified as summarized in Figure 1: (a) treated table olives (lye-treated olives; often referred to as Spanish-style olives), de-bittered with an alkaline solution (1.5–4.5% w/v of NaOH), rinsed with tap water, packed in brine (10–11% w/v of NaCl), and fermented for 3–7 months, mainly by lactic acid bacteria (LAB); (b) natural table olives (also called Greek-style olives), directly placed in brine (6–10% w/v of NaCl) and fermented for 8–12 months by yeasts and/or LAB (depending on the salt concentration); (c) dehydrated and/or shrivelled table olives, exposed (or not) to a mild alkaline treatment, and then stored in brine or partially dehydrated in dry salt (15% w/w of NaCl) and/or by heating or other technological process; (d) olives darkened by oxidation (Californian-style olives), preserved in brine, fermented or not, darkened by oxidation in an alkaline medium, stored in hermetically sealed containers, and sterilized; (e) specialties, i.e., olives that can be prepared with processes other than those listed above (e.g., Castelvetrano Sicilian-style green olives, Taggiasca Ligurian-style black olives, Maiatica di Ferrandina-oven-dried black olives produced in Italy [3]; and “alcaparras” produced in Portugal [4]).
In fermented olives, the fermentative process is almost always spontaneous and mainly depends on the drupes-associated microbiota.

2. The Microbiota of Spontaneous Fermentation

The microbial communities of fermented table olives partially reflect that of unprocessed fruits, and the environment, equipment, and operative conditions (e.g., alkaline treatment, temperature, salt content, and fermentation) during production may strongly affect the composition and dynamism of the olives-associated microbiota.
The microbiota of fresh drupes is complex and mainly consists of yeasts and bacteria [6,7,8,9,10,11,12], whose composition in species and strains depends on the geographical area, olive cultivars, agronomic practices, degree of ripening, harvesting time, and techniques and storage conditions before processing [13,14,15].
The microbiota of unprocessed fruits may lead to spontaneous fermentation, and the effects on the final properties of products (e.g., quality improvement, or alteration and deterioration phenomena) depend on the ability of microbial groups to survive and cope with factors associated with the production process and thrive under the selective conditions of fermentation.
LAB and/or yeasts (Y), generally, dominate the spontaneous fermentation process. Among LAB, Lactiplantibacillus plantarum and Lpb. pentosus are the most abundant isolated species, although other lactobacilli (Lpb. paraplantarum, Companilactobacillus alimentarius, Comp. farciminis, Levilactobacillus brevis, Loigolactobacillus coryniformis, Limosilactobacillus fermentum, Lacticaseibacillus casei, Lcb. paracasei) were also found in several fermented products of Mediterranean countries [5,16,17]. Members of the genera Leuconostoc (mainly Leuc. mesenteroides/paramesenteroides), Pediococcus (mainly Pc. ethanolidurans, Pc. acidilactici, Pc. pentosaceus), Enterococcus (mainly E. durans, E. faecalis, E. faecium) and Lactococcus (Lc. lactis) have also been found in fermented table olives.
The yeast microbiota mainly consists of species belonging to the genera Candida (C. diddensiae, C. boidinii, C. tropicalis, and to a lesser extent C. aaseri, C. apicola, C. oleophila, C. olivae, C. parapsilosis, C. quersitrusa, C. sorbose, C. tartarivorans), Pichia (P. membranifaciens, and to a lesser extent P. galeiformis, P. guilliermondii, P. kluyveri, P. kudriavzevii, P. manshurica), Saccharomyces (S. cerevisiae), Debaryomyces (D. hansenii) and Wickerhamomyces (W. anomalus); however, other non-dominant species contribute to the yeast diversity of fermented table olives (Aureobasidium pullulans, Metschnikowia pulcherrima, Rhodotorula glutinis, R. graminis, R. diobovatum, R. mucilaginosa, Schwanniomyces ethcellsii, Zygowilliopsis californica, Zygosaccharomyces mrakii; [17,18,19,20,21]).
The use of High-Throughput Sequencing (HTS) technologies for the assessment of table olive microbiota [12,13,14,15,16,17,18,19,20,21,22], has revealed a wider diversity among microbial communities, and several other genera (also including halophilic and alkaliphilic LAB) have been recognised as important members of table olive microbiota (i.e., Marinilactibacillus spp. [23,24,25,26]; Alkalibacterium spp. [25,26]; Celerinatantimonas spp. [19,20,24,26]; Halomonas spp. [23,25]).
Moreover, spoilage bacteria (e.g., Enterobacteriaceae, Clostridium spp., Marinomonas spp. [27], Pseudomonas spp., Staphylococcus spp., Vibrio spp.) and occasionally moulds (e.g., Penicillium spp., Aerobasidium spp., Geotrichum spp.) can be found in the early stage of fermentation (slow and acidification) or in low-quality table olives [5,7,12,22,28].
During the olive fermentation, bacteria and yeasts coexist, but population dynamics and balance depend on several factors, such as type of process (NaOH-treated vs. natural), as well as on the fermentation starting parameters (salt concentration, pH, temperature, etc.).
In the first stage of the lye-treated process (reduced content of polyphenols; pH ranging from 8.0 to 9.0), members of Enterobacteriaceae and halophilic/alkaliphilic LAB are dominant. In the middle stage of the process, when the brine pH decreases (up to 6.0–7.0), Leuconostoc ssp. and Pediococcus spp. can be detected, and the genus Lactiplantibacillus gradually increases in abundance, becoming foremost at the end of fermentation (107–108 cfu/mL), leading to a significant lowering of the brine pH (down to 4.0) and, consequently, a reduction in the abundance of other microbial groups [23,29]. Yeast populations may reach 104–106 cfu/mL at the end of the process [12,13,30].
The composition of microbiota present in Greek-style processes is slightly more complex. In the first step of fermentation, several drupes-associated bacteria (e.g., Enterobacteriaceae, Pseudomonas spp., Vibrio spp. and Clostridium spp.) as well as halophilic/halotolerant bacteria (mainly from brine, e.g., Halomonas spp., Salinicola spp., Marinobacter spp., Aliidiomarina spp.) are mainly found, while LAB generally do not exceed 104–105 cfu/mL [12]. Nutrient availability, microbial competition and phenolic compound content, in fact, may inhibit LAB populations and reduce their occurrence during fermentation. Yeasts, being more tolerant than LAB to high concentrations of salt and phenolic compounds, can become the dominant group (107–108 cfu/mL) at the end of fermentation. The composition and the diversity of yeast biota, however, may differ from those found in a NaOH-treated process [29,30,31,32].
In spontaneous fermentations, regardless of the type of process, the right ratio between LAB and yeasts, as well as a low occurrence of undesirable microorganisms, is suitable for obtaining good-quality products [12,33,34,35]. In non-optimal fermentative conditions (e.g., reduced salt content; slow and insufficient acidification, pH above 4.0), in fact, the development of undesired microorganisms (e.g., proteolytic bacteria, heterofermentative LAB, pectinolytic yeasts) may lead to several organoleptic defects (e.g., off-flavours and off-odours, swelling, drupe softening) that can significantly affect the quality of the final product [34,36,37,38,39]. Moreover, although the occurrence of foodborne pathogens in table olives is low, several studies (challenge test-based data) confirmed their survival in conditions occurring in the early stages of fermentation [40,41,42].
Therefore, controlling spoilage microbiota and potential pathogens during the fermentative process is crucial to guarantee the stability, the organoleptic features and the safety of table olives, especially for those commercialised without heat treatments.

3. Starter Cultures in Driven Fermentations

To date, the production of table olives is mainly based on spontaneous fermentations, which may have several drawbacks (see Section 2) compared to fermentative processes driven by starter cultures. The use of appropriate LAB, yeasts or their combinations, in fact, may help prevent failures occurring in brine fermentations with indigenous microbiota and may contribute to the production of high-quality products.
The main species used as starter cultures for the production of table olives have been widely reviewed [5,7,12,13,14,16,28] and are reported in Table 1 and Table 2.
Selection criteria (i.e., ability to cope with harsh conditions, biofilm formation, adhesion to olive surface, hydrolysis of phenolic compounds, debittering capability, brine acidification, production of antimicrobial compounds) also have been extensively addressed [5,7,12,13,14,16,28].
The effects of starter cultures, of course, depend on several factors, including the type of process (e.g., starters are mainly used for Spanish-style olives), the type of microorganisms (LAB and yeasts have different functionalities) and the type of inoculum (single strain, mixtures of LAB or yeasts or LAB/yeasts; Table 1 and Table 2).

3.1. Effect of Starter Cultures on the Features of Fermented Table Olives

During the fermentative processes, LAB (mainly Lpb. plantarum and Lpb. pentosus) promote brine acidification through the production of lactic acid from fermentable sugars, lower the pH, and increase in titratable acidity, which may inhibit the growth of spoilage microorganisms, improving the microbiological stability and shelf-life of the final product. Additionally, several strains may synthetize antimicrobial compounds (e.g., bacteriocins active against some pathogens) that, further, contribute to the preservation and safety of table olives [5,7,12,13,14,28].
In natural table olives, LAB are involved in the hydrolysis of oleuropein (because of β-glucosidase activity), reducing the debittering time and increasing the formation of some phenolic compounds (e.g., hydroxytyrosol) that improve the nutritional value of the products [43,44].
Yeast starters (mainly belonging to C. boidinii, C. diddensiae, D. hansenii, S. cerevisiae, W. anomalus, alone or in combination with LAB) also contribute to the debittering and degradation of phenolic compounds. Some strains, moreover, prevent oxidation of unsaturated fatty acid and peroxide formation (due to catalase and peroxidase activities; [45,46]) and lead to the production of important compounds (e.g., vitamins, amino acids, purines, and hydrocarbons [7,28,33,47]) that stimulate the growth of LAB.
For a long time, studies on the effect of starter cultures were mainly focused on the changes in pH, titratable acidity, phenolic compounds (total concentration; sometimes the overall profile) and production of the main metabolites (e.g., lactic and acetic acids, ethanol). Recent data based on chromatographic analyses (i.e., Headspace-Solid-Phase Micro-Extraction/Gas Chromatography-Mass Spectrometry, HS-SPME/GC-MS; High Performance Liquid Chromatography, HPLC; Liquid Chromatography with tandem Mass Spectrometry, LC-MS/MS), combined with sensory evaluation, confirmed that LAB and yeast metabolism positively affected the aroma profile (organic acids, volatile organic compounds), texture (brightness, crunchiness, colour) and sensory properties (high overall acceptability) of table olives. Table 1 shows the effects of starter cultures on the phenolic profile and organoleptic properties of different types of fermented olives. For a better understanding of data, we reported only the trials that included also the spontaneous fermentations as control.

3.2. Effect of Starter Cultures on the Microbiota of Fermented Table Olives

Metataxonomic studies have increased knowledge on the microbiota of fermented olives, revealing a complex microbial diversity that could not be detected using the conventional culture-dependent methods. Amplicon Targeted High-Throughput Sequencing (AT–HTS) techniques (16S rRNA– and ITS–based, respectively, for bacterial and fungal communities) have been widely used to investigate the microbial ecology of spontaneous fermentation [17,19,20,24,25,26,29,48,49,50,51] and to describe the microbiota of commercial table olives, [27,52,53,54,55,56], mainly belonging to the Italian and Spanish varieties (both with natural and lye-treated methods).
The first metataxonomic approach was applied by Cocolin et al. [23], to investigate the effect of NaOH treatment on the microbial ecology of Nocellara Etnea olives; since then, many other studies have been performed [12], allowing the discovery of dominant, emerging and spoilage species of fermented table olives.
However, only a few studies have been focused on the effect of starter cultures on the dynamics of olive microbiota during fermentation. Most of the available data are based on experimental evidence obtained with traditional culture-dependent methods (i.e., plate counting; [8,15,44,57,58,59,60]), which indicate how starter cultures affect the evolution of microbial groups (e.g., bacteria, yeasts) during fermentation, but do not give a detailed description of changes occurring in the composition of microbial communities of fermented olives.
De Angelis et al. [61], for the first time, applied a metataxonomic approach to investigate the effect of different starter cultures on the microbiota of Bella di Cerignola olives. Subsequently, some other studies (Table 2) have been carried-out, confirming the competitiveness of starters (mainly Lpb. plantarum and Lpb. pentosus) and the ability to reduce undesired bacteria (e.g., Enterobacteriaceae, some halophilic and alkalophilic bacteria). The effect of starters on other LAB species, on the contrary, depended on the type of cultivar and process. However, almost all studies reported in Table 2 (except data from Ruiz-Barba et al. [62]) referred only to the bacterial diversity (16S rRNA-based), but did not consider the effect of starter cultures on the changes in fungal communities. These data suggest that future metataxonomy and metagenomic studies should also be tuned to the study of mycobiota, to have a more faithful description of the evolution of microbial communities in fermented olives. In Table 2, we report only the trials that included spontaneous fermentations as control.
Table 1. Effect of starter cultures on metabolite production and phenolic compounds of fermented table olives.
Table 1. Effect of starter cultures on metabolite production and phenolic compounds of fermented table olives.
Olive
cultivar		Type of Process and
Fermentative Conditions		Species and Strains
Used as Starter Cultures		Effect on Metabolite Production and Phenolic CompoundsAnalytical Method †Ref.
Starter cultures: Lactic Acid Bacteria (*)
Tonda di Cagliari
(Sardinia, Italy)		Natural process: Greek-style. Brine: 7% (w/v) NaCl. Fermentation time and T °C: 156 days at 27 °C, up to pH stead-state, and then 24 °C.LAB starter
SSL: Lpb. plantarum S1T10A; SIE: undefined autochthonous mixed starter of Lpb. pentosus.
NF: natural fermentation, control.
Inoculum level: 6.82 (SSL) and 7.25 (SIE) log cfu/mL		Final-stage fermentation (156 days, olives)—NF: lowest levels of hydroxytyrosol and highest levels of oleuropein. SIE and SSL: higher concentration of hydroxytyrosol. SSL, SIE: completely debittering after 156 days; NF needed 12 months.
NF sample had higher cohesiveness, springiness. SIE: more elasticity and cohesiveness than SSL samples.		HPLC[63]
Kalamon
(Peloponnese, Greece)		Natural process: Greek-style. Brine: 5% (w/v) NaCl. Fermentation time and T °C: 70 days at room T °C (22 °C).LAB starter
B1: spontaneous fermentation.
B2: Lpb. pentosus DSM 16366; B3: Leuconostoc mesenteroides subsp. mesenteroides Lm139.
Inoculum level: 6 log cfu/mL		Early-stage fermentation (7–10 days, brines)—B2, B3: faster glucose consumption (7 days) compared to B1 (10 days); B2, B3: mannitol consumption was observed.
Final-stage fermentation (70 days, brines)—B2, B3: higher amount of lactic, acetic and succinic acids compared to B1.		HPLC[60]
Nocellara Etnea
(Adrano, Sicily, Italy)		Natural process: Sicilian style. Brine: 8% (w/v) marine salt. Fermentation time and T °C: 120 days at room T °C (20 ± 2 °C)LAB starter
BC1: Lpb. plantarum UT2.1, Lcb. paracasei N24, Lpb. pentosus TH969; BC2: Lpb. plantarum UT2.1; BC3: Lcb. paracasei N24, Lpb. pentosus TH969; BC4: Lpb. plantarum UT2.1, Lpb. pentosus TH969; BC5: Lpb. plantarum UT2.1, Lcb. paracasei N24; BC6: Lpb. pentosus TH969.
C: uninoculated samples.
Inoculum level: 7 log cfu/mL		Early-stage fermentation (1 day, brines)—C, BC1, BC2: high aldehydes content. Correlation among aldehydes and alcohols (octanal, nonanal, decanal, 1-nonanol, 1-undecanol, 1-dodecanol, and 1-octanol) and presence of Proteobacteria.
Middle-stage fermentation (60 days, brines)—All samples: aldehydes content decreased, whereas alcohols, acids, esters and phenols increased.
Final-stage fermentation (120 days, brines)—BC3, C: highest VOC content; BC1: lowest VOC content. C: high ethanol content. Correlation among ester products (ethyl-acetate, ethyl-propanoate, ethyl-butanoate, ethyl-lactate, butanoic acid 2-methylester, butanoic-acid 3-methylester, ethyl decanoate, and ethyl-benzoate) and Slb. paracollinoides, Pc. parvulus, and Lgb. acidipiscis (BC1, BC3, BC4, BC6).		SPME/
GC-MS		[64]
Itrana (Fogliano, Rocca
Massima, Latium, Italy)		Natural process: Greek-style. Brine: 6% (w/v) NaCl. Fermentation time and T °C: 30 days at room T °C.LAB starter
A: Fogliano, less irrigation, Lpb. pentosus C8 and C11; B: Fogliano, more irrigation, Lpb. pentosus C8 and C11; C: Rocca Massima, rainfed, Lpb. pentosus C8 and C11; D: Rocca Massima, irrigation, Lpb. pentosus C8 and C11.
Ac, Bc, Cc, Dc: related spontaneous fermentation.
Inoculum level: 8 log cfu/mL		Final-stage fermentation (120 days, olives pulp)—Inoculated samples provided a strong decrease in oleuropein, dimethyl oleuropein, and 3,4-DHPEA-EDA, and an increase in hydroxytyrosol.HPLC[15]
Nocellara Etnea
(Adrano, Sicily, Italy)		Natural process: Sicilian style. Brine: 4, 5, 6, 8% (w/v) NaCl. Fermentation time and T °C: 120 days at room T °C (18 ± 2 °C).LAB starter
Lpb. plantarum UT2.1 and Lcb. paracasei N21 (1:1 ratio). E1–E4: inoculated fermentations with 4, 5, 6, 8% NaCl, respectively.
C1–C4: related spontaneous fermentations.
Inoculum level: 7 log cfu/mL		Final-stage fermentation (120 days, brines)—E1–E4: high content of hexanoic and propionic acids, low content of acetic acid, ethanol, isoamyl and phenyl-ethyl alcohol. E2: highest content of esters (butanoic-acid-2-methylester), acids, alcohols, phenols, aldehydes. C: high acidity.
E1–E4: high acceptability score.		SPME/
GC-MS		[8]
Picual (whole and cracked
olives; Nicosia, Cyprus)		Natural process: Greek-style. Brine: 7% (w/v) or 10% (w/v) NaCl and 3.3% (v/v) citric acid. Fermentation time and T °C: 120 days at room T °C (23 ± 2 °C)LAB starter
S1, S4: spontaneous fermentations in cracked and whole olives, respectively. S2, S5: commercial starter Lpb. plantarum (Vege-Start 600, Chr. Hansen A/S) in 10% NaCl and 3.3% citric acid, cracked and whole olives, respectively; S3, S6: Lpb. plantarum (Vege-Start 600) in 7% NaCl and 3.3% citric acid, cracked and whole olives, respectively.
Inoculum level: 5 log cfu/mL		Middle-stage fermentation (60 days, brines)—All inoculated samples: rapid glucose depletion (undetectable after 45 days of fermentation).
Final-stage fermentation (120 days, brines)—All inoculated samples: highest lactic acid content, production of succinic acid and a faster degradation of oleuropein, resulting in the production of higher levels of hydroxytyrosol (especially in S3 and S6 samples) compared to the control ones (S1 and S4).		HPLC[43]
Tonda di Cagliari
(Sardina, Italy)		Natural process: Greek-style. Brine: 7% (w/v) NaCl. Fermentation time and T °C: 180 days at 25 °CLAB starter
SIE: undefined mixed culture of Lpb. pentosus strains isolated from previous fermentations; Double-strain starter (DSS): Lpb. pentosus D104 and D702 isolated from SIE.
NF: spontaneous fermentation.
Inoculum level: 6 log cfu/mL		Final-stage fermentation (180 days, olive pulp)—SIE: undetectable level of oleuropein and high content of hydroxytyrosol, followed by verbascoside, tyrosol, luteolin, luteolin 7-glucoside. DSS and NF: comparable level of tyrosol, luteolin, luteolin 7-glucoside.HPLC[65]
Nocellara Etnea (Adrano and Paternò, Sicily, Italy)Natural process: Sicilian style. Brine: 5% or 8% (w/v) NaCl. Fermentation time and T °C: 80 days at room T °C (18 ± 2 °C)LAB starter
O1: Lpb. plantarum F1.16 and F3.5, in 5% NaCl. O2: Lpb. plantarum C11C8, F1.16, and F3.5, in 5% NaCl.
C5 and C8: uninoculated samples with 5% or 8% NaCl, respectively.
Inoculum level: 7 log cfu/mL		Middle-stage fermentation (15 days, olives)—O2: highest content of 2-butanone-3-hydroxy (acetoin), ethyl acetate, and lactic acid ethyl ester.
Final-stage fermentation (80 days, olives)—O2: highest content of acetic acid, 3-methyl-1-butanol, esters (phenylethyl alcohol, acetic acid 2-methyl ester, 2-heptanal, benzene propanoic acid methyl ester (with pleasant flavours)). C5, C8: higher content of 4-ethyl-phenol, 2-methoxy-phenol, associated with off-flavour. 		HS-SPME/
GC-MS		[66]
Itrana
(Latina province, Italy)		Natural process: Greek-style. Brine: 8% (w/v) NaCl (sea salt). Fermentation time and T °C: 240 days at room T °C.LAB starter
A: spontaneous fermentation.
B: Lpb. plantarum B1; C: Lpb. plantarum B1, Lpb. plantarum B51, Lpb. plantarum B124 (1:1:1 ratio).
Inoculum level: 6 log cfu/mL		Final-stage fermentation (240 days, olives)—B, C: reduced debittering time, faster degradation of secoiridoids and higher production of hydroxytyrosol (especially in C, probably due to the multiple-strain starter).HPLC[44]
Manzanilla
(Seville province, Spain)		Treated process: 2.3% NaOH solution for 5.5 h. Brine: 12.0% (w/v) NaCl. Fermentation time and T °C: 7 months; T °C: n.a. (**)LAB starter
M1, M2: spontaneous fermentation.
M3, M4: Lpb. pentosus LP99.
Inoculum level: 8 log cfu/mL at day 5, 7 log cfu/mL at day 12.		Final-stage fermentation (7 months, olive pulp)—All samples: fermentation significantly increased the number and concentrations of VOCs. M3, M4: highest amounts of 1-heptanol, 6-methyl-5-hepten-2-ol, isoamyl acetate, methyl benzoate and of 4-ethylphenol. The latter compound was associated with off-flavour, but the sensory evaluation indicated that not-significant differences were found among driven and spontaneous fermentations.HS-SPME/
GC-MS		[67]
Starter cultures: Lactic Acid Bacteria and Yeasts
Arbequina
(Tarragona, Spain)		Natural process: Greek-style. Brine: 8% NaCl. Fermentation time and T °C: 52 days at room T °C (20 °C).LAB and Y starter
A: Spontaneous fermentation.
B: C. diddensiae C6B19; C: Lpb. plantarum V10A2; D: Lpb. pentosus FxMA1; E: Lpb. pentosus 5E3A18; F: Lpb. pentosus 5E3A18, C. diddensiae C6B19; G: Lpb. pentosus 5E3A18, Lpb. plantarum V10A2; H: Lpb. pentosus 5E3A18, Lpb. pentosus FxMA1.
Inoculum level: 6 log cfu/mL		Final-stage fermentation (90 days)—Y and LAB/Y starter: higher content of citric acid, lower content of malic acid (B, F). LAB starter: G and H significant increase in lactic acid compared with single LAB starter (C, D, E fermentations). D: high content of acetic acid.HPLC[68]
Bella di Cerignola
(Modugno, Apulia, Italy)		Natural process: Greek-style. Brine: 7% (w/v) NaCl. Fermentation time and T °C: 90 days at room T °C (18–25 °C).LAB and Y starter
S: commercial Lpb. plantarum (Sacco Srl company); SY: commercial Lpb. plantarum (Sacco Srl) and autochthon Wickerhamomyces anomalus DiSSPA73; SYL: commercial Lpb. plantarum (Sacco Srl) and autochthons W. anomalus DiSSPA73, Lpb. plantarum DiSSPA1A7, Lpb. pentosus DiSSPA7.
Ctrl: spontaneous fermentation.
Inoculum level: 7 log cfu/mL		Final-stage fermentation (90 days, brines)—SY: ethanol (↑); S, SY, SYL: acetic acid (↑), ethyl acetate (↑), 1-hexanol (↑), propionic acid (↓).SPME/GC-MS[61]
Cellina di Nardò, Leccino, Kalamàta,
Conservolea (Salento, Apulia, Italy)
(Salento, Apulia, Italy)		Natural process: Greek-style. Brine: 8% (w/v; for Kalamàta and Conservolea cv) or 12% (w/v; for Cellina di Nardò and Leccino cv) NaCl. Fermentation time and T °C: 90 days at room T °C.LAB and Y starter (sequential inoculum)
Leccino cv: S. cerevisiae LI 180-7 (DSMZ27800) and then Lpb. plantarum L 180-11 (DSMZ27925); Cellina di Nardò cv: P. anomala CL 30-29 and then Lpb. plantarum C180-34; Kalamàta cv: S. cerevisiae KI 30-16 (DSMZ27801) and then Leuc. mesenteroides K T5-1 (DSMZ27926); Conservolea cv: D. hansenii A15-44 and then Lpb. plantarum A135-5.
Control spontaneous fermentation.
Inoculum level: 6 log cfu/mL		Final-stage fermentation (90 days)—Inoculated samples: complete consumption of glucose (except for Leccino cv); high levels of lactic (Leccino and Conservolea cv) and acetic (Cellina di Nardò and Kalamàta cv) acids. Higher content of hydroxytyrosol and tyrosol. VOCs (mainly alcohols and esters) increased in starter-driven fermentations, especially when Y were used.
The use of starter significantly reduced the time of fermentation process from 180 to 90 days.		HPLC
SPME/
GC-MS		[39]
Kalamàta and Conservolea
(Arta, Greece)		Natural process: Greek-style. Brine: 8% NaCl. Fermentation time and T °C: 105 days at room T °C (12–21 °C).LAB and Y starter
Sequential inoculum:
Kalamàta cv—Leuc. mesenteroides KT5-1, then S. cerevisiae KI30-16 (LY) or viceversa (YL). Conservolea cv: Lpb. plantarum A135-5, then D. hansenii A15-44 (LY) or viceversa (YL).
Mixtures (MIX):
Kalamàta cv—Leuc. mesenteroides KT5-1 and S. cerevisiae KI30-16. Conservolea cv: Lpb. plantarum A135-5 and D. hansenii A15-44 (LY).
Sp: spontaneous fermentation.
Inoculum level: 8 log cfu/mL		Final-stage fermentation (105 days)—Conservolea olives: YL and LY: higher level of esters and alcohols; LY: high content of terpenes; MIX and YL: high amount of hydrocarbons. Kalamàta olives: MIX: higher levels of esters, alcohols, hydrocarbons and terpenes.SPME/
GC-MS		[69]
Middle-stage fermentation (14 and 63 days, brines)—Conservolea brines: MIX and LY: presence of oleoside after 14 and 63 days of fermentation, respectively.
Final-stage fermentation (105 days, brines)—Conservolea brines, YL: higher content of tyrosol and hydroxytyrosol. Kalamàta brines: YL: caffeic and coumaric acid were not detected; MIX: high oleuropein content; LY: higher content of decarboxymethyl elenolic acid linked to hydroxytyrosol.		LC-MS/MS
Manzanilla
(Seville region, Spain)		Treated process: Spanish-style; treatment with 3.2% (w/v) NaOH solution containing 2.2% (w/v) NaCl and 0.89% (w/v) CaCl2 for 7 h. Brine: 12.0% (w/v) NaCl, 0.13% (w/v) CaCl2, and 0.08% (v/v) HCl.
Fermentation time and T °C: 65 days, at uncontrolled T °C (ranging from 29 °C to 16 °C).		LAB and Y starter
T1: Lpb. pentosus LPG1; T2: Lpb. pentosus Lp13; T3: Lpb. plantarum Lpl15; T4: W. anomalus Y12; sequential starter T5: W. anomalus Y12 followed by a combination of Lpb. pentosus LPG1, Lp13, Lpb. plantarum Lpl15.
T6: spontaneous fermentation.
Inoculum level: 7 log cfu/mL for single strains (T1, T2, T3, T4; after 8th days of brining); 5 log cfu/mL for W. anomalus Y12 (1st day of brining) and 7 log cfu/mL for LAB mixture (after 8th days of brining) in T5 fermentation.		Final-stage fermentation (65 days, brines)—T1: reduced methanol, β-damascenone, but increased 2-phenylethyl acetate, 2-butanol, 1-butanol, 3-methyl-3-buten-1-ol, 2-methyl-3-hexanol; T2: high 1-butanol content; T3: presence of methanol, isoxylaldehyde and 4-ethylphenol, and reduced content of coumarin, 5-tert-butylpyrogalol and vanillin; T4: presence of 1-butanol, ethanol, methyl acetate, ethyl acetate, 2-phenylethyl acetate, or 2-methyl-1-butanol production, and lower levels of methanol, coumarin, and vanillin; T5: high total VOC content (except for ethanol, 1–heptanol, or cis-5-octen-1-ol).SPME/
GC-MS		[70]
Starter cultures: Yeasts
Kalamàta, Picual and Manzanilla
(Marsa Matrouh, Egypt)		Natural process: Greek-style. Brine: 11% (w/v) NaCl. Fermentation time and T °C: 40 days at room T °C (19–27 °C).Yeasts starter
M1, P1, K1: Manzanilla, Picual, Kalamàta spontaneous fermentation with 1% v/v) vinegar in brines at the start of fermentation.
M2, P2: Manzanilla, Picual olives with
S. cerevisiae LI-180-7 (DSMZ27800); K2: Kalamàta olives with S. cerevisiae KI30-16 (DSMZ27801); M3, P3, K3: Manzanilla, Picual, Kalamàta olives with commercial S. cerevisiae baker’s yeast.
Inoculum level: 7 log cfu/mL		Final-stage fermentation (40 days; olives)—All inoculated samples: oleuropein degradation and increased hydroxytyrosol content. Compared to spontaneous fermentation, inoculated samples had a more complex profile in esters (e.g., isoamyl acetate, ethyl lactate, ethyl hexanoate, ethyl octanoate, phenyl acetate), alcohols (e.g., 2,3-methyl-1-butanol, phenylethanol, hexanol, cis 3-hexen-1-ol, 1-heptanol., associated with positive flavour (e.g., fruity-green notes).HPLC
HS-SPME/
GC-MS		[71]
Kalamàta
(Northern Greece)		Natural process: Greek-style. Brine: 7% (w/v) NaCl acidified with 0.5% (v/v) vinegar (ca. 6.0%, v/v, acetic acid). Fermentation time and T °C: 150 days at room T °C.Yeasts starter
A: C. boidinii Y27; B: C. boidinii Y28; C: C. boidinii Y30; D: C. boidinii Y31; E: S. cerevisiae Y34; F: spontaneous fermentation.
Inoculum level: 6 log cfu/mL		Final-stage fermentation (150 days)—Y starter exhibited different behaviour in metabolite production. A: highest amount of lactic and succinic acids; C: highest level of acetic and citric acids; E: highest amount of ethanol. Y27 showed the highest survival rate within olive fermentation; on the contrary, Y34 had the lowest survival. HPLC[72]
(*) The current taxonomy for lactobacilli (ex-Lactobacillus genus) was used in this study, according to Zheng et al. [73]. Genus abbreviations for lactobacilli: Lacticaseibacillus, Lcb.; Lactiplantibacillus, Lpb.; Lentilactobacillus, Lnb., Ligilactobacillus, Lgb; Secundilactobacillus, Slb. (**): not available. † Analytical method abbreviations: HPLC, High Performance Liquid Chromatography; HS-SPME/GC-MS: Headspace-Solid-Phase Micro-Extraction/Gas Chromatography-Mass Spectrometry; LC-MS/MS, Liquid Chromatography with tandem Mass Spectrometry. ↑: increase; ↓: decrease.
Table 2. Effect of starter cultures on the microbiota of fermented table olives.
Table 2. Effect of starter cultures on the microbiota of fermented table olives.
Olive cultivarType of Process and
Fermentative Conditions		Species and Strains
Used as Starter Cultures		Effect on the MicrobiotaSequencing MethodRef.
Starter cultures: Lactic Acid Bacteria (*)
Nocellara Etnea
(Adrano, Sicily, Italy)		Natural process: Sicilian style, without lye treatment. Brine: 8% (w/v) marine salt. Fermentation time and T °C: 120 days at room T °C (20 ± 2 °C).LAB starter
BC1: Lpb. plantarum UT2.1, Lcb. paracasei N24, Lpb. pentosus TH969; BC2: Lpb. plantarum UT2.1; BC3: Lcb. paracasei N24, Lpb. pentosus TH969; BC4: Lpb. plantarum UT2.1, Lpb. pentosus TH969; BC5: Lpb. plantarum UT2.1, Lcb. paracasei N24; BC6: Lpb. pentosus TH969.
C: uninoculated samples.
Inoculum level: 7 log cfu/mL		Early-stage fermentation (1-day, brines)—All samples: Halomonas spp., Achromobacter spp., Marinobacter spp., Serratia spp., Bradyrhizobium spp. were the most abundant genera in C samples; lactobacilli (ex-Lactobacillus genus) dominated all inoculated samples.
Middle-stage fermentation (60 days, brines)—BC2, BC3: Salinicola spp. (↑). BC2, BC3, BC6: Enterobacteriaceae (↑). BC3, BC6: Pediococcus parvulus (↑), Secundilactobacillus paracollinoides (↑), Ligilactobacillus acidipiscis (↑), Salinicola spp. (↑). BC6: Lactococcus lactis (↑). BC3, BC6: Lpb. plantarum (↓).
Final-stage fermentation (120 days, brines)—BC1, BC3, BC4, BC6: Pediococcus parvulus (↑), Slb. paracollinoides (↑), Lgb. acidipiscis (↑). BC1, BC2, BC3, BC4, BC5: Salinicola spp. (↑). BC2: Marinilactibacillus spp. (↑), Halomonas spp. (↑). BC5: Lcb. casei/paracasei group (↑). BC2, BC5, C: Lpb. plantarum (↑). BC1, BC3, BC4, BC6: Lpb. plantarum (↓, although remained the most abundant group). All inoculated samples: Enterobacteriaceae (↓).		Ion Torrent PGM
(V3 region of
16S rRNA gene)		[64]
Picual (whole and cracked olives; Nicosia, Cyprus)Natural process: Greek-style. Brine: 7% (w/v) or 10% (w/v) NaCl and 3.3% (v/v) citric acid. Fermentation time and T °C: 120 days at room T °C (23 ± 2 °C).LAB starter
S1, S4: spontaneous fermentations in cracked and whole olives, respectively. S2, S5: commercial starter Lpb. plantarum (Vege-Start 600, Chr. Hansen A/S) in 10% NaCl and 3.3% citric acid, cracked and whole olives, respectively.
S3, S6: Lpb. plantarum (Vege-Start 600) in 7% NaCl and 3.3% citric acid, cracked and whole olives, respectively.
Inoculum level: 5 log cfu/mL		Early-stage fermentation (1-day, olives)—All samples: Thermogemmatispora onikobensis, Chitinophaga soli (dominant species), Thiomonas thermosulfata, Bradyrhizobium pachyrhizi (co-dominant species), Lewinella lutea, Brevibacterium casei, Lpb. plantarum group (secondary species).
Middle- and final-stage fermentation (60 and 120 days, brines)—S2, S5, S3, S6: Lpb. plantarum group (↑), Lcb. manihotivorans (↑). S1: Lcb. brantae (↑), Lentilactobacillus parakefiri (↑); Lcb. plantarum group (↓). S4: high diversity, Lcb. plantarum group was the most abundant species, followed by Lcb. manihotivorans, T. onikobensis, T. thermosulfata, Lcb. brantae, Lnb. parafarraginis, and Lnb. parakefiri.		Illumina MiSeq (V3–V4 region of 16S rRNA gene)[43]
Nocellara Etnea (Adrano and Paternò, Sicily, Italy)Natural process: Sicilian style, without lye treatment. Brine: 5% or 8% (w/v) NaCl. Fermentation time and T °C: 80 days at room T °C (18 ± 2 °C).LAB starter
O1: Lpb. plantarum F1.16 and F3.5, in 5% NaCl. O2: Lpb. plantarum C11C8, F1.16, and F3.5, in 5% NaCl.
C5 and C8: uninoculated samples with 5% or 8% NaCl, respectively.
Inoculum level: 7 log cfu/mL		Middle- and final-stage fermentation (15 and 80 days, olives)—O1, O2: lactobacilli (ex-Lactobacillus genus; including Lpb. plantarum) dominated all inoculated samples; low occurrence of Enterobacter spp.
Middle- and final-stage fermentation (15 and 80 days, olives)—C5: Enterobacter spp. and Weissella spp. (↑) at 15 days; Enterobacter spp. and lactobacilli (ex-Lactobacillus genus) (↑) at 80 days. C8: Weissella spp. was dominant at 15 and 80 days; low abundance of Bacteroides spp., Faecalibacterium spp., Klebsiella spp., Raoultella spp. at 15 days.		Illumina MiSeq
(V3 region of
16S rRNA
gene)		[66]
Kalamata
(Greece)		Natural process: Greek-style. Brine: 6% (w/v) NaCl. Fermentation time and T °C: 150 days, at 20 °C.LAB starter
A: spontaneous fermentation.
B: Lcb. rhamnosus GG ATCC53103; C: Levilactobacillus brevis ATCC8287 starter culture; D: Lpb. plantarum ATCC14917.
Inoculum level: n.a. (**)		Final-stage fermentation (150 days, olives)—All samples: starter cultures did not significantly affect the microbiota composition. Lactiplantibacillus (mainly Lpb. plantarum, followed by Lpb. pentosus, Lpb. plajomi, Lpb. paraplantarum) and Leuconostoc (mainly Leuc. mesenteroides, and then Leuc. gelidum) were the most abundant species.Nanopore MinION™ (near full-length V1–V9 region of 16S rRNA gene)[74]
Manzanilla
(Seville region, Spain)		Treated process: Spanish-style; treatment with 2.3% (w/v) NaOH solution for 7 h. Brine: 11.0% (w/v) NaCl acidified with 37% HCl. Fermentation time and T °C: 83 days, at room T °C.LAB starter
I: commercial starter containing 3 Lpb. pentosus strains (OleicaStarter Advance, TAFIQS in FOODs, Seville, Spain).
U: spontaneous fermentation.
F: fruits; B: brines (for coding samples)
Inoculum level: 5 log cfu/mL		Early-stage fermentation (0 days, olives and brines)—U: high diversity, Vibrio spp., Salinivibrio spp., Marinilactobacillus spp., Alkalibacterium spp., Halolactibacillus spp., Aerococcus spp.; I: mainly Vibrio spp., Marinilactobacillus spp., Alkalibacterium spp., Halolactibacillus spp.
Middle-stage fermentation (24 days, olives and brines)—U samples: high diversity and variability; UF: Vibrio spp., Marinilactobacillus spp., Alkalibacterium spp., Lactiplantibacillus spp. (↑); UB: Lactiplantibacillus spp. was dominant (↑). IF, IB: Lactiplantibacillus spp. was dominant (↑), followed by Vibrio spp. and Marinilactobacillus spp.
Final-stage fermentation (83 days, olives and brines)—U samples: high diversity and variability; UF, UB, IF, IB: Lactiplantibacillus spp. was dominant (↑), Vibrio spp. (↓) and Marinilactobacillus spp. (↓).		Illumina MiSeq (V3–V4 region of 16S rRNA gene)[54]
Starter cultures: Lactic Acid Bacteria and Yeasts
Bella di Cerignola
(Modugno, Apulia, Italy)		Natural process: Greek-style. Brine: 7% (w/v) NaCl. Fermentation time and T °C: 90 days at room T °C (18–25 °C)LAB and Y starter
S: commercial Lpb. plantarum (Sacco Srl company); SY: commercial Lpb. plantarum (Sacco Srl) and autochthon Wickerhamomyces anomalus DiSSPA73; SYL: commercial Lpb. plantarum (Sacco Srl) and autochthons W. anomalus DiSSPA73, Lpb. plantarum DiSSPA1A7, Lpb. pentosus DiSSPA7.
Ctrl: spontaneous fermentation.
Inoculum level: 7 log cfu/mL		Un-processed olives: Hafnia spp. and Methylobacterium spp. were dominant.
Early-stage fermentation (1 day, brines)—Ctrl: Hafnia spp. (Hafnia alvei) (↑) was dominant. S, SY: co-occurrence of Hafnia spp. and Lpb. plantarum (↑); SYL: Lpb. plantarum/Lpb. pentosus (↑) were dominant.
Middle-stage fermentation (75 days, brines)—Ctrl: co-occurrence of Lpb. plantarum (↑) and Lactococcus lactis (↑), presence of other minor genera; Lpb. plantarum (↑) for S, SY or Lpb. plantarum/Lpb. pentosus (↑) for SYL were completely dominant.
Final-stage fermentation (90 days, brines)—Ctrl: Lpb. plantarum was the most abundant and metabolically active, together with a low fraction of Clostridium spp.; Lpb. plantarum (↑) for S, SY or Lpb. plantarum/Lpb. pentosus (↑) for SYL were completely dominant and metabolically active.
Final-stage fermentation (90 days, olives)—Ctrl: Lpb. plantarum was the most abundant and metabolically active, together with a low fraction of Lc. lactis spp., Clostridium spp. (↓); Lpb. plantarum (↑) for S, SY or Lpb. plantarum/Lpb. pentosus (↑) for SYL were completely dominant and metabolically active, together with a low fraction of Methylobacterium spp.		Bacterial tag-encoded FLX amplicon pyrosequencing (V1–V3 region of 16S rRNA gene—on both DNA and RNA)[61]
Manzanilla
(Seville region, Spain)		Treated process: Spanish-style; treatment with 3.2% (w/v) NaOH solution containing 2.2% (w/v) NaCl and 0.89% (w/v) CaCl2 for 7 h. Brine: 12.0% (w/v) NaCl, 0.13% (w/v) CaCl2, and 0.08% (v/v) HCl. Fermentation time and T °C: 65 days, at uncontrolled T °C (ranging from 29 °C to 16 °C).LAB and Y starter
T1: Lpb. pentosus LPG1; T2: Lpb. pentosus Lp13; T3: Lpb. plantarum Lpl15; T4: Wickerhamomyces anomalus Y12; sequential starter T5: W. anomalus Y12 followed by a combination of Lpb. pentosus LPG1, Lp13, Lpb. plantarum Lpl15.
T6: spontaneous fermentation.
Inoculum level: 7 log cfu/mL for single strains (T1, T2, T3, T4; after 8th days of brining); 5 log cfu/mL for W. anomalus Y12 (1st day of brining) and 7 log cfu/mL for LAB mixture (after 8th days of brining) in T5 fermentation.		Final-stage fermentation (65 days, olives)—All samples: Marinilactibacillus spp., Halolactibacillus spp., Lactobacillus spp. (Lpb. plantarum and/or Lpb. pentosus) and Alkalibacterium spp. were the most abundant genera, with a significant prevalence of Marinilactibacillus spp. (approximately from 40% to 60%).
The highest %: Marinilactibacillus spp. in T1; Lactobacillus spp. (Lpb. plantarum and Lpb. pentosus) in T5; Halolactibacillus spp. in T2; Alkalibacterium spp. in T3 and T4.
Aerococcus spp., Halomonas spp. and Bacillaceae family were also detected in all samples at very low occurrence.		Illumina MiSeq (V3–V4 region of 16S rRNA
gene)		[70]
(*) The current taxonomy for lactobacilli (ex-Lactobacillus genus) was used in this study, according to Zheng et al. [73]. Genus abbreviations for lactobacilli: Lacticaseibacillus, Lcb.; Lactiplantibacillus, Lpb.; Lentilactobacillus, Lnb., Ligilactobacillus, Lgb; Secundilactobacillus, Slb. (**): not available. ↑: increase; ↓: decrease.

4. “Omics” Approaches to Investigate the Functions of Table Olive Microbiomes and the Role of Starter Cultures

As already highlighted, data related to the microbiomes of fermented olives are mainly based on the AT-HTS approaches which, in recent years, allowed an increase in knowledge on the composition, taxonomic diversity and dynamism of microbial communities during fermentation (although with a greater focus on bacteriome than mycobiome). Unlike other fermented foods, further “omics”, “meta-omics” and “multi-omics” approaches (including tools and bioinformatics [75,76]) have been scantly applied to fermented table olives.
Shotgun metagenomics, a more powerful tool in depicting the diversity and functionality of microbiomes, have not been applied to fermented olives. To our knowledge, only Soto-Giron et al. [77] used a metagenome-assembled genome (MAG) approach to investigate the microbial communities of green olives, focusing attention on the genomic diversity and functionalities of 5 LAB-like MAGs (n.1 Loigolactobacillus coryniformis, n.2 Lentilactobacillus buchneri, n.2 Lactobacillus acetotolerans).
Available proteomic data are related to the proteome profile and functionalities of some LAB isolated from olives and/or brines [78,79,80], but, to date, no metaproteomic protocols have been exploited to study the in situ functionalities (during fermentation) of starter cultures and olives-associated microbiomes.
More recently, López-García et al. [81] investigated the transcriptome profile of Lpb. pentosus LPG1 during Manzanilla cv. fermentation (Spanish-style treatment, 60 days incubation), suggesting that many genes were differentially expressed in both brine- and biofilm-associated cells. As for metatranscriptome analysis (needed to investigate the metabolically active fraction of microbiomes), to date, no data are available for fermented table olives.
Although metabolomic approaches (i.e., HS-SPME/GC-MS, HPLC, LC-MS/MS) have been mostly used to evaluate the effect of the fermentative process in table olives (for both commercial and experimentally obtained products [22]; this study), the available information is poorly integrated with other “omic” data, not allowing adequate correlations between the composition, evolution and functionalities of microbiota and the final features of the products.

5. Conclusions

Starter cultures also play an important role in fermented table olives, preventing or reducing the growth of undesired microorganisms and improving the properties of final products. The effects of starter cultures on fermented olives have been investigated for several decades, mainly with a focus on the acidifying capability, antimicrobial activity, degradation of phenolic compounds, and production of some metabolites. Information on the genomic diversity of the strains, as well as on their metabolic interactions with other members of olive microbiota, is still limited.
The recent AT-HTS data improved the knowledge on the composition and evolution of microbial communities during olive fermentation and, in some cases, the effect of starter cultures on the indigenous microbiota. Much of the information, however, still describes the microbiota at the genus level, not providing a faithful picture of microbial dynamics during the fermentative process. Most of HTS approaches, moreover, have been exclusively targeted on hypervariable regions of the 16S rRNA gene, neglecting the fungal diversity of olives microbiota and using the genomic DNA as a template, overlooking the metabolically active microorganisms during fermentation.
Other “omics” techniques were scantily applied to the olive ecosystem, including the starter cultures, thus limiting the studies to a single or few technological traits, rather than to complex microbial interactions that occur during the fermentative process. Therefore, as for other fermented foods, future investigations based on the integration of “omics” or “meta-omics” data could be helpful to understand and predict the metabolic potential of starter cultures and indigenous microbiota, respectively, and improve the properties of table olives.
Additionally, although the use of starter cultures for olive fermentation can be advantageous and attractive for the food industry, further research and industrial-scale validation are needed to develop tailored formulations, place them on the market, and make them commercially available, as has already happened with other cultures exploited for other fermented foods.

Author Contributions

Conceptualization, M.G. and T.Z.; methodology, M.G. and T.Z.; investigation, M.G. and T.Z.; data curation, M.G., E.L. and T.Z.; writing—original draft preparation, M.G. and T.Z.; writing—review and editing, M.G., E.L., A.R. and T.Z.; visualization, M.G., E.L., A.R. and T.Z.; supervision, T.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partially supported by the European Commission—NextGenerationEU, Project “Strengthening the MIRRI Italian Research Infrastructure for Sustainable Bioscience and Bioeconomy”, code n. IR0000005.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Fermentation 10 00351 g001
Figure 1. Schematic representation of the main steps in table olive production ([5], modified). Dotted lines indicated optional steps.
Figure 1. Schematic representation of the main steps in table olive production ([5], modified). Dotted lines indicated optional steps.
Fermentation 10 00351 g001
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Giavalisco, M.; Lavanga, E.; Ricciardi, A.; Zotta, T. Starter Cultures for the Production of Fermented Table Olives: Current Status and Future Perspectives. Fermentation 2024, 10, 351. https://doi.org/10.3390/fermentation10070351

AMA Style

Giavalisco M, Lavanga E, Ricciardi A, Zotta T. Starter Cultures for the Production of Fermented Table Olives: Current Status and Future Perspectives. Fermentation. 2024; 10(7):351. https://doi.org/10.3390/fermentation10070351

Chicago/Turabian Style

Giavalisco, Marilisa, Emanuela Lavanga, Annamaria Ricciardi, and Teresa Zotta. 2024. "Starter Cultures for the Production of Fermented Table Olives: Current Status and Future Perspectives" Fermentation 10, no. 7: 351. https://doi.org/10.3390/fermentation10070351

APA Style

Giavalisco, M., Lavanga, E., Ricciardi, A., & Zotta, T. (2024). Starter Cultures for the Production of Fermented Table Olives: Current Status and Future Perspectives. Fermentation, 10(7), 351. https://doi.org/10.3390/fermentation10070351

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