Genotyping, identification and multifunctional features of yeasts associated to Bosana naturally black table olive fermentations

Impact of lactic acid bacteria inoculation on fungal diversity during Spanish-style green table olive fermentations

This study delved into the evolution of fungal population during the fermentation of Spanish-style green table olives (Manzanilla cultivar), determining the influence of different factors such as fermentation matrix (brine or fruit) or the use of a lactic acid bacteria inoculum, on its distribution. The samples (n = 24) were directly obtained from industrial fermentation vessels with approximately 10.000 kg of fruits and 6.000 L of brines. Our findings showcased a synchronized uptick in lactic acid bacteria counts alongside fungi proliferation. Metataxonomic analysis of the Internal Transcribed Spacer (ITS) region unearthed noteworthy disparities across different fermentation time points (0, 24, and 83 days). Statistical analysis pinpointed two Amplicon Sequence Variants (ASV), Candida and Aureobasidium, as accountable for the observed variances among the different fermentation time samples. Notably, Candida exhibited a marked increase during 83 days of fermentation, opposite to Aureobasidium, which demonstrated a decline. Fungal biodiversity was slightly higher in brines than in fruits, whilst no effect of inoculation was noticed. At the onset of fermentation, prominently detected genera were also Mycosphaerella (19.82 %) and Apohysomyces (16.31 %), hitherto unreported in the context of table olive processing. However, their prevalence dwindled to nearly negligible levels from 24th day fermentation onwards (<2 %). On the contrary, they were replaced by the fermentative yeasts Saccharomyces and Isstachenkia. Results obtained in this work will be useful for designing new strategies for better control of table olive fermentations.

Enhancing the quality and safety of Nocellara del Belice green table olives produced using the Castelvetrano method

The Castelvetrano method is the most widely used among the various table olive processing styles in Sicily. After debittering, the product is stored at low temperatures to prevent the growth of undesirable microorganisms. In an effort to enhance the production process, yeast isolates underwent genotypic characterization and technological screening. The screening process identified two yeast strains Candida norvegica OC10 and Candida boidinii LC1, which can grow at low temperatures and tolerate high pH values (up to 10) and salinity [10% (w/v)]. During the monitoring period, the inoculated trials showed limited presence of spoilage/pathogenic microorganisms. Additionally, the yeasts limited oxidative phenomena and softening of the drupes. The organic compounds detected were higher in the inoculated trials than in the control, and cold storage induced aromatic decay, which was less pronounced in the trial inoculated with C. norvegica. Sensory analysis revealed that the inoculated trials scored higher in sweetness, hardness and crispness.

Application of Immobilized β-Glucosidase from Candida boidinii in the Hydrolysis of Delignified Sugarcane Bagasse

Candida boidinii is a methylotrophic yeast with wide geographical distribution. In the present study, the microorganism was isolated from the Bahian semiarid and the enzymatic extract containing β-glucosidase was obtained through submerged fermentation. Response surface methodology was employed to optimize of fermentation medium. The higher production of β-glucosidase was obtained after 71 h of fermentation in an optimized medium composed of 3.35% glucose, 1.78% yeast extract and 1% peptone. The optimum pH and temperature of enzymatic activity were 6.8 (citrate-phosphate buffer) and 71.7 °C, respectively. Salts tested (10 mM) CaCl2, Na2SO4 and ZnSO4 promotes the increase of 91%, 45% and 80% of activity, respectively. The enzyme retained 64% ± 2.3 of its initial activity after 1 h heating at 90 °C. The production of reducing sugars was 95.94% after 24 h of hydrolysis and, with the addition of metal ions, this value increased more than 2 times. Among the supports analyzed for immobilization, chitosan showed higher residual activity during reuse. The immobilized enzyme showed higher activity at 60 °C with pH 6 and preserved almost 100% of the initial activity after 30 min at 70 °C.

Investigation of Corrosion Inhibition of Mild Steel in 0.5 M H2SO4 with Lachancea fermentati Inhibitor Extracted from Rotten Grapefruits (Vitis vinifera): Adsorption, Thermodynamic, Electrochemical, and Quantum Chemical Studies

Corrosion inhibition of mild steel (MS) was studied using Lachancea fermentati isolate in 0.5 M H2SO4, which was isolated from rotten grapes (Vitis vinifera) via biofilm formation. Biofilm over the MS surface was asserted by employing FT-IR and FE-SEM with EDXS, electrochemical impedance spectroscopy (EIS), AFM, and DFT-ESP techniques. The weight loss experiments and temperature studies supported the physical adsorption behavior of the corrosion inhibitors. The maximum inhibition efficiency (IE) value (90%) was observed at 293 K for 9 × 106 cfu/mL of Lachancea fermentati isolate. The adsorption of Lachancea fermentati isolate on the surface of MS confirms Langmuir's adsorption isotherm model, and the -ΔG values indicate the spontaneous adsorption of inhibitor over the MS surface. Electrochemical studies, such as potentiodynamic polarization (PDP) and EIS were carried out to investigate the charge transfer (CT) reaction of the Lachancea fermentati isolate. Tafel polarization curves reveal that the Lachancea fermentati isolate acts as a mixed type of inhibitor. The Nyquist plots (EIS) indicate the increase in charge transfer resistance (Rct) and decrease of double-layer capacitance (Cdl) values when increasing the concentration of Lachancea fermentati isolate. The spectral studies, such as UV-vis and FT-IR, confirm the formation of a complex between MS and the Lachancea fermentati isolate inhibitor. The formation of biofilm on the MS surface was confirmed by FE-SEM, EDXS, and XPS analysis. The proposed bioinhibitor shows great potential for the corrosion inhibition of mild steel in acid media.

Effect of microbial fermentation on functional traits and volatiloma profile of pâté olive cake

In this study, the pâté olive cake (POC), a by-product of the olive oil industry, was subjected to fermentation in a bioreactor using three microbial strains, Lactiplantibacillus plantarum, Wickerhamomyces anomalus and Candida boidinii, previously isolated from fermented table olive brines. Chemical, microbiological and molecular analyses were carried out at the beginning and at the end of fermentation. The lowest pH value (4.09) was reached after 10 days in sample inoculated with C. boidinii. Microbiological analyses exhibited the dominance of yeasts throughout the whole process (from 5.5 to 7.80 Log10 CFU/g), as confirmed by PCR-DGGE analysis. The microbial cultures affected both phenolic and volatile organic compound profiles. Moreover, the POC samples treated with different microbial strains were investigated for biological assays. The sample fermented with W. anomalus showed the greatest diffusion speed of transepithelial transport through Caco-2 cell, the highest inhibitory activity towards the tested cyclooxygenases and the highest antioxidant activity.

In Vitro Evaluation of the Technological and Probiotic Potential of Pichia kudriavzevii Strains Isolated from Traditional Fermented Foods

The isolation of endogenous yeast strains from traditionally fermented food products to use as functional starter cultures has become more popular for improved food safety, quality, and beneficial health effects. In this study, 107 Pichia kudriavzevii strains were isolated from sourdough, shalgam, tarhana, artisanal Tulum cheese, and yogurt. The strains were identified by DNA fingerprinting using iPBS-PCR method before technological and probiotic characterization. The multivariate statistical approach revealed that five strains were most promising in terms of technological characterization, including different harsh growth conditions. These strains were also examined in terms of probiotic properties with a commercial S. cerevisiae var boulardii MYA-796 strain. The multivariate statistical analyses indicated that P. kudriavzevii 5S5 were most promising in in vitro probiotic properties such as surviving in human GI conditions, adhering to intestinal cell lines, and exhibiting high hydrophobicity. Therefore, it seems to be a great starter candidate for the production of functional fermented food products.

Delving into the study of lactic acid bacteria and yeasts distribution in table olive biofilms using a non-destructive procedure

To turn table olives into appropriate carriers of beneficial bacteria and yeasts to consumers, it is essential to have reliable methods for analysing microorganisms in biofilms. This work validates the application of a non-destructive procedure to study the lactic acid bacteria and yeasts distribution in fruits during Spanish-style green table olive fermentations. Laboratory-scale fermentations were inoculated simultaneously with three Lactiplantibacillus pentosus strains (LPG1, 119, and 13B4) and two yeasts (Wickerhamomyces anomalus Y12 and Saccharomyces cerevisiae Y30), all of them natives of table olive fermentations. Data showed that L. pentosus LPG1 and yeasts W. anomalus Y12 were quite prone to colonise olive biofilms, but only the Lactiplantibacillus strain also can penetrate the epidermis of the fruit and colonise the flesh. Applying a non-destructive treatment consisting in shelling the fruits with glass beads led to obtaining similar lactic acid bacteria and yeast recovery than the classical stomacher destructive method. However, the glass bead procedure improved the quality of the metagenomics analysis (especially when using 16 S rRNA gene-based sequencing). Results show the great utility of procedures that do not destroy the fruit for studying fermented vegetable biofilms.

Assessment of Starters of Lactic Acid Bacteria and Killer Yeasts: Selected Strains in Lab-Scale Fermentations of Table Olives (Olea europaea L.) cv. Leccino

Olives debittering, organoleptic quality and safety can be improved with yeasts and lactic acid bacteria (LABs) selected strain starters, that allow for better fermentation control with respect to natural fermentation. Two selected killer yeasts (Wickerhamomyces anomalus and Saccharomyces cerevisiae) and Lactobacillus plantarum strains were tested for olive (cv. Leccino) fermentation to compare different starter combinations and strategies; the aim was to assess their potential in avoiding pretreatments and the use of excessive salt in the brines and preservatives. Lactobacilli, yeasts, molds, Enterobacteriaceae and total aerobic bacteria were detected, as well as pH, soluble sugars, alcohols, organic acids, phenolic compounds, and rheological properties of olives. Sugars were rapidly consumed in the brines and olives; the pH dropped quickly, then rose until neutrality after six months. The oleuropein final levels in olives were unaffected by the treatments. The use of starters did not improve the LABs’ growth nor prevent the growth of Enterobacteriaceae and molds. The growth of undesirable microorganisms could have been induced by the availability of selective carbon source such as mannitol, whose concentration in olive trees rise under drought stress. The possible role of climate change on the quality and safety of fermented foods should be furtherly investigated. The improvement of olives’ nutraceutical value can be induced by yeasts and LABs starters due to the higher production of hydroxytyrosol.

Use of Slightly Pressurized Carbon Dioxide to Enhance the Antimicrobial Properties of Brines in Naturally Processed Black Table Olives

Naturally fermented black table olives are processed at low pH in the presence of high sodium chloride concentrations ranging from 8 to 12% (w v⁻¹). Reducing the salt content of brine has become an urgent issue as it is responsible for several health and environmental problems. The study aim was to evaluate slightly pressurized CO₂ (spCO₂) as a third barrier to microbial growth in naturally processed black table olives with low pH and a reduced NaCl concentration. Based on the assessments performed on a pilot plant scale, an spCO₂ of 1 bar completely inhibited the growth of the bacteria and molds in the presence of reduced saline concentrations. Furthermore, the amount of yeast decreased in the brine as a function of the NaCl content. Laboratory tests performed under spCO₂ conditions using a single yeast species from the same habitat confirmed the high sensitivity of some oxidizing yeasts and indicated that the fermenting yeast, Saccharomyces cerevisiae, is the most tolerant species. Overall, in the brine of naturally processed olives with a low pH between 4 and 4.2, the antimicrobial properties observed with the high concentrations of NaCl can be achieved with a lower salt dose of 5% (w v⁻¹) when combined with spCO₂.

Fermentation of cv. Kalamata Natural Black Olives with Potential Multifunctional Yeast Starters

The purpose of this study was to explore the inoculated fermentation of cv. Kalamata natural black olives using selected strains of yeast cultures with multifunctional potential. For this purpose, five yeast starters belonging to Candida boidinii (four starters) and Saccharomyces cerevisiae (one starter), previously isolated from table olive fermentation of the same variety and screened for their technological characteristics and probiotic potential, were inoculated in brines at the beginning of fermentation. Microbial populations (lactic acid bacteria, yeasts, and Enterobacteriaceae), pH, titratable acidity, organic acids, and ethanol were monitored during fermentation for a period of 5 months. At the same time, the survival of each starter was assessed by culture-dependent molecular identification at the beginning (0 days), middle (75 days), and final stages (150 days) of fermentation in the brines and olives (at the end of the process only). The results revealed the coexistence of yeasts and lactic acid bacteria (LAB) throughout fermentation in most processes and also the absence of Enterobacteriaceae after the first 20 days of brining. The population of yeasts remained 2 log cycles below LAB counts, except for in the inoculated treatment with C. boidinii Y28, where the yeast starter prevailed from day 60 until the end of the fermentation, as well as in the inoculated treatment with C. boidinii Y30, where no LAB could be detected in the brines after 38 days. At the end of the process, LAB ranged between 4.6 and 6.8 log₁₀ CFU/mL, while yeasts were close to 5.0 log₁₀ CFU/mL, except for the inoculated fermentation with C. boidinii Y27 and spontaneous fermentation (control), in which the yeast counts were close to 3.5 log₁₀ CFU/mL. At the end of fermentation, the recovery percentage of C. boidinii Y27 was 50% in the brines and 45% in the olives. C. boidinii Y28 and S. cerevisiae Y34 could be recovered at 25% and 5% in the brine, respectively, whereas neither starter could be detected in the olives. For C. boidinii Y30, the recovery percentage was 25% in the brine and 10% in the olives. Finally, C. boidinii Y31 could not be detected in the brines and survived at a low percentage (10%) in the olives.

In Vitro Characterization and Identification of Potential Probiotic Yeasts Isolated from Fermented Dairy and Non-Dairy Food Products

This study is about the isolation of yeast from fermented dairy and non-dairy products as well as the characterization of their survival in in vitro digestion conditions and tolerance to bile salts. Promising strains were selected to further investigate their probiotic properties, including cell surface properties (autoaggregation, hydrophobicity and coaggregation), physiological properties (adhesion to the HT-29 cell line and cholesterol lowering), antimicrobial activities, bile salt hydrolysis, exopolysaccharide (EPS) producing capability, heat resistance and resistance to six antibiotics. The selected yeast isolates demonstrated remarkable survivability in an acidic environment. The reduction caused by in vitro digestion conditions ranged from 0.7 to 2.1 Log₁₀. Bile salt tolerance increased with the extension in the incubation period, which ranged from 69.2% to 91.1% after 24 h. The ability of the 12 selected isolates to remove cholesterol varied from 41.6% to 96.5%, and all yeast strains exhibited a capability to hydrolyse screened bile salts. All the selected isolates exhibited heat resistance, hydrophobicity, strong coaggregation, autoaggregation after 24 h, robust antimicrobial activity and EPS production. The ability to adhere to the HT-29 cell line was within an average of 6.3 Log₁₀ CFU/mL after 2 h. Based on ITS/5.8S ribosomal DNA sequencing, 12 yeast isolates were identified as 1 strain for each Candidaalbicans and Saccharomyces cerevisiae and 10 strains for Pichia kudriavzevii.

Assessment of Yeasts as Potential Probiotics: A Review of Gastrointestinal Tract Conditions and Investigation Methods

Probiotics are microorganisms (including bacteria, yeasts and moulds) that confer various health benefits to the host, when consumed in sufficient amounts. Food products containing probiotics, called functional foods, have several health-promoting and therapeutic benefits. The significant role of yeasts in producing functional foods with promoted health benefits is well documented. Hence, there is considerable interest in isolating new yeasts as potential probiotics. Survival in the gastrointestinal tract (GIT), salt tolerance and adherence to epithelial cells are preconditions to classify such microorganisms as probiotics. Clear understanding of how yeasts can overcome GIT and salt stresses and the conditions that support yeasts to grow under such conditions is paramount for identifying, characterising and selecting probiotic yeast strains. This study elaborated the adaptations and mechanisms underlying the survival of probiotic yeasts under GIT and salt stresses. This study also discussed the capability of yeasts to adhere to epithelial cells (hydrophobicity and autoaggregation) and shed light on in vitro methods used to assess the probiotic characteristics of newly isolated yeasts.

Role of yeasts in the qualitative structuring of extra virgin olive oil

This review sought to describe the role played by some components of the microbiota of extra virgin olive oil (EVOO), particularly yeasts, in structuring the physicochemical and sensorial quality of freshly produced olive oil. Yeasts can survive during the entire storage period of the product. To date, approximately 25 yeast species isolated from oil produced in more than six countries have been identified, eight of which are classified as new species. Some yeast species with probiotic traits improve the health qualities of oil, whereas many others improve the chemical composition and sensory characteristics based on β-glucosidase and esterase enzymes, which are involved in the hydrolysis of the bitter glucoside known as oleuropein. However, some species, which are typically favored by the high water content in the oily matrix, such as lipase-producing yeasts, can worsen the initial chemical characteristics of EVOO oil during storage. Some physical treatments that are compatible with the EVOO production specification affect the biotic component of the oil by reducing the concentration of yeasts. The possibility of minimizing the invasive action on the biotic component of the oil by appropriately selecting the physical treatment for each oil is discussed.

Current Status, Recent Advances, and Main Challenges on Table Olive Fermentation: The Present Meets the Future

Table olives are among the most well-known fermented foods, being a vital part of the Mediterranean pyramid diet. They constitute a noteworthy economic factor for the producing countries since both their production and consumption are exponentially increasing year by year, worldwide. Despite its significance, olive’s processing is still craft based, not changed since antiquity, leading to the production of an unstable final product with potential risk concerns, especially related to deterioration. However, based on industrial needs and market demands for reproducible, safe, and healthy products, the modernization of olive fermentation processing is the most important challenge of the current decade. In this sense, the reduction of sodium content and more importantly the use of suitable starter cultures, exhibiting both technological and potential probiotic features, to drive the process may extremely contribute to this need. Prior, to achieve in this effort, the full understanding of table olive microbial ecology during fermentation, including an in-depth determination of microbiota presence and/or dominance and its functionality (genes responsible for metabolite production) that shape the sensorial characteristics of the final product, is a pre-requisite. The advent of meta-omics technology could provide a thorough study of this complex ecosystem, opening in parallel new insights in the field, such as the concept of microbial terroir. Herein, we provide an updated overview in the field of olive fermentation, pointing out some important challenges/perspectives that could be the key to the olive sector’s advancement and modernization.

Probiotic Properties of Lactobacillus Strains Isolated from Table Olive Biofilms

In this work, 16 strains with promising probiotic characteristics belonging to the Lactobacillus pentosus (13) and Lactobacillus plantarum (3) species and isolated from table olive biofilms were tested for adherence to cell lines and to solvents, immunomodulatory, and anti-proliferative properties on epithelial human cellular lines. Most Lactobacillus strains were able to regulate the production of cytokines by stimulating the production of pro-inflammatory (IL-6) and anti-inflammatory (IL-10) interleukins on macrophages, and by suppressing the secretion of IL-8 on HT-29 TNF-α-induced model. Lactobacillus strains also showed anti-proliferative activity on the HT-29 cell line. No clear relation was found between adhesion to solvents and adhesion to HT-29 human cell line. Lactobacillus pentosus LPG1, which showed the best anti-inflammatory and immunomodulatory properties, was then tested in a dinitro-benzene sulfonic acid (DNBS)-induced chronic colitis murine model. As a measure of the inflammation, gut permeability and weight loss, as well as cytokine profiles, were determined. Lactobacillus pentosus LPG1 improved mice health as observed by a significant reduction of weight loss, gut permeability, and beneficial cytokine modulation. Macroscopic scores and tissue damage were also lower in mice administered with LPG1 with respect to the DNBS-treated group. These results showed that L. pentosus LPG1 isolated from plant could have potential as probiotic for use as an anti-inflammatory and immunomodulatory agent for patients with inflammatory bowel disease.

Microbial Application to Improve Olive Mill Wastewater Phenolic Extracts

Olive mill wastewater (OMW) contains valuable and interesting bioactive compounds, among which is hydroxytyrosol, which is characterized by a remarkable antioxidant activity. Due to the health claims related to olive polyphenols, the aim of this study was to obtain an extract from OMW with an increased level of hydroxytyrosol by means of microbial enzymatic activity. For this purpose, four commercial adsorbent resins were selected and tested. The beta-glucosidase and esterase activity of strains of Wickerhamomyces anomalus, Lactiplantibacillus plantarum, and Saccharomyces cerevisiae were also investigated and compared to those of a commercial enzyme and an Aspergillus niger strain. The W. anomalus strain showed the best enzymatic performances. The SP207 resin showed the best efficiency in selective recovery of hydroxytyrosol, tyrosol, oleuropein, and total phenols. The bioconversion test of the OMW extract was assessed by using both culture broths and pellets of the tested strains. The results demonstrated that the pellets of W. anomalus and L. plantarum were the most effective in hydroxytyrosol increasing in phenolic extract. The interesting results suggest the possibility to study new formulations of OMW phenolic extracts with multifunctional microorganisms.

Probiotic properties of yeasts isolated from Brazilian fermented table olives

AIMS

To investigate the probiotic potential of yeasts isolated from naturally fermented Brazilian table olives.

METHODS AND RESULTS

Eighteen yeast strains were tested in terms of: safety; survival of gastrointestinal and digestion conditions; antimicrobial activity; cellular hydrophobicity; autoaggregation ability and adhesion to epithelial cells; coaggregation and inhibition of pathogenic bacteria adhesion. Six yeasts showed favourable results for all probiotic attributes: Saccharomyces cerevisiae CCMA 1746, Pichia guilliermondii CCMA 1753, Candida orthopsilosis CCMA 1748, Candida tropicalis CCMA 1751, Meyerozyma caribbica CCMA 1758 and Debaryomyces hansenii CCMA 1761. These yeasts demonstrated resistance to 37°C, pH 2·0 and bile salts, and survived in vitro digestion (≥10⁶  CFU per ml). Furthermore, the yeasts exhibited a hydrophobic cell surface (42·5-92·2%), autoaggregation capacity (41·0-91·0%) and adhesion to Caco-2 (62·0-82·8%) and HT-29 (57·6-87·3%) epithelial cell lines. Also, the strains showed antimicrobial activity against Salmonella Enteritidis as well as the ability to coaggregate and reduce the adhesion of this pathogen to intestinal cells.

CONCLUSIONS

Autochthonous yeasts from naturally fermented Brazilian table olives have probiotic properties, with potential for development of new probiotic food products.

SIGNIFICANCE AND IMPACT OF STUDY

These data are important and contribute to the knowledge of new potential probiotic yeasts capable of surviving gastrointestinal tract conditions and inhibiting pathogenic bacteria.

Technological and enzymatic characterization of the yeasts isolated from natural fermentation media of Gemlik olives

AIM

To determine the technological and enzymatic characteristics of 54 yeast strains belonging to 16 species previously isolated from natural fermentation media of Gemlik olives. The distinguishing feature of these strains, according to their selective technological and enzymatic properties using principal component analysis (PCA), was also intended.

METHODS AND RESULTS

The technological properties of yeast strains, growth characteristics at different temperatures, pH and salt concentrations were examined. Besides, yeast strains' abilities to use oleuropein as a sole carbon source, to assimilate citric acid and to produce H₂ S were examined and their catalase, pectolytic, proteolytic and killer activities were also tested. All strains could grow between 15 and 28°C which are favourable temperatures for natural olive fermentation and they were able to tolerate high salt concentration and low pH in the brine of natural fermentation media. As a result of enzymatic characterization with API-ZYM test system, all strains have esterase activity, which is an important feature for developing table olive aroma. In this research, β-glucosidase activity, which contributes to removing bitterness out of olives, was one of the main distinguishing features of yeast strains. Several strains of Candida hellenica, Pichia anomala and Candida pelliculosa species had β-glucosidase activity. PCA tested yeasts and several strains belonging to C. hellenica (AF84-1), P. anomala (BF1-1, BF46-2) and C. pelliculosa (BF46-3, BF143-2) species have promising technological and enzymatic properties for natural table olive production.

CONCLUSION

Five promising strains belonging to C. hellenica, P. anomala and C. pelliculosa species may be suitable adjunct starter cultures with lactic acid bacteria in natural fermentation media of table olive.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has been the first contribution to the enzymatic and technological characterization of yeasts isolated from Gemlik olives in Turkey. Some strains could be proposed as a promising adjunct culture in the production of table olives.

Microbial Diversity of Fermented Greek Table Olives of Halkidiki and Konservolia Varieties from Different Regions as Revealed by Metagenomic Analysis

Current information from conventional microbiological methods on the microbial diversity of table olives is insufficient. Next-generation sequencing (NGS) technologies allow comprehensive analysis of their microbial community, providing microbial identity of table olive varieties and their designation of origin. The purpose of this study was to evaluate the bacterial and yeast diversity of fermented olives of two main Greek varieties collected from different regions-green olives, cv. Halkidiki, from Kavala and Halkidiki and black olives, cv. Konservolia, from Magnesia and Fthiotida-via conventional microbiological methods and NGS. Total viable counts (TVC), lactic acid bacteria (LAB), yeast and molds, and Enterobacteriaceae were enumerated. Microbial genomic DNA was directly extracted from the olives' surface and subjected to NGS for the identification of bacteria and yeast communities. Lactobacillaceae was the most abundant family in all samples. In relation to yeast diversity, Phaffomycetaceae was the most abundant yeast family in Konservolia olives from the Magnesia region, while Pichiaceae dominated the yeast microbiota in Konservolia olives from Fthiotida and in Halkidiki olives from both regions. Further analysis of the data employing multivariate analysis allowed for the first time the discrimination of cv. Konservolia and cv. Halkidiki table olives according to their geographical origin.

Yeast biofilm in food realms: occurrence and control

In natural environments, microorganisms form microbial aggregates called biofilms able to adhere to a multitude of different surfaces. Yeasts make no exception to this rule, being able to form biofilms in a plethora of environmental niches. In food realms, yeast biofilms may cause major problems due to their alterative activities. In addition, yeast biofilms are tenacious structures difficult to eradicate or treat with the current arsenal of antifungal agents. Thus, much effort is being made to develop novel approaches to prevent and disrupt yeast biofilms, for example through the use of natural antimicrobials or small molecules with both inhibiting and dispersing properties. The aim of this review is to provide a synopsis of the most recent literature on yeast biofilms regarding: (i) biofilm formation mechanisms; (ii) occurrence in food and in food-related environments; and (iii) inhibition and dispersal using natural compounds, in particular.

FoodOmics as a new frontier to reveal microbial community and metabolic processes occurring on table olives fermentation

Table olives are considered the most widespread fermented food in the Mediterranean area and their consumption is expanding all over the world. This fermented vegetable can be considered as a natural functional food thanks to their high nutritional value and high content of bioactive compounds that contribute to the health and well-being of consumers. The presence of bioactive compounds is strongly influenced by a complex microbial consortium, traditionally exploited through culture-dependent approaches. Recently, the rapid spread of omics technologies has represented an important challenge to better understand the function, the adaptation and the exploitation of microbial diversity in different complex ecosystems, such as table olives. This review provides an overview of the potentiality of omics technologies to in depth investigate the microbial composition and the metabolic processes that drive the table olives fermentation, affecting both sensorial profile and safety properties of the final product. Finally, the review points out the role of omics approaches to raise at higher sophisticated level the investigations on microbial, gene, protein, and metabolite, with huge potential for the integration of table olives composition with functional assessments.

Industrial scale bio-detoxification of raw olive mill wastewaters by the use of selected microbial yeast and bacterial strains to obtain a new source for fertigation

The Olive Mill Wastewaters (OMWs) are one of the most important agro-industrial wastes of the Mediterranean Countries and the disposal by draining them onto land has been proved to be damaging for soils, plants and groundwater due to their polluting power. The present report describes a new method for bio-detoxification of undiluted fresh OMW based on the driven selection of aerobic yeasts and bacteria. The identified yeast Candida boidinii A5y and the bacterium Paenibacillus albidus R32b strains allowed the treatment of freshly produced raw OMW characterized by very high COD value and phenolic content, when applied as sequential inoculum. The treated OMW showed the absence of antimicrobial effects and a strongly reduction of phytotoxic activity on the germination of several plant seeds. The process was successfully validated on an industrial scale without any pre-treatment, dilution and/or supplementation of the raw waste. Bio-detoxified OMW produced by this sustainable and low-cost process would be suitable for new non-chemical fertigation or soilless applications. The described procedure represents a virtuous example of circular economy efficaciously applied for a depleting agri-food resource.

The utility of iPBS retrotransposons markers to analyze genetic variation in yeast

Yeasts are one of the main organisms in the food industry and effective components of many ecosystems. The method for identifying and detecting certain yeast species or strains is a crucial step for the food industry and should be simple, reliable, fast, and inexpensive. In our study, inter-priming binding sites (iPBS) retrotransposon marker system was employed to elucidate the genetic variability at intraspecies and interspecies levels among 112 yeast strains belonging to eight species previously obtained from fermented foods. The molecular identification of yeast strains was firstly confirmed by sequencing the D1/D2 domain of the 26S rRNA. The eight selected retrotransposon-based primers produced 278 bands, all of which were polymorphic with an average of 34.75 polymorphic fragments per primer. The averages of polymorphism information contents and the resolving power values for the iPBS marker system were 0.23 and 10.11, respectively. The genetic parameters within each yeast species obtained from iPBS markers were observed as; the percentage of polymorphic loci for each species ranging from 19.23% to 71.21%, Nei's gene diversity from 0.085 to 0.228, while Shannon's information index values ranging from 0.125 to 0.349. The value of gene flow (0.09) and genetic variation among the populations (0.85) showed higher genetic variation among the species. UPGMA analyses demonstrated considerable genetic variability in the yeast strains, clustered them according to their species, and revealed the intraspecific variation. Each of the selected iPBS primer provided enough species-discrimination. Present evaluations suggest the utility of iPBS marker system to estimate the genetic variation of yeast strains. This study is a preliminary point for further studies on the identification methodology, and population genetics of yeast species having importance in the food industry with iPBS markers.

Table Olives More than a Fermented Food

Table olives are one of the oldest vegetable fermented foods in the Mediterranean area. Beside their economic impact, fermented table olives represent also an important healthy food in the Mediterranean diet, because of their high content of bioactive and health-promoting compounds. However, olive fermentation is still craft-based following traditional processes, which can lead to a not fully predictable final product with the risk of spontaneous alterations. Nowadays, food industries have to face consumer demands for safe and healthy products. This review offers an overview about the main technologies used for olive fermentation and the role of lactic acid bacteria and yeasts characterizing this niche during the fermentation. Particular attention is offered to the selection and use of microorganisms as starter cultures to fasten and improve the safety of table olives. The development and implementation of multifunctional starter cultures in order to obtain heath-oriented table olives is also discussed.

Bacterial Biodiversity of Extra Virgin Olive Oils and Their Potential Biotechnological Exploitation

Bacterial diversity of 15 extra virgin olive oils, obtained from different Italian varieties, including Frantoio, Coratina, Bosana, and Semidana, was analyzed in this study. All bacterial isolates were genotyped using RAPD and REP-PCR method and grouped by means of cluster analyses. Sequencing of 16S rDNA of 51 isolates, representative of 36 clusters, led to the identification of Bacillus spp., Brevibacillus spp., Micrococcus spp., Staphylococcus spp., Pantoea spp., Kocuria spp., Lysinbacillus spp., and Lactobacillus spp., most of which reported for first time in olive oils. Phenotypic characterization of the 51 isolates, some of which ascribed to potentially probiotic species, indicate that two of them have beta-glucosidase activity while 37% present lipolytic activity. Preliminary evaluation of probiotic potential indicates that 31% of the isolates show biofilm formation ability, 29% acidic pH resistance, and 25% bile salt resistance. Finally, 29% of the isolates were sensitive to antibiotics while the remaining 71%, that include bacterial species well-recognized for their ability to disseminate resistance genes in the environment, showed a variable pattern of antibiotic resistance. The results obtained underline that microbial diversity of extra virgin olive oils represents an unexpected sink of microbial diversity and poses safety issues on the possible biotechnological exploitation of this microbial biodiversity.

Yeast killer toxins: from ecological significance to application

Killer toxins are proteins that are often glycosylated and bind to specific receptors on the surface of their target microorganism, which is then killed through a target-specific mode of action. The killer phenotype is widespread among yeast and about 100 yeast killer species have been described to date. The spectrum of action of the killer toxins they produce targets spoilage and pathogenic microorganisms. Thus, they have potential as natural antimicrobials in food and for biological control of plant pathogens, as well as therapeutic agents against animal and human infections. In spite of this wide range of possible applications, their exploitation on the industrial level is still in its infancy. Here, we initially briefly report on the biodiversity of killer toxins and the ecological significance of their production. Their actual and possible applications in the agro-food industry are discussed, together with recent advances in their heterologous production and the manipulation for development of peptide-based therapeutic agents.

Biodiversity and Multifunctional Features of Lactic Acid Bacteria Isolated From Table Olive Biofilms

In the present study, a total of 554 lactic acid bacteria (LAB) isolates were obtained from the olive surface of Manzanilla, Gordal, and Aloreña cultivars processed as green Spanish-style or directly brined (natural) olives. The isolates obtained from industrial processes were genotyped by rep-PCR with primer GTG₅, collecting a total of 79 different genotypes. The α-biodiversity indexes showed that the LAB diversity was higher in the biofilms on the fruits which followed the Spanish-style process than in those just brined. Sixteen genotypes had a frequency higher >1% and were identified, by multiplex PCR recA gene and 16S gene sequencing, as belonging to Lactobacillus pentosus (n = 13) and Lactobacillus plantarum (n = 3) species. A multivariate analysis based on a dataset with 89,744 cells, including technological (resistance to salt and pH, production of lactic acid, auto and co-aggregation with yeast species, β-glucosidase and esterase activities), and potential probiotic characteristics (survival to gastric and pancreatic digestions, resistance to antibiotics, inhibition of pathogens, presence of bsh genes, cholesterol removal, hemolytic, α-glucosidase, β-galactosidase, and phytase activities) showed that the 16 genotypes could be grouped into 3 great phenotypes. Thus, the genotype biodiversity in table olive biofilms was limited but, at phenotype level, it was even lower since L. pentosus predominated clearly (80.15% isolates). L. pentosus Lp13 was the genotype with the most promising characteristics for its use as a multifunctional starter, with this strain being and ubiquitous microorganism present in both natural and lye-treated olive fermentations.

Efficacy of yeast starters to drive and improve Picual, Manzanilla and Kalamàta table olive fermentation

BACKGROUND

Table olive fermentation is an unpredictable process and frequently performed using traditional practices often inadequate to obtain products with acceptable quality and safety standards. In the present study, the efficacy of selected yeast strains as starters to drive fermentations of green and black table olives by the Greek method was investigated. Pilot-scale production by spontaneous fermentation as a control, olives started with previously selected Saccharomyces cerevisiae strains and fermentation driven by commercial S. cerevisiae baker's yeast strain were carried out for each of Manzanilla, Picual and Kalamàta table olive cultivars.

RESULTS

Time of fermentation was significantly shortened to 40 days to complete the transformation process for all three tested cultivars. Inoculated table olives were enhanced in their organoleptic and nutritional properties in comparison with corresponding samples obtained by spontaneous fermentation. The use of starters was also able to improve safety traits of table olives in terms of biogenic amine reduction as well as absence of undesired microorganisms at the end of the process.

CONCLUSIONS

Autochthonous, but also non-autochthonous, yeasts can be used to start and control table olive fermentations and can significantly improve quality and safety aspects of table olives produced by many smallholder farmers. © 2018 Society of Chemical Industry.

Effect of Sequential Inoculum of Beta-Glucosidase Positive and Probiotic Strains on Brine Fermentation to Obtain Low Salt Sicilian Table Olives

In the present study, the β-glucosidase positive strain Lactobacillus plantarum F3. 3 was used as starter during the fermentation of Sicilian table olives (Nocellara Etnea cultivar) at two different salt concentrations (5 and 8%), in order to accelerate the debittering process. The latter was monitored through the increase of hydroxytyrosol compound. In addition, the potential probiotic Lactobacillus paracasei N24 strain was added after 60 days of fermentation. Un-inoculated brine samples at 5 and 8% of salt were used as control. The fermentation was monitored till 120 days through physico-chemical and microbiological analyses. In addition, volatile organic compounds and sensorial analyses were performed during the process and at the end of the fermentation, respectively. Lactic acid bacteria and yeasts were, in depth, studied by molecular methods and the occurrence of the potential probiotic N24 strain in the final products was determined. Results highlighted that inoculated brines exhibited a higher acidification and debittering rate than control ones. In addition, inoculated brines at 5% of salt exhibited higher polyphenols (hydoxytyrosol, tyrosol, and verbascoside) content compared to samples at 8% of NaCl, suggesting a stronger oleuropeinolytic activity of the starter at low salt concentration. Lactobacilli and yeasts dominated during the fermentation process, with the highest occurrence of L. plantarum and Wickerhamomyces anomalus, respectively. Moreover, the potential probiotic L. paracasei N24 strain was able to survive in the final product. Hence, the sequential inoculum of beta-glucosidase positive and potential probiotic strains could be proposed as a suitable technology to produce low salt Sicilian table olives.

Biofilms in Food Processing Environments: Challenges and Opportunities

This review examines the impact of microbial communities colonizing food processing environments in the form of biofilms on food safety and food quality. The focus is both on biofilms formed by pathogenic and spoilage microorganisms and on those formed by harmless or beneficial microbes, which are of particular relevance in the processing of fermented foods. Information is presented on intraspecies variability in biofilm formation, interspecies relationships of cooperativism or competition within biofilms, the factors influencing biofilm ecology and architecture, and how these factors may influence removal. The effect on the biofilm formation ability of particular food components and different environmental conditions that commonly prevail during food processing is discussed. Available tools for the in situ monitoring and characterization of wild microbial biofilms in food processing facilities are explored. Finally, research on novel agents or strategies for the control of biofilm formation or removal is summarized.

Yeast Identification During Fermentation of Turkish Gemlik Olives

Naturally fermented black table olives of the Gemlik variety are one of the most consumed fermented products in Turkey. The objective of this work was to identify yeast strains isolated during their natural fermentation by using Restriction Fragments Lengths Polymorphism-Polimerase Chain Reaction (RFLP-PCR) and DNA sequencing methods. The study also focused on determining the effect of regional differences on yeast microflora of naturally fermented Gemlik olives. A total of 47 yeast strains belonging to 12 different species which had been previously isolated from the natural brine of Akhisar and Iznik-Gemlik cv. olives were characterized by molecular methods. Forty-two of the tested strains could be identified by RFLP-PCR to species level. These yeast species were determined as Candida mycetangi, Candida hellenica, Candida membranaefaciens, Candida famata, Candida pelliculosa, Saccharomyces cerevisiae, and Zygosaccharomyces mrakii. Five strains were identified by DNA sequencing. These strains belonged to three different species: Aureobasidium pullulans, Kloeckera apiculate, and Cryptococcus saitoi. The most frequent species were C. famata and C. pelliculosa in both regions.

PRACTICAL APPLICATION

This work studies the yeasts from Turkish table olives which could prove to be of importance to the food industry in that area. On the other hand, it compares identification by molecular and classical biochemical methods and offers an idea about the differences between the ecosystems of Gemlik olives in the Akhisar (AO) and Iznik (IO) regions. The study could be useful in characterizing a very important product and, in this way, could help to promote its marketing.

Technologies and Trends to Improve Table Olive Quality and Safety

Table olives are the most widely consumed fermented food in the Mediterranean countries. Peculiar processing technologies are used to process olives, which are aimed at the debittering of the fruits and improvement of their sensory characteristics, ensuring safety of consumption at the same time. Processors demand for novel techniques to improve industrial performances, while consumers' attention for natural and healthy foods has increased in recent years. From field to table, new techniques have been developed to decrease microbial load of potential spoilage microorganisms, improve fermentation kinetics and ensure safety of consumption of the packed products. This review article depicts current technologies and recent advances in the processing technology of table olives. Attention has been paid on pre processing technologies, some of which are still under-researched, expecially physical techniques, such ad ionizing radiations, ultrasounds and electrolyzed water solutions, which are interesting also to ensure pesticide decontamination. The selections and use of starter cultures have been extensively reviewed, particularly the characterization of Lactic Acid Bacteria and Yeasts to fasten and safely drive the fermentation process. The selection and use of probiotic strains to address the request for functional foods has been reported, along with salt reduction strategies to address health concerns, associated with table olives consumption. In this respect, probiotics enriched table olives and strategies to reduce sodium intake are the main topics discussed. New processing technologies and post packaging interventions to extend the shelf life are illustrated, and main findings in modified atmosphere packaging, high pressure processing and biopreservaton applied to table olive, are reported and discussed.

Evolution of Yeast Consortia during the Fermentation of Kalamata Natural Black Olives upon Two Initial Acidification Treatments

The objective of this study was to elucidate the yeast consortia structure and dynamics during Greek-style processing of Kalamata natural black olives in different brine solutions. Olives were subjected to spontaneous fermentation in 7% (w/v) NaCl brine solution (control treatment) or brine acidified with (a) 0.5% (v/v) vinegar, and (b) 0.1% (v/v) lactic acid at the onset of fermentation. Changes in microbial counts, pH, acidity, organic acids, sugars, and alcohols were analyzed for a period of 187 days. Yeast consortia diversity was evaluated at days 4, 34, 90, 140, and 187 of fermentation. A total of 260 isolates were characterized at sub-species level by rep-PCR genomic fingerprinting with the oligo-nucleotide primer (GTG)5. The characterization of yeast isolates at species level was performed by sequencing of the D1/D2 domain of 26S rRNA gene. Results showed that yeasts dominated the process presenting a relatively broad range of biodiversity composed of 11 genera and 21 species. No lactic acid bacteria (LAB) or Enterobacteriaceae could be enumerated after 20 and 10 days of fermentation, respectively. The dominant yeast species at the beginning were Aureobasidium pullulans for control and vinegar acidification treatments, and Candida naeodendra for lactic acid treatment. Between 34 and 140 days the dominant species were Candida boidinii, Candida molendinolei and Saccharomyces cerevisiae. In the end of fermentation the dominant species in all processes were C. boidinii and C. molendinolei, followed by Pichia manshurica and S. cerevisiae in lactic acid acidification treatment, P. manshurica in vinegar acidification treatment, and Pichia membranifaciens in control fermentation.