Lactic Acid Bacteria and Yeast Inocula Modulate the Volatile Profile of Spanish-Style Green Table Olive Fermentations

Study of the effects of pasteurization and selected microbial starters on functional traits of fermented table olives

Table olives are one of the most known fruit consumed as fermented food, being a fundamental component of the Mediterranean diet. Their production and consumption continue to increase globally and represent an important economic source for the producing countries. One of the most stimulating challenges for the future is the modernization of olive fermentation process. Besides the demand for more reproducible and safer production methods that could be able to reduce product losses and potential risks, producers and consumers are increasingly attracted by the final product characteristics and properties on human health. In this study, the contribution of microbial starters to table olives was fully described in terms of specific enzymatic and microbiological profiles, nutrient components, fermentation-derived compounds, and content of bioactive compounds. The use of microbial starters from different sources was tested considering their technological features and potential ability to improve the functional traits of fermented black table olives. For each fermentation assay, the effects of controlled temperature (kept at 20 °C constantly) versus not controlled environmental conditions (oscillating between 7 and 17 °C), as well as the consequences of the pasteurization treatment were tested on the final products. Starter-driven fermentation strategies seemed to increase both total phenolic content and total antioxidant activity. Herein, among all the tested microbial starters, we provide data indicating that two bacterial strains (Leuconostoc mesenteroides KT 5-1 and Lactiplantibacillus plantarum BC T3-35), and two yeast strains (Saccharomyces cerevisiae 10A and Debaryomyces hansenii A15-44) were the better ones related to enzyme activities, total phenolic content and antioxidant activity. We also demonstrated that the fermentation of black table olives under not controlled environmental temperature conditions was more promising than the controlled level of 20 °C constantly in terms of technological and functional properties considered in this study. Moreover, we confirmed that the pasteurization process had a role in enhancing the levels of antioxidant compounds.

Biclustering data analysis: a comprehensive survey

Biclustering, the simultaneous clustering of rows and columns of a data matrix, has proved its effectiveness in bioinformatics due to its capacity to produce local instead of global models, evolving from a key technique used in gene expression data analysis into one of the most used approaches for pattern discovery and identification of biological modules, used in both descriptive and predictive learning tasks. This survey presents a comprehensive overview of biclustering. It proposes an updated taxonomy for its fundamental components (bicluster, biclustering solution, biclustering algorithms, and evaluation measures) and applications. We unify scattered concepts in the literature with new definitions to accommodate the diversity of data types (such as tabular, network, and time series data) and the specificities of biological and biomedical data domains. We further propose a pipeline for biclustering data analysis and discuss practical aspects of incorporating biclustering in real-world applications. We highlight prominent application domains, particularly in bioinformatics, and identify typical biclusters to illustrate the analysis output. Moreover, we discuss important aspects to consider when choosing, applying, and evaluating a biclustering algorithm. We also relate biclustering with other data mining tasks (clustering, pattern mining, classification, triclustering, N-way clustering, and graph mining). Thus, it provides theoretical and practical guidance on biclustering data analysis, demonstrating its potential to uncover actionable insights from complex datasets.

The Rising Role of Omics and Meta-Omics in Table Olive Research

Table olives are often the result of fermentation, a process where microorganisms transform raw materials into the final product. The microbial community can significantly impact the organoleptic characteristics and safety of table olives, and it is influenced by various factors, including the processing methods. Traditional culture-dependent techniques capture only a fraction of table olives' intricate microbiota, prompting a shift toward culture-independent methods to address this knowledge gap. This review explores recent advances in table olive research through omics and meta-omics approaches. Genomic analysis of microorganisms isolated from table olives has revealed multiple genes linked to technological and probiotic attributes. An increasing number of studies concern metagenomics and metabolomics analyses of table olives. The former offers comprehensive insights into microbial diversity and function, while the latter identifies aroma and flavor determinants. Although proteomics and transcriptomics studies remain limited in the field, they have the potential to reveal deeper layers of table olives' microbiome composition and functionality. Despite the challenges associated with implementing multi-omics approaches, such as the reliance on advanced bioinformatics tools and computational resources, they hold the promise of groundbreaking advances in table olive processing technology.

Microbial community and volatilome changes in brines along the spontaneous fermentation of Spanish-style and natural-style green table olives (Manzanilla cultivar)

Microbial community and volatilome of brines were monitored during the spontaneous fermentations of Spanish-style and Natural-style green table olives from Manzanilla cultivar. Fermentation of olives in the Spanish style was carried out by lactic acid bacteria (LAB) and yeasts, whereas halophilic Gram-negative bacteria and archaea, along with yeasts, drove the fermentation in the Natural style. Clear differences between the two olive fermentations regarding physicochemical and biochemical features were found. Lactobacillus, Pichia, and Saccharomyces were the dominant microbial communities in the Spanish style, whereas Allidiomarina, Halomonas, Saccharomyces, Pichia, and Nakazawaea predominated in the Natural style. Numerous qualitative and quantitative differences in individual volatiles between both fermentations were found. The final products mainly differed in total amounts of volatile acids and carbonyl compounds. In addition, in each olive style, strong positive correlations were found between the dominant microbial communities and various volatile compounds, some of them previously reported as aroma-active compounds in table olives. The findings from this study provide a better understanding of each fermentation process and may help the development of controlled fermentations using starter cultures of bacteria and/or yeasts for the production of high-quality green table olives from Manzanilla cultivar.

Microbial and Chemical Characterization of Natural-Style Green Table Olives from the Gordal, Hojiblanca and Manzanilla Cultivars

Microbial and biochemical changes in the brine during the spontaneous fermentation of Gordal, Hojiblanca and Manzanilla olive cultivars processed according to the natural style were monitored. The microbial composition was assessed through a metagenomic study. Sugars, ethanol, glycerol, organic acids and phenolic compounds were quantified by standard methods. In addition, the volatile profiles, contents of phenolic compounds in the olives and quality parameters of the final products were compared. Fermentation in Gordal brines was conducted by lactic acid bacteria (mainly Lactobacillus and Pediococcus) and yeasts (mainly Candida boidinii, Candida tropicalis and Wickerhamomyces anomalus). In Hojiblanca and Manzanilla brines, halophilic Gram-negative bacteria (e.g., Halomonas, Allidiomarina and Marinobacter) along with yeasts (mainly, Saccharomyces) were responsible for the fermentation. Higher acidity and lower pH values were reached in Gordal brines compared to Hojiblanca and Manzanilla. After 30 days of fermentation, no sugars were detected in Gordal brine, but residual amounts were found in the brines from Hojiblanca (<0.2 g/L glucose) and Manzanilla (2.9 g/L glucose and 0.2 g/L fructose). Lactic acid was the main acid product in Gordal fermentation, whereas citric acid was the predominant organic acid in the Hojiblanca and Manzanilla brines. Manzanilla brine samples showed a greater concentration of phenolic compounds than Hojiblanca and Gordal brines. After a 6-month fermentation, Gordal olives were superior compared to the Hojiblanca and Manzanilla varieties regarding product safety (lower final pH and absence of Enterobacteriaceae), content of volatile compounds (richer aroma), content of bitter phenolics (lower content of oleuropein, which resulted in less perceived bitterness) and color parameters (more yellow and lighter color, indicating a higher visual appraisal). The results of the present study will contribute to a better understanding of each fermentation process and could help to promote natural-style elaborations using the above-mentioned olive cultivars.

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.

Industrial Processing of Algerian Table Olive Cultivars Elaborated as Spanish Style

Olives from the Sigoise, Verdale, and Sevillana cultivars were elaborated as Spanish-style table olives by four Algerian factories, and the quality and food safety of the industrial table olives have been studied by the analysis of physicochemical and microbiological parameters. Differences were observed between the treatments carried out by the different factories throughout the manufacturing process, especially during the washing stage, but no significant differences were found between the analyzed samples for the concentration of sugars and polyphenols. The final pH values reached at the end of fermentation ranged between 5.04 and 4.27, and the titratable acidity was above 0.4% for all samples. Lactic and acetic acids were produced in mean concentrations of 0.68% and 0.21% as a result of lactic acid bacteria (LAB) and yeast metabolism, respectively. However, the presence of butyric, isobutyric, and propionic acids was also detected, and was related to the growth of undesirable spoilage microorganisms, responsible for secondary fermentations. The high-throughput sequencing of bacterial DNA suggested the dominance of LAB species belonging to genera Lactiplantibacillus, Leuconostoc, Pediococcus, Oenococcus, or Enterococcus. The Enterobacteriaceae family was detected during the first days of brining and in only one sample after 120 days of fermentation. Other spoilage microorganisms were found, such as Lentilactobacillus buchneri or the Pectinatus and Acetobacter genera, capable of consuming lactic acid and these played an essential role in the onset of spoilage. The Clostridium and Enterobacter genera, producers of butyric and propionic acids, were responsible for the malodorous fermentation present in the industrial samples that were analyzed. The study concluded that the safety of the table olives analyzed was compromised by the presence of undesirable microorganisms and microbial stability was not guaranteed. The elaboration process can be improved by reducing the washing steps and the time should be reduced to avoid the loss of fermentable matter, with the goal of reaching a pH < 4.0 after the fermentation and preventing the possibility of the growth of spoilage microorganisms and foodborne pathogens.

Application of mixed starter culture for table olive production

The fermentation of olives is usually carried out spontaneously by natural microbiota. Spontaneous fermentation has some disadvantages, such as the formation of defects in the end product due to the activities of undesirable microorganisms. The use of starter cultures could be a promising option to provide a more controlled fermentation environment and to reduce the risk of spoilage. Mixed starter culture use (generally selected Lactobacillus strains with or without yeasts) could reduce pH in a shorter time, producing a higher amount of lactic acid and enhancing microbial safety compared to fermentation with starter cultures containing single species or natural fermentation. Their use could also enhance the organoleptical properties of table olives. Particularly the use of yeast (such as strains of W. anomolus, S. cerevisiae) in the fermentation of olives, in combination or sequentially with lactic acid bacteria could result in an increase in volatile compounds and a more aromatic final product.

Multi-Statistical Approach for the Study of Volatile Compounds of Industrial Spoiled Manzanilla Spanish-Style Table Olive Fermentations

Table olives can suffer different types of spoilage during fermentation. In this work, a multi-statistical approach (standard and compositional data analysis) was used for the study of the volatile organic compounds (VOCs) associated with altered (butyric, sulfidic, and putrid) and non-altered (normal) Manzanilla Spanish-style table olive fermentations. Samples were collected from two industrial fermentation yards in Seville (Spain) in the 2019/2020 season. The VOC profiles of altered (n = 4) and non-altered (n = 6) samples were obtained by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS). Ninety-one VOCs were identified and grouped into alcohols (30), esters (21), carbonyl compounds (12), acids (10), terpenes (6), phenols (6), sulfur compounds (2), and others (4). The association of the VOCs with spoilage samples depended on the standard or compositional statistical methodology used. However, butyric spoilage was strongly linked by several techniques to methyl butanoate, ethyl butanoate, and butanoic acid; sulfidic spoilage with 2-propyl-1-pentanol, dimethyl sulfide, methanol, 2-methylbutanal, 2-methyl-2-butenal, ethanol, 2-methyl-3-buten-2-ol, and isopentanol, while putrid was mainly related to D-limonene and 2-pentanol. Our data contribute to a better characterisation of non-zapatera spoiled table olive fermentations and show the convenience of using diverse statistical techniques for a most robust selection of spoilage VOC markers.

Volatile Composition of Industrially Fermented Table Olives from Greece

Table olives represent one of the most important fermented products in Greece. Their highly appreciated flavor is directly associated with the volatile composition. However, extensive data on the volatile profile of table olives from Greek cultivars are scarce in the literature. For this reason, the volatile components of industrially fermented table olives from Kalamata, Conservolea and Halkidiki cultivars grown in different geographical areas within Greece were determined using headspace solid-phase microextraction combined with gas chromatography–mass spectrometry. More than 100 volatile compounds were identified and distributed over different chemical classes. All samples were rich in esters, alcohols and acids, whereas the samples of cv. Halkidiki were also characterized by increased levels of volatile phenols. Both qualitative and quantitative differences were observed, which resulted in the discrimination of the table olives according to olive cultivar and growing location. To the best of our knowledge, this is the first systematic study on the volatile profiles of table olives from Greek cultivars that also highlights the pronounced effect of olives’ growing location.

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.

Characterization and Processing of Table Olives: A Special Issue

Table olives are recognized as an essential component of the Mediterranean diet, having been explicitly included in the second level of its nutritional pyramid as an aperitif or culinary ingredient, with a recommended daily consumption of one to two portions (15–30 g). Producers demand innovative techniques improving the performance and industrial sustainability, as well as the development of new products that respond efficiently to increasingly demanding consumers. The purpose of this special issue was to publish high-quality papers with the aim to cover the state-of-the-art, recent progress and perspectives related to characterization and processing of table olives. Two reviews offer an overview about the processing and storage effects on the nutritional and sensory properties of table olives, as well as the main technologies used for olive fermentation, and the role of lactic acid bacteria and yeasts characterizing this niche during the fermentation. A total of 10 research papers cover a broad range of aspects such as characterization of their chemical composition, bioavailability, advances in the processing technology, chemical and microbiological changes, optimized use of starter cultures for the improvement of the different fermentative processes, and new strategies to reduce sodium and additives to stabilize the organoleptic properties and avoid defects.

Relating starter cultures to volatile profile and potential markers in green Spanish-style table olives by compositional data analysis

This work relates native lactic acid bacteria (LAB) (Lactobacillus pentosus LPG1, L. pentosus Lp13, and Lactobacillus plantarum Lpl15) and yeast (Wickerhamomyces anomalus Y12) starters to the volatile components (VOCs) produced in green Spanish-style table olives. For this aim, the VOC profile was considered as compositional data (CoDa). The CoDa analysis generated new information on the relationship among inocula and VOCs through the tetrahedral plot, CoDa-biplot, variation array matrix, and CoDa dendrogram. The ilr (which includes pivot) coordinates (Euclidean space) from VOCs produced more reliable starters' clustering than the original data. The potential VOC markers, identified by a test based on the pairwise comparison of the logratio variation arrays from the whole data set and the individual groups, were (starters in the parenthesis): 2-phenylethyl acetate (LPG1, Y12, Y12 + LAB), methanol (Lpl15), cis-2-penten-1-ol (LPG1, Y12, Y12 + LAB), 2-methyl-3-hexanol (LPG1, Y12), U (non-identified) C (m/z 83-112-97) (Y12) and UF (m/z 95-154-110) (LPG1, Y12 + LAB). Besides, some VOCs were partial/totally inhibited by specific starters: 2-methyl-1-propanol (Lp13, Y12 + LAB), 2-phenyl ethanol (Lp13), furfuryl methyl ether (Y12 + LAB), purpurocatechol (Y12, Y12 + LAB), 4-ethyl guaiacol (Lp13, Lpl15), 4-ethyl phenol (Lpl15), 5-tert-butylpyrogallol (Lp13, Lpl15), and UE (m/z 111-198) (Lp13). A better understanding of the relationship between starters and their VOC may facilitate modelling the flavour and quality of Spanish-style green table olive fermentations.

A Holistic Review on Euro-Asian Lactic Acid Bacteria Fermented Cereals and Vegetables

Lactic acid fermentation is one of the oldest methods used worldwide to preserve cereals and vegetables. Europe and Asia have long and huge traditions in the manufacturing of lactic acid bacteria (LAB)-fermented foods. They have different cultures, religions and ethnicities with the available resources that strongly influence their food habits. Many differences and similarities exist with respect to raw substrates, products and microbes involved in the manufacture of fermented products. Many of them are produced on industrial scale with starter cultures, while others rely on spontaneous fermentation, produced homemade or in traditional events. In Europe, common LAB-fermented products made from cereals include traditional breads, leavened sweet doughs, and low and non-alcoholic cereal-based beverages, whereas among vegetable ones prevail sauerkraut, cucumber pickles and olives. In Asia, the prevailing LAB-fermented cereals include acid-leavened steamed breads or pancakes from rice and wheat, whereas LAB-fermented vegetables are more multifarious, such as kimchi, sinki, khalpi, dakguadong, jiang-gua, soidon and sauerkraut. Here, an overview of the main Euro-Asiatic LAB-fermented cereals and vegetables was proposed, underlining the relevance of fermentation as a tool for improving cereals and vegetables, and highlighting some differences and similarities among the Euro-Asiatic products. The study culminated in "omics"-based and future-oriented studies of the fermented products.

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.

Evolution of Bacterial Communities, Physicochemical Changes and Sensorial Attributes of Natural Whole and Cracked Picual Table Olives During Spontaneous and Inoculated Fermentation

Table olives are one of the most well-known traditionally fermented products, and their global consumption is exponentially increasing. In direct brining, table olives are produced spontaneously, without any debittering pre-treatment. Up to date, fermentation process remains empirical and inconstant, as it is affected by the physicochemical attributes of the fruit, tree and fruit management of pro and post-harvest. In the present study, whole and cracked Picual table olives were fermented at industrial scale for 120 days, using three distinct methods (natural fermentation, inoculation with lactic acid bacteria (LAB) at a 7 or a 10% NaCl concentration). Microbial, physicochemical and sensorial alterations monitored during the whole process, and several differences were observed between treatments. Results indicated that in all treatments, the dominant microflora were LAB. Yeasts also detected in noteworthy populations, especially in non-inoculated samples. However, LAB population was significantly higher in inoculated compared to non-inoculated samples. Microbial profiles identified by metagenomic approach showed meaningful differences between spontaneous and inoculated treatments. As a result, the profound dominance of starter culture had a severe effect on olives fermentation, resulting in lower pH and higher acidification, which was mainly caused by the higher levels of lactic acid produced. Furthermore, the elimination of Enterobacteriaceae was shortened, even at lower salt concentration. Although no effect observed concerning the quantitated organoleptic parameters such as color and texture, significantly higher levels in terms of antioxidant capacity were recorded in inoculated samples. At the same time, the degradation time of oleuropein was shortened, leading to the production of higher levels of hydroxytyrosol. Based on this evidence, the establishment of starter culture driven Picual olives fermentation is strongly recommended. It is crucial to mention that the inoculated treatment with reducing sodium content was highly appreciated by the sensory panel, enhancing the hypothesis that the production of Picual table olives at reduced NaCl levels is achievable.