Significance and management of acetic acid bacteria culture collections

Acetic acid bacteria (AAB) are obligate aerobic microorganisms which have large significance in human life. Traditionally, AAB species have been used to produce fermented food and beverages thanks to their ability to oxidize ethanol to acetic acid. Moreover, in the last decades, they have been extensively investigated for other industrial biotechnology applications as the development of processes for highvalue products or biosensors. The potential exploitation of AAB diversity requires the existence of microbial culture collections, which are able to supply not only strains but essential data for fundamental microbial research. Therefore, microbial collections can be helpful to provide critical insights into AAB physiology and metabolism as well as integrate sequence data with transcriptional and functional studies to better define complex traits and develop new potential microbial processes. This article reviews the significance of microbial collections, with an overview of the well-known European Biological Resources Centers (BRCs) collecting AAB, and provides an insight into their cultivability and metabolic activity. It also discusses appropriate techniques in preserving authentic strains, quality control implications, databases and BRC networking as well as connections among collections and stakeholders

Peptidomic study of casein proteolysis in bovine milk by Lactobacillus casei PRA205 and Lactobacillus rhamnosus PRA331

Lactobacilli contain different cell envelope proteinases (CEPs) responsible for the hydrolysis of caseins and the release of various bioactive peptides. In this work, we explored the CEP activity of Lactobacillus casei PRA205 and Lactobacillus rhamnosus PRA331 whole cells towards β-, αS1-, κ- and αS2-caseins in bovine milk. Mass spectrometry analysis of fermented milk hydrolysates identified a total of 331 peptides, which were mainly derived from β-caseins (59.0 and 60.1% for PRA205 and PRA331, respectively). Analysis of αS1-casein (f1–23) cleavage site specificity congruently supports that Lb. casei PRA205 and Lb. rhamnosus PRA331 exhibited a mixed-type CEPI/III activity. PRA205 and PRA331 CEPs also showed cleavage site specificity toward β-casein. These CEPs cleaved the peptide bond preferentially when hydrophobic or negatively charged amino acids were present. 13.5% and 13.7% of peptides released by Lb. casei PRA205 and Lb. rhamnosus PRA331 CEPs were found to have 100% homology with previously identified bioactive peptides

Acetobacter pasteurianus strain AB0220: cultivability andphenotypic stability over 9 years of preservation

Acetobacter species are members of the a-subclassof Proteobacteria, which harbors a large number of bacteriarecalcitrant to cultivation. Strain AB0220 was isolatedfrom a superficial acetification system and preserved for9 years by short and long time methods. Under short timepreservation it was estimated that 540.54 number of generationsoccurred, whereas in long time preservation conditionsthe number of generations was 17.40. Ethanoloxidation to acetic acid was stable and confirmed, as wellas acetate assimilation during long time preservation.Cultivability checks showed persistence of phenotypictraits (growth on ethanol and methanol, growth on differentcarbon sources and cellulose production) over the extendedpreservation time. 16S rRNA gene sequences analysisshowed 100 % of similarity with A. pasteurianus (Accessionnumber GQ240636). Stability of subcultures related tothe culture age and subcultures frequency, tested by ERIC/PCR, confirmed the suitability of long term preservationat least over a period of 9 years

Fermentation strategy to produce high gluconate vinegar

Gluconic acid is a non-volatile acid that has many applications in food, pharmaceutical and cleaning fields. Gluconic acid has been detected as main oxidation product of Acetobacter and Gluconobacter strains growing on grape must, and it plays an important role in Traditional Balsamic Vinegar. Commonly, high gluconate vinegars have a greater physical stability and a greater preference by consumers because are perceived less pungent. In fact, gluconic acid reduces the pH and increases fixed acidity of the vinegar without increasing the sensation of pungency typical of acetic acid. Its taste is acid but mild sweet and, therefore, gluconic acid has influence on the sensory complexity of the vinegar. The aim of this work is to set up a fermentation procedure that improves the quality of balsamic vinegar by using selected yeasts and acetic acid bacteria strains able to oxidize glucose in grape must-based media having a different sugars concentration. In particular, Saccharomycodes ludwigii UMCC 297 and Acetobacter pasteurianus UMCC 1754 strains were chosen as selected starter cultures for small-scale fermentation of cooked grape must, to evaluate the physical-chemical parameters affecting gluconic acid production in the obtained vinegar. The strains used and the control of all production process have been fundamental for obtaining the vinegar with the desired characteristics

I balsamici: fermentazione acetica, viscosit\ue0 e parametri sensoriali

La produzione di aceto di vino \ue8 un processo che utilizza materie prime dal valore relativamente basso per ottenere un prodotto che raggiunge prezzi relativamente alti. La categoria merceologica che maggiormente beneficia dell\u2019uso di questi prodotti \u201cpoveri\u201d \ue8 quella relativa ai condimenti alimentari agrodolci a base di mosto concentrato e/o cotto e aceto di vino, cio\ue8 tutti i prodotti che hanno un esplicito riferimento al termine \u201cbalsamico\u201d. Indubbiamente la diffusione di prodotti balsamici sul mercato \ue8 in forte crescita, anche grazie allo sviluppo di nuove forme di presentazione e di utilizzo del prodotto base (come glasse, creme, spume, spray) e una continua ricerca dell\u2019aromatizzazione distintiva e particolare (attraverso l\u2019utilizzo di fragranze o seguendo processi di produzione peculiari). Nelle province di Modena e Reggio Emilia \ue8 concentrata l\u2019intera produzione di aceti \u201cbalsamici\u201d a denominazione protetta italiani: due DOP per l\u2019aceto balsamico tradizionale di Modena (ABTM) e quello di Reggio Emilia (ABTRE) e una IGP per l\u2019aceto balsamico di Modena (ABM). L\u2019ABT non \ue8 aceto di vino bens\uec di mosto cotto, tuttavia nell\u2019ABM l\u2019acidit\ue0 deriva dal comune aceto di vino ottenuto per fermentazione in sommerso. La linea di prodotti sviluppati coniuga gli aspetti migliori dal punto di vista qualitativo ed economico delle due tipologie, introducendo numerose innovazioni: i) le fermentazioni dirette e in condizioni statiche consentono un risparmio energetico notevole e favoriscono la formazione di composti secondari sensorialmente positivi, anche grazie all\u2019impiego di lieviti e batteri acetici specifici e selezionati appositamente per le loro caratteristiche fermentative; ii) il processo di concentrazione del mosto tramite cottura \ue8 assente o fortemente limitato mentre l\u2019invecchiamento \ue8 accelerato tramite l\u2019utilizzo di tecniche di condizionamento ambientale ecosostenibile; iii) non sono presenti additivi e conservanti di nessun genere in quanto vengono impiegate tecniche di conservazione basate sull\u2019impiego oculato degli stessi microrganismi usati nelle fermentazioni; iv) le condizioni di cottura applicate limitano al minimo la formazioni di composti tossici

High-glutathione producing yeasts obtained by genetic improvement strategies: a focus on adaptive evolution approaches for novel wine strains

Glutathione (GSH) is the most abundant non-protein thiol in living organisms. Due to its important antioxidant role, it is widely used in medicine, as a food additive, and in the cosmetic industry. Recently, GSH has received growing attention in winemaking because of its ability to control oxidative spoilage damage and to protect various aromatic compounds. Indeed, GSH concentration in wine is highly variable and several factors are involved in its regulation, ranging from grape must to yeast fermentation activity. This short review aims at highlighting the common genetic strategies, useful for obtaining wine yeasts with enhanced GSH production, paying particular attention to the adaptive evolution approaches. Moreover, other strategies, such as random mutagenesis, metabolic engineering and hybridization have been briefly reviewed with a stress on both their strengths and weaknesses in terms of actual feasibility and acceptance by wine consumers

Exploring the Microbial Community of Traditional Sourdoughs to Select Yeasts and Lactic Acid Bacteria

Sourdoughs represent an awesome example of ecosystem in which yeasts and lactic acid bacteria (LAB) interact with each other, defining the characteristics of the final product in terms of composition, texture, taste and flavor. Therefore, the identification of dominant yeasts and LAB involved in the fermentation process can lead to the selection of starters with suitable fermentation aptitude and capable of producing desired aromas and/or aromatic precursors. In this work, two sourdoughs samples (A and B) for Panettone production were collected from an artisan bakery. Yeasts and bacteria were isolated at different fermentation steps on selective agar media. A total of 120 isolates were obtained and firstly characterized by conventional microbiological methods. Afterward, genomic DNA was extracted from the cultures, and (GTG)5-PCR fingerprinting analysis was carried out to reduce the redundance among the isolates. Representative yeasts and LAB strains, having a unique profile, were identified by sequencing the D1/D2 domain of the 26S rRNA and the 16S rRNA genes, respectively. The results highlighted the occurrence of Kazachstania humilis and Fructilactobacillus sanfranciscensis in both sourdoughs. Among LAB, also some other strains belonging to Lactobacillus genus were found. Moreover, Saccharomyces cerevisiae and Staphylococcus spp. strains were detected in sample B. In this study, a pool of yeasts and LAB strains for producing starter cultures with specific technological traits for sourdoughs production was obtained

Selection of Promising Exopolysaccharide-Producing Starter Cultures for Gluten-Free Sourdough

Celiac disease is an autoimmune enteropathy that affects the small intestine and is caused by the gliadin fraction of wheat gluten and other alcohol-soluble proteins (prolamines) of barley and rye in genetically predisposed subjects. Nowadays, the only recognized cure for this pathology is the use of gluten-free (GF) products. Although the market for GF products has grown in the last few years, their improvement is still a challenge for the food industry. With regard to GF bakery products, some of them can result in an unappetizing taste with a high fat content. These inconveniences can be minimized or solved by using sourdough fermentation. Sourdough is a stable culture of lactic acid bacteria (LAB) and yeast in a mixture of flour and water. In particular, GF sourdough represents a rich source of naturally occurring LAB and wild yeasts, which play important roles in food fermentation. This is mainly due to their potential in improving functional, technological, and probiotics properties, contributing to safe food with a better taste. Moreover, exopolysaccharide (EPS)-producing strains can also contribute to improving the sensory and rheological quality of the different GF products. This study aims to isolate and characterize the microbial pool from a GF sourdough made with rice flour and to evaluate the ability of selected LAB strains to produce exopolysaccharides (EPS). The yeast and LAB were isolated in selective agar media. A total of 220 isolates (110 yeasts and 110 bacteria) were obtained. They were taxonomically identified and characterized using both traditional and molecular approaches. Sequencing analysis of the D1/D2 domain of the 26S rRNA and the 16S rRNA genes, for yeasts and bacteria, respectively, revealed the occurrence of Saccharomyces cerevisiae as predominant yeasts and Lactiplantibacillus plantarum and Pediococcus pentosaceus as dominant LAB. Regarding the EPS production, 25 strains were able to produce dextran-like EPS with a maximum yield of 2 g/L. This study allowed the isolation and selection of promising EPS-producing starter cultures for the different types of flour sourdough, in particular, GF sourdoug

Zero- and Low-Alcohol Fermented Beverages: A Perspective for Non-Conventional Healthy and Sustainable Production from Red Fruits

The growing health consciousness among consumers is leading to an increased presence of functional foods and beverages on the market. Red fruits are rich in bioactive compounds such as anthocyanins with high antioxidant activity. In addition, red fruits contain sugars and are rich in phenolic compounds, vitamin C, dietary fibers, and manganese. Due to these characteristics, they are also suitable substrates for fermentation. Indeed, nowadays, microbial transformation of red fruits is based on alcoholic or lactic fermentation, producing alcoholic and non-alcoholic products, respectively. Although products fermented by acetic acid bacteria (AAB) have been thoroughly studied as a model of health benefits for human beings, little evidence is available on the acetic and gluconic fermentation of red fruits for obtaining functional products. Accordingly, this review aims to explore the potential of different red fruits, namely blackberry, raspberry, and blackcurrant, as raw materials for fermentation processes aimed at producing low- and no-alcohol beverages containing bioactive compounds and no added sugars. AAB are treated with a focus on their ability to produce acetic acid, gluconic acid, and bacterial cellulose, which are compounds of interest for developing fruit-based fermented beverages

Anti-Spoilage Activity and Exopolysaccharides Production by Selected Lactic Acid Bacteria

In this study, eight lactic acid bacteria (LAB) strains, previously isolated from traditional and gluten-free sourdoughs, and selected for their potential in improving the sensory and rheological quality of bakery products, were screened against some common spoilage agents. The anti-mould activity was tested using strains of the species Fusarium graminearum, Aspergillus flavus, Penicillium paneum and Aspergillus niger. Regarding the antibacterial activity, it was assessed against four strains of the species Escherichia coli, Campylobacter jejuni, Salmonella typhimurium and Listeria monocytogenes. Furthermore, LAB strains were evaluated for their ability to produce exopolysaccharides, which are gaining considerable attention for their functional properties and applicability in different food industrial applications. A strain-specific behaviour against the moulds was observed. In particular, F. graminearum ITEM 5356 was completely inhibited by all the LAB strains. Regarding the antibacterial activity, the strains Leuconostoc citreum UMCC 3011, Lactiplantibacillus plantarum UMCC 2996, and Pediococcus pentosaceus UMCC 3010 showed wide activity against the tested pathogens. Moreover, all the LAB strains were able to produce exopolysaccharides, which were preliminarily characterized. The assessed features of the LAB strains allow us to consider them as promising candidates for single or multiple starter cultures for food fermentation processes