Physiology of acetic acid bacteria and their role in vinegar and fermented beverages

Acetic acid bacteria (AAB) have, for centuries, been important microorganisms in the production of fermented foods and beverages such as vinegar, kombucha, (water) kefir, and lambic beer. Their unique form of metabolism, known as â oxidativeâ fermentation, mediates the transformation of a variety of substrates into products, which are of importance in the food and beverage industry and beyond; the most well-known of which is the oxidation of ethanol into acetic acid. Here, a comprehensive review of the physiology of AAB is presented, with particular emphasis on their importance in the production of vinegar and fermented beverages. In addition, particular reference is addressed toward Gluconobacter oxydans due to its biotechnological applications, such as its role in vitamin C production. The production of vinegar and fermented beverages in which AAB play an important role is discussed, followed by an examination of the literature relating to the health benefits associated with consumption of these products. AAB hold great promise for future exploitation, both due to increased consumer demand for traditional fermented beverages such as kombucha, and for the development of new types of products. Further studies on the health benefits related to the consumption of these fermented products and guidelines on assessing the safety of AAB for use as microbial food cultures (starter cultures) are, however, necessary in order to take full advantage of this important group of microorganisms

The influence of microgravity on invasive growth in Saccharomyces cerevisiae

This study investigates the effects of microgravity on colony growth and the morphological transition from single cells to short invasive filaments in the model eukaryotic organism Saccharomyces cerevisiae. Two-dimensional spreading of the yeast colonies grown on semi-solid agar medium was reduced under microgravity in the Sigma 1278b laboratory strain but not in the CMBSESA1 industrial strain. This was supported by the Sigma 1278b proteome map under microgravity conditions, which revealed upregulation of proteins linked to anaerobic conditions. The Sigma 1278b strain showed a reduced invasive growth in the center of the yeast colony. Bud scar distribution was slightly affected, with a switch toward more random budding. Together, microgravity conditions disturb spatially programmed budding patterns and generate strain-dependent growth differences in yeast colonies on semi-solid medium

A universal fixation method based on quaternary ammonium salts (RNAlater) for omics-technologies: Saccharomyces cerevisiae as a case study

Abstract Genomics, transcriptomics, proteomics and fluxomics are powerful omics-technologies that play a major role in today's research. For each of these techniques good sample quality is crucial. Major factors contributing to the quality of a sample is the actual sampling procedure itself and the way the sample is stored directly after sampling. It has already been described that RNAlater can be used to store tissues and cells in a way that the RNA quality and quantity are preserved. In this paper, we demonstrate that quaternary ammonium salts (RNAlater) are also suitable to preserve and store samples from Saccharomyces cerevisiae for later use with the four major omics-technologies. Moreover, it is shown that RNAlater also preserves the cell morphology and the potential to recover growth, permitting microscopic analysis and yeast cell culturing at a later stage

Exploitation of the flavour potential of hop and sour cherry glycosides by Saccharomyces and Brettanomyces glycoside hydrolase activities

Fruits, flowers or other plant parts, possess a characteristic aroma which is formed by the presence of flavour-active volatile compounds. Besides volatiles in a free form, volatiles also occur in a glycosidic boundform. Conjugation of volatile compounds to sugar substances like β-D-glucose results in water soluble, non-volatile and odourless compounds. Physiologically, this glycoconjugation plays a role in the accumulation, storage and transport of different types of compounds in the plant. Hops (Humulus lupulus L.) and sour cherries (Prunus cerasus L.) contain glycosidically bound flavour compounds as well. Hence, when adding these raw materials during the production of beverages like beer, free volatiles as well as glycosidically bound volatiles are extracted into the medium. Although the bound fraction is not readily perceivable as aroma, it forms a pool of flavour precursors. This work aimed at the exploitation of the flavour potential through enzymatic hydrolysis ofthese glycosidically bound volatiles. The global enzymatic activity responsible for hydrolysis of glycosidically bound volatile compounds is referred to as glycoside hydrolase activity . In fermented beverages, a method for introducing this glycoside hydrolase activity into the medium is the use of an appropriately selected yeast strain.Hence, the aim of this work was to acquire insight in the hydrolase activity of yeast towards glycosidically bound flavour compounds from hops and sour cherry. To that end, enzymatically released flavour compounds from hop and sour cherry glycosides were examined and a characterization of the glycoside hydrolase activity in Saccharomyces and Brettanomyces brewing yeasts was carried out, both on model substrates and onglycosides from hops and cherry. Hop and sour cherry glycoside extracts were obtained by solid-phase extraction (SPE). Enzymatic hydrolysis of the hop glycoside extract released well-known (e.g. linalool) and less typical (e.g. methyl salicylate) hop volatiles. Dihydroedulan I & II and theaspiranes A & B levels increased after enzymatic hydrolysis and were identified for the first time in hops and in beer. After enzymatic hydrolysis of the sour cherry glycoside extract, important cherry flavour contributors like benzaldehyde, linalool and eugenol were released. The compounds cis- and trans-isoeugenol and α ionol were identified for the first time in sour cherry.To examine the glycoside hydrolase activity in yeast, different screening methods were tested on 41 Saccharomyces and 18 Brettanomyces yeasts. The studied Saccharomyces yeasts did not show 1,4-β-glucosidase activity, but a strain dependent exo-1,3-β-glucanase activity was found which is responsible for a limited glycoside hydrolysis. Among Brettanomyces species with 1,4-β-glucosidase activity, the most pronounced 1,4-β-glucosidase activity was found in Brettanomyces custersii LD72. Fermentations with this strain as pure culture or as co-culture with S. cerevisiae led to the highest release of flavour compounds from hop glycosides. Hence, the glycoside hydrolase activity of Brettanomyces custersii LD72 was further characterized. The 1,4-β-glucosidase activity was found to be mainly cellassociated and localized for the most part in the cell wall and cytosolfractions. The extracellular fraction consisted mainly of an exo-1,3-β-glucanase activity. Besides β-glucosidase and exo-1,3-β-glucanase activities, a β-xylosidase activity was found.The requirement of Brettanomyces species in the production of lambic and gueuze beer is already well-known. Refermentation of sour cherry supplemented beer by Brettanomyces custersii led to higher concentrations, compared to refermentation by S. cerevisiae, of important cherryflavour contributors like benzaldehyde, benzyl alcohol, eugenol and linalool. From these results, it seems that Brettanomyces species may play a crucial role in the flavour development of fruit lambic beers like Kriek .Finally, the influence of the glycoside hydrolase activity was examinedon hop glycosides extracted during a dry hopping process. Treatment of the dry hopped beers with an enzyme preparation with glycosidase activities led to the highest increase of volatiles like cis-3-hexen-1-ol, 1-octen-3-ol, methyl salicylate, α-terpineol and theaspirane B. Among different yeast treatments, Brettanomyces custersii led to the highest hydrolase activity on a synthetic substrate, but release of glycosidically bound hop volatiles was less pronounced. However, theaspirane B was always found in higher concentrations. Additional researchis required to determine the impact of theaspiranes on the overall flavour. At higher dry hopping ratios (15.0 g/l), an increase in the levels of the aglycones cis-3-hexen-1-ol and α terpineol was also observed after treatment with B. custersii. Further, an unknown enzyme activity was noticed in Brettanomyces, especially in B. custersii, catalyzing the transformation of β-ionone to yet undetected compounds.In conclusion, this work provides new insights into the glycoside hydrolase activities of Saccharomyces and Brettanomyces brewing yeasts on glycosidically bound flavour compounds from hops and sour cherry. The acquired knowledge can be applied in methods to exploit the flavour potential of raw materials more efficiently, especially during fermentation and refermentation, to obtain beverages with an improved and refined flavour and to create new types of beverages.nrpages: 177status: publishe

Aging characteristics of different beer types

Eight commercial beers (3 lager beers, 2 dark ales and 3 high-alcoholic ales) were aged for one year under normal storage conditions, and the changes with time of flavour profile and the concentration of 15 volatile compounds were monitored. The compounds were chosen as markers to evaluate the importance of different reactions in the aging process of each beer type. The development of typical aging flavours during beer storage could be linked to the Maillard reaction, the formation of linear aldehydes, ester formation, ester degradation, acetal formation, etherification and the degradation of hop bitter compounds. A difference in the nature of aging flavours between lager and specialty beers was found and seemed to be mainly the result of an increased Maillard reaction in specialty beers. Based on the results, some practical strategies are proposed to improve the flavour stability, depending on the beer type. (c) 2006 Elsevier Ltd. All rights reserved.status: publishe

An update on water kefir

Water kefir is a sparkling, slightly acidic fermented beverage produced by fermenting a solution of sucrose, to which dried fruits have been added, with water kefir grains. These gelatinous grains are a symbiotic culture of bacteria and yeast embedded in a polysaccharide matrix. Lactic acid bacteria, yeast and acetic acid bacteria are the primary microbial members of the sugary kefir grain. Amongst other contributions, species of lactic acid bacteria produce the exopolysaccharide matrix from which the kefir grain is formed, while yeast assist the bacteria by a nitrogen source that can be assimilated. Exactly which species predominate within the grain microbiota, however, appears to be dependent on the geographical origin of the grains and the fermentation substrate and conditions. These factors ultimately affect the characteristics of the beverage produced in terms of aroma, flavour, and acidity, for example, but can also be controlled and exploited in the production of a beverage of desired characteristics. The production of water kefir has traditionally occurred on a small scale and the use of defined starter cultures is not commonly practiced. However, as water kefir increases in popularity as a beverage - in part because of consumer lifestyle trends and in part due to water kefir being viewed as a health drink with its purported health benefits â the need for a thorough understanding of the biology and dynamics of water kefir, and for defined and controlled production processes, will ultimately increase. The aim of this review is to provide an update into the current knowledge of water kefir

Screening and evaluation of the glucoside hydrolase activity in Saccharomyces and Brettanomyces yeasts

Aims: The aim of this study was to select and examine Saccharomyces and Brettanomyces brewing yeasts for hydrolase activity towards glycosidically bound volatile compounds. Methods and Results: A screening for glucoside hydrolase activity of 58 brewing yeasts belonging to the genera Saccharomyces and Brettanomyces was performed. The studied Saccharomyces brewing yeasts did not show 1,4-b-glucosidase activity, but a strain dependent b-glucanase activity was observed. Some Brettanomyces species did show 1,4-b-glucosidase activity. The highest constitutive activity was found in Brettanomyces custersii. For the most interesting strains the substrate specificity was studied and their activity was evaluated in fermentation experiments with added hop glycosides. Fermentations with Br. custersii led to the highest release of aglycones. Conclusions: Pronounced exo-b-glucanase activity in Saccharomyces brewing yeasts leads to a higher release of certain aglycones. Certain Brettanomyces brewing yeasts, however, are more interesting for hydrolysis of glycosidically bound volatiles of hops. Significance and Impact of the Study: The release of flavour active compounds from hop glycosides opens perspectives for the bioflavouring and product diversification of beverages like beer. The release can be enhanced by using Saccharomy- ces strains with high exo-b-glucanase activity. Higher activities can be found in Brettanomyces species with b-glucosidase activity.status: publishe

80 years of industrial dry hopping knowledge

peer reviewe

Influence of Substrate on the Fermentation Characteristics and Culture-Dependent Microbial Composition of Water Kefir

Water kefir is a sparkling fermented beverage produced by fermenting water kefir grains in a sucrose solution containing dried fruits or fruit extracts. The objective of this study was to investigate the influence of substrate composition on the fermentation kinetics and culture-dependent microbial composition of water kefir. First, the impact of different fruit substrates and nitrogen limitation was examined. Fermentation of different fruit-based media with a single water kefir culture demonstrated that the substrate mainly influenced the type and ratio of the organic acids produced. These organic acid profiles could be linked to the culture-dependent microbial composition. In addition, the microbial composition and the associated dominant microorganisms observed were influenced by the water kefir fermentation conditions. Investigation of the effect of nitrogen limitation on the fermentation kinetics of several water kefir cultures showed that under such conditions, the fermentative capacity of the cultures declined. However, this decline was not immediate, and specific water kefir microorganisms may have enabled some cultures to maintain a higher fermentative capacity for longer. Thus, the water kefir fermentation kinetics and characteristics could be linked to the substrate composition, microorganisms present, and the process conditions under which the fermentations were performed