The Monthly Digest – September 2016

Use of a flor velum yeast for modulating colour, ethanol and major aroma compound contents in red wine

The most important and negative effect of the global warming for winemakers in warm and sunny regions is the observed lag between industrial and phenolic grape ripeness, so only it is possible to obtain an acceptable colour when the ethanol content of wine is high. By contrast, the actual market trends are to low ethanol content wines. Flor yeast growing a short time under velum conditions, decreases the ethanol and volatile acidity contents, has a favorable effect on the colour and astringency and significantly changes the wine content in 1-propanol, isobutanol, acetaldehyde, 1,1-diethoxiethane and ethyl lactate. The Principal Component Analysis of six enological parameters or five aroma compounds allows to classify the wines subjected to different velum formation conditions. The obtained results in two tasting sessions suggest that the flor yeast helps to modulate the ethanol, astringency and colour and supports a new biotechnological perspective for red winemakers.

Moreno J et al. (2016) Food Chemistry 213:90-97

 

Selection and technological potential of Lactobacillus plantarum bacteria suitable for wine malolactic fermentation and grape aroma release

Lactobacillus plantarum strains have resistance mechanisms that enable them to survive and proliferate in wine, which makes them potential malolactic fermentation (MLF) starter cultures. This work focused on the technological characterization of 11 L. plantarumstrains isolated from Southern Italian wines that undergo spontaneous MLF, and proposes a selection of new L. plantarum malolactic starters. These strains were characterized according to their oenological characteristics, their ability to produce biogenic amines and bacteriocins, their response to the presence of phenolic compounds, their enzymatic activities and their ability to produce wine odorant aglycones from odourless grape glycosidic aroma precursors. Finally, the malolactic activity of one selected strain was assessed in Cabernet Sauvignon wine, using two inoculation methods. L. plantarum strains tested were not producers of biogenic amines. In particular, the M10 strain showed a good resistance to high levels of ethanol and low pH, it has a good malolactic performance and β-glucosidase activity, this last one demonstrated both directly through the measurement of this enzymatic activity and indirectly by following the release of volatile aglycones from commercial and natural grape glycosidic odourless precursors. These results demonstrated the potential applicability of M10 as a new MLF starter culture, especially for high-ethanol wines.

Iorizzo M et al. (2016) LWT – Food Science and Technology 73:557-566

 

Aroma profile and composition of Barbera wines obtained by mixed fermentations of Starmerella bacillaris (synonym Candida zemplinina) and Saccharomyces cerevisiae

In recent years there is an increasing global interest for the use of selected non-Saccharomyces yeasts by the winemaking industry, mainly due to their positive contribution to the wine complexity. In this study, Starmerella bacillaris (synonymCandida zemplinina) and Saccharomyces cerevisiae were evaluated in mixed (co-inoculated and sequentially) inoculated fermentations with the aim of improving the aroma profile of Barbera wine. The different inoculation protocols and combination of strains tested, influenced the interactions and the fermentation behaviour of the two yeast species. The wines produced with mixed cultures contained higher amounts of glycerol and pleasant esters compared to the wine fermented with S. cerevisiae alone. The use of mixed culture fermentations with selected yeast strains and appropriate inoculation strategies could be considered as a tool to enhance the aroma profile of wines produced from non-floral grape varieties like Barbera.

Englezos V et al. (2016) LWT – Food Science and Technology 73:567-575

 

Quorum-sensing in yeast and its potential in wine making

This mini-review synthesises the present knowledge of microbial quorum-sensing, with a specific focus on quorum-sensing in yeast, and especially in wine yeast. In vine and wine ecosystems, yeast co-interact with a large variety of microorganisms, thereby affecting the fermentation process and, consequently, the flavour of the wine. The precise connections between microbial interactions and quorum-sensing remain unclear, but we describe here how and when some species start to produce quorum-sensing molecules to synchronously adapt their collective behaviour to new conditions. In Saccharomyces cerevisiae, the quorum-sensing molecules were identified as 2-phenylethanol and tryptophol. However, it was recently shown that also a quorum-sensing molecule formerly identified only in Candida albicans, tyrosol, appears to be regulated in S. cerevisiae according to cell density. This review describes the methods for detection and quantification of those quorum-sensing molecules, their underlying mechanisms of action, and their genetic background. It also examines the external stimuli that evoke the quorum-sensing mechanism in the wine-processing environment. The review closes with insight into the biotechnological applications that are already making use of the advantages of quorum-sensing systems and indicates the important questions that still need to be addressed in future research into quorum-sensing. This mini-review synthesises the present knowledge of microbial quorum-sensing, with a specific focus on quorum-sensing in yeast, and especially in wine yeast. In vine and wine ecosystems, yeast co-interact with a large variety of microorganisms, thereby affecting the fermentation process and, consequently, the flavour of the wine. The precise connections between microbial interactions and quorum-sensing remain unclear, but we describe here how and when some species start to produce quorum-sensing molecules to synchronously adapt their collective behaviour to new conditions. In Saccharomyces cerevisiae, the quorum-sensing molecules were identified as 2-phenylethanol and tryptophol. However, it was recently shown that also a quorum-sensing molecule formerly identified only in Candida albicans, tyrosol, appears to be regulated in S. cerevisiae according to cell density. This review describes the methods for detection and quantification of those quorum-sensing molecules, their underlying mechanisms of action, and their genetic background. It also examines the external stimuli that evoke the quorum-sensing mechanism in the wine-processing environment. The review closes with insight into the biotechnological applications that are already making use of the advantages of quorum-sensing systems and indicates the important questions that still need to be addressed in future research into quorum-sensing.

Avbelj M et al. (2016) Applied Microbiology and Biotechnology 100:7841-7852

 

Could non-Saccharomyces yeasts contribute on innovative brewing fermentations?

With the advances in the production of beer worldwide, more challenges arise each year in the search for new approaches to the development of distinctive beverages. Attempts to obtain products with more complex sensory characteristics have led experts and brewers to prospect for non-conventional yeasts, i.e., non-Saccharomyces yeasts that may provide a new range of perspectives in terms of techniques and approaches. Besides the widespread use of Dekkera/Brettanomyces for the production of sour beers, other species are emerging for presenting unusual metabolic features that include the production of fruity esters, and a distinctive enzymatic apparatus. Wickerhamomyces anomalus and Torulaspora delbrueckii stand out as the most promising yeasts in brewing processes. Such new tendencies in the use of non-Saccharomyces yeasts comprise the production of low-alcohol beers, functional beers, and bioflavoring approaches. This is a little explored field in brewing practice, still requiring extensive research with practical application. In this sense, this review aims to present the main points for the application of non-conventional yeasts in beer production, and thus contribute to future advances in the topic.

Basso RF et al. (2016) Food Research International 86:112-120

 

Gene expression in wheat beer yeast strains and the synthesis of acetate esters

The synthesis of aroma compounds represents one of the most important parameters in beer production. Although it has been a historical topic of research, exactly how aroma components are formed has yet to be fully explained. Moreover, all of the research that has been published on yeast strains is focused on lagers and ales. Wheat beer yeast strains have not been the focus of aroma and flavour research. In this study, five different wheat beer yeasts were analysed to determine their capacity for producing acetate esters. In this study, the most commonly used wheat beer yeast strains for the production of German-style wheat beer were analysed. This involved measuring the level of expression of the alcohol acetyl transferase genes ATF1, ATF2 and IAH1 over a period of 4 days (during primary fermentation) and plotting the data to observe the development of expression of the genes over time. Results confirmed their capacity to form acetate esters and showed a distinct correlation with increasing expression of the gene ATF1. However, the findings also indicated that gene expression in different yeast strains can vary considerably during fermentation.

Schneiderbanger H et al. (2016) Journal of Institute of Brewing 122:403-411

 

Lactic acid bacteria as sensory biomodulators for fermented cereal-based beverages

Today’s consumer demands functional, healthy and diversified food products that satisfy nutrition-related conditions such as food intolerances, allergies and malabsorption, and lifestyle choices, e.g. vegetarianism, veganism, low-fat or low-salt. Cereal-based beverages have been tested as functional and probiotic foods because of their nutritious and health-promoting properties, e.g. soluble fibres and phytoestrogens. A way to add functionality and improve the low organoleptic attributes of raw cereals is through fermentation using lactic acid bacteria (LAB). The use of starter cultures with known flavour- and texture-enhancing properties offers a promising tool for in situ product enhancement, innovation and diversification of cereal-based beverages. This review highlights studies that have principally addressed flavour and textural changes in model liquid cereal-based substrates using defined LAB starter cultures. The main biochemical mechanisms involved in the formation of compounds that play a central role in the acceptance of cereal beverages are reviewed, and possibilities for enhancing organoleptic and rheological properties are discussed. Starter cultures able to release desired flavours or to positively change the food structure have been successfully used to increase the palatability of cereal beverages and replace the need for additives, i.e. flavourings, enzymes or thickeners. However, predicting the presence of organoleptically-active compounds is often a difficult task, as such compounds are affected by biological and non-biological factors. The outcomes from fermentations done with defined cereal and culture combinations could increase our understanding of which compounds are important for the final acceptance of cereal beverages, and how these components can be enhanced using different technological conditions and starter cultures.

Peyer LC et al. (2016) Trends in Food Science & Technology 54:17-25

 

Flavor of lactic acid fermented malt based beverages: Current status and perspectives

Although several research studies have described potentialities of lactic acid fermented cereal beverages as functional beverages, their market and industrial applications are quasi non-existing. Poor sensory quality, low acceptance, and lack of production technology seem to be the challenges. Sensory characteristics, commonly described as sour, sweet, cereal-like, and malty, are not always regarded as positive by consumers and represent therefore an important hurdle for their acceptance. Neither their aroma composition has been studied in depth for overall aroma understanding, nor has an attempt for sensory profile improvement been done. Aroma type and quantity might depend on several factors like starter culture, substrate, and fermentation process. In this review, we discussed the potential of cereal malt wort as a precursor medium for aroma compound formation during lactic acid fermentation; sensory characteristics and aroma-active compounds of lactic acid fermented cereal beverages are also described; strategies that can be exploited for flavor improvement are proposed with focus on existing technologies. Case studies based on existing products are included for technological innovation in order to meet increasing consumer’s demands for new tastes. Further works on characterization of aroma compounds, elucidation of key aroma compounds that contribute to the overall aroma, flavor impact of the interactions aroma – organic acids, consumer’s needs investigation, lactic acid bacteria starter culture selection and fermentation process management will provide significant advances towards the flavor improvement of cereal beverages for a promising market.

Dongmo SN et al. (2016) Trends in Food Science & Technology 54:37-51

 

Effect of reuterin-producing Lactobacillus reuteri coupled with glycerol on the volatile fraction, odour and aroma of semi-hard ewe milk cheese

The effect of the biopreservation system formed by Lactobacillus reuteri INIA P572, a reuterin-producing strain, and glycerol (required for reuterin production), on the volatile fraction, aroma and odour of industrial sized semi-hard ewe milk cheese (Castellano type) was investigated over a 3-month ripening period. The volatile compounds were extracted and analyzed by SPME-GC-MS and cheese odour and aroma profiles were studied by descriptive sensory analysis. Control cheese was made only with a mesophilic starter and experimental cheeses with L. reuteri were made with and without glycerol. The addition of L. reuteri INIA P572 to milk enhanced the formation of six volatile compounds. Despite the changes in the volatile compounds profile, the use of L. reuteriINIA P572 did not noticeably affect the sensory characteristics of cheese. On the other hand, the addition of L. reuteri INIA P572 coupled with 30 mM glycerol enhanced the formation of twelve volatile compounds, but decreased the formation of five ones. The use of the biopreservation system did not affect overall odour and aroma quality of cheese although it resulted in a significant decrease of the odour intensity scores. In addition, this cheese received significant higher scores for “cheesy” aroma and significant lower scores for the aroma attributes “milky”, “caramel” and “yogurt-like”. The first two axes of a principal component analysis (PCA) performed for selected volatile compounds and sensory characteristics, accounting for 75% of the variability between cheeses, separated cheeses made with L. reuteri INIA P572 and glycerol from the rest of cheeses, and also differentiated control cheese from cheeses made with L. reuteri INIA P572 from day 60 onward. Our results showed that the reuterin producing L. reuteri INIA P572 strain, when coupled with glycerol, may be a suitable biopreservation system to use in cheese without affecting odour and aroma quality.

Gómez-Torres N et al. (2016) International Journal of Food Microbiology 232:103-110

 

Sensory quality of Camembert-type cheese: Relationship between starter cultures and ripening molds

Starter cultures and ripening molds used in the manufacture of moldy cheese aimed at obtaining characteristic flavors and textures considerably differ among dairy industries. Thus, the study of variables inherent to the process and their influence on sensory patterns in cheese can improve the standardization and control of the production process. The aim of this work was to study the influence of three different variables on the sensory quality of Camembert-type cheese: type of lactic bacteria, type of ripener molds and inoculation method. Batches of Camembert-type cheese were produced using O or DL-type mesophilic starter culture, ripened with Penicillium camemberti or Penicillium candidum and mold inoculation was made directly into the milk or by spraying. All batches were sensorially evaluated using Quantitative Descriptive Analysis (QDA) with panelists trained for various attributes. Among the combinations analyzed, those resulting in more typical Camembert-type cheese were those using O-type mesophilic starter culture and P. candidum maturation mold directly applied into the milk or sprayed and those using DL-type mesophilic starter and P. camemberti ripener mold applied by surface spraying. These results demonstrate, therefore, that the combination of different ripener molds, inoculation methods and starter cultures directly influences the sensory quality of Camembert-type cheese, modifying significantly its texture, appearance, aroma and taste.

Galli BD et al. (2016) International Journal of Food Microbiology 234:71-75

 

Autolysis of Aspergillus oryzae mycelium and effect on volatile flavor compounds of soy sauce

The autolyzed mycelia of Aspergillus oryzae are rich in proteins, nucleic acids, sugar, and other biomacromolecules, and are one of the main contributors to the flavor profile of commercially important fermented goods, including soy sauce and miso. We induced autolysis of the mycelia of A. oryzae over 1 to 10 d, and found that the maximum dissolved amounts of total protein and nucleic acid ratio accounted for 28.63% and 88.93%, respectively. The organic acid content, such as citric acid, tartaric acid, succinic acid, lactic acid, and acetic acid, initially increased and then decreased as autolysis progressed, corresponding to changes in pH levels. The main characteristic flavor compounds in soy sauce, namely, ethanol, 2-phenylethanol, and 2-methoxy-4-vinylphenol, were all detected in the autolysate. Subsequently, we tested the effect of adding mycelia of A. oryzae during the fermentation process of soy sauce for 60 d, and found that addition of 1.2‰ A. oryzae mycelia provided the richest flavor. Overall, our findings suggest that compounds found in the autolysate of A. oryzae may promote the flavor compounds of soy sauce, such as alcohols, aldehydes, phenols, and esters.

Xu N et al. (2016) Journal of Food Science 81:C1883-C1890

 

Characterization of the recombinant Brettanomyces anomalus β-glucosidase and its potential for bioflavouring

Plant materials used in the food industry contain up to five times more aromas bound to glucose (glucosides) than free, unbound aromas, making these bound aromas an unused flavouring potential. The aim of this study was to identify and purify a novel β-glucosidase from Brettanomyces yeasts that are capable of releasing bound aromas present in various food products. We screened 428 different yeast strains for β-glucosidase activity and are the first to sequence the whole genome of two Brettanomyces yeasts (Brettanomyces anomalus and Brettanomyces bruxellensis) with exceptionally high β-glucosidase activity. Heterologous expression and purification of the identified B. anomalus β-glucosidase showed that it has an optimal activity at a higher pH (5.75) and lower temperature (37°C) than commercial β-glucosidases. Adding this B. anomalus β-glucosidase to cherry beers and forest fruit milks resulted in increased amounts of benzyl alcohol, eugenol, linalool and methyl salicylate compared to Aspergillus niger and Almond glucosidase. The newly identified B. anomalus β-glucosidase offers new possibilities for food bioflavouring. This study is the first to sequence the B. anomalus genome and to identify the β-glucosidase-encoding genes of two Brettanomyces species, and reports a new bioflavouring enzyme.

Vervoort Y et al. (2014) Journal of Applied Microbiology 121:721-733

 

High-throughput screening of a large collection of non-conventional yeasts reveals their potential for aroma formation in food fermentation

Saccharomyces yeast species are currently the most important yeasts involved in industrial-scale food fermentations. However, there are hundreds of other yeast species poorly studied that are highly promising for flavour development, some of which have also been identified in traditional food fermentations. This work explores natural yeast biodiversity in terms of aroma formation, with a particular focus on aromas relevant for industrial fermentations such as wine and beer. Several non-Saccharomyces species produce important aroma compounds such as fusel alcohols derived from the Ehrlich pathway, acetate esters and ethyl esters in significantly higher quantities than the well-known Saccharomyces species. These species are: Starmera caribaea, Hanseniaspora guilliermondii, Galactomyces geotrichum, Saccharomycopsis vini and Ambrosiozyma monospora. Certain species revealed a strain-dependent flavour profile while other species were very homogenous in their flavour profiles. Finally, characterization of a selected number of yeast species using valine or leucine as sole nitrogen sources indicates that the mechanisms of regulation of the expression of the Ehrlich pathway exist amongst non-conventional yeast species.

Gamero et al. (2016) Food Microbiology 60:147-159

 

Scroll to Top