Microbial pectinolytic enzymes: A review

The most mysterious aspect of wine is the endless variety of flavours that stem from a complex, completely non-linear system of interactions among many hundreds of compounds. In its widest sense, wine flavour refers to the overall impression of both aroma and taste components. Aroma is usually associated with odorous, volatile compounds; the bouquet of wine refers to the more complex flavour compounds which evolve as a result of fermentation, elevage and ageing. With the exception of terpenes in the aromatic grape varieties and alkoxypyrazines in the herbaceous cultivars, perceived flavour is the result of absolute amounts and specific ratios of many of these interactive compounds, rather than being attributable to a single "impact" compound. Without underestimating the complexity of these interactive effects or negating the definitive role played by the accumulated secondary grape metabolites in the varietal character of wine, this review will focus mainly on the contribution of yeast fermentation to the sensorial quality of the final product. Yeast and fermentation conditions are claimed to be the most important factors influencing the flavours in wine. Both spontaneous and inoculated wine fermentations are affected by the diversity of yeasts associated with the vineyard and winery. During the primary alcoholic fermentation of sugar, the wine yeast, Saccharomyces cerevisiae, together with other indigenous non-Saccharomyces species, produce ethanol, carbon dioxide and a number of by-products. Of these yeast-derived metabolites, the alcohols, acetates and C4-C8 1tfatty acid ethyl esters are found in the highest concentration in wine. While the volatile metabolites contribute to the fermentation bouquet ubiquitous to all young wines, the production levels of these by-products are variable and yeast strain specific. Therefore, this article also highlights the importance of untapping the hidden wealth of indigenous yeast species present on grapes, and the selection and genetic development of yeast starter culture strains with improved flavour profiles. In the future, some winemakers may prefer to use mixtures of indigenous yeast species and tailored S. cerevisiae strains as starter cultures to reflect the biodiversity and stylistic distinctiveness of a given region. This will help winemakers to fullfil the consumer's demand for individual wines with intact local character and to ensure the survival of wine's most enthralling aspect - its endless variety.

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Yeast and its Importance to Wine Aroma - A Review

The first stage of chocolate production consists of a natural, seven-day microbial fermentation of the pectinaceous pulp surrounding beans of the tree Theobroma cacao. There is a microbial succession of a wide range of yeasts, lactic-acid, and acetic-acid bacteria during which high temperatures of up to 50°C and microbial products, such as ethanol, lactic acid, and acetic acid, kill the beans and cause production of flavor precursors. Over-fermentation leads to a rise in bacilli and filamentous fungi that can cause off-flavors. The physiological roles of the predominant micro-organisms are now reasonably well understood and the crucial importance of a well-ordered microbial succession in cocoa aroma has been established. It has been possible to use a synthetic microbial cocktail inoculum of just 5 species, including members of the 3 principal groups, to mimic the natural fermentation process and yield good quality chocolate. Reduction of the amount of pectin by physical or mechanical means can also lead t...

The Microbiology of Cocoa Fermentation and its Role in Chocolate Quality

https://digital.csic.es/bitstream/10261/46861/3/food_phenolics_lactic_acid_bacteria_Rodriguez.pdf

Food phenolics and lactic acid bacteria

Effect of fermentation on the antioxidant activity in plant-based foods

When grown in the appropriate medium, several yeast species produce pectinases able to degrade pectic substances. It is mainly exocellular endopolygalacturonases that break pectins or pectate down by hydrolysis of α-1,4-glycosidic linkages in a random way. Biochemical characterisation of these enzymes has shown that they have an optimal pH in the acidic region and an optimal temperature between 40 and 55°C. Their production by yeasts is a constitutive feature and is repressed by the glucose concentration and aeration. Pectic substances and their hydrolysis products are used as carbon sources by a limited number of yeasts and hence these enzymes must be involved in the colonisation of different parts of plants, including fruits. The first yeast pectic enzyme (encoded by the PSE3 gene) was cloned from Tichosporon penicillatum. Recently, a polygalacturonase-encoding gene from Saccharomyces cerevisiae has been cloned and overexpressed in several strains and the gene for an extracellualar endopolygalacturonase from Kluyveromyces marxianus has also been described. Taking all the results together, the idea is now emerging that this type of yeast enzyme could offer an alternative to fungal enzymes for industrial applications.

Production of pectic enzymes in yeasts

Fourteen strains of the yeastSaccharomyces cerevisiae were isolated from three wineries in the Salnes wine region (N.W. Spain) at the three different periods of the natural fermentation. Each wild yeast was screened for production of acetaldehyde, ethyl acetate, isobutanol,n-propanol, amylic alcohol and other important enological compounds during laboratory scale fermentations of grape juice. After 25 days at 20°C, the analytical results evidenced variations in the production of acetaldehyde (from 13.1 to 24.3 mg/l), isobutanol (from 27.7 to 51.1 mg/l), amyl alcohols (from 111 to 183 mg/l) and ethyl acetate (from 19.3 to 43.7 mg/l). Although isolated from the same wine region, differences in the wine composition were observed depending on the particular yeast strain used for the vinification experiments.

Production of higher alcohols, ethyl acetate, acetaldehyde and other compounds by 14Saccharomyces cerevisiae wine strains isolated from the same region (Salnés, N.W. Spain).

A collection of malolactic bacteria isolated from musts and wines of northwestern Spain (Rias Baixas) was used to determine their ability to produce aryl β-D-glucosidases. A β-glucosidase (EC 3.2.1.21) was purified to homogeneity from cell-free extracts of a strain of Lactobacillus plantarum. The enzyme had a molecular mass of about 40 kDa, as determined by molecular-exclusion chromatography. The enzyme was most active at pH 5.0, and was stable between pH 4.5 and 7.5. The optimum temperature was 45 °C and the enzyme was active against a wide range of aryl β-glucosides and β-linked disaccharides. The Km and Vmax values for 4-nitrophenyl-β-D-glucopyranoside were 1.82 mM and 4.89 nmol/ml/min, respectively.

β-Glucosidase Activity in a Lactobacillus Plantarum Wine Strain

HPLC testing of the carotenoid content of the halobacteria Halobacterium salinarium, Haloarcula hispanica and Haloferax mediterranei showed that all contained high amounts of ketocarotenoids. Halobacterium salinarium produced 2400 μg of total carotenoids per gram of dried bacteria, including 265 μg of trans-astaxanthin (11%), and 588 μg of 3-hydroxy-echinenone (24%). The biotechnological properties of Halobacterium salinarium as a natural pigment source are also presented. The results are compared with those from the yeast Phaffia rhodozyma currently used in the industry as a source of trans-astaxanthin.

Ketocarotenoids in halobacteria: 3-hydroxy echinenone and trans astaxanthin

Acridine orange, an intercalating dye usually employed in the curing of bacterial plasmids, was tested for its ability to cure K1 and K2 killer strains (laboratory and wine strains). The results showed a high curing percentage of the killer character. This was demonstrated by the loss of M1 or M2 dsRNAs (responsible for toxin production and resistance to it) and because the meiotic products exhibited non-Mendelian segregation. The curing percentages varied, depending on the strain but not on the killer type, and showed similar efficiency as compared with other known curing agents.

T. G. Villa

Papers

Production of pectic enzymes in yeasts

Production of higher alcohols, ethyl acetate, acetaldehyde and other compounds by 14Saccharomyces cerevisiae wine strains isolated from the same region (Salnés, N.W. Spain).

β-Glucosidase Activity in a Lactobacillus Plantarum Wine Strain

Ketocarotenoids in halobacteria: 3-hydroxy echinenone and trans astaxanthin

Curing of the killer character of Saccharomyces cerevisiae with acridine orange.