Fermentation phenolic compounds

Red wine color results from maceration of grape solids (skins, pips and sometimes stalks) dnring alcoholic fermentation. Phenolic compound extraction thus depends on many factors grape variety. 

Vanilla flavour is not only determined and characterised by the vanillin molecule, but also by many more phenolic compounds and vanillin derivatives. Two examples of molecules that recently obtained FEMA-GRAS status are vanillyl ethyl ether and vanillin 2,3-butanediol acetal (Scheme 13.11). Vanillin can be hydrogenated to form vanillyl alcohol, which is also used in vanilla flavours. Vanillyl alcohol can be reacted with ethanol to form vanillyl ethyl ether. Vanillin can also form an acetal with 2,3-butanediol (obtained by fermentation of sugars) catalysed byp-toluene sulfonic acid in toluene. 

The fermentation inhibitors include furan aldehydes, aliphatic acids, and phenolic compounds. The furan aldehydes, furfural, and hydroxymethyl furfural (HMF), are formed from pentoses and hexoses, respectively (4,5). Several studies indicate that furfural inhibits Saccharomyces cerevisiae, at least when present in high concentrations (6-10). HMF has a similar effect (11,12). 

The breakdown of furan aldehydes leads to the formation of formic and levulinic acid. Moreover, acetic acid is formed during the degradation of hemicellulose. Partial breakdown of lignin can generate a variety of phenolic compounds (23), which also inhibit S. cerevisiae (14,15). In contrast to furan aldehydes and aliphatic acids, the toxic effect of specific phenolic compounds is highly variable (15). Different raw materials and different approaches to prepare lignocellulose hydrolysates will result in different concentrations of the fermentation inhibitors (16,17). 

In an analytical experimental series (Fig. 1), the effluent was collected in fractions. These fractions were analyzed with respect to pH, fermentable sugars, furan aldehydes, phenolic compounds, aliphatic acids, sulfate, and ultraviolet (UV) absorption at 280 nm. 

From the reported data (Figs. 1 and 2, Table 1) the optimum condition to obtain a pentose-rich hydrolysate from dilute-acid hydrolysis of BSG at 130°C was 15 min (CS 1.94). Such hydrolysate contains about 43.5 g/L of glucose, xylose, and arabinose (ratio of 10 67 32), together with a low content of furfural, HMF, acetic acid, formic acid, and total phenolic compounds (Table 2). This condition was chosen for subsequent production of hydrolysates for fermentation. 

Bitartrate Stabilization. Potassium and tartaric acid are natural constituents of the grape. Wine content of these constituents depends on a number of variables, not all well understood variety, vintage, and weather pattern degree of skin contact alcohol level bitartrate holding capacity of phenolic compounds and potassium binding capacity of the wine (30, 35). Most wines after fermentation are supersaturated solutions of potassium bitartrate. This compound is less soluble at lower temperatures, and, thus, lower temperatures will cause precipitation of bitartrate crystals. This lowering of temperature and subsequent removal of crystals by filtration is called cold stabilization. 

Nishimura, T., Kometani, T., Takii, H.,Terada, Y., and Okada, S. 1994. Purification and some properties of a-amylase from Bacillus subtilis X-23 that glucosylates phenolic compounds such as hydroquinone. /. Ferment. Bioeng., 78, 31-36. 

Hernandez, T., Estrella, I., CarlavUla, D., Martin-Alvarez, P.J., Moreno-Arribas, M.V. (2006). Phenolic compounds in red wine subjected to industrial malolactic fermentation and ageing on lees. Anal. Chim. Acta, 563, 116-125. 

During alcoholic fermentation, the degree of maceration is the first factor that affects the extraction of some compounds present in the grape skin, especially phenolic compounds, which are responsible for the color of the wine. However, not only does the maceration affect the extraction of polyphenols but also of other grape components, such as proteins, polysaccharides and, also, amino acids, which are precursors of biogenic amines. In most red wines, alcoholic fermentation takes place... 

As early as 1964 it was recognized that 4-ethyl phenol and 4-ethyl guaiacol were produced by yeast and bacteria during fermentation by the decarboxylation of the hydroxyciimamic acids p-coumaric and fendic acid (88). Later it was reported that among yeast only Brettanomyces species possess the metabolic ability to enzymatically decarboxylate hydroxycinnamic acids to produce ethyl derivatives (29, 89). Heresztyn was the first to identify 4-ethyl phenol and 4t-ethyl guaiacol as the major volatile phenolic compounds formed by Brettanomyces yeast (84). ... 

Dyes are also classified on the basis of their application. The water-soluble dyes which are the salts of sulfonic acid or phenolic compounds are named acid dyes] those which are the salts of amino compounds are called basic. If the dyeing is accomplished without use of mordants the dyes are called direct. Dyes which require the use of metallic oxides, tannin, and other substances to give fast shades are called mordant dyes. The water-insoluble dyes are known as vat dyes. The insoluble colored substance is reduced in a fermentation vat or by hydrosulfite to a soluble form which is applied to the fiber then oxidized by air to the insoluble color. Finally ingrain dyes are produced by performing one or more of the chemical reactions used for the preparation of the dye directly on the fiber. 

A general method for the evaluation of phenolic compounds in fermented beverages, fruit juices and plant extracts was developed using gradient HPLC and coulometric detection. In a 10 p,L injection it was possible to identify and determine 36 different flavonoids and simple and complex phenols, without sample extraction, purification or concentration, in several kinds of beers, red and white wines, lemon juice and soya, forsythia and tobacco extracts. This may also be useful for the characterization of beverages and extracts . 

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