Model fermentations

Artificial intelligence, for monitoring and modelling fermentation, 77 41 Artificial kidneys, 75 844-845 Artificial neural networks... 

Keywords. Oxygen absorption. Three-phase mass transfer. Dispersed phase. Heterogeneous model. Fermentation, Bulk oxygen concentration... 

Figure 5. FID trace from the HRGC-FTIR study of silica gel fraction III of fermentation byproducts obtained in model fermentation studies with Saccharomvces cerevisiae Column 30 m x 0.32 mm i.d. CP 57 CB (df = 0.2) (Chrompack). 50-130° C, 2°/min. 130-200°C, 5°/min.

The production of the higher alcohols, the acetates of isoamyl alcohol and phenylethyl alcohol, and the ethyl esters of the C6-C10 fatty acids has been studied in semiaerobic sugar fermentations by strains of . cerevisiae and S. uvarum. S. cerevisiae generally produced more esters than S. uvarum. Isoamyl acetate was the main ester produced by >. cerevisiae. and others, in decreasing order, were ethyl caprylate, ethyl caproate, ethyl caprate and phenylethyl acetate(39). Several unusual thio compounds have been produced by Saccharomvces in model anaerobic fermentations using amino acids such as methionine as the sole carbon source(21). These model fermentations produce methylthiopropanal and traces of other sulfur containing compounds, such as methionyl acetate and 2-methyltetrahydrothiophene-3-one. 

Model Fermentations. A chemically-defined grape juice medium at pH 3.5, with amino acids as the nitrogen source, was used for the model experiments (72). Sugar (D(+)-glucose 200 g/L) was included unless ofiierwise indicated. For those model fermentations that were conducted in the presence of tannins (1.5 g/L), the medium was sonicated for 15 minutes at room temperature after the tannin addition, and the insoluble material was removed by centrifugation at 48000 g for 15 minutes. In ferments containing added anthocyanins, the enriched anthocyanin preparation was sterile filtered (0.2 pm), and 1.6 mL were added to 47.4 mL of sterile filtered chemically-defined grape juice medium for each model fermentation. 

Formation of Pigmented Polymers in Model Fermentation Experiments... 

Figure 6. HPLC chromatograms using the rocket column, measured at 520nm, of (a) pigments present at the end (9 days) of a model ferment to which Mv (500mg/L) and catechin (300mg/L) had been added prior to the start of fermentation (b) pigments extracted from the yeast lees after completion of fermentation (9 days).

In addition to theanaphthoquinone, two new oxidation products of theaflavin, bistheaflavin A (7) and dehydrotheaflavin (8), were isolated in similar model fermentation experiments using banana fruit and tea leaf homogenates, respectively. On the other hand, auto-oxidation of theaflavin in a phosphate buffer at pH 7.3 yielded a yellow pigment, bistheaflavin B (9), along with 6 (figure 5.4). The dimer 9 is deduced to be formed by coupling of the reduced form (6a) of theanaphthoquinone with theaflavin-quinone (5b). The results demonstrated that theanaphthoquinone was also formed nonenzymatically from theaflavin. 

In the oxidation of tea catechins, the initial reaction gave simple catechin quinones. However, subsequent cross-coupling reactions of the quinones yielded many products. Some of these products were unstable and decomposed to give further complex products. These cascade-type reactions account for the complexity of the black tea polyphenols (figure 5.9). Although many of the oxidation products described here were obtained by model fermentation experiments, the presence of compounds 21, 24,26,28, and 29, as well as theaflavins (theaflavin and its galloyl esters), theasinensins (14-17), and oolongtheanins (18), in commercial black tea were confirmed. 

Model fermentation medium, supplemented with 5 mg/1 p-coumaric acid, anaerobic conditions, 25°C. 

Graves, T, Narendranath, N., Power, R. Development of a Stress Model fermentation system for fuel ethanol yeast strains. J Inst Brew. 2007, 113,263-271. 

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