Maltose yeasts

In fermentations, the amylases are either present in or added to the polysaccharide substrate at activity levels sufficient to hydrolyze starch to maltose. Yeast does not generate the amylases, so malt (germinated grain) is relied on to augment their concentration. The importance of yeast is to produce maltase for converting maltose to glucose. 

Assuming that sucrose and maltose are equally accessible to their hydrolytic enzymes, further analysis confirmed that yeasts unable to utilize raffinose may utilize sucrose by means of a maltosehydrolyzing enzyme. Here, three substrates are treated simultaneously, namely, sucrose, raffinose, and maltose, which is not possible from the information given in Table XVI. Thus, yeasts that are [sucrose +, raffinose +] are divided into those that are maltose + or maltose— yeasts that are [sucrose+, raffinose—] are similarly divided, and so on. Only four yeasts that were [sucrose +, raffinose — ] were reported to be maltose —. 

Williamson s medium L Contains ui opped beer, maltose, yeast extract, liver extract, casein hydrolysate, either polymyxin or phenylethanol with CO atmosphere (25 Q, supports lactic acid bacteria. Polymyxin suppresses gram-negative bacteria. Phenylethanol supports Pediococcus rather than Lactobacillus... 

Maltase pancreas, small intes tine, yeast maltose glucose 6-1 (gut) 6 6 (yeast)... 

Fermentabihty of com symps by yeast is important in certain food appHcations, eg, baking and brewing. The fermentable sugars present in corn symp are dextrose, maltose, and maltotriose. Fermentabihty of maltose or maltotriose depends on the specific fermentation process and organism. In general, greater fermentabihty is obtained at higher DE levels. 

Yeast (qv) metabolize maltose and glucose sugars via the Embden-Meyerhof pathway to pymvate, and via acetaldehyde to ethanol. AH distiUers yeast strains can be expected to produce 6% (v/v) ethanol from a mash containing 11% (w/v) starch. Ethanol concentration up to 18% can be tolerated by some yeasts. Secondary products (congeners) arise during fermentation and are retained in the distiUation of whiskey. These include aldehydes, esters, and higher alcohols (fusel oHs). NaturaHy occurring lactic acid bacteria may simultaneously ferment within the mash and contribute to the whiskey flavor profile. 

The converted mash is pumped to a clean sterilised fermentor and the yeast inoculum is added. The set temperature range for whiskey fermentation of 72 hours is usually 17—21°C. At the beginning, the mash converted composition is approximately 80% sugars, mainly maltose and some (<1%) dextrose (primary conversion). The pH is adjusted to reduce initial bacterial growth. Grain neutral spidts are usually set at 27—29°C to expedite fermentation. Temperatures above 35°C inhibit yeast reproduction and promote rapid bacterial growth. Above 40°C actual yeast kill occurs. 

After 30 hours, the maximum and critical fermentation is underway and the pH must remain above 4.0 for optimal fermentation. However, accompanying bacterial contamination from various sources such as yeast contamination, improper cleaning procedures, slow yeast growth, or excessive temperatures can result in a pH below 4.0. The remaining amylase enzymes, referred to as secondary conversion agents, are inactivated and can no longer convert the dextrins to maltose. Under these circumstances, the fermentor pH continues to drop because of acid production of the bacteria, and the pH can drop to as low as 3.0. The obvious result is a low ethanol yield and quaUty deterioration. 

The yield was highest with starch or dextrin, intermediate and about the same with sucrose, glucose, maltose and lactose and poorest with glycerol. Kanamycin was produced by media containing soybean meal, peanut meal, cottonseed meal, corn steep liquor, peptone, yeast extract or meat extract, with or without sodium nitrate. Commercially available soybean meal was recognized to be one of the best nitrogen sources. The addition of corn steep liquor, peptone, yeast extract or nitrate to the soybean meal promoted the production of kanamycin. 

Despite the similarities of their structures, cellobiose and maltose have dramatically different biological properties. Cellobiose can t be digested by humans and can t be fermented by yeast. Maltose, however, is digested without difficulty and is fermented readily. 

The distinctive aroma of ammonia is often apparent in bakeries but not in the final product. Bakers yeast performs its leavening function by fermenting such sugars as glucose, fructose, maltose, and sucrose. The principal products of the fermentation process are carbon dioxide gas and ethanol, an important component of the aroma of freshly baked bread. The fermentation of the sugar, glucose—an example of a decomposition reaction — is given by the equation in Fig. 5.19.1. 

Fehr, M., Frommer, W. B. and Lalonde, S. (2002). Visualization of maltose uptake in living yeast cells by fluorescent nanosensors. Proc. Natl. Acad. Sci. USA 99, 9846-51. 

Glucose or maltose by selective fermentation with washed baker s yeast dextrine by difference. b Average degrees of polymerization of dextrine were calculated from their reducing values as follows ... 

Fischer then examined the lactose yeast in the same manner as he did the Frohberg yeast and found it to contain both an invertin-like enzyme and a lactose-cleaving enzyme, which he termed lactase. From these results he concluded that the first step in the fermentation of lactose, as for the fermentation of sucrose and maltose, is the hydrolysis of the disaccharide to mono-sacharide. From this observation, he drew the landmark conclusion that he considered it most unlikely that any polysaccharide (the term included di-saccharides) can be fermented without first being hydrolyzed to hexose (31). 

The production of ethanol from cooked rice starch (Moebus and Teuber, 1985) differs from the normal process of spraying the carbon source into the bed since all of the carbon source is made available at the start of the run, subject only to the breakdown of starch to glucose (and maltose) by amylases. The starch (0.3 mm particles), amylases and yeast pellets were mixed in the bed and water sprayed in to maintain the fermentative activity of the yeast. The fermentation was carried out at 31.5°C. 

Prior to fermentation, the wort is then cooled to temperatures below 85°F (30°C), and the pH is adjusted to about 5. Yeast such as Saccharomyces cerevisiae, Saccharomyces carlsbergensis or Candida brassicae are added and fermentation proceeds for 2 to 3 days under batch processing conditions. Yeast produces the enzymes maltase, zymase, and invertase. Maltase converts maltose to glucose. Zymase converts glucose to ethanol. Invertase converts any sucrose present to fermentable sugar. The following equations illustrate the enzymatic conversion of starch to ethanol ... 

FlC. 1.—Relative Rates of Activity Against Glycosides at Various pH Values. [A. Hydrolysis of sucrose by /3-D-fructofuranosidase of Saccharomyces cerevisiae O, intact cells and A, toluene-treated cells (results of Wilkes and Palmer40). B. Maltose , fermentation by intact baker s yeast A, hydrolysis by a-D-glucosidase (results of Hestrin41 see also Ref. 42).]... 

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