Sucrose zymase

In 1878, the "fragments" identified by Pasteur were named enzymes by the German physiologist Wilhelm Kuhne. In 1897, Eduard Buchner, a German chemist, accidentally discovered that a yeast juice could convert sucrose to ethanol. He was able to show that the sugar was fermented even in the absence of living yeast cells in the mixture, and named the factor responsible for the fermentation of sucrose zymase. In 1907, he received the Nobel Prize in Chemistry. The 40 years of biochemical research that followed yielded the details of the chemical reactions of fermentation. 

Yeast contains a number of enzymes, more particularly inyertase and zymase. Invertase catalyses the hydrolysis of sucrose to glucose and fructose (cf. the catalysis of this reaction by acids, p. 369). 

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 ... 

The catalytic action of living organisms, or rather of the proteins they contain, had received the beginnings of an explanation with the experiments of Payen and Persoz on malt amylase separation in 1833 and with J. J, Berzelius s catalyst theory in 1835. In 1897 Eduard Buchner demonstrated that a yeast extract could turn sucrose into ethyl alcohol, Fermentation took place without the presence of living organisms through enzymes. In this case zymase was the catalyst. 

The inversion of sucrose results either from the action of acid or of a special enzyme, invertase, which is present in yeast. In either case the process results in one equivalent each of dextrose and fructose. Sucrose, itself, does not ferment, that is, does not break up into alcohol and carbon dioxide under the influence of the enzyme, zymase. However, since most yeasts also contain invertase, the fermentation of sucrose proceeds as soon as this latter enzyme has had a little time to act. 

Sucrose does not ferment when treated with zymase the enzyme which brings about the conversion of dextrose and levulose into alcohol and carbon dioxide. It does ferment, however, under the influence of ordinary yeast, which contains in addition to zymasej another enzyme, called invertase on account of the fact that it causes the inversion of sucrose to dextrose and levulose. 

Extensive research has been extended toward the fermentation of sucrose and giucose into ethanoi. As we saw in Section 1 6.1 2.d, invertase enzymes in yeast can convert sucrose into a mixture of giucose and fructose. An enzyme called zymase, also available in yeast, can then convert glucose into ethanol as part of the fermentation process, creating CO2 as a by-product. A variety of carbohydrate sources can be used in these fermentation steps, including corn, sugar beets, and sugar cane. 

The most important conversions in the context of green chemistry is with the help of enzymes. Enzymes are also referred to as biocatalysts and the transformations are referred to as biocatalytic conversions. Enzymes are now easily available and are an important tool in organic synthesis. The earliest biocatalytic conversion known to mankind is the manufacture of ethyl alcohol from molasses, the mother liquor left after the crystallisation of cane sugar from concentrated cane juice. This transformation is brought about by the enzyme invertase which converts sucrose into glucose and fructose and finally by the enzyme zymase which converts glucose and fiuctose into ethyl alcohol. It is well known that most of the antibiotics have been prepared using enzymes (enzymatic fermentation). 

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