METABOLIC PRODUCTS 275 



Fungus amylases are used to replace malt amylase for the saccharifica- 

 tion of starch, Myrback (1948) is of the opinion that amylase from A. 

 niger is an a-amylase, but it differs from a-amylase of malt in that it has a 

 higher capacity for saccharification. For a comparison of fungus and 

 malt amylase and the economic considerations involved, see Underkofler 

 et al. (194G). The yield of alcohol is said to be slightly higher when 

 fungus amylase is used in place of malt for saccharification. 



Fungi are the source of other enzymes of commercial interest, including 

 pectinase and sucrase. Pectinase is used in the clarification of fruit 

 juices. For a survey of the commercial production of fungus enzymes 

 seeL. Wallerstein (1939). 



ALCOHOLIC FERMENTATION 



Yeasts are used almost exclusively for the commercial production of 

 fermentation alcohol, but alcoholic fermentation is not restricted to these 

 fungi. Pasteur (1872) observed that Penicillium glaucum, Aspergillus 

 glaucus, and Mucor raceniosus produced alcohol under anaerobic condi- 

 tions. Further information on alcohol production by filamentous fungi 

 may be found in the monograph of Raistrick et al. (1931), who determined 

 complete carbon balances for 96 species of Aspergillus, 75 species of 

 Penicillium, 8 species of Citromyces (Penicillium) , 23 species of Fusarium 

 and 36 miscellaneous species. The original report should be consulted 

 for details and the quantitative methods used. All the 23 species of 

 Fusarium studied produced alcohol. From this and other reports in the 

 literature, it must be concluded that this property is common among 

 species of this genus. Many species of Aspergillus and Penicillium pro- 

 duced alcohol, as did species of other genera. Only a few of the species 

 studied failed to produce detectable amounts of alcohol. The apparatus 

 used in these studies is shown in Fig. 53. 



The concentration of alcohol which inhibits the growth of fungi varies 

 with the species or strain. In general, yeasts are more tolerant of alcohol 

 than the filamentous fungi. The upper limit for most yeasts is about 12 

 per cent alcohol, although some strains are more tolerant. The suscepti- 

 bility to alcohol limits the alcohol concentration of naturally fermentt>? 

 beverages. The rate of fermentation decreases as the concentration (k 

 alcohol increases. 



Not all isolates of a species are equally efficient in producing alcohcu 

 For example, eight isolates of Fusarium lini produced varying amountfe 

 of alcohol on the same medium. The more virulent pathogens on flax 

 produced the most alcohol (Letcher and Willaman, 1926). A correlation 

 between sporulation and alcohol production by Aspergillus flavus was 

 noted by Yuill (1928). In general, sporulating cultures produced less 

 alcohol than nonsporulating cultures. 



The most important condition w^hich governs alcoholic fermentation 



