(5). The production of  citric acid  from sugars was believed  by Wehmer  (60)  to  be  characteristic  of  a  particular group  of Penicillium-like  fungi which he appropriately  termed “Citro- myces.”  He,  likewise,  believed  that  the  formation  of oxalic acid was  characteristic of  the Aspergilli.  The separa- tion  of  the  two groups  of  fungi  based  on this  physiological difference was later abandoned after Zahorski (66) and Thom and Currie  (47) had  shown  that citric  acid was readily pro- duced  by  many  different  strains  of  Aspergillus  niger.  Nu- merous  other  fungi have  since been  studied  which  produce citric acid from sugars. The  citric acid  process  has  been  studied  in  great  detail, and in  much  of  this  work  Aspergillus  niger  has  been em- ployed.  Thom  and Church  (46) pointed  out  that  the  term “Aspergillus  niger  does  not  designate  a definite  strain  or species”  but  is  used  to  designate ‘ia whole  group  of  black Aspergilli  with fundamental  characters  in  common.”  The great  variations  in  acid  production  by  different  Aspergillus niger  strains which  have  been recorded  is,  therefore, not  at all surprising.  The activity  of  inpidual strains frequently varies  so  much  that  the  stabilization  or  maintenance  of a high acid-producing capacity of  the organism is recognized as one of  the most  difficult  problems  encountered in dealing 6t&  the process. Doelger  and Prescott  (20)  recently  car- ried  out  studies with  the object of  determining methods for maintaining uniformity  of  conditions which would  result  in consistent yields of  acid  in successive fermentations. The influence of  various  factors which affect the citric acid fermentation has been  studied by  many workers.  In  1917 Currie  (19) made a thorough investigation of  the production of  citric  acid  by  selected  strains  of  Aspergillus  niger  and showed  that,  by  properly controlling  the  pH  and  the  con- centrations of  the inorganic nutrient  salts,  the proportion  of citric  and  oxalic  acids  could  be varied  almost  at will.  He found  that  oxalic  acid  formation  was  almost  completely suppressed  under  conditions which were most favorable  for the  formation of  citric acid.  The  importance of  a preliminary acidification with hydrochloric acid  to pH 3.5  for suppressing oxalic acid formation, preventing undesirable spore formation and minimizing  the danger  of  infection  by other  organisms, was clearly demonstrated.  It is known  that  contamination difficulties were  at least partially  responsible for  the  failure of  early attempts made in Europe  to establish  the fermenta- tion  process  on a  commercial  scale.  This was  undoubtedly due in  part to the practice  of  neutralizing  the acid  formed with  calcium  carbonate.  Acid  sterilization  has without doubt played an important part in the successful coriunercial- scale development of  the process, both  in this country and in Europe.  The work of  Currie  (19), which was  carried out in the United  States Department  of  Agriculture,  later formed the  basis for  the  timely  commercial  development  of  the process  in  the  laboratories  of  the Charles  Pfizer Company, of  Brooklyn. The process is usuaUy carried out between 2.5" and 35" C., although  temperatures  as low  as 20" and  as high  as  40'  C. have  been employed.  The optimum temperature  probably depends somewhat  on  the  organism  used.  Aeration is un- doubtedly  an  important  factor, although  little  information concerning  it  is  available.  We may  assume  that  relatively small  amounts  of  air  are  required  to supply  the  necessary oxygen for  the  life processes  of  the  organism, since Porges (S9) and Doelger and Prescott ($0)  have observed  that  large amounts of  air adversely affected acid yields. It is impossible to make any general conclusions regardiiig the kind  and  amount of  inorganic nutrients  that  ndl in  all cases yield  the best results for citric acid production.  From the vast  amount  of  work  reported,  it appears  that  the  nu- trient  requirements depend  to some extent on the inpidnal characteristics of  the organism nsed. Aside from the carbon and  nitrogen  sources,  the  only  essential  elements  are  po- tassium,  phosphorus, magnesium,  and  sulfur  as  shown by Currie  (19) and by  Doelger  and  Prescott  (20). Nonever, many investigators claim that small amounts of zinc and iron am essential for the best growth of  the organism, and in some instances  it seems fairly well established  that these elements exert  a  beneficial effect on acid  prodnetion.  The essential elements, aside  from carbon, oxygen, and  nitrogen,  are con- veniently snpplied  as  KNJQ  in  amounts  varying  from 0.03 to 0.1 per  cent and  as MgS01.7Hz0 in  amounts from 0.01 to 0.05 pep cent.  The highest yields of  acid have nsnally been obtained from sucrose and fructose as the carbon source (3, 4, SG);  in some instances glucose appears  to serve about as well  (I#,  53).  Sugar concentrations of  15 to 20 per  cent are  necessary for high yields  of  citric  acid.  Kitragen  is supplied either  as ammonium salts or as nitrates.  In most cases  ammonium  nitrate  in concentrations  of  0.16  to  0.32 per cent has been reported  to give the higliest yields of acid. 柠檬酸工业英文文献和中文翻译(4):http://www.youerw.com/fanyi/lunwen_30316.html