Am.  jour.  Pharm.  \  Current  Literature.  a7 
January,  igio.    J  *t I 
CURRENT  LITERATURE.  ' 
SCIENTIFIC  AND  TECHNICAL  ABSTRACTS. 
Citric  Acid  Fermentation  of  Aspergillus  Niger. — In  the 
citric  acid  fermentation  of  sucrose  by  Aspergillus  nig er  the  myce- 
lium floats  on  the  surface  of  the  substratum  and  wrinkles  up  in 
such  a  manner  as  to  present  a  very  large  surface  of  contact.  These 
wrinkled  structures  often  project  5-6  Cm.  into  the  medium  and 
exhaustion  of  the  substratum  proceeds  under  very  favorable  cir- 
cumstances. By  a  judicious  selection  of  cultures  and  conditions  the 
yield  of  citric  acid  can  be  varied  from  nil  to  over  50  per  cent,  of 
the  sugar  consumed.  Conditions  especially  favorable  to  citric-acid 
formation  are  low  nitrogen  supply,  high  concentration  of  sugar,  and 
the  use  of  ammonium  salts  instead  of  nitrates.  As  regards  the  re- 
action of  the  medium,  the  hydrogen-ion  concentration  is  a  far  more 
important  factor  than  the  titratable  acidity.  For  a  given  hydrogen- 
ion  concentration  (pn)  a  mineral  acid,  such  as  hydrochloric,  is  less 
toxic  than  an  organic  acid.  The  addition  of  calcium  carbonate  is 
disadvantageous  rather  than  helpful ;  the  cultures  readily  produce  a 
solution  of  10  per  cent,  citric  acid  and  the  limiting  hydrogen-ion  con- 
centration is  exceptionally  high.  Fermentation  can  be  started  at  a 
hydrogen-ion  concentration,  which  will  greatly  reduce  the  chance 
of  infection  without  interfering  with  the  growth.  Higher  yields  in 
a  shorter  time  are  obtained  without  calcium  carbonate  than  with  it, 
as  the  carbonate  partially  precipitates  the  magnesium  and  phosphate 
nutrients;  moreover  the  formation  of  calcium  citrate  is  a  hindrance 
in  recovering  the  citric  acid.  It  is  possible  to  ferment  two  or  three 
batches  of  medium  in  succession  with  the  same  mycelial  felt  by 
draining  off  the  liquid  and  running  in  a  fresh  batch.  The  most 
suitable  medium  for  conducting  the  citric  acid  fermentation  has  the 
following  approximate  composition  per  liter:  Sucrose,  125-150 
Gms. ;  ammonium  nitrate,  2.0-2.5  5  potassium  dihydrogen  phosphate, 
0.75-1.0;  crystallized  magnesium  sulphate,  0.20-0.25  Gm. ;  hydro- 
chloric acid  to  ph  =  34-3.5  (5-4  Cc.  of  A/5  acid).  The  use  of  this 
quantity  of  hydrochloric  acid  makes  it  possible  to  sterilize  the  liquid 
completely  by  steaming  at  atmospheric  pressure  for  30  mins.  and 
prevents  subsequent  infection  without  interfering  with  the  fermenta- 
tion.   In  a  medium  of  this  nature  there  is  little  development  of 
