إنتاج وتنقية حامض اللاكتيك من خلايا مقيّدة لبكتريا Lactobacillus المعزولة محلياً

Production and Purification of Lactic Acid from Immobilized Lactobacillus Local Isolates

The present study included the isolation and identification of  Lactobacillus from different sources in addition to investigate their abilities    in lactic acid production .The study also used the cell immobilization technique  for the efficient isolates , lactic acid was purified from the immobilized  cell .the results revealed the following :

• Twenty bacterial isolates belonged to the  genus of  Lactobacillus  were  obtained  from different  sources included raw milk , pickles , rural dairy, whey and yoghurt . The above  isolates ( in addition to three isolates belong to the same genus obtained from College of Veterinary / Baghdad University and one  isolate  of  Lactobacillus acidophilus  obtained  from College of  Agriculture / Baghdad University ) were subjected to a screening  program  to test their  abilities for lactic acid production  using different incubation  conditions . Results showed that acidophilus and  Lactobacillus sp. (25) were the higher producer isolates and chosed to be used for further studies .

• The optimum cultural conditions for the production of lactic acid  from L. acidophilus and Lactobacillus  (25) were studied . Highest production of lactic acid was obtained  by using date juice (6 and 8) % (reducing  sugars) for the two isolates , respectively supplemented with  0.7 % yeast extract and  1 % calcium carbonate , adjusted to pH  6.5  ; inoculated with cells at inoculums size (4)% and incubated in static conditions  at 37 °C  for( 60 and 48) hours to the two mentioned isolates , respectively .

• Cells of acidophilus and Lactobacillus sp. (25) were immobilized using entrapment method with two different supports . Results showed that agar – agar was more efficient in lactic acid production in compare with sodium alginate . Factors affect cells immobilization were studied and the results showed  that (3)%  agar – agar as a support with (1×10⁹) cell / ml gave the highest production of lactic acid .

• Some of the optimal conditions for lactic acid production from the  immobilized cells of acidophilus and Lactobacillus sp.(25) were studied . The results revealed the following :

• The best date juice concentration and yeast extract for lactic acid production were (4 and 0.3)% for both isolates , respectively .

• The optimal incubation periods for lactic acid production were (60 and 72) hours for acidophilus and Lactobacillus sp. (25), respectively.

• The immobilized cells for both isolates were stable during five repeated cycles and no acid production loss was observed during the studied periods.

• Lactic acid was isolated from culture filtrate of  acidophilus and Lactobacillus sp.(25) . The isolation procedure included Clarification step, Ion exchange with anionic exchanger ( Amberlite  IR- 400) and Ion exchange with cationic exchanger ]Amberlite IR 120- (H)[. Lactic acid yield obtained were (88.75 and 91.56)% for the above mentioned isolates , respectively .

• Purified lactic acid from both isolates used in this study showed a single spot when separated in thin layer chromatography with an R_f value of (0.535 and 0.541) for the acids purified from acidophilus and lactobacillus  sp. (25) , respectively .
• Results showed the absence of plasmids in both Lactobacillus isolates used in this study indicating that the genes responsible for the production of lactic acid are chromosomally located .