Lactic Acid Production

Lactic acid production

the lactic acid was discovered by Scelle in 1780 .

Microorganism used in lactic acid production

Mostly two types of microorganism used in lactic acid production are hetero fermentative and homo fermentative

Hetero fermentative

The microorganisms which are used in the fermentative production mainly give products are lactic acid and sometimes trace amount of carbon dioxide ,ethanol, acetic acid and few other products.

Homo fermentative microorganisms

Commercially lactic acid production utilise is homo fermentative strains of lactic acid bacteria which produce only trace amounts of end products other than lactic acid.

The common bacteria for industrial production of lactic acids are

Lactobacillus delbrueckii:

it acts on substrate corn dextrose media.

L.bulgaricus : It acts on substrate whey media.

L.pentosus : It acts on substrate sulphide waste liquor

other bacteria use for lactic acid productions are L. casei and Streptococcus lactis

Medium and raw materials used:

In united state lactic acid is commercially produced from media containing semi refined corn, sugar molasses or whey.

While in other countries potato starch is used which required preliminary hydrolysis and other carbon substrate.

Media composition

A typical medium contains 10 to 15% dextrose 10% calcium carbonate and small amount of nitrogenous substrate such as Malt sprouts.

Calcium carbonate is employed to neutralise the lactic acid bacteria as it is produced because the lactic acid bacteria do not tolerate high concentration of acid the merged sprout and other nitrogenous substrate supplies the growth factor.

Production and fermentation

lactic acid fermentation is carried out in tanks made up of wood or lined with stainless steel because other materials cannot with stand the corrosive nature of lactic acid

Inoculum

5% Lactobacillus delbrueckii is mainly used as inoculum.

Temperature

The optimum temperature for lactic acid production is 45 to 50 degrees Celsius but the initial temperature is lower that is 30 degrees Celsius but if fermentation Organism is Lactobacillus pentoses or orL.casei or Streptococcus the pH should be 5.5 to 6.5

Agitation

medium is not aerated but agitation is employed to keep the calcium carbonate in suspension.

so that it will react with lactic acid as it is produced due to fermentation fermentation completed within six days or less depending upon amount of time required by microorganism to deplete the sugar of medium the resulting lactic acid yield 80 to 90% waste on sugar But fermentation yield 93 to 94% conversion of sugar to lactic acid.

There is no contamination when strains of Lactobacillus delbrueckii is used during fermentation because of high incubation temperature.

Fermentation process

it involves the following steps

• Continuous fermentation

continues lactic acid fermentation have been practiced to a limited extent on commercial scale but these fermentation encounter difficulty because the residual sugar in the partly fermented medium as withdrawn during continuous fermentation hinders recovery of lactic acid

• Extraction and recovery

at harvest additional calcium carbonate is added to the medium but pH is set to 10 the fermentation broth is then heated and filtered after this all the lactic acid converted to calcium lactate

Recovery and purification method

lactic acid is mainly purified by precipitation method in this method heated and filtered growth is concentrated to allow crystallization of calcium lactate followed by edition of sulfuric acid from acidilators to remove the calcium as calcium sulfate

the lactic acid is then recrystallised as calcium lactate and activated by charcoal or carbon to remove coloured impurities.

The lactic acid is solid in various commercial grades the grade of lactic acid is coloured edible and marked 50 to 80% strength