Lactic
acid is an organic acid with a wide range of applications in the food,
pharmaceutical and cosmetics industries. It has recently been studied with
great interest as a biodegradable poly lactic acid (PLA) that can be used to
improve physical properties in the production of food packaging, plastic
utensils, garbage bags and agricultural plastic sheeting, thereby replacing products made from petroleum.
Lactic
acid can be obtained either by the action of fermentative microorganisms or
chemical synthesis
The
fermentation process has the advantage of being more cost effective.
Approximately 90% of all lactic acid worldwide is produced by bacterial
fermentation
Lactic
acid bacteria are traditionally fastidious microorganisms and have complex
nutrient requirements due to their limited ability to biosynthesize B-vitamins
and amino acids Refined sugars, such as glucose or sucrose, have been used more
frequently as a carbon source to produce lactic acid than raw starchy
substrates, such as barley, corn, or wheat Furthermore, a considerable amount
of an expensive complex nitrogen source, such as yeast extract, must be added
to the medium in order to produce lactic acid within a reasonable timeframe.
However, this is economically unfavourable.
According
to Tejayadi and Cheryan (1995), raw materials account for 68% of the overall cost
of lactic acid production from whey and yeast extract using Lactobacillus bulgaricus.
A
number of industrial by-products or wastes have been evaluated as substrates
for lactic acid production with the aim of decreasing the cost of the process,
such as sugarcane, molasses and whey as carbon sources and CSL (Bustos et al.,
2004) as a nitrogen source.
CSL
is an excellent source of nitrogen for most microorganisms due to its high
concentration of amino acids and polypeptides, with considerable amounts of
B-complex vitamins Sugarcane molasses is an industrial by-product of sugar and
alcohol processing and is rich in fermentable sugars (Lima et al., 1975), nitrogen
and vitamins.
This
substrate is inexpensive and highly available in Brazil, with an annual production
of 17.9 million tons during the sugar manufacturing process.
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