З.1. Lactic Acid

Annual world lactic acid production in 2007 was 150,000 metric tons and the forecasted production for 2017 is expected to reach 367,300 metric tons [64]. Approximately 70% of the lactic acid produced is used in the food industry with the remainder being used in the cosmetic and pharmaceutical industries. A novel outlet is in the production of biodegradable plastics where lactic acid serves as precursor for polymers [60, 62].

Table 1. Summary of the types of lactose derivatives discussed in this chapter along with

their structures and applications

Name

Structure

Application

Ref

Lactic

acid

Dairy acid, preservative, flavor ingredient, biodegradable packaging, precursor for polymers and small chemicals

[62]

Lacto-

bionic

acid

Calcium fortification, cold storage organ transport

[59]

Lactulose

Prebiotic, laxative, alleviates chronic hepatic encephalopathy

[59]

Name

Structure

Application

Ref

Lacto-

sucrose

Prebiotic, calcium absorption

[59]

Tagatose

Low-calorie sweetener, toothpaste ingredient, ingredient in cosmetic and pharmaceutical industry

[63]

Lactitol

Laxative, low-calorie sweetener

[59]

Industrial production of lactic acid can be accomplished via chemical synthesis or by lactic acid fermentation [62, 65]. Currently, the latter is the primary production technique, accounting for 90% of lactic acid production [66]. Chemical synthesis requires harsh reaction conditions and a need for efficient cleaning procedures to reduce heavy metal catalysts [67]. Furthermore, chemical synthesis yields a racemic mixture of both L-(+)- and D-(-)-lactic acid. With appropriate microorganism selection, fermentation can produce either pure L- or D- lactic acid, a feature which is required for producing biodegradable plastics, where only L- (+)-lactic acid serves as precursor. Additional features of fermentation processes include the possibility of using milder reaction conditions and not using catalysts. In addition, inexpensive raw materials could be used as starting materials [67]. Despite the advantages of fermentation compared to chemical synthesis, which include low energy costs, some drawbacks include low productivity, low purity in the final product, and the formation of large quantities of gypsum as a byproduct [66, 68].

Raw materials containing either mono- or disaccharides and polymers such as starchy or lignocellulosic materials can be used for the fermentative production of lactic acid. A hydrolytic pretreatment of the polymeric material is required to yield fermentable sugars for the bacteria [62]. Whey permeate is therefore a promising raw material due to its high lactose content [67]. Depending on the microorganism chosen, whey permeate can be used as-is or after the hydrolysis of lactose by P-galactosidases. As all microorganisms have specific nutrient requirements which must be considered for bioprocess optimization, nutrients may need to be added [62, 69]. Various growth supplements have been investigated for lactic acid production from whey permeate due to its low nitrogen content [60, 70]. Adding readily available nitrogen sources like casein hydrolysate or ammonium citrate to whey permeate increased the lactic acid yield from 1.2g to 24.3g [70]. Although a purity of more than 98% was achieved, the addition of casein hydrolysate significantly increases processing costs. While the addition of nitrogen sources effectively sped up fermentation rate, adding complex matrices to an already complex food matrix, such as whey permeate make the isolation of small metabolites a very difficult task [71].

For both chemical and fermentative production, the lactic acid produced has to be further separated and purified. The isolation of small metabolites from whey permeate is challenged by the presence of naturally occurring contaminants such as minerals and peptides. Techniques such as nanofiltration, chromatography, and ion exchange are necessary to improve the purity of the recovered compounds. These steps have a significant impact on the overall process costs but are necessary to reach high yields and purities. Possible additional methods include reactive distillation followed by hydrolysis, crystallization or membrane technologies with bipolar membrane electrodialysis [62, 65, 72].

An innovative process has been validated using mathematical modeling where the fermentation broth was treated by ultrafiltration, followed by ion exchange, reverse osmosis and vacuum evaporation. The final product obtained by this procedure is 50% w/w lactic acid, which is comparable to commercial products available, but production costs are lower [73]. Research on lactic acid production from whey permeate on a large-scale is needed, and downstream processing must become cost-effective to become commercially viable.

 
Source
< Prev   CONTENTS   Source   Next >