New trends and challenges in lactic acid production on renewable biomass

Abstract

Lactic acid is a relatively cheap chemical with a wide range of applications: as a preservative and acidifying agent in food and dairy industry, a monomer for biodegradable poly-lactide polymers (PLA) in pharmaceutical industry, precursor and chemical feedstock for chemical, textile and leather industries. Traditional raw materials for fermentative production of lactic acid, refined sugars, are now being replaced with starch from corn, rice and other crops for industrial production, with a tendency for utilization of agro-industrial wastes. Processes based on renewable waste sources have ecological (zero CO2 emission, eco-friendly byproducts) and economical (cheap raw materials, reduction of storage costs) advantages. An intensive research interest has been recently devoted to develop and improve the lactic acid production on more complex industrial by-products, like thin stillage from bioethanol production, corncobs, paper waste, straw etc. Complex and variable chemical composition and purity of these raw materials and high nutritional requirements of lacid acid bacteria (LAB) are the main obstacles in these production processes. Media supplementation to improve the fermentation is an important factor, especially from an economic point of view. Today, a particular challenge is to increase the productivity of lactic acid production on complex renewable biomass. Several strategies are currently being explored for this purpose such as process integration, use of LAB with amylolytic activity, employment of mixed cultures of LAB and/or utilization of genetically engineered microorganisms. Modern techniques of genetic engineering enable construction of microorganisms with desired characteristics and implementation of single step processes without or with minimal pre-treatment. In addition, new bioreactor constructions (such as membrane bioreactors), utilization of immobilized systems are also being explored. Electrodialysis, bipolar membrane separation process, enhanced filtration techniques etc., can provide some progress in purification technologies, although it is still remaining the most expensive phase in the lactic acid production. A new approach of parallel production of lactic bacteria biomass with probiotic activity and lactic acid could provide additional benefit and profit rise in the production process.

Potražnja za mlečnom kiselinom beleži snažan rast u poslednjoj deceniji, prvenstveno zbog razvoja biodegradabilnih polimera na bazi mlečne kiseline i njene primene u prehrambenoj, farmaceutskoj i drugim industrijama. Savremena proizvodnja mlečne kiseline se zasniva na principima održivosti, ekonomske i ekološke povoljnosti u biotehnološkim postupcima na obnovljivim i otpadnim poljoprivrednim sirovinama. U ovom radu su razmatrane mogućnosti fermentativne proizvodnje mlečne kiseline na različitim obnovljivim sirovinama, sa detaljnijom analizom mogućnosti korišćenja tečne džibre kao sirovine. Poseban izazov je povećati produktivnost proizvodnje na obnovljivim sirovinama korišćenjem novih tipova bioreaktora, bakterija mlečne kiseline (BMK) sa amilolitičkom aktivnošću, mešovitih kultura BMK ili pak genetički modifikovanih mikroorganizama. Primena novih tehnoloških rešenja koja uključuju integraciju određenih tehnoloških faza ili procesa, primenu imobilisanih sistema kao i uporednu proizvodnju mlečne kiseline i probiotske biomase je razmatrana u ovom radu.