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In line with the goals of sustainable development and environmental protection today great attention is directed towards new technologies for waste and industrial by-products utilization. Waste products represent potentially good raw material for production other valuable products, such as bioethanol, biogas, biodiesel, organic acids, enzymes, microbial biomass, etc. Since the first industrial production to the present, lactic acid has found wide application in food, cosmetic, pharmaceutical and chemical industries. In recent years, the demand for lactic acid has been increasing considerably owing to its potential use as a monomer for the production of poly-lactic acid (PLA) polymers which are biodegradable and biocompatible with wide applications. Waste and industrial by-products such are whey, molasses, stillage, waste starch and lignocellulosic materials are a good source of fermentable sugars and many other substances of great importance for the growth of microorganisms, such as proteins, minerals and vitamins. Utilization of waste products for production of lactic acid could help to reduce the total cost of lactic acid production and except the economic viability of the process offers a solution of their disposal. Fermentation process depends on chemical and physical nature of feedstocks and the lactic acid producer. This review describes the characteristics, abilities and limits of microorganisms involved in lactic acid production, as well as the characteristics and types of waste products for lactic acid production. The fermentation methods that have been recently reported to improve lactic acid production are summarized and compared. In order to improve processes and productivity, fed-batch fermentation, fermentation with immobilized cell systems and mixed cultures and opportunities of open (non-sterilized) fermentation have been investigated.

BACKGROUND Utilization of wastes and industrial by-products for production of valuable bio-based chemicals has economic and environmental advantages. The aim of this study was to investigate utilization of two industrial by-products, distillery stillage and sugar beet molasses combined as a substrate for lactic acid and biomass production. A selection of the most appropriate lactic acid bacteria that could effectively utilize this waste substrate was performed. In addition, the effect of initial sugar concentration on lactic acid production and growth of lactic acid bacteria on the combined waste substrate was evaluated. RESULTS Lactobacillus paracasei NRRL B-4564 was selected as the most promising for lactic acid production on distillery stillage and sugar beet molasses. The highest lactic acid productivity of 1.42 g L−1 h−1 and yield of 0.91 g g−1 were achieved on stillage/molasses media at initial sugar concentration of 56.74 g L−1. The highest number of L. paracasei cells at 5.3 × 109 CFU mL−1 was achieved at initial sugar concentration of 78.22 g L−1. CONCLUSION Combined distillery stillage and sugar beet molasses could provide valuable nutrients for growth of fastidious lactic acid bacteria and enable efficient lactic acid production, while processing industrial waste in this way has great environmental relevance. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

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