Abstract

Research into fermentative production of lactic acid from agricultural by-products has recently concentrated on the direct conversion of biomass, whereby pure sugars are replaced with inexpensive feedstock in the process of lactic acid production. In our studies, for the first time, the source of carbon used is sugar beet pulp, generated as a by-product of industrial sugar production. In this paper, we focus on the simultaneous saccharification of lignocellulosic biomass and fermentation of lactic acid, using mixed cultures with complementary assimilation profiles. Lactic acid is one of the primary platform chemicals, and can be used to synthesize a wide variety of useful products, including green propylene glycol. A series of controlled batch fermentations was conducted under various conditions, including pretreatment with enzymatic hydrolysis. Inoculation was performed in two sequential stages, to avoid carbon catabolite repression. Biologically-synthesized lactic acid was catalytically reduced to propylene glycol over 5% Ru/C. The highest lactic acid yield was obtained with mixed cultures. The yield of propylene glycol from the biological lactic acid was similar to that obtained with a water solution of pure lactic acid. Our results show that simultaneous saccharification and fermentation enables generation of lactic acid, suitable for further chemical transformations, from agricultural residues.

Highlights

  • Lactic acid (2-hydroxypropionic or 2-hydroxypropanoic) is the most widely produced acid using biotechnological methods [1]

  • The aim of the present research was to increase the efficiency of the process of lactic acid biosynthesis, through attenuation of the arabinose and galactose present in the fermented sugar beet pulp hydrolyzates after processes conducted with lactic acid bacteria (LAB)

  • Lactic acid bacteria are able to assimilate most of the carbohydrates from the hydrolyzates

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Summary

Introduction

Lactic acid (2-hydroxypropionic or 2-hydroxypropanoic) is the most widely produced acid using biotechnological methods [1]. Research on the fermentative production of lactic acid from agricultural by-products has recently concentrated on the direct conversion of biomass. Inexpensive raw materials, such as starch or molasses, have been used to replace pure sugars in lactic acid production processes [3]. Lignocellulose, another carbohydrate source, is widely available and in large quantities. The carbon sources used in fermentative processes are Molecules 2016, 21, 1380; doi:10.3390/molecules21101380 www.mdpi.com/journal/molecules

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