L-(+)-Lactic Acid from Reed: Comparing Various Resources for the Nutrient Provision of B. coagulans

Linda Schroedter,Lisa Remus,Joachim Venus,Roland Schneider

doi:10.3390/resources9070089

Abstract

Biotechnological production of lactic acid (LA) is based on the so-called first generation feedstocks, meaning sugars derived from food and feed crops such as corn, sugarcane and cassava. The aim of this study was to exploit the potential of a second generation resource: Common reed (Phragmites australis) is a powerfully reproducing sweet grass which grows in wetlands and creates vast monocultural populations. This lignocellulose biomass bears the possibility to be refined to value-added products, without competing with agro industrial land. Besides utilizing reed as a renewable and inexpensive substrate, low-cost nutritional supplementation was analyzed for the fermentation of thermophilic Bacillus coagulans. Various nutritional sources such as baker’s and brewer’s yeast, lucerne green juice and tryptone were investigated for the replacement of yeast extract. The structure of the lignocellulosic material was tackled by chemical treatment (1% NaOH) and enzymatic hydrolysis (Cellic® CTec2). B. coagulans DSM ID 14-300 was employed for the homofermentative conversion of the released hexose and pentose sugars to polymerizable L-(+)-LA of over 99.5% optical purity. The addition of autolyzed baker’s yeast led to the best results of fermentation, enabling an LA titer of 28.3 g L−1 and a yield of 91.6%.

Highlights

Lactic acid (LA), or 2-hydroxy propionic acid, is considered to be one of the main chemical building blocks for enabling the transition to a sustainable bio-based economy [1,2]
Various substances were obtained to investigate their potential as nutrient source for the fermentation of B. coagulans 14-300: Yeast extract and tryptone (Carl Roth, Karlsruhe, Germany), peptone from soymeal and malt extract (Merck Millipore, Darmstadt, Germany), baker’s yeast (RUF, Quakenbrück, Germany), brewer’s yeast
Lignocellulose of the reed stems was analyzed according to the guidelines of the National Renewable Energy Laboratory (NREL) [31,32,33]

Summary

Introduction

Lactic acid (LA), or 2-hydroxy propionic acid, is considered to be one of the main chemical building blocks for enabling the transition to a sustainable bio-based economy [1,2]. Used in the food industry as preserver and mild acidifier, the applications for LA have broadened since its capacity to polymerize under certain conditions to polylactic acid (PLA) has been put to use [3]. Occurring in the two stereochemical forms L-(+) and D-(−), the L-LA is preferably used for the production of PLA [4]. PLA had been introduced for medical applications like bone fixation devices, stents or drug delivery systems, benefiting from L-LA’s compatibility with the human body [5]. With the decline of PLA’s competitive cost, its production for various industrial applications is on the rise. Various consumer goods packaging like bags, cups or bottles are already available on the market [4,6]

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Conclusion