Influence of Nitrogen Sources on D-Lactic Acid Biosynthesis by Sporolactobacillus laevolacticus DSM 442 Strain

Alicja Katarzyna Michalczyk,Jerzy Zakrzewski,Sylwia Garbaczewska,Arkadiusz Białek,Bolesław Morytz

doi:10.3390/fermentation7020078

Alicja Katarzyna Michalczyk, Jerzy Zakrzewski + Show 3 more

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https://doi.org/10.3390/fermentation7020078

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Abstract

The purpose of this study was to explore the possibility of replacing an expensive yeast extract contained in the fermentation medium for D-lactic acid (D-LA, R-lactic acid) biosynthesis with an alternative nitrogen source. The screening studies were conducted under stationary conditions and showed that pea seed hydrolysate was the most beneficial substrate in the process of D-LA biosynthesis by the strain Sporolactobacillus laevolacticus DSM 442 among the used inorganic and organic nitrogen sources, waste materials, food and agricultural products. After 96 h, 75.5 g/L D-LA was obtained in batch cultures in a medium containing pea seed hydrolysate, with an average productivity of 0.79 g/L/h, yield of 75.5%, and optical purity of 99.4%. In batch cultures fed once, in a medium with an analogous composition, 122.6 g/L D-LA was obtained after 120 h, and the average yield, productivity and optical purity were 87.6%, 1.021 g/L/h, and 99.6%, respectively. Moreover, the amount of D-LA obtained in the fermentation medium enriched with the above-mentioned cheap agricultural product was similar to the amounts obtained in the medium containing yeast extract in both stationary and bioreactor cultures. Our research shows that hydrolyzed pea seeds, which belong to the legume family, may be a promising nitrogen source for the production of D-LA on an industrial scale.

Highlights

Lactic acid (LA) is an organic acid produced on an industrial scale
Both organic and inorganic sources of nitrogen can be used as substitutes for yeast extract in the D-LA biosynthesis process
Our research has shown that increasing the amount of nitrogen in the medium with pea hydrolysate did not significantly increase D-LA biosynthesis, which can considerably reduce the cost of the process

Summary

Introduction

Lactic acid (LA) is an organic acid produced on an industrial scale. Its production primarily involves the participation of microorganisms, mainly lactic acid bacteria. Numerous attempts have been made to improve the lactic fermentation process; these have focused mainly on improving the performance and reducing the costs of obtaining LA in biotechnological processes. This includes the selection of appropriate production strains, depending on the desired characteristics of the final fermentation product (L or D-LA isomer), or their improvement, e.g., through genetic engineering, and the use of low-cost, renewable, commonly available raw materials for low-cost processing and the production of LA [1,2,3,4,5,6,7,8,9,10]. Reducing the costs of LA production is important in the context of the growing demand for biodegradable plastics, especially polylactide (PLA: polymers synthesized from both D- as well as L-lactic acid), which is known as the material of the 21st century

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