Microbial production of d‐lactic acid from dried distiller's grains with solubles

Abstract

d‐Lactic acid production is gaining increasing attention due to the thermostable properties of its polymer, poly‐d‐lactic acid . In this study, Lactobacillus coryniformis subsp. torquens, was evaluated for its ability to produce d‐lactic acid using Dried Distiller's Grains with Solubles (DDGS) hydrolysate as the substrate. DDGS was first subjected to alkaline pretreatment with sodium hydroxide to remove the hemicellulose component and the generated carbohydrate‐rich solids were then subjected to enzymatic hydrolysis using cellulase mixture Accellerase® 1500. When comparing separate hydrolysis and fermentation and simultaneous saccharification and fermentation (SSF) of L. coryniformis on DDGS hydrolysate, the latter method demonstrated higher d‐lactic acid production (27.9 g/L, 99.9% optical purity of d‐lactic acid), with a higher glucose to d‐lactic acid conversion yield (84.5%) compared to the former one (24.1 g/L, 99.9% optical purity of d‐lactic acid). In addition, the effect of increasing the DDGS concentration in the fermentation system was investigated via a fed‐batch SSF approach, where it was shown that the d‐lactic acid production increased to 38.1 g/L and the conversion yield decreased to 70%. In conclusion, the SSF approach proved to be an efficient strategy for the production of d‐lactic acid from DDGS as it reduced the overall processing time and yielded high d‐lactic acid concentrations.

Purification and polymerisation of microbial d-lactic acid from DDGS hydrolysates fermentation

“…Dried Distillers Grains with Solubles (DDGS) was supplied from a bioethanol plant (Vivergo, Yorkshire, UK) and was alkaline pretreated as described by Zaini et al [28]. Alkaline treated DDGS consisted of 52.6 g glucose, 25.0 g xylose, 10.3 g arabinose, and 0.04 g protein per 100 g of dried material.…”

“…D-lactic acid was produced by L. coryniformis subsp. torquens (DSM 20004) using a Simultaneous Saccharification and Fermentation (SSF) process of alkaline treated DDGS in a 2 L stirred tank bioreactor (Biostat B, Sartorious, Germany) [28]. The process was initiated by the simultaneous addition of Accellerase® 1500 (1 ml enzyme : 0.33 g cellulose) and L.…”

“…hydrolysate [28]. Subsequently, the purified D-lactic acid was used as monomer for PDLA synthesis by employing an azeotropic polycondensation approach.…”

Physicochemical properties and application in film preparation of prolamin from distiller's grains

“…In addition, their high acidity is easy to cause environmental pollution. At present, distiller's grains are mainly consumed as cheap animal feed, which produces very low economic benefits (Zaini et al ., 2019). Therefore, how to improve the comprehensive utilisation and increase the added value of distiller's grains is a great challenge for the spirits industry.…”

Feasibility of exhausted sugar beet pulp as raw material for lactic acid production

“… However, to achieve high lactic acid yields (g lactic acid per g sugar), SSF carried out in fed‐batch mode is demonstrated to be the preferred strategy. Thus, fed batch SSF has been efficiently applied to obtain second‐generation lactic acid from a vast range of raw material such as NaOH‐pretreated corn stover, ethylenediamine pretreated rice straw, alkaline pretreated dried distiller's grains or cheese whey powder, amongst others . All of these studies demonstrated that the SSF approach resulted in faster and higher production of d ‐lactic acid compared to conventional SHF.…”