Production of D-lactic acid by Lactobacillus delbrueckii ssp. delbrueckii from orange peel waste: techno-economical assessment of nitrogen sources

High cell density continuous fermentation for L-lactic acid production from cane molasses

Commercial production of lactic acid (LA) utilizes mostly glucose or lactose coupled with yeast extract (YE) as a supplement. With sugars, nitrogen, and vitamin supplementation being most of the LA production costs, the use of inexpensive molasses, a by-product of the sugar industry, can provide considerable cost savings. There are just a few publications on the production of LA from molasses; consequently, the present investigation was conducted using molasses supplemented with yeast extract. The research was done in a continuous-flow, high-cell-density (HCD) bioreactor with an external membrane microfiltration device for cell recycling. The system, run at 1 L with Lactobacillus delbrueckii NCIM 2025, produced a LA yield of 0.95-0.98 g/g from ∼100 g sugars/L when supplemented with 1 g/L YE. Dilution rates in the range of 0.04-0.36 h-1 resulted in volumetric lactic acid productivities in the range of 4.3-27.6 g/L h, which compares favorably with the highest values recorded in literature, for glucose in the presence of YE, which was as high as 30 g/L. The utilization of cane molasses has a significant impact on the economics of lactic acid production, as measured by a comparison of costs with commercial glucose.

Recent Advances and Outlook in 2D Nanomaterial-Based Flame-Retardant PLA Materials

Poly (lactic acid) or polylactide (PLA) has gained widespread use in many industries and has become a commodity polymer. Its potential as a perfect replacement for petrochemically made plastics has been constrained by its extreme flammability and propensity to flow in a fire. Traditional flame-retardants (FRs), such as organo-halogen chemicals, can be added to PLA without significantly affecting the material's mechanical properties. However, the restricted usage of these substances causes them to bioaccumulate and endanger plants and animals. Research on PLA flame-retardants has mostly concentrated on organic and inorganic substances for the past few years. Meanwhile, there has been a significant increase in renewed interest in creating environmentally acceptable flame-retardants for PLA to maintain the integrity of the polymer, which is the current trend. This article reviews recent advancements in novel FRs for PLA. The emphasis is on two-dimensional (2D) nanosystems and the composites made from them that have been used to develop PLA nanocomposite (NCP) systems that are flame retarding. The association between FR loadings and efficiency for different FR-PLA systems is also briefly discussed in the paper, as well as their influence on processing and other material attributes. It is unmistakably established from the literature that adding 2D nanoparticles to PLA matrix systems reduces their flammability by forming an intumescent char/carbonized surface layer. This creates a barrier effect that successfully blocks the filtration of volatiles and oxygen, heat and mass transfer, and the release of combustible gases produced during combustion.

Microbial Synthesis of Lactic Acid from Cotton Stalk for Polylactic Acid Production

Cotton stalk, a waste product in agriculture, serves as a beneficial, low-cost material as a medium for microbial synthesis of lactic acid as desired for polylactic acid synthesis. Cotton stalk was used as a substrate for microbial lactic acid synthesis, and a novel strain of Lactococcus cremoris was reported to synthesize 51.4 g/L lactic acid using cellulose recovered from the cotton stalk. In total, 18 Lactobacillus isolates were isolated from kitchen waste, soil, sugarcane waste, and raw milk samples screened for maximum lactic acid production. It was found that one of the Lactococcus cremoris isolates was found to synthesize maximum lactic acid at a concentration of 51.4 g/L lactic acid in the hydrolysate prepared from cotton stalk. The upstream process parameters included 10% inoculum size, hydrolysate containing reducing sugars 74.23 g/L, temperature 37 °C, agitation 220 rpm, production age 24 h. Only the racemic (50:50) mixture of D-LA and L-LA (i.e., D/L-LA) is produced during the chemical synthesis of lactic acid, which is undesirable for the food, beverage, pharmaceutical, and biomedical industries because only the L-form is digestible and is not suitable for biopolymer, i.e., PLA-based industry where high optically purified lactic acid is required. Furthermore, polylactic acid was synthesized through direct polycondensation methods using various catalysts such as chitosan, YSZ, and Sb2O3. PLA is biocompatible and biodegradable in nature (its blends and biocomposites), supporting a low-carbon and circular bioeconomy.

Valorization of orange peels exploiting fungal solid-state and lacto-fermentation

BACKGROUND

Orange peels can serve as a cost-effective raw material for the production of lactic acid. Indeed, given their high concentration of carbohydrates and low content of lignin, they represent an important source of fermentable sugars, recoverable after a hydrolytic step.

RESULTS

In the present article, the fermented solid, obtained after 5 days of Aspergillus awamori growth, was used as the only source of enzymes, mainly composed of xylanase (40.6 IU g^-1 of dried washed orange peels) and exo-polygalacturonase (16.3 IU g^-1 of dried washed orange peels) activities. After the hydrolysis, the highest concentration of reducing sugars (24.4 g L^-1 ) was achieved with 20% fermented and 80% non-fermented orange peels. The hydrolysate was fermented with three lactic acid bacteria strains (Lacticaseibacillus casei 2246 and 2240 and Lacticaseibacillus rhamnosus 1019) which demonstrated good growth ability. The yeast extract supplementation increased the lactic acid production rate and yield. Overall, L. casei 2246 produced the highest concentration of lactic acid in mono-culture.

CONCLUSION

To the best of our knowledge this is the first study exploiting orange peels as low-cost raw material for the production of lactic acid avoiding the employment of commercial enzymes. The enzymes necessary for the hydrolyses were directly produced during A. awamori fermentation and the reducing sugars obtained were fermented for lactic acid production. Despite this preliminary work carried out to study the feasibility of this approach, the concentrations of reducing sugars and lactic acid produced were encouraging, leaving open the possibility of other studies for the optimization of the strategy proposed here. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Towards efficient production of highly optically pure d-lactic acid from lignocellulosic hydrolysates using newly isolated lactic acid bacteria

This study presents the production of D-lactic acid with high enantiomeric purity using lignocellulosic hydrolysates from newly isolated lactic acid bacterial (LAB) strains. Six strains, 4 heterofermentative and 2 homofermentative, were investigated for their ability to grow and produce lactic acid on sugar beet pulp (SBP) hydrolysates, containing a mixture of hexose and pentose sugars. Among the strains tested, three were isolates designated as A250, A257 and A15, all of which belonged to the genus Leuconostoc. Only strain A250 could be reliably identified as Leuconostoc pseudomesenteroides based on cluster analysis of Maldi-ToF spectra. All strains produced D-lactic acid in the presence of SBP hydrolysates, but with varying optical purities. The homofermentative strains achieved higher D-lactic acid optical purities, but without assimilating the pentose sugars. Co-cultivation of the homofermentative strain Lactobacillus coryniformis subsp. torquens DSM 20005 together with the heterofermentative isolate A250 led to the production of 21.7 g/L D-lactic acid with 99.3 % optical purity. This strategy enabled the complete sugar utilization of the substrate. Nanofiltration of the SBP hydrolysate enhanced the enantiomeric purity of the D-lactic acid produced from the isolates A250 and A15 by about 5 %. The highest D-lactic acid concentration (40 g/L) was achieved in fed-batch cultures of A250 isolate with nanofiltered SBP, where optical purity was 99.4 %. The results of this study underline the feasibility of a novel isolate as an efficient D-lactic acid producer using lignocellulosic hydrolysates.

An Overview on Wood Waste Valorization as Biopolymers and Biocomposites: Definition, Classification, Production, Properties and Applications

Bio-based polymers, obtained from natural biomass, are nowadays considered good candidates for the replacement of traditional fossil-derived plastics. The need for substituting traditional synthetic plastics is mainly driven by many concerns about their detrimental effects on the environment and human health. The most innovative way to produce bioplastics involves the use of raw materials derived from wastes. Raw materials are of vital importance for human and animal health and due to their economic and environmental benefits. Among these, wood waste is gaining popularity as an innovative raw material for biopolymer manufacturing. On the other hand, the use of wastes as a source to produce biopolymers and biocomposites is still under development and the processing methods are currently being studied in order to reach a high reproducibility and thus increase the yield of production. This study therefore aimed to cover the current developments in the classification, manufacturing, performances and fields of application of bio-based polymers, especially focusing on wood waste sources. The work was carried out using both a descriptive and an analytical methodology: first, a description of the state of art as it exists at present was reported, then the available information was analyzed to make a critical evaluation of the results. A second way to employ wood scraps involves their use as bio-reinforcements for composites; therefore, the increase in the mechanical response obtained by the addition of wood waste in different bio-based matrices was explored in this work. Results showed an increase in Young's modulus up to 9 GPa for wood-reinforced PLA and up to 6 GPa for wood-reinforced PHA.

New efficient meta-fermentation process for lactic acid production from municipal solid waste

BACKGROUND

The global market for lactic acid is witnessing growth on the back of increasing applications of lactic acid for manufacturing polylactic acid. Indeed, the lactic acid market is expected to reach 9.8 billion US dollars by 2025. The new concept of meta-fermentation has been proposed in recent years as an alternative to fermentation with pure cultures, due to multiple advantages such as lower susceptibility to contamination, no need for sterilization of culture media or lower raw material costs. However, there are still challenges to overcome to increase the conversion efficiency, decrease formation of by-products and facilitate fermentation control. In this context, the purpose of the study was to develop a robust meta-fermentation process to efficiently produce lactic acid from the OFMSW, stable at pre-industrial scale (1500 L). To maximize lactic acid production, operating conditions (pH, HRT) were modified, and a novel bioaugmentation strategy was tested.

RESULTS

A LAB-rich inoculum was generated with LAB isolated from the digestate and grown in the laboratory with MRS medium. After feeding this inoculum to the digester (bioaugmentation), lactic acid accumulation up to 41.5 gO2/L was achieved under optimal operating conditions. This corresponds to more than 70% of the filtered COD measured in the digestate. The amount of lactic acid produced was higher than the volatile fatty acids under all feeding strategies applied.

CONCLUSIONS

The operating conditions that enhanced the production of lactic acid from mixed cultures were 55ºC, 2 days HRT and pH 4.8-5.7, with pH-control once a day. The bioaugmentation strategy improved the results obtained in the prototype without applying reinoculation. Lactic acid was the main product along with other carboxylic acids. Further improvements are needed to increase purity as well as lactic acid concentration to reach economic feasibility of the whole process (digestion of OFMSW and downstream).

D-Lactic acid production from agricultural residues by membrane integrated continuous fermentation coupled with B vitamin supplementation

Background

d-Lactic acid played an important role in the establishment of PLA as a substitute for petrochemical plastics. But, so far, the d-lactic acid production was limited in only pilot scale, which was definitely unable to meet the fast growing market demand. To achieve industrial scale d-lactic acid production, the cost-associated problems such as high-cost feedstock, expensive nutrient sources and fermentation technology need to be resolved to establish an economical fermentation process.

Results

In the present study, the combined effect of B vitamin supplementation and membrane integrated continuous fermentation on d-lactic acid production from agricultural lignocellulosic biomass by Lactobacillus delbrueckii was investigated. The results indicated the specific addition of vitamins B₁, B₂, B₃ and B₅ (VB₁, VB₂, VB₃ and VB₅) could reduce the yeast extract (YE) addition from 10 to 3 g/l without obvious influence on fermentation efficiency. By employing cell recycling system in 350 h continuous fermentation with B vitamin supplementation, YE addition was further reduced to 0.5 g/l, which resulted in nutrient source cost reduction of 86%. A maximum d-lactate productivity of 18.56 g/l/h and optical purity of 99.5% were achieved and higher than most recent reports.

Conclusion

These findings suggested the novel fermentation strategy proposed could effectively reduce the production cost and improve fermentation efficiency, thus exhibiting great potential in promoting industrial scale d-lactic acid production from lignocellulosic biomass.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02124-y.

High d-lactic acid productivity is achieved by L. delbrueckii from rice straw.

B vitamins are satisfied substitute of yeast extract for d-lactic acid fermentation.

A process of membrane-integrated continuous fermentation with B vitamin is developed.

High fermentation efficiency is achieved by the novel fermentation process.

Repurposing anaerobic digestate for economical biomanufacturing and water recovery

Due to mounting impacts of climate change, particularly increased incidence of drought, hence water scarcity, it has become imperative to develop new technologies for recovering water from nutrient-rich, water-replete effluents other than sewage. Notably, anaerobic digestate could be harnessed for the purpose of water recovery by repurposing digestate-borne minerals as nutrients in fermentative processes. The high concentrations of ammonium, phosphate, sulfate, and metals in anaerobic digestate are veritable microbial nutrients that could be harnessed for bio-production of bulk and specialty chemicals. Tethering nutrient sequestration from anaerobic digestate to bio-product accumulation offers promise for concomitant water recovery, bio-chemical production, and possible phosphate recovery. In this review, we explore the potential of anaerobic digestate as a nutrient source and as a buffering agent in fermentative production of glutamine, glutamate, fumarate, lactate, and succinate. Additionally, we discuss the potential of synthetic biology as a tool for enhancing nutrient removal from anaerobic digestate and for expanding the range of products derivable from digestate-based fermentations. Strategies that harness the nutrients in anaerobic digestate with bio-product accumulation and water recovery could have far-reaching implications on sustainable management of nutrient-rich manure, tannery, and fish processing effluents that also contain high amounts of water. KEY POINTS: • Anaerobic digestate may serve as a source of nutrients in fermentation. • Use of digestate in fermentation would lead to the recovery of valuable water.

Production of Fumaric Acid by Rhizopus arrhizus NRRL 1526: A Simple Production Medium and the Kinetic Modelling of the Bioprocess

Fumaric acid is a promising monomer to obtain biomass-based polyesters and polyamides, and it is mainly produced by fungi of the Rhizopus genus in medium to high titters. The use of glucose, a main component of starchy and cellulosic food waste, as carbon source, together with a low-nitrogen source concentration, is a promising route to reduce process costs. In this work, the effects of nitrogen and carbonate sources on Rhizopus arrhizus NRRL 1526 morphology and fumaric acid productivity were analysed, simplifying the traditional production broth composition. Moreover, a non-structured, non-segregated kinetic model was proposed and fitted to concentration data of all relevant components obtained in batches performed in triplicate with the selected production broth at 34 °C and 200 rpm in an orbital shaker.

L-Lactate oxidase-mediated removal of L-lactic acid derived from fermentation medium for the production of optically pure D-lactic acid

BACKGROUND

There has been an increasing demand for optically pure D-lactic and L-lactic acid for the production of stereocomplex-type polylactic acid. The D-lactic acid production from lignocellulosic biomass is important owing to its great abundance in nature. Corn steep liquor (CSL) is a cheap nitrogen source used for industrial fermentation, though it contains a significant amount of L-lactic acid, which decreases the optical purity of D-lactic acid produced.

METHOD AND RESULTS

To remove L-lactic acid derived from the CSL-based medium, L-lactate oxidase (LoxL) from Enterococcus sp. NBRC 3427 was expressed in an engineered Lactiplantibacillus plantarum (formally called Lactobacillus plantarum) strain KOLP7, which exclusively produces D-lactic acid from both hexose and pentose sugars. When the resulting strain was applied for D-lactic acid fermentation from the mixed sugars consisting of the major constituent sugars of lignocellulose (35 g/L glucose, 10 g/L xylose, and 5 g/L arabinose) using the medium containing 10 g/L CSL, it completely removed L-lactic acid derived from CSL (0.52 g/L) and produced 41.7 g/L of D-lactic acid. The L-lactic acid concentration was below the detection limit, and improvement in the optical purity of D-lactic acid was observed (from 98.2% to > 99.99%) by the overexpression of LoxL.

CONCLUSION AND IMPLICATIONS

The LoxL-mediated consumption of L-lactic acid would enable the production of optically pure D-lactic acid in any medium contaminated by L-lactic acid. This article is protected by copyright. All rights reserved.

Valorization of municipal organic waste into purified lactic acid

Municipal organic waste (biowaste) consists of food derived starch, protein and sugars, and lignocellulose derived cellulose, hemicellulose, lignin and pectin. Proper management enables nutrient recycling and sustainable production of platform chemicals such as lactic acid (LA). This review gathers the most important information regarding use of biowaste for LA fermentation covering pre-treatment, enzymatic hydrolysis, fermentation and downstream processing to achieve high purity LA. The optimal approach was found to treat the two biowaste fractions separately due to different pre-treatment and enzyme needs for achieving enzymatic hydrolysis and to do continues fermentation to achieve high cell density and high LA productivity up to 12 g/L/h for production of both L and D isomers. The specific productivity was 0.4 to 0.5 h^-1 but with recalcitrant biomass, the enzymatic hydrolysis was rate limiting. Novel purification approaches included reactive distillation and emulsion liquid membrane separation yielding purities sufficient for polylactic acid production.

Bioproduction of l- and d-lactic acids: advances and trends in microbial strain application and engineering

Lactic acid is an important platform chemical used in the food, agriculture, cosmetic, pharmaceutical, and chemical industries. It serves as a building block for the production of polylactic acid (PLA), a biodegradable polymer, which can replace traditional petroleum-based plastics and help to reduce environmental pollution. Cost-effective production of optically pure l- and d-lactic acids is necessary to achieve a quality and thermostable PLA product. This paper evaluates research advances in the bioproduction of l- and d-lactic acids using microbial fermentation. Special emphasis is given to the development of metabolically engineered microbial strains and processes tailored to alternative and flexible feedstock concepts such as: lignocellulose, glycerol, C1-gases, and agricultural-food industry byproducts. Alternative fermentation concepts that can improve lactic acid production are discussed. The potential use of inducible gene expression systems for the development of biosensors to facilitate the screening and engineering of lactic acid-producing microorganisms is discussed.

Valorisation of fungal hydrolysates of exhausted sugar beet pulp for lactic acid production

BACKGROUND

Exhausted sugar beet pulp pellets (ESBPP) were used as raw material for lactic acid (LA) fermentation. The enzymatic hydrolysis of ESBPP was performed with the solid obtained after the fungal solid-state fermentation of ESBPP as a source of hydrolytic enzymes. Subsequently, a medium rich in glucose and arabinose was obtained, which was used to produce LA by fermentation. For LA production, two Lactobacillus strains were assayed and the effects of the supplementation of the hydrolysate with a nitrogen source and the mode of pH regulation of the fermentation were investigated. Moreover, a kinetic model for LA fermentation by Lactobacillus plantarum of ESBPP hydrolysates was developed.

RESULTS

L. plantarum produced a LA concentration 34% higher than that produced by L. casei. The highest LA concentration (30 g L^-1 ) was obtained with L. plantarum when the hydrolysate was supplemented with 5 g L^-1 yeast extract and the pH was controlled with CaCO₃ . The concentration of acetic acid differed depending on the concentration of CaCO₃ added, producing its maximum value with 27 g L^-1 CaCO₃ . The proposed kinetic model was able to predict the evolution of substrates and products depending on the variation of the pH in the hydrolysate, according to the amount of CaCO₃ added.

CONCLUSIONS

ESBPP can be revalorised to produce LA. A pure LA stream or a mixture of LA and acetic acid, depending on the pH control method of the fermentation, can be produced. Thus, this control is of great interest depending on the destination of the effluent. © 2020 Society of Chemical Industry.

Enhancement of biohydrogen production rate in Rhodospirillum rubrum by a dynamic CO-feeding strategy using dark fermentation

BACKGROUND

Rhodospirillum rubrum is a purple non-sulphur bacterium that produces H₂ by photofermentation of several organic compounds or by water gas-shift reaction during CO fermentation. Successful strategies for both processes have been developed in light-dependent systems. This work explores a dark fermentation bioprocess for H₂ production from water using CO as the electron donor.

RESULTS

The study of the influence of the stirring and the initial CO partial pressure (p_CO) demonstrated that the process was inhibited at p_CO of 1.00 atm. Optimal p_CO value was established in 0.60 atm. CO dose adaptation to bacterial growth in fed-batch fermentations increased the global rate of H₂ production, yielding 27.2 mmol H₂ l^-1 h^-1 and reduced by 50% the operation time. A kinetic model was proposed to describe the evolution of the molecular species involved in gas and liquid phases in a wide range of p_CO conditions from 0.10 to 1.00 atm.

CONCLUSIONS

Dark fermentation in R. rubrum expands the ways to produce biohydrogen from CO. This work optimizes this bioprocess at lab-bioreactor scale studying the influence of the stirring speed, the initial CO partial pressure and the operation in batch and fed-batch regimes. Dynamic CO supply adapted to the biomass growth enhances the productivity reached in darkness by other strategies described in the literature, being similar to that obtained under light continuous syngas fermentations. The kinetic model proposed describes all the conditions tested.

Monomers, Materials and Energy from Coffee By-Products: A Review

In recent years, the circular economy and sustainability have gained attention in the food industry aimed at recycling food industrial waste and residues. For example, several plant-based materials are nowadays used in packaging and biofuel production. Among them, by-products and waste from coffee processing constitute a largely available, low cost, good quality resource. Coffee production includes many steps, in which by-products are generated including coffee pulp, coffee husks, silver skin and spent coffee. This review aims to analyze the reasons why coffee waste can be considered as a valuable source in recycling strategies for the sustainable production of bio-based chemicals, materials and fuels. It addresses the most recent advances in monomer, polymer and plastic filler productions and applications based on the development of viable biorefinery technologies. The exploration of strategies to unlock the potential of this biomass for fuel productions is also revised. Coffee by-products valorization is a clear example of waste biorefinery. Future applications in areas such as biomedicine, food packaging and material technology should be taken into consideration. However, further efforts in techno-economic analysis and the assessment of the feasibility of valorization processes on an industrial scale are needed.

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

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.

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

BACKGROUND

Exhausted sugar beet pulp pellets (ESBPP), a sugar industry by-product generated after sugar extraction in the sugar production process, have been used as a raw material for lactic acid (LA) production via hydrolysis and fermentation by Lactobacillus casei. To design a more cost-effective process, simultaneous saccharification and fermentation (SSF) of ESBPP is proposed in the present study. The effects of pH control, nutrient supplementation and solid addition in fed-batch SSF on lactic acid production were investigated.

RESULTS

The highest LA concentration (26.88 g L^-1 ) was reached in fed-batch SSF at a solid/liquid loading of 0.2 g mL^-1 , with pH control (by adding 30 g L^-1 CaCO₃ to the medium) and nutrient supplementation (by adding 20 mL of MRS medium per 100 mL of buffer). Under these conditions, a maximum productivity of 0.63 g L^-1 h^-1 was achieved, which is 2.7 times higher than that attained in the control experiment (SSF inoculated at time 0 h). However, a slightly lower LA yield was obtained, revealing the need of an increasing dose of enzymes at high solid loading SSF.

CONCLUSION

An efficient fed-batch SSF strategy with pH control and MRS supplementation is described in the present study, attaining higher LA productivity compared to separate hydrolysis and fermentation and SSF. © 2020 Society of Chemical Industry.

Production of D-Lactic Acid by the Fermentation of Orange Peel Waste Hydrolysate by Lactic Acid Bacteria

Lactic acid is one the most interesting monomer candidates to replace some petroleum- based monomers. The application of conventional poly-lactic acid (PLA) is limited due to insufficient thermal properties. This limitation can be overcome by blending poly-D and poly-L-lactic acid. The main problem is the limited knowledge of D-lactic acid (D-LA) production. Efficient biochemical processes are being developed in order to synthesize D-LA from orange peel waste (OPW). OPW is an interesting renewable raw material for biorefinery processes of biocatalytic, catalytic or thermal nature owing to its low lignin and ash content. Bioprocessing of the pretreated OPW is carried out by enzymatic hydrolysis and fermentation of the released sugars to produce D-LA. Several strains of the species Lactobacillus delbrueckii ssp. bulgaricus have been evaluated for the production of D-LA from OPW hydrolysate using Lactobacillus delbrueckii ssp. delbrueckii CECT 286 as a reference strain since its performance in this kind of substrate have been widely reported in previous studies. Preliminary results show that Lactobacillus delbrueckii ssp. bulgaricus CECT 5037 had the best performance with a yield of 84% w/w for D-LA production and up to 95% (e.e.).

Transcriptome Mechanism of Utilizing Corn Steep Liquor as the Sole Nitrogen Resource for Lipid and DHA Biosynthesis in Marine Oleaginous Protist Aurantiochytrium sp

In the current study, corn steep liquor (CSL) is evaluated as an ideal raw agro-material for efficient lipid and docosahexaenoic acid DHA production by Aurantiochytrium sp. Low CSL level in medium (nitrogen deficiency) stimulated the biosynthesis of lipids and DHA while inhibiting cellular growth. The transcriptomic profiles of the Aurantiochytrium sp. cells are analyzed and compared when cultured under high (H group), normal (N group), and low (L group) levels of CSL in the medium. The discriminated transcriptomic profiles from the three groups indicates that changes in CSL level in medium result in a global change in transcriptome of Aurantiochytrium sp. The overall de novo assembly of cDNA sequence data generated 61,163 unigenes, and 18,129 of them were annotated in at least one database. A total of 5105 differently expressed (DE) genes were found in the N group versus the H group, with 2218 downregulated and 2887 upregulated. A total of 3625 DE genes were found in the N group versus the L group, with 1904 downregulated and 1721 upregulated. The analysis and categorization of the DE genes indicates that the regulation mechanism of CSL involved in the perception and transduction of the limited nitrogen signal, the interactions between the transcription factors (TFs) and multiple downstream genes, and the variations in downstream genes and metabolites, in sequence, are illuminated for the first time in the current study.

Steps Toward High-Performance PLA: Economical Production of d-Lactate Enabled by a Newly Isolated Sporolactobacillus terrae Strain

Optically pure d-lactate production has received much attention for its critical role in high-performance polylactic acid production. However, the current technology can hardly meet the comprehensive demand of industrialization on final titer, productivity, optical purity, and raw material costs. Here, an efficient d-lactate producer strain, Sporolactobacillus terrae (S. terrae) HKM-1, is isolated for d-lactate production. The strain HKM-1 shows extremely high d-lactate fermentative capability by using peanut meal, soybean meal, or corn steep liquor powder as a sole nitrogen source; the final titers (205.7 g L-1 , 218.9 g L-1 , and 193.9 g L-1 , respectively) and productivities (5.56 g L-1  h-1 , 5.34 g L-1  h-1 , and 3.73 g L-1  h-1 , respectively) of d-lactate reached the highest level ever reported. A comparative genomic analysis between S. terrae HKM-1 and previously reported d-lactate high-producing Sporolactobacillus inulinus (S. inulinus) CASD is conducted. The results show that many unrelated genetic features may contribute to the superior performance in d-lactate production of S. terrae HKM-1. This d-lactate producer HKM-1, along with its fermentation process, is promising for sustainable d-lactate production by using agro-industrial wastes.

Simultaneous Bioconversion of Gelatinized Starchy Waste from the Rice Noodle Manufacturing Process to Lactic Acid and Maltose-Forming α-Amylase by Lactobacillus plantarum S21, Using a Low-Cost Medium

A direct bioconversion of gelatinized starchy waste (GSW) to lactic acid by amylolytic lactic acid bacterium Lactobacillus plantarum S21 was investigated. Corn steep liquor (CSL) was selected as the most suitable low-cost nitrogen source for replacing yeast extract, beef extract, and peptone in De Man, Rogosa and Sharpe (MRS) medium. Plackett–Burman design results indicated that GSW and CSL were the two most nutrients that significantly influence lactic acid production, among eight medium components, including GSW, CSL, K2HPO4, CH3COONa, (NH4)2HC6H5O7, MgSO4, MnSO4, and Tween 80. A new low-cost medium containing only GSW (134.4 g/L) and CSL (187.7 g/L) was achieved as omitting other six components from the optimized medium had no effect on lactic acid yield. Batch fermentation at 37 °C both in 1 L and 10 L jar fermenters showed non-significantly different productivity. A by-product, maltose-forming α-amylase, was successfully achieved up to 96% recovery yield using an ultrafiltration unit equipped with a 50 kDa cut-off membrane. Crude lactic acid exhibited the additional benefit of antimicrobial activity against food and feed pathogens Salmonella enterica serovar Typhimurium TISTR 292, Vibrio cholerae TH-001, and also E. coli ATCC 25922. This study presents a promising bioprocess for the simultaneous production of lactic acid, and a value-added food enzyme, using only two industrial wastes, GSW and CSL, as the medium components.

Electrolyzing lactic acid in situ in fermentation broth to produce pyruvic acid in electrolysis cell

Pyruvic acid is an important chemical in the carboxylate platform. Obstacles for its implementation are the need for high energy in chemical synthesis and additives in fermentation leading to increased production costs. Here, pyruvic acid generation from direct conversion of lactic acid in fermentation broth by electrolysis method is presented. It was found that lactic acid could be converted to pyruvic acid in the electrolysis cell under alkaline conditions. Using 12.53 g/L lactic acid fermentation broth as anolyte, 7.01 g/L pyruvic acid could be produced and productivity to lactic acid was 57.66% at initial pH 11.74 and 5.0 V applied a voltage in the electrolysis cell. Meanwhile, 0.472 mol hydrogen was produced at the cathode. The electric energy efficiency was 76.18%. Lactic acid fermentation is relatively cheap and can be performed on many kinds of wastes and biomasses. The results suggest that pyruvic acid production from direct electrolysis of lactic acid fermentation broth can be economically feasible.

Recent Advances in d-Lactic Acid Production from Renewable Resources: Case Studies on Agro-Industrial Waste Streams

The production of biodegradable polymers as alternatives to petroleum-based plastics has gained significant attention in the past years. To this end, polylactic acid (PLA) constitutes a promising alternative, finding various applications from food packaging to pharmaceuticals. Recent studies have shown that d-lactic acid plays a vital role in the production of heat-resistant PLA. At the same time, the utilization of renewable resources is imperative in order to decrease the production cost. This review aims to provide a synopsis of the current state of the art regarding d-lactic acid production via fermentation, focusing on the exploitation of waste and byproduct streams. An overview of potential downstream separation schemes is also given. Additionally, three case studies are presented and discussed, reporting the obtained results utilizing acid whey, coffee mucilage and hydrolysate from rice husks as alternative feedstocks for d-lactic acid production.