Enhanced Lactic Acid Production by Adaptive Evolution of Lactobacillus paracasei on Agro-industrial Substrate

Exploitation of microbial activities at low pH to enhance planetary health

Awareness is growing that human health cannot be considered in isolation but is inextricably woven with the health of the environment in which we live. It is, however, under-recognized that the sustainability of human activities strongly relies on preserving the equilibrium of the microbial communities living in/on/around us. Microbial metabolic activities are instrumental for production, functionalization, processing, and preservation of food. For circular economy, microbial metabolism would be exploited to produce building blocks for the chemical industry, to achieve effective crop protection, agri-food waste revalorization, or biofuel production, as well as in bioremediation and bioaugmentation of contaminated areas. Low pH is undoubtedly a key physical-chemical parameter that needs to be considered for exploiting the powerful microbial metabolic arsenal. Deviation from optimal pH conditions has profound effects on shaping the microbial communities responsible for carrying out essential processes. Furthermore, novel strategies to combat contaminations and infections by pathogens rely on microbial-derived acidic molecules that suppress/inhibit their growth. Herein, we present the state-of-the-art of the knowledge on the impact of acidic pH in many applied areas and how this knowledge can guide us to use the immense arsenal of microbial metabolic activities for their more impactful exploitation in a Planetary Health perspective.

Potential and Restrictions of Food-Waste Valorization through Fermentation Processes

Food losses (FL) and waste (FW) occur throughout the food supply chain. These residues are disposed of on landfills producing environmental issues due to pollutants released into the air, water, and soil. Several research efforts have focused on upgrading FL and FW in a portfolio of added-value products and energy vectors. Among the most relevant research advances, biotechnological upgrading of these residues via fermentation has been demonstrated to be a potential valorization alternative. Despite the multiple investigations performed on the conversion of FL and FW, a lack of comprehensive and systematic literature reviews evaluating the potential of fermentative processes to upgrade different food residues has been identified. Therefore, this article reviews the use of FL and FW in fermentative processes considering the composition, operating conditions, platforms, fermentation product application, and restrictions. This review provides the framework of food residue fermentation based on reported applications, experimental, and theoretical data. Moreover, this review provides future research ideas based on the analyzed information. Thus, potential applications and restrictions of the FL and FW used for fermentative processes are highlighted. In the end, food residues fermentation must be considered a mandatory step toward waste minimization, a circular economy, and the development of more sustainable production and consumption patterns.

Potential of New Bacterial Strains for a Multiproduct Bioprocess Application: A Case Study Using Isolates of Lactic Acid Bacteria from Pineapple Silage of Costa Rican Agro-Industrial Residues

Lactic acid bacteria (LAB) with potential for the development of multi-product processes are necessary for the valorization of side streams obtained during the biotechnological production of lactic acid (LA). In this study, 14 LAB strains isolated from pineapple agro-industrial residues in Costa Rica were cultivated in microplates, and the six strains with the highest growth were selected for fermentation in microbioreactors to evaluate the production of LA and acetic acid, and the consumption of glucose. Lacticaseibacillus paracasei 6710 and L. paracasei 6714 presented the highest OD600 values (1.600 and 1.602, respectively); however, the highest LA (in g/L) production was observed in L. paracasei 6714 (14.50 ± 0.20) and 6712 (14.67 ± 0.42). L. paracasei 6714 was selected for bioreactor fermentation and reached a maximum OD600 of 6.3062 ± 0.141, with a LA yield of 84.9% and a productivity of 1.06 g L−1 h−1 after 21 h of fermentation. Finally, lipoteichoic acid (LTA) detection from biomass was performed and the antimicrobial activity of the compounds present in the supernatant was studied. LTA was detected from L. paracasei 6714 biomass, and its supernatant caused significant inhibition of foodborne surrogate microorganisms. LAB isolated from pineapple silage have biotechnological potential for multiproduct processes.

Enterococcus faecium s6 Enabled Efficient Homofermentative Lactic Acid Production from Xylan-Derived Sugars

A thermotolerant Enterococcus faecium s6 strain exhibited homoferementative lactic acid (LA) production at high xylose concentration (≥50 g/L). In batch fermentation at 45 °C and controlled pH of 6.5, strain E. faecium s6 produced up to 72.9 g/L of LA with a yield of 0.99 g/g-consumed xylose and productivity of 1.74 g/L.h from 75 g/L xylose. An increased LA concentration and productivities with high yields were obtained in repeated batch fermentation that was conducted for 24 runs. In this mode, the strain could produce LA up 81.1 g/L within 5 h fermentation at a high productivity of 13.5 g/L.h and a yield of 1.02 g/g-consumed xylose. The strain was unable to consume birchwood xylan as sole carbon source. However, it could efficiently utilize xylooligosaccharides of xylobiose, xylotriose, xylotetraose, xylopentaose, and xylohexaose. The intracellular xylosidase activity was induced by xylose. Using xylooligosaccharide (50 g/L)/xylose (5 g/L) mixtures, the strain was able to produce maximum LA at 48.2 g/L within 120 h at a yield of 1.0 g/g-consumed sugar and productivity of 0.331 g/L.h. These results indicate that E. faecium s6 is capable of directly utilizing xylan-hydrolyzate and will enable the development of a feasible and economical approach to the production of LA from hemicellulosic hydrolysate.

Recent Advances in Lactic Acid Production by Lactic Acid Bacteria

Lactic acid can synthesize high value-added chemicals such as poly lactic acid. In order to further minimize the cost of lactic acid production, some effective strategies (e.g., effective mutagenesis and metabolic engineering) have been applied to increase productive capacity of lactic acid bacteria. In addition, low-cost cheap raw materials (e.g., cheap carbon source and cheap nitrogen source) are also used to reduce the cost of lactic acid production. In this review, we summarized the recent developments in lactic acid production, including efficient strain modification technology (high-efficiency mutagenesis means, adaptive laboratory evolution, and metabolic engineering), the use of low-cost cheap raw materials, and also discussed the future prospects of this field, which could promote the development of lactic acid industry.

Adaptive laboratory evolution principles and applications in industrial biotechnology

Adaptive laboratory evolution (ALE) is an innovative approach for the generation of evolved microbial strains with desired characteristics, by implementing the rules of natural selection as presented in the Darwinian Theory, on the laboratory bench. New as it might be, it has already been used by several researchers for the amelioration of a variety of characteristics of widely used microorganisms in biotechnology. ALE is used as a tool for the deeper understanding of the genetic and/or metabolic pathways of evolution. Another important field targeted by ALE is the manufacturing of products of (high) added value, such as ethanol, butanol and lipids. In the current review, we discuss the basic principles and techniques of ALE, and then we focus on studies where it has been applied to bacteria, fungi and microalgae, aiming to improve their performance to biotechnological procedures and/or inspect the genetic background of evolution. We conclude that ALE is a promising and efficacious method that has already led to the acquisition of useful new microbiological strains in biotechnology and could possibly offer even more interesting results in the future.

Valorization of Vegetable Food Waste and By-Products Through Fermentation Processes

There is a general interest in finding new ways of valorizing fruit and vegetable processing by-products. With this aim, applications of industrial fermentation to improve nutritional value, or to produce biologically active compounds, have been developed. In this sense, the fermentation of a wide variety of by-products including rice, barley, soya, citrus, and milling by-products has been reported. This minireview gives an overview of recent fermentation-based valorization strategies developed in the last 2 years. To aid the designing of new bioprocesses of industrial interest, this minireview also provides a detailed comparison of the fermentation conditions needed to produce specific bioactive compounds through a simple artificial neural network model. Different applications reported have been focused on increasing the nutritional value of vegetable by-products, while several lactic acid bacteria and Penicillium species have been used to produce high purity lactic acid. Bacteria and fungi like Bacillus subtilis, Rhizopus oligosporus, or Fusarium flocciferum may be used to efficiently produce protein extracts with high biological value and a wide variety of functional carbohydrates and glycosidases have been produced employing Aspergillus, Yarrowia, and Trichoderma species. Fermentative patterns summarized may guide the production of functional ingredients for novel food formulation and the development of low-cost bioprocesses leading to a transition toward a bioeconomy model.

Evolutionary engineering of Lactobacillus bulgaricus reduces enzyme usage and enhances conversion of lignocellulosics to D-lactic acid by simultaneous saccharification and fermentation

BACKGROUND

Simultaneous saccharification and fermentation (SSF) of pre-treated lignocellulosics to biofuels and other platform chemicals has long been a promising alternative to separate hydrolysis and fermentation processes. However, the disparity between the optimum conditions (temperature, pH) for fermentation and enzyme hydrolysis leads to execution of the SSF process at sub-optimal conditions, which can affect the rate of hydrolysis and cellulose conversion. The fermentation conditions could be synchronized with hydrolysis optima by carrying out the SSF at a higher temperature, but this would require a thermo-tolerant organism. Economically viable production of platform chemicals from lignocellulosic biomass (LCB) has long been stymied because of the significantly higher cost of hydrolytic enzymes. The major objective of this work is to develop an SSF strategy for D-lactic acid (D-LA) production by a thermo-tolerant organism, in which the enzyme loading could significantly be reduced without compromising on the overall conversion.

RESULTS

A thermo-tolerant strain of Lactobacillus bulgaricus was developed by adaptive laboratory evolution (ALE) which enabled the SSF to be performed at 45 °C with reduced enzyme usage. Despite the reduction of enzyme loading from 15 Filter Paper Unit/g_LCB (FPU/g_LCB) to 5 FPU/g_LCB, we could still achieve ~ 8% higher cellulose to D-LA conversion in batch SSF, in comparison to the conversion by separate enzymatic hydrolysis and fermentation processes at 45 °C and pH 5.5. Extending the batch SSF to SSF with pulse-feeding of 5% pre-treated biomass and 5 FPU/g_LCB, at 12-h intervals (36th-96th h), resulted in a titer of 108 g/L D-LA and 60% conversion of cellulose to D-LA. This is one among the highest reported D-LA titers achieved from LCB.

CONCLUSIONS

We have demonstrated that the SSF strategy, in conjunction with evolutionary engineering, could drastically reduce enzyme requirement and be the way forward for economical production of platform chemicals from lignocellulosics. We have shown that fed-batch SSF processes, designed with multiple pulse-feedings of the pre-treated biomass and enzyme, can be an effective way of enhancing the product concentrations.

Integrated and Consolidated Review of Plastic Waste Management and Bio-Based Biodegradable Plastics: Challenges and Opportunities

Cumulative plastic production worldwide skyrocketed from about 2 million tonnes in 1950 to 8.3 billion tonnes in 2015, with 6.3 billion tonnes (76%) ending up as waste. Of that waste, 79% is either in landfills or the environment. The purpose of the review is to establish the current global status quo in the plastics industry and assess the sustainability of some bio-based biodegradable plastics. This integrative and consolidated review thus builds on previous studies that have focused either on one or a few of the aspects considered in this paper. Three broad items to strongly consider are: Biodegradable plastics and other alternatives are not always environmentally superior to fossil-based plastics; less investment has been made in plastic waste management than in plastics production; and there is no single solution to plastic waste management. Some strategies to push for include: increasing recycling rates, reclaiming plastic waste from the environment, and bans or using alternatives, which can lessen the negative impacts of fossil-based plastics. However, each one has its own challenges, and country-specific scientific evidence is necessary to justify any suggested solutions. In conclusion, governments from all countries and stakeholders should work to strengthen waste management infrastructure in low- and middle-income countries while extended producer responsibility (EPR) and deposit refund schemes (DPRs) are important add-ons to consider in plastic waste management, as they have been found to be effective in Australia, France, Germany, and Ecuador.

Lactic acid production - producing microorganisms and substrates sources-state of art

Lactic acid is an organic compound produced via fermentation by different microorganisms that are able to use different carbohydrate sources. Lactic acid bacteria are the main bacteria used to produce lactic acid and among these, Lactobacillus spp. have been showing interesting fermentation capacities. The use of Bacillus spp. revealed good possibilities to reduce the fermentative costs. Interestingly, lactic acid high productivity was achieved by Corynebacterium glutamicum and E. coli, mainly after engineering genetic modification. Fungi, like Rhizopus spp. can metabolize different renewable carbon resources, with advantageously amylolytic properties to produce lactic acid. Additionally, yeasts can tolerate environmental restrictions (for example acidic conditions), being the wild-type low lactic acid producers that have been improved by genetic manipulation. Microalgae and cyanobacteria, as photosynthetic microorganisms can be an alternative lactic acid producer without carbohydrate feed costs. For lactic acid production, it is necessary to have substrates in the fermentation medium. Different carbohydrate sources can be used, from plant waste as molasses, starchy, lignocellulosic materials as agricultural and forestry residues. Dairy waste also can be used by the addition of supplementary components with a nitrogen source.

Improvement and Metabolomics-Based Analysis of d-Lactic Acid Production from Agro-Industrial Wastes by Lactobacillus delbrueckii Submitted to Adaptive Laboratory Evolution

To decrease d-lactic acid production cost, sugarcane molasses and soybean meal, low-cost agro-industrial wastes, were selected as feedstock. First, sugarcane molasses was used directly by Lactobacillus delbrueckii S-NL31, and the nutrients were released from soybean meal by protease hydrolysis. Subsequently, to ensure intensive substrate utilization and enhanced d-lactic acid production from sugarcane molasses and soybean meal, adaptation of L. delbrueckii S-NL31 to substrates was performed through adaptive laboratory evolution. After two-phase adaptive laboratory evolution, the evolved strain L. delbrueckii S-NL31-CM3-SBM with improved cell growth and d-lactic acid production on sugarcane molasses and soybean meal was obtained. To decipher the potential reasons for improved fermentation performance, a metabolomics-based approach was developed to profile the differences of intracellular metabolism between initial and evolved strain. The in-depth analysis elucidated how the key factors exerted influence on d-lactic acid biosynthesis. The results revealed that the enhancement of glycolysis pathway and cofactor supply was directly associated with increased lactic acid production, and the reinforcement of pentose phosphate pathway, amino acid metabolism, and oleic acid uptake improved cell survival and growth. These might be the main reasons for significantly improved d-lactic acid production by adaptive laboratory evolution. Finally, fed-batch simultaneous enzymatic hydrolysis of soybean meal and fermentation process by evolved strain resulted in d-lactic acid levels of 112.3 g/L, with an average production efficiency of 2.4 g/(L × h), a yield of 0.98 g/g sugar, and optical purity of 99.6%. The results show the applicability of d-lactic acid production in L. delbrueckii fed on agro-industrial wastes through adaptive laboratory evolution.

A review on bioactive compounds of beet (Beta vulgaris L. subsp. vulgaris) with special emphasis on their beneficial effects on gut microbiota and gastrointestinal health

This review discusses the available literature concerning the bioactive compounds of beet (Beta vulgaris L.) and their ability to modulate the gut microbiota and parameters indicative of gastrointestinal health. Data of published literature characterize beet as a source of a variety of bioactive compounds (e.g. diet fiber, pectic-oligosaccharides, betalains and phenolics) with proven beneficial effects on human health. Beet extracts and pectin and pectic-oligosaccharides from beet have shown able to modulate positively gut microbiota composition and activity, with noticeable bifidogenic effects, in addition to stimulate the growth and metabolism of probiotics. Beet betalains and phenolics seem to increase the production of metabolites (e.g. short chain fatty acids) by gut microbiota and probiotics, which are linked with different beneficial effects on host health. The outstanding contents of betalains and phenolics with antioxidant, anti-inflammatory and anti-carcinogenic properties have been linked to the positive effects of beet on gastrointestinal health. Beet should be a healthy choice for use in domestic meal preparations and a source of ingredients to formulate added-value functionalized food products.

Non-thermal plasma and ultrasound-assisted open lactic acid fermentation of distillery stillage

Stillage is the main by-product of bioethanol production and the cost of its treatment significantly affects the economy of bioethanol production. A process of thermal sterilization before lactic acid fermentation (LAF) is energy demanding and is causing deterioration of valuable compounds in stillage. In this study, ultrasound (UT) and plasma (PT) treatments were used for microbial inactivation, and a significant reduction in the number of viable microorganisms in the stillage after PT and UT was observed. After application of treatment, LAF by Lactobacillus rhamnosus ATCC 7469 was initiated. The concentration of LA is used to quantify the efficiency of the stillage revalorization. The highest LA productivity of 1.21 g/Lh and yield of 0.82 g/g were obtained after PT, while UT of 10 min provided productivity of 1.02 g/Lh and LA yield of 0.69 g/g. The results were benchmarked against closed LAF. Around 20% better revalorization of stillage by PT was achieved when compared with conventional sterilization. In addition, an excellent L (+) LA stereoselectivity of 95.5% was attained after PT. From the aspect of energy efficiency, that of PT was three times lower than UT and almost ten times lower than thermal sterilization, but it is the most expensive due to the high consumption of gas which could reduce application of closed Ar atmosphere on larger scales. This way, a simpler and energy efficient process for LA production on stillage was accomplished by "open" fermentation.

Bioprocessing of agro-industrial residues into lactic acid and probiotic enriched livestock feed

BACKGROUND

Growing challenges of resource depletion, food security and environmental protection are putting stress on the development of biorefinery processes for bioprocessing of residues from food and agro-industry into value-added products. In this study, the simultaneous production of lactic acid (LA) and livestock feed on a combined substrate based on molasses and potato stillage by Lactobacillus paracasei NRRL B-4564 immobilized onto sunflower seed hull (SSH), brewer's spent grain (BSG) and sugar beet pulp (SBP) was studied.

RESULTS

The highest total LA concentration of 399 g L^-1 with overall productivity of 1.27 g L^-1  h^-1 was achieved in repeated batch fermentation by SBP-immobilized biocatalyst, followed by BSG- and SSH-immobilized cells. Fermentation improved the content of proteins and ash, and decreased the content of fibers in all three support materials. In addition, the fermentation had favorable effect on in vitro dry matter digestibility and energy values of SSH and BSG. According to assessment of probiotic potential, L. paracasei demonstrated a favorable probiotic profile, exhibiting high resistance to simulated ruminant digestive tract and significant antioxidant and antimicrobial activity.

CONCLUSIONS

The proposed strategy enables valorization of agro-industrial residues as value-added ruminant feed and simultaneous LA production. Following principles of circular economy, the developed process combines different raw materials and integrates them into a biorefinery process, improving the overall profitability and productivity. © 2019 Society of Chemical Industry.