Lactic acid production from co-fermentation of food waste and spent mushroom substance with Aspergillus niger cellulase

Status and development of spent mushroom substrate recycling: A review

The edible mushroom industry is the sixth largest after grain, cotton, oil, vegetables and fruits, and the annual production of edible mushrooms in China exceeds 40 million tons. Edible mushroom cultivation produces a class of by-products consisting mainly of mycelium remnants and lignocellulosic waste, known as Spent Mushroom Substrate (SMS) or Spent Mushroom Compost (SMC). SMS/SMC is rich in nutrients and active ingredients and has an extremely high recycling potential. This review paper summarizes SMS recycling strategies from the perspectives of "environmental remediation" and "circular economy", and briefly discusses the legitimacy, possible challenges and future research of SMS recycling. It is hoped that this will assist researchers in related fields and promote the development of the SMS recycling industry, thereby contributing to sustainable environmental and economic development.Implications: The efficient management of SMS is important for many countries around the world, particularly major mushroom producing countries. Traditional disposal methods (incineration, burial, piling) can cause serious damage to the environment and waste resources. The correct disposal method can protect the natural environment and provide certain economic benefits. This study presents the main methods of SMS processing from both an "environmental remediation" and "circular economy" perspective. In general, this paper emphasizes the importance of SMS processing, introduces the current mainstream processing methods and briefly discusses the legality of their processing methods.

An overview on the current status and future prospects in Aspergillus cellulase production

Cellulase is a new research point besides glucoamylase, amylase, and protease in the enzyme industry. Cellulase can decompose lignocellulosic biomass into small-molecule sugars, which facilitates microbial utilization; thus, it has a vast market potential in the field of feed, food, energy, and chemistry. The Aspergillus was the first strain used in cellulase preparation because of its safety and non-toxicity, strong growth ability, and high enzyme yield. This review provides the latest research and advances on preparing cellulase from Aspergillus. The metabolic mechanisms of cellulase secretion by Aspergillus, the selection of fermentation substrates, the comparison of the fermentation modes, and the effect of fermentation conditions have been discussed in this review. Also, the subsequent separation and purification techniques of Aspergillus cellulase, including salting out, organic solvent precipitation, ultrafiltration, and chromatography, have been declared. Further, bottlenecks in Aspergillus cellulase preparation and corresponding feasible approaches, such as genetic engineering, mixed culture, and cellulase immobilization, have also been proposed in this review. This paper provides theoretical support for the efficient production and application of Aspergillus cellulase.

Electrochemical promotion of organic waste fermentation: Research advances and prospects

The current methods of treating organic waste suffer from limited resource usage and low product value. Research and development of value-added products emerges as an unavoidable trend for future growth. Electro-fermentation (EF) is a technique employed to stimulate cell proliferation, expedite microbial metabolism, and enhance the production of value-added products by administering minute voltages or currents in the fermentation system. This method represents a novel research direction lying at the crossroads of electrochemistry and biology. This article documents the current progress of EF for a range of value-added products, including gaseous fuels, organic acids, and other organics. It also presents novel value-added products, such as 1,3-propanediol, 3-hydroxypropionic acid, succinic acid, acrylic acid, and lysine. The latest research trends suggest a focus on EF for cogeneration of value-added products, studying microbial community structure and electroactive bacteria, exploring electron transfer mechanisms in EF systems, developing effective methods for nutrient recovery of nitrogen and phosphorus, optimizing EF conditions, and utilizing biosensors and artificial neural networks in this area. In this paper, an analysis is conducted on the challenges that currently exist regarding the selection of conductive materials, optimization of electrode materials, and development of bioelectrochemical system (BES) coupling processes in EF systems. The aim is to provide a reference for the development of more efficient, advanced, and value-added EF technologies. Overall, this paper aims to provide references and ideas for the development of more efficient and advanced EF technology.

Bioconversion of spray corn husks into L-lactic acid with liquid hot water pretreatment

Agricultural by-products like rice husk, bran, and spray corn husks, often utilized as feed, are considered less desirable. This study aims to enhance the utilization rate of these materials by subjecting then to liquid hot water (LHW) pretreatment, followed by enzymatic hydrolysis to produce fermentable sugars. We investigated the production of L-lactic acid using two methods: simultaneous saccharification fermentation (SSF) and separate hydrolysis fermentation (SHF), following varying intensities of LHW pretreatment. The results showed that the optimal enzymatic hydrolysis efficiency was achieved from spray corn husks under the pretreatment conditions of 155 °C and 15 min. SHF was generally more effective than SSF. The glucose L-lactic acid conversion rate in SHF using spray corn husks can reach more than 90 %. Overall, this work proposed a novel, environmental-friendly strategy for efficient and for L- lactic acid production from spray corn husks.

Metagenomic characterization of the cecal microbiota community and functions in finishing pigs fed fermented Boehmeria nivea

Ramie (Boehmeria nivea, BN) is used as livestock forage through suitable silage fermentation owing to its nutritional value. To date, relatively few studies have investigated the effects of dietary fermented BN (FBN) on gut health in finishing pigs. The aim of the present study was to investigate the effects of dietary supplementation with 20% FBN on intestinal morphology, gene expression, and the functional response of the gut microbiota in finishing pigs. We found that FBN did not significantly affect serum antioxidant enzyme activities, ileal morphology, or the expression of genes encoding antioxidant enzymes, inflammatory cytokines, or tight junction proteins in the liver of the pigs. However, the gene expression levels of aryl hydrocarbon receptor (AHR) and interleukin 6 (IL6) were significantly downregulated in the ileum. A metagenomic analysis demonstrated that, compared with that seen in the control group, the cecal microbiota of pigs in the FBN treatment group was more closely clustered and contained a greater number of unique microbes. Bacteria were the predominant kingdom in the cecal microbiota, while Firmicutes, Bacteroidetes, and Proteobacteria were the dominant phyla, and Streptococcus, Lactobacillus, and Prevotella were the dominant genera. Dietary FBN significantly increased the abundance of the probiotic bacterium Roseburia inulinivorans (p < 0.05). Functional analysis of the cecal microbiota showed that ABC transporter levels and glycolysis/gluconeogenesis-associated functions were diminished in FBN-fed pigs. Meanwhile, CAZyme analysis revealed that dietary FBN significantly downregulated the contents of carbohydrate-active enzymes, such as GT2, GH1, GH25, and GH13_31. In addition, cytochrome P450 analysis revealed that the abundance of CYP51 and CYP512 decreased with FBN treatment. An assessment of antibiotic resistance based on the Comprehensive Antibiotic Resistance Database (CARD) annotation indicated that the cecal microbes from pigs in the FBN treatment group had increased resistance to lincosamide, streptogramin, and chloramphenicol and reduced resistance to amikacin, isepamicin, neomycin, lividomycin, gentamicin, paromomycin, ribostamycin, and butirosin. Finally, virulence factor-related analysis showed that putative hemolysin-associated functions were decreased, whereas fibronectin-binding protein, flagella, and alginate-associated functions were increased. Taken together, our data showed that FBN supplementation exerted only minor effects on intestinal morphology and microbial community composition, suggesting that it is potentially safe for use as a supplement in the diets of finishing pigs. However, more studies are needed to validate its functionality.

Anaerobic fermentation of organic solid waste: Recent updates in substrates, products, and the process with multiple products co-production

The effective conversion and recycling of organic solid waste contribute to the resolution of widespread issues such as global environmental pollution, energy scarcity and resource depletion. The anaerobic fermentation technology provides for the effective treatment of organic solid waste and the generation of various products. The analysis, which is based on bibliometrics, concentrates on the valorisation of affordable and easily accessible raw materials with high organic matter content as well as the production of clean energy substances and high value-added platform products. The processing and application status of fermentation raw materials such as waste activated sludge, food waste, microalgae and crude glycerol are investigated. To analyse the status of the preparation and engineering applications of the products, the fermentation products biohydrogen, VFAs, biogas, ethanol, succinic acid, lactic acid, and butanol are employed as representatives. Simultaneously, the anaerobic biorefinery process with multiple product co-production is sorted out. Product co-production can reduce waste discharge, enhance resource recovery efficiency, and serve as a model for improving anaerobic fermentation economics.

Biosynthesis, Spectrophotometric Follow-Up, Characterization, and Variable Antimicrobial Activities of Ag Nanoparticles Prepared by Edible Macrofungi

The biosynthesis of silver nanoparticles (Ag NPs) could play a significant role in the development of commercial antimicrobials. Herein, the biosynthesis of Ag NPs was studied using the edible mushroom Pleurotus floridanus, and following its formation, spectrophotometry was used to detect the best mushroom content, pH, temperature, and silver concentration. After that, the morphology was described via transmission electron microscopy (TEM), and nanoscale-size particles were found ranging from 11 to 13 nm. The best conditions of Ag content and pH were found at 1.0 mM and 11.0, respectively. In addition, the best mushroom extract concentration was found at 30 g/L. According to XRD analysis, the crystal structure of the formed amorphous Ag NPs is cubic with a space group of fm-3m and a space group number of 225. After that, the function groups at the surface of the prepared Ag NPs were studied via FTIR analysis, which indicated the presence of C=O, C-H, and O-H groups. These groups could indicate the presence of mushroom traces in the Ag NPs, which was confirmed via the amorphous characteristics of Ag NPs from the XRD analysis. The prepared Ag NPs have a high impact against different microorganisms, which could be attributed to the ability of Ag NPs to penetrate the cell bacterial wall.

Efficient production of lactic acid from cellulose and xylan in sugarcane bagasse by newly isolated Lactiplantibacillus plantarum and Levilactobacillus brevis through simultaneous saccharification and co-fermentation process

Sugarcane bagasse is one of the promising lignocellulosic feedstocks for bio-based chemicals production. However, to date, most research focuses mainly on the cellulose conversion process, while hemicellulose remains largely underutilized. The conversion of glucose and xylose derived from lignocellulosic biomass can be a promising strategy to improve utilization efficiencies of resources, energy, and water, and at the same time reduce wastes generated from the process. Here, attempts were made to convert cellulose and xylan in sugarcane bagasse (SB) into lactic acid (LA) through a pre-hydrolysis and simultaneous saccharification and co-fermentation (SScF) process using newly isolated Lactiplantibacillus plantarum TSKKU P-8 and Levilactobacillus brevis CHKKU N-6. The process yielded 91.9 g/L of LA, with a volumetric productivity of 0.85 g/(L·h). This was equivalent to 137.8 ± 3.4 g-LA, a yield on substrate (pretreated SB) of 0.86 g/g, and a productivity of 1.28 g/h, based on a final volume of 1.5 L. On the other hand, pre-hydrolysis and simultaneous saccharification and fermentation (SSF) process using La. plantarum TSKKU P-8 as a monoculture gave 86.7 ± 0.2 g/L of LA and a volumetric productivity of 0.8 g/(L·h), which were equivalent to 104.8 ± 0.3 g-LA, a yield on substrate of 0.65 g/g, and a productivity of 0.97 g/h, based on a final volume of 1.2 L. Mass balance calculated based on mass of raw SB entering the process showed that the SScF process improved the product yield by 32% as compared with SSF process, resulting in 14% improvement in medium-based economic yield.

Improving lactic acid yield of hemicellulose from garden garbage through pretreatment of a high solid loading coupled with semi-hydrolysis using low enzyme loading

Byproduct (acetate and ethanol) generation and carbon catabolite repression are two critical impediments to lactic acid production from the hemicellulose of lignocellulosic biomass. To reduce byproduct generations, acid pretreatment with high solid loading (solid-liquid ratio 1:7) of garden garbage was conducted. The byproduct yield was only 0.30 g/g during in the subsequent lactic acid fermentation from acid pretreatment liquid and 40.8% lower than that of low solid loading (0.48 g/g). Furthermore, semi-hydrolysis with low enzyme loading (10 FPU/g garden garbage cellulase) was conducted to regulate and reduce glucose concentration in the hydrolysate, thereby relieving carbon catabolite repression. During the lactic acid fermentation process, the xylose conversion rate was restored from 48.2% (glucose-oriented hydrolysis) to 85.7%, eventually achieving a 0.49 g/g lactic acid yield of hemicellulose. Additionally, RNA-seq revealed that semi-hydrolysis with low enzyme loading down-regulated the expression of ptsH and ccpA, thereby relieving carbon catabolite repression.

The dissolution of polysaccharides and amino acids enhanced lactic acid production from household food waste during pretreatment process

A large amount of household food waste (HFW) is produced yearly, resulting in environmental problems and financial burdens. Bio-production of lactic acid (LA), a high value-added platform chemical, from HFW by anaerobic fermentation is a promising way of resource recovery. However, the LA production yield from HFW is low. This paper compared several pretreatment methods (hydrothermal pretreatment, chemical pretreatment, and combined hydrothermal and chemical pretreatment) to improve LA production from HFW. The result showed that the combined pretreatment (alkali-thermal pretreatment at pH 10 and 120 °C) significantly increased the LA production than single hydrothermal and chemical pretreatment. The pretreatment process promoted the dissolution of organics, especially the polysaccharides and amino acids, and further influenced the LA production by Lactobacillus rhamnosus ATCC 7469. Among the amino acids, aspartic acid (Asp), threonine (Thr), glutamic acid (Glu), glycine (Gly), alanine (Ala), cystine (Cys), valine (Val), isoleucine (Ile), arginine (Arg), and proline (Pro) significantly correlated with LA concentration.

Spent Mushroom Substrate Hydrolysis and Utilization as Potential Alternative Feedstock for Anaerobic Co-Digestion

Valorization of lignocellulosic biomass, such as Spent Mushroom Substrate (SMS), as an alternative substrate for biogas production could meet the increasing demand for energy. In view of this, the present study aimed at the biotechnological valorization of SMS for biogas production. In the first part of the study, two SMS chemical pretreatment processes were investigated and subsequently combined with thermal treatment of the mentioned waste streams. The acidic chemical hydrolysate derived from the hydrothermal treatment, which yielded in the highest concentration of free sugars (≈36 g/100 g dry SMS, hydrolysis yield ≈75% w/w of holocellulose), was used as a potential feedstock for biomethane production in a laboratory bench-scale improvised digester, and 52 L biogas/kg of volatile solids (VS) containing 65% methane were produced in a 15-day trial of anaerobic digestion. As regards the alkaline hydrolysate, it was like a pulp due to the lignocellulosic matrix disruption, without releasing additional sugars, and the biogas production was delayed for several days. The biogas yield value was 37 L/kg VS, and the methane content was 62%. Based on these results, it can be concluded that SMS can be valorized as an alternative medium employed for anaerobic digestion when pretreated with both chemical and hydrothermal hydrolysis.

Recent achievements in platform chemical production from food waste

Food waste conversion/valorization to produce bio-based chemicals plays a key role toward achieving carbon neutrality by 2050. Food waste valorization to renewable chemicals is thus an attractive and eco-friendly approach to handling food waste. The production of platform chemicals from food waste is crucial for making highly value-added renewable chemicals. However, earlier reviews dealing with food waste valorization to produce value-added chemicals have emphasized the enhancement of methane, hydrogen, and ethanol production. Along these lines, the existing methods of food waste to produce platform chemicals (e.g., volatile fatty acids, glucose, hydroxymethylfurfural, levulinic acid, lactic acid, and succinic acid) through physical, chemical, and enzymatic pretreatments, hydrolysis, fermentation, and hydrothermal conversion are extensively reviewed. Finally, the challenges faced under these methods are discussed, along with suggestions for future research on platform chemical production from food waste.

Emerging challenges for the agro-industrial food waste utilization: A review on food waste biorefinery

Modernization and industrialization has undoubtedly revolutionized the food and agro-industrial sector leading to the drastic increase in their productivity and marketing thereby accelerating the amount of agro-industrial food waste generated. In the past few decades the potential of these agro-industrial food waste to serve as bio refineries for the extraction of commercially viable products like organic acids, biochemical and biofuels was largely discussed and explored over the conventional method of disposing in landfills. The sustainable development of such strategies largely depends on understanding the techno economic challenges and planning for future strategies to overcome these hurdles. This review work presents a comprehensive outlook on the complex nature of agro-industrial food waste and pretreatment methods for their valorization into commercially viable products along with the challenges in the commercialization of food waste bio refineries that need critical attention to popularize the concept of circular bio economy.

Direct lactic acid production from household food waste by lactic acid bacteria

China is vigorously promoting garbage classification, but the treatment of classified waste, especially household food waste (HFW) has yet to be studied. Lactic acid (LA), a high value-added platform molecule has broad market prospects. Although there have been many studies on the production of LA from food waste, open fermentation often produces lots of by-products, while the traditional fermentation under a pure bacteria system often requires the saccharification process, which increases the production cost. We sought to analyze the comprehensive properties of classified HFW in Shanghai, then to produce LA by inoculating lactic acid bacteria (LAB) directly. The effects of strains, temperature, sterilized or not, initial pH, inoculum size, and substrate concentration on LA production were investigated. HFW was rich in nutrients and growth factors which provided the possibility for direct LA production from HFW by inoculating LAB. The results showed that Lactobacillus rhamnosus ATCC 7469, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus all could be used as the inoculum, however, no significant synergistic effect of the three strains on LA production was found. LA concentration of 30.25 g/L at 37 °C, pH 6.8 could be obtained by inoculating Lactobacillus rhamnosus ATCC 7469 from sterilized HFW. High inoculum size and substrate concentration resulted in high LA concentration, but not high LA yield. The result of ANOVA indicated that there was a significantly positive relationship between substrate concentration and LA concentration (r = 0.942, p < 0.01), while no statistically significant difference between these groups at different inoculum size was evident (p = 0.318). In addition, an average LA concentration of 26.8 g/L, LA yield of 0.20 g/g TCOD was obtained by repeated batch fermentation for 32 d.

Improving production of lactic acid and volatile fatty acids from dairy cattle manure and corn straw silage: Effects of mixing ratios and temperature

Anaerobic co-fermentation (AcoF) of dairy cattle manure (DCM) and corn straw silage (CSS) for producing lactic acid (LA) and volatile fatty acids (VFAs) was investigated. Batch experiments were conducted at seven different DCM/CSS ratios and at mesophilic and thermophilic temperatures. Results indicated that the highest concentration of LA was 17.50 ± 0.70 g/L at DCM:CSS ratio of 1:3 and thermophilic temperature, while VFAs was 18.23 ± 2.45 g/L at mono-CSS fermentation and mesophilic temperature. High solubilization of thermophilic conditions contributed to LA accumulation in AcoF process. Presence of the CSS increased the relative abundance of Lactobacillus for LA production at thermophilic. Meanwhile, the abundance of Bifidobacterium was increased when CSS was added at mesophilic, which could conduce to VFAs production. This study provides a new route for enhancing the biotransformation of DCM and CSS into short-chain fatty acids, potentially bringing economic benefits to agricultural waste treatment.

Semi-continuous mesophilic-thermophilic two-phase anaerobic co-digestion of food waste and spent mushroom substance: Methanogenic performance, microbial, and metagenomic analysis

The methanogenic efficiency and system stability of anaerobic co-digestion of food waste (FW) and spent mushroom substance (SMS) are important for its application. A 90-day semi-continuous study was conducted to compare the co-digestion performance of an ethanologenic-methanogenic two-phase system and an acidogenic-methanogenic system using FW and SMS as substrates. The results showed that the ethanologenic-methanogenic system increased the contents of ethanol and acetate in the hydrolytic acidification phase. Microbial-community analysis showed that ethanologenic-methanogenic system enriched hydrolytic acidifying bacteria and methanogens such as Methanoculleus, resulting in an increase in the average methane yield of methanogenic phase by 1.91-2.43 times at the same organic loading rate (OLR = 3.0-4.0 g-VS·L^-1·d^-1). Metagenomic analysis indicated that the ethanologenic-methanogenic system increased the abundance of enzyme-encoding genes and promoted the degradation of acetate and CO₂/H₂, thereby enhancing methanogenic metabolic pathways, compared to the acidogenic-methanogenic system.

Critical challenges and technological breakthroughs in food waste hydrolysis and detoxification for fuels and chemicals production

Organic waste has increased as the global population and economy have grown exponentially. Food waste (FW) is posing a severe environmental issue because of mismanaged disposal techniques, which frequently result in the squandering of carbohydrate-rich feedstocks. In an advanced valorization strategy, organic material in FW can be used as a viable carbon source for microbial digestion and hence for the generation of value-added compounds. In comparison to traditional feedstocks, a modest pretreatment of the FW stream utilizing chemical, biochemical, or thermochemical techniques can extract bulk of sugars for microbial digestion. Pretreatment produces a large number of toxins and inhibitors that affect bacterial fuel and chemical conversion processes. Thus, the current review scrutinizes the FW structure, pretreatment methods (e.g., physical, chemical, physicochemical, and biological), and various strategies for detoxification before microbial fermentation into renewable chemical production. Technological and commercial challenges and future perspectives for FW integrated biorefineries have also been outlined.

Lactic acid production from food waste hydrolysate by Lactobacillus pentosus: Focus on nitrogen supplementation, initial sugar concentration, pH, and fed-batch fermentation

Lactic acid production from food waste via fermentation is environmentally sustainable. However, the characteristics of food waste fermentation to produce lactic acid are not well understood due to the complexity of food waste. This study aims to understand the effects of key variables on the characteristics of food waste fermentation to maximize lactic acid production. Food waste was enzymatically hydrolyzed and fermented by Lactobacillus pentosus. Key fermentation variables, including nitrogenous nutrient supplementation, initial sugar concentration, and pH, were investigated in batch fermentation to unveil their effects on fermentation titer, yield, and productivity. The results showed that supplementation of 0.25% (w/v%) yeast extract and peptone to the food waste fermentation media significantly improved fermentation titer and productivity, but further increase in the supplementation level did not improve fermentation. Increasing the initial sugar concentration from 40 g/L to 100 g/L increased the fermentation titer from 41.0 g/L to 93.0 g/L and productivity from 0.34 g/L/h to 0.76 g/L/h. pH 6.0 was the optimal pH for the fermentation. At the optimal conditions, food waste fermentation resulted in the highest fermentation titer, yield, and productivity of 106.7 g/L, 1.12 g/g, and 3.09 g/L/h, respectively. The high fermentation yield of 1.12 g/g might be explained by the extra lactic acid production from unidentified compounds in food waste hydrolysates. By applying fed-batch fermentation, the lactic acid concentration reached 157.0 g/L with a yield and overall productivity of 0.92 g/g and 2.0 g/L/h, respectively. Based on the mass balance, a total of 251 kg lactic acid was produced from 1000 kg food waste. PRACTICAL APPLICATION: Food waste is one of the largest municipal solid wastes in the US, and most food waste ends up in landfills, causing significant economic losses and environmental concerns. In this study, we developed a fermentation process to convert food waste into biorenewable lactic acid and demonstrated that food waste is a superior feedstock for fermentation due to its embedded nutrients. Moreover, due to the embedded nutrients in food waste, the supplementation of yeast extract and peptone to fermentation can be reduced by over 50%, which can reduce the operating cost of lactic acid fermentation on an industrial scale.

High Cell Density Cultivation of Paracoccus sp. on Sugarcane Juice for Poly(3-hydroxybutyrate) Production

High cell density cultivation is a promising approach to reduce capital and operating costs of poly (3-hydroxybutyrate) (PHB) production. To achieve high cell concentration, it is necessary that the cultivation conditions are adjusted and controlled to support the best growth of the PHB producer. In the present study, carbon to nitrogen (C/N) ratio of a sugarcane juice (SJ)-based medium, initial sugar concentration, and dissolved oxygen (DO) set point, were optimized for batch cultivation of Paracoccus sp. KKU01. A maximum biomass concentration of 55.5 g/L was attained using the C/N ratio of 10, initial sugar concentration of 100 g/L, and 20% DO set point. Fed-batch cultivation conducted under these optimum conditions, with two feedings of SJ-based medium, gave the final cell concentration of 87.9 g/L, with a PHB content, concentration, and yield of 36.2%, 32.1 g/L, and 0.13 g/g-sugar, respectively. A medium-based economic analysis showed that the economic yield of PHB on nutrients was 0.14. These results reveal the possibility of using SJ for high cell density cultivation of Paracoccus sp. KKU01 for PHB production. However, further optimization of the process is necessary to make it more efficient and cost-effective.

An innovative approach for reducing the water and alkali consumption in the lactic acid fermentation via the reuse of pretreated liquid

This study focuses on enhancing lactic acid (LA) production and declining water and alkali consumption by reusing the pretreated liquid (PL) of spent mushroom substance (SMS) in the co-fermentation of food waste (FW) and SMS. First, the compositions of PL are identified, and the effects of the PL inhibitors on enzymatic hydrolysis and fermentation are explored. The PL phenol concentrations exceeded 2 g/L, which affected LA fermentation. Therefore, PL phenols were removed by adjusting the pH value, and the detoxified PL (DPL) phenol concentrations were 70.3% lower than those of PL. Different PL:DPL ratios were established to reuse in the fermentation process, and the LA concentration in the 50% PL + 50% DPL group was the highest (56.7 g/L). Then, pretreated SMS was not water-washed, and a neutralizer was prepared with the PL, LA production remained unchanged. Water and NaOH consumption decreased by 84.6% and 52.0%, respectively, and no wastewater was produced.

Microbial production of lactic acid from food waste: Latest advances, limits, and perspectives

A significant amount of food waste (FW) is produced every year. If it is not disposed of timeously, human health and the ecological environment can be negatively affected. Lactic acid (LA), a high value-added product, can be produced by fermentation from FW as a substrate, realizing the concurrent treatment and recycling of FW, which has attracted increasing research interest. In this paper, the latest advances and deficiencies were presented from the following aspects: microorganisms involved in LA fermentation and the metabolic pathways of Lactobacillus, fermentation conditions, and methods of enhanced biotransformation and LA separation. The limitations of the LA fermentation of FW are mainly associated with low LA concentration and yield, the low purity of L(+)-LA, and the high separation costs. The establishment of biorefineries of FW with lactic acid as the target product is the future development direction, but there are still many research studies to be done.

Fermentative lactic acid production from seaweed hydrolysate using Lactobacillus sp. And Weissella sp

Lactic acid (LA) is an essential commodity chemical, with bio-based LA ruling the market share. Macroalgae are a desirable feedstock for LA fermentation due to their high carbohydrate and low lignin content. Ulva sp., Gracilaria sp., and Sargassum cristaefolium were evaluated as a feedstock for LA fermentation. Mild acid-thermal hydrolysis (sulfuric acid concentrations < 5%) resulted in superior reducing sugar recovery. Gracilaria sp. attained maximum reducing sugar recovery (0.39 g/g biomass) and lactate yield (0.94 g/g). LA fermentation of fucose-rich hydrolysate of Sargassum cristaefolium is demonstrated for the first time, with 0.81 g/g LA yield and 0.36 g/g reducing sugars. Ulva sp. attained 0.21 g/g reducing sugars and 0.85 g/g LA yield. The efficiency of macroalgae for lactate bioconversion was in the order: red macroalgae > green macroalgae > brown macroalgae. L. rhamnosus and L. plantarum could efficaciously utilize seaweed sugars for LA production. Macroalgae can potentially replace lignocellulosic biomass as a feedstock in LA fermentation.

Effects of different lignocellulosic wastes on alleviating acidification of L-lactic acid production from food waste fermentation

In this study, the effects of different lignocellulosic wastes on alleviating acidification in the fermentation of lactic acid (LA) from food waste (FW) were studied. Amongst three lignocellulosic wastes, spent mushroom substance (SMS) could reach 95.22% lignin removal efficiency through simple NaOH pretreatment. Results showed pretreated SMS was best choice for FW co-fermentation, the maximum LA concentration could reach 46.12 g/L. And the NaOH solution as neutraliser could save 5.69 mL compared with the other two lignocellulosic wastes. The reason for alleviating acidification was 4.71% calcium salt in SMS and the porous structure of SMS. Then, 50% of pretreated liquid (PL) produced in SMS pretreatment was reused in the co-fermentation process. Compared with the group with 0% PL loading, that with 50% PL loading showed an increase in LA concentration and optical purity of L-LA, reaching 50.95 g/L and 96.28%, and NaOH consumption also further decreased by 24.65%.

Effect of Several Pretreatments on the Lactic Acid Production from Exhausted Sugar Beet Pulp

Exhausted sugar beet pulp (ESBP), a by-product of the sugar industry, has been used as a substrate to produce lactic acid (LA). Due to the fact that ESBP contains a high percentage of pectin and hemicellulose, different pretreatments were studied to solubilize them and to facilitate the access to cellulose in the subsequent enzymatic hydrolysis. Several pretreatments were studied, specifically biological, oxidant with alkaline hydrogen peroxide (AHP), and thermochemical with acid (0.25, 0.5, or 1% w/v of H₂SO₄). Pretreated ESBP was enzymatically hydrolysed and fermented with the strain Lactiplantibacillus plantarum for LA production. The hydrolysis was carried out with the commercial enzymes Celluclast^®, pectinase, and xylanase, for 48 h. After that, the hydrolysate was supplemented with yeast extract and calcium carbonate before the bacteria inoculation. Results showed that all the pretreatments caused a modification of the fibre composition of ESBP. In most cases, the cellulose content increased, rising from 25% to 68% when ESBP was pretreated thermochemically at 1% w/v H₂SO₄. The production of LA was enhanced when ESBP was pretreated thermochemically. However, it was reduced when biological and AHP pretreatments were applied. In conclusion, thermochemical pretreatment with 1% w/v H₂SO₄ had a positive impact on the production of LA, increasing its concentration from 27 g/L to 50 g/L.