Identification of Gluconacetobacter xylinus LYP25 and application to bacterial cellulose production in biomass hydrolysate with acetic acid

Bacterial cellulose (BC) is a remarkable biomacromolecule with potential applications in food, biomedical, and other industries. However, the low economic feasibility of BC production processes hinders its industrialization. In our previous work, we obtained candidate strains with improved BC production through random mutations in Gluconacetobacter. In this study, the molecular identification of LYP25 strain with significantly improved productivity, the development of chestnut pericarp (CP) hydrolysate medium, and its application in BC fermentation were performed for cost-effective BC production process. As a result, the mutant strain was identified as Gluconacetobacter xylinus. The CP hydrolysate (CPH) medium contained 30 g/L glucose with 0.4 g/L acetic acid, whereas other candidates known to inhibit fermentation were not detected. Although acetic acid is generally known as a fermentation inhibitor, it improves the BC production by G. xylinus when present within about 5 g/L in the medium. Fermentation of G. xylinus LYP25 in CPH medium resulted in 17.3 g/L BC, a 33 % improvement in production compared to the control medium, and BC from the experimental and control groups had similar physicochemical properties. Finally, the overall process of BC production from biomass was evaluated and our proposed platform showed the highest yield (17.9 g BC/100 g biomass).

Utilization of coffee waste as a sustainable feedstock for high-yield lactic acid production through microbial fermentation

Lactic acid is an important industrial precursor; however, high substrate costs are a major challenge in microbial fermentation-based lactic acid production. Coffee waste is a sustainable feedstock alternative for lactic acid production via microbial fermentation. Herein, the feasibility of coffee waste as a feedstock was explored by employing appropriate pretreatment methods and optimizing enzyme combinations. Coffee waste pretreatment with hydrogen peroxide and acetic acid along with a combination of Viscozyme L, Celluclast 1.5 L, and Pectinex Ultra SP-L achieved the 78.9 % sugar conversion rate at a substrate concentration of 4 % (w/v). Lactiplantibacillus plantarum WiKim0126-induced fermentation with a 4 % solid loading yielded a lactic acid concentration of 22.8 g/L (99.6 % of the theoretical maximum yield) and productivity of 0.95 g/L/h within 24 h. These findings highlight the viability of coffee waste as an eco-friendly resource for sustainable lactic acid production.

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.

Effect of Spent Coffee Grounds on the Crystallinity and Viscoelastic Behavior of Polylactic Acid Composites

This work investigated the addition of spent coffee grounds (SCG) as a valuable resource to produce biocomposites based on polylactic acid (PLA). PLA has a positive biodegradation effect but generates poor proprieties, depending on its molecular structure. The PLA and SCG (0, 10, 20 and 30 wt.%) were mixed via twin-screw extrusion and molded by compression to determine the effect of composition on several properties, including mechanical (impact strength), physical (density and porosity), thermal (crystallinity and transition temperature) and rheological (melt and solid state). The PLA crystallinity was found to increase after processing and filler addition (34-70% in the 1st heating) due to a heterogeneous nucleation effect, leading to composites with lower glass transition temperature (1-3 °C) and higher stiffness (~15%). Moreover, the composites had lower density (1.29, 1.24 and 1.16 g/cm³) and toughness (30.2, 26.8 and 19.2 J/m) as the filler content increased, which is associated with the presence of rigid particles and residual extractives from SCG. In the melt state, polymeric chain mobility was enhanced, and composites with a higher filler content became less viscous. Overall, the composite with 20 wt.% SCG provided the most balanced properties being similar to or better than neat PLA but at a lower cost. This composite could be applied not only to replace conventional PLA products, such as packaging and 3D printing, but also to other applications requiring lower density and higher stiffness.

Microbial production of lactic acid using organic wastes as low-cost substrates

Lactic acid is a natural organic acid with diverse of applications in food, pharmaceutical, cosmetics, and chemical industry. Recently, the demand of lactic acid has been grown due to its utilization for polylactic acid production. Microbial production of lactic acid production is preferable due to optical purity of product, utilization of low cost substrates, and low energy requirement. Lignocellulosic biomass and other organic wastes are considered potential raw materials for cost-effective production of lactic acid. The raw materials are either hydrolyzed by enzymes or dilute acids to release the reducing sugars that are fermented in to lactic acid. This review has been focussed on microbial production of lactic acid using different organic wastes as low cost substrate.

Optimization of Major Extraction Variables to Improve Recovery of Anthocyanins from Elderberry by Response Surface Methodology

Elderberry, which is well known for its richness in anthocyanin, is attracting attention in the bioindustry as a functional material with high antioxidant capacity. The aim of this study is to optimize extraction conditions to more effectively recover anthocyanins from elderberry. In a fundamental experiment to determine the suitable solvent, various GRAS reagents, such as acetone, ethanol, ethyl acetate, hexane, and isopropyl alcohol, were used, and total phenol and anthocyanin contents were detected as 9.0 mg/g-biomass and 5.1 mg/g-biomass, respectively, only in the extraction using ethanol. Therefore, ethanol was selected as the extraction solvent, and an experimental design was performed to derive a response surface model with temperature, time, and EtOH concentration as the main variables. The optimal conditions for maximal anthocyanin recovery were determined to be 20.0 °C, 15.0 min, and 40.9% ethanol, and the total anthocyanin content was 21.0 mg/g-biomass. In addition, the total phenol and flavonoid contents were detected as 67.4 mg/g-biomass and 43.8 mg/g-biomass, respectively. The very simple and economical extraction conditions suggested in this study contributed to improving the utilization potential of anthocyanin, a useful antioxidant derived from elderberry.

Microbial Production of Bacterial Cellulose Using Chestnut Shell Hydrolysates by Gluconacetobacter xylinus ATCC 53524

Bacterial cellulose (BC) is gaining attention as a carbon-neutral alternative to plant cellulose, and as a means to prevent deforestation and achieve a carbon-neutral society. However, the high cost of fermentation media for BC production is a barrier to its industrialization. In this study, chestnut shell (CS) hydrolysates were used as a carbon source for the BC-producing bacteria strain, Gluconacetobacter xylinus ATCC 53524. To evaluate the suitability of the CS hydrolysates, major inhibitors in the hydrolysates were analyzed, and BC production was profiled during fermentation. CS hydrolysates (40 g glucose/l) contained 1.9 g/l acetic acid when applied directly to the main medium. As a result, the BC concentration at 96 h using the control group and CS hydrolysates was 12.5 g/l and 16.7 g/l, respectively (1.3-fold improved). In addition, the surface morphology of BC derived from CS hydrolysates revealed more densely packed nanofibrils than the control group. In the microbial BC production using CS, the hydrolysate had no inhibitory effect during fermentation, suggesting it is a suitable feedstock for a sustainable and eco-friendly biorefinery. To the best of our knowledge, this is the first study to valorize CS by utilizing it in BC production.

Valorization of Cheese Whey as a Feedstock for Production of Cyclosporin A by Tolypocladium inflatum

Food waste-based biorefineries are considered an essential concept for the implementation of a sustainable circular economy. In this study, cheese whey powder (CWP), a dairy industry waste, was utilized to produce cyclosporin A (CsA). As it is difficult to valorize CWP because its components vary depending on the origin, a process for sugar conversion via acid hydrolysis was designed to obtain reproducible results using refined whey powder (WP) of a consistent quality. Acid hydrolysis was carried out using 2% (w/w) HCl and biomass loading of 50 g/L at 121 °C for 20 min. CWP hydrolysates were utilized to ferment Tolypocladium inflatum ATCC 34921. CsA production was found to be 51.3 mg/L at 12 days, a 1.4-fold increase compared to the control (commercial glucose, 36.3 mg/L). Our results showed that 100 g CWP can be converted to 81.8 mg of CsA. This finding demonstrated that CWP can be used as a sustainable feedstock for biorefineries.

Screening of a Novel Lactiplantibacillus plantarum MMB-05 and Lacticaseibacillus casei Fermented Sandwich Seaweed Scraps: Chemical Composition, In Vitro Antioxidant, and Volatile Compounds Analysis by GC-IMS

Lactic acid fermentation is a promising method for developing sandwich seaweed scraps. The objectives of this study were to investigate the effect of fermentation with Lactiplantibacillus plantarum MMB-05, Lactiplantibacillus casei FJAT-7928, mixed bacteria (1:1, v/v) and control on the physicochemical indexes, in vitro antioxidant activity, and volatile compounds of Porphyra yezoensis sauce. Sensory evaluation was also performed. The results indicated that all lactic acid bacteria strains grew well in P. yezoensis sauce after 72 h of fermentation, with the viable cell counts of L. plantarum MMB-05 exceeding 10.0 log CFU/mL, the total phenolic content increasing by 16.54%, and the lactic acid content increasing from 0 to 44.38 ± 0.11 mg/mL. Moreover, the metabolism of these strains significantly increased the content of umami, sweet and sour free amino acids in P. yezoensis sauce. The total antioxidant capacity of L. plantarum MMB-05, L. casei FJAT-7928, mix and control groups increased by 594.59%, 386.49%, 410.27%, and 287.62%, respectively. Gas chromatography-ion mobility spectrometry (GC-IMS) analysis suggested that aldehydes and ketones accounted for the largest proportion, and the relative contents of acids and alcohols in P. yezoensis sauce increased significantly after lactic acid bacteria fermentation. In addition, the analysis of dynamic principal component analysis (PCA) and fingerprinting showed that the volatile components of the four treatment methods could be significantly distinguished. Overall, the L. plantarum MMB-05 could be recommended as an appropriate starter for fermentation of sandwich seaweed scraps, which provides a fundamental knowledge for the utilization of sandwiched seaweed scraps.

Energy-efficient glucose recovery from chestnut shell by optimization of NaOH pretreatment at room temperature and application to bioethanol production

Biofuel policies are currently being implemented globally to reduce greenhouse gas emissions. The recent European regulation, Renewable Energy Directive (RED) II, states that renewable resources should be used as raw materials. In this study, chestnut shell (CNS), a food processing residue, was utilized as a feedstock for bioethanol production. Statistical optimization was performed to improve biomass-to-glucose conversion (BtG) from the CNS. In order to design an energy-efficient process, the pretreatment was fixed at room temperature in the numerical optimization. The optimal conditions derived from the predicted model are as follows: temperature of 25 °C, reaction time of 2.8 h, and NaOH concentration of 1.9% (w/w). Under optimal conditions, both predicted and experimental BtG were 31.0%, while BtG was approximately 3.3-fold improved compared to the control group (without pretreatment). The recovered glucose was utilized for bioethanol fermentation by Saccharomyces cerevisiae K35 and the ethanol yield was achieved to be 98%. Finally, according to the mass balance based on 1000 g CNS, glucose of 310 g can be recovered by the pretreatment; the bioethanol production was approximately 155 g. This strategy suggests a direction to utilize CNS as a potential feedstock for biorefinery through the design of an economical and energy-efficient pretreatment process by lowering the reaction temperature to room temperature.

Fermentative Lactic Acid Production From Lignocellulosic Feedstocks: From Source to Purified Product

The second (lignocellulosic biomass and industrial wastes) and third (algal biomass) generation feedstocks gained substantial interest as a source of various value-added chemicals, produced by fermentation. Lactic acid is a valuable platform chemical with both traditional and newer applications in many industries. The successful fractionation, separation, and hydrolysis of lignocellulosic biomass result in sugars’ rich raw material for lactic acid fermentation. This review paper aims to summarize the investigations and progress in the last 5 years in lactic acid production from inexpensive and renewable resources. Different aspects are discussed—the type of raw materials, pretreatment and detoxification methods, lactic acid-producers (bacteria, fungi, and yeasts), use of genetically manipulated microorganisms, separation techniques, different approaches of process organization, as well as main challenges, and possible solutions for process optimization.

Valorization of Spent Coffee Grounds as Precursors for Biopolymers and Composite Production

Spent coffee grounds (SCG) are a current subject in many works since coffee is the second most consumed beverage worldwide; however, coffee generates a high amount of waste (SCG) and can cause environmental problems if not discarded properly. Therefore, several studies on SCG valorization have been published, highlighting its waste as a valuable resource for different applications, such as biofuel, energy, biopolymer precursors, and composite production. This review provides an overview of the works using SCG as biopolymer precursors and for polymer composite production. SCG are rich in carbohydrates, lipids, proteins, and minerals. In particular, carbohydrates (polysaccharides) can be extracted and fermented to synthesize lactic acid, succinic acid, or polyhydroxyalkanoate (PHA). On the other hand, it is possible to extract the coffee oil and to synthesize PHA from lipids. Moreover, SCG have been successfully used as a filler for composite production using different polymer matrices. The results show the reasonable mechanical, thermal, and rheological properties of SCG to support their applications, from food packaging to the automotive industry.

Enhanced Production of Bacterial Cellulose from Miscanthus as Sustainable Feedstock through Statistical Optimization of Culture Conditions

Biorefineries are attracting attention as an alternative to the petroleum industry to reduce carbon emissions and achieve sustainable development. In particular, because forests play an important role in potentially reducing greenhouse gas emissions to net zero, alternatives to cellulose produced by plants are required. Bacterial cellulose (BC) can prevent deforestation and has a high potential for use as a biomaterial in various industries such as food, cosmetics, and pharmaceuticals. This study aimed to improve BC production from lignocellulose, a sustainable feedstock, and to optimize the culture conditions for Gluconacetobacter xylinus using Miscanthus hydrolysates as a medium. The productivity of BC was improved using statistical optimization of the major culture parameters which were as follows: temperature, 29 °C; initial pH, 5.1; and sodium alginate concentration, 0.09% (w/v). The predicted and actual values of BC production in the optimal conditions were 14.07 g/L and 14.88 g/L, respectively, confirming that our prediction model was statistically significant. Additionally, BC production using Miscanthus hydrolysates was 1.12-fold higher than in the control group (commercial glucose). Our result indicate that lignocellulose can be used in the BC production processes in the near future.

Rapid and concise quantification of mycelial growth by microscopic image intensity model and application to mass cultivation of fungi

The microbial food fermentation industry requires real-time monitoring and accurate quantification of cells. However, filamentous fungi are difficult to quantify as they have complex cell types such as pellet, spores, and dispersed hyphae. In this study, numerous data of microscopic image intensity (MII) were used to develop a simple and accurate quantification method of Cordyceps mycelium. The dry cell weight (DCW) of the sample collected during the fermentation was measured. In addition, the intensity values were obtained through the ImageJ program after converting the microscopic images. The prediction model obtained by analyzing the correlation between MII and DCW was evaluated through a simple linear regression method and found to be statistically significant (R2 = 0.941, p < 0.001). In addition, validation with randomly selected samples showed significant accuracy, thus, this model is expected to be used as a valuable tool for predicting and quantifying fungal growth in various industries.

Improvement of Enzymatic Glucose Conversion from Chestnut Shells through Optimization of KOH Pretreatment

Worldwide, about one-third of food produced for human consumption is wasted, which includes byproducts from food processing, with a significant portion of the waste still being landfilled. The aim of this study is to convert chestnut shells (CNSs) from food processing into a valuable resource through bioprocesses. Currently, one of the highest barriers to bioprocess commercialization is low conversion of sugar from biomass, and KOH pretreatment was suggested to improve enzymatic digestibility (ED) of CNS. KOH concentration of 3% (w/w) was determined as a suitable pretreatment solution by a fundamental experiment. The reaction factors including temperature, time and solid/liquid (S/L) ratio were optimized (77.1 g/L CNS loading at 75 °C for 2.8 h) by response surface methodology (RSM). In the statistical model, temperature and time showed a relatively significant effect on the glucan content (GC) and ED, but S/L ratio was not. GC and ED of the untreated CNS were 45.1% and 12.7%, respectively. On the other hand, GC and ED of pretreated CNS were 83.2% and 48.4%, respectively, and which were significantly improved by about 1.8-fold and 3.8-fold compared to the control group. The improved ED through the optimization is expected to contribute to increasing the value of byproducts generated in food processing.