Ethanol and lactic acid production as affected by sorghum genotype and location

Dilute sulfuric acid fractionation of Korean food waste for ethanol and lactic acid production by yeast

The continuous production of lactic acid from deproteinized whey by immobilized single and mixed culture of L. casei and L. lactis in Ca‐alginate beads has been investigated. A coimmobilized culture system gave better results than immobilized single cultures regarding lactic acid concentration, productivity, yield, and lactose utilization. Maximum lactic acid productivity of 7 g/lh was obtained at D=0.4 h−1 with a yield of 70% lactic acid and 50% lactose utilization. At a dilution rate of 0.1 h−1, a lactic acid productivity of 2.5 g/lh was obtained with a 55.5% lactic acid yield and 90% lactose utilization. The bioreactor system was operated at a constant dilution rate of 0.1 h−1 for 20 days without loss of original activity. In this case, the average lactic acid productivity, lactic acid yield and lactose utilization were 24 g/lh, 55% and 90%, respectively.

Production of lactic acid from renewable sugars has received growing attention as lactic acid can be used for making renewable and bio-based plastics. However, most prior studies have focused on production of lactic acid from glucose despite that cellulosic hydrolysates contain xylose as well as glucose. Microbial strains capable of fermenting both glucose and xylose into lactic acid are needed for sustainable and economic lactic acid production. In this study, we introduced a lactic acid-producing pathway into an engineered Saccharomyces cerevisiae capable of fermenting xylose. Specifically, ldhA from the fungi Rhizopus oryzae was overexpressed under the control of the PGK1 promoter through integration of the expression cassette in the chromosome. The resulting strain exhibited a high lactate dehydrogenase activity and produced lactic acid from glucose or xylose. Interestingly, we observed that the engineered strain exhibited substrate-dependent product formation. When the engineered yeast was cultured on glucose, the major fermentation product was ethanol while lactic acid was a minor product. In contrast, the engineered yeast produced lactic acid almost exclusively when cultured on xylose under oxygen-limited conditions. The yields of ethanol and lactic acid from glucose were 0.31 g ethanol/g glucose and 0.22 g lactic acid/g glucose, respectively. On xylose, the yields of ethanol and lactic acid were <0.01 g ethanol/g xylose and 0.69 g lactic acid/g xylose, respectively. These results demonstrate that lactic acid can be produced from xylose with a high yield by S. cerevisiae without deleting pyruvate decarboxylase, and the formation patterns of fermentations can be altered by substrates.

In the current work, date wastes were used for lactic acid (LA) production under thermo-alkaline conditions to overcome some fermentation challenges. Amongst 27 bacterial isolates that produced LA from date juice, isolate D-218 exhibited better growth stability and LA production under various stressed conditions. This isolate was characterized as Bacillus coagulans D-218 using physiological and molecular identification methods. In batch fermentation mode, strain D-218 could not completely utilize 80 g/L of the total sugar and produced only 45.8 ± 2.8 g/L of LA at LA productivity of 0.214 g/L.h and high residual sugar (29.2 g/L) was unutilized in the fermentation media. Different repeated batch fermentations with different initial sugar concentrations and gradual increase in sugar concentrtions were conducted to maximize LA productivity. Starting with 60 g/L of total sugar, four runs of repeated batch fermentations were conducted that enhanced the LA productivity (70%) to 0.49 g/L.h. Another 9 runs were initiated with 40 g/L which further improved LA productivity that reached up to 0.77 g/L.h. Surprisingly, initiating fermentations with 20 g/L of total sugar successfully attained long-term fermentation (18 runs) with high LA yield and productivity without carbon loss of initiated startup sugar of date waste. In this process, strain D-218 could completely consume 80 g/L sugars with high LA production titer (72.9 ± 0.56 g/L), yield (0.92 g/g), and productivity (0.71 g/L.h). This study is the first to exploit date waste in a cost-effective system for high-titer lactic acid production under thermo-alkaline conditions (pH 9.0; 50 °C) and to report repeated batch fermentation for LA production from date wastes.

A rotating fibrous-bed bioreactor (RFB) was developed for fermentation to produce L(+)-lactic acid from glucose and cornstarch by Rhizopus oryzae. Fungal mycelia were immobilized on cotton cloth in the RFB for a prolonged period to study the fermentation kinetics and process stability. The pH and dissolved oxygen concentration (DO) were found to have significant effects on lactic acid productivity and yield, with pH 6 and 90% DO being the optimal conditions. A high lactic acid yield of 90% (w/w) and productivity of 2.5 g/L.h (467 g/h.m(2)) was obtained from glucose in fed-batch fermentation. When cornstarch was used as the substrate, the lactic acid yield was close to 100% (w/w) and the productivity was 1.65 g/L.h (300 g/h.m(2)). The highest concentration of lactic acid achieved in these fed-batch fermentations was 127 g/L. The immobilized-cells fermentation in the RFB gave a virtually cell-free fermentation broth and provided many advantages over conventional fermentation processes, especially those with freely suspended fungal cells. Without immobilization with the cotton cloth, mycelia grew everywhere in the fermentor and caused serious problems in reactor control and operation and consequently the fermentation was poor in lactic acid production. Oxygen transfer in the RFB was also studied and the volumetric oxygen transfer coefficients under various aeration and agitation conditions were determined and then used to estimate the oxygen transfer rate and uptake rate during the fermentation. The results showed that the oxygen uptake rate increased with increasing DO, indicating that oxygen transfer was limited by the diffusion inside the mycelial layer.

Photocatalytic conversion of biomass is considered an effective, clean, and environmentally friendly route to obtain high-valued chemicals and hydrogen. However, the limited conversion efficiency and poor selectivity are still the main bottlenecks for photocatalytic biomass conversion. Herein, we report the highly selective photocatalytic conversion of glucose solution on holo-symmetrically spherical three-dimensionally ordered macroporous TiO₂-CdSe heterojunction photonic crystal structure (s-TCS). The obtained s-TCS photocatalysts show excellent stability and strong light harvesting, uniform mass diffusion and exchange, and efficient photogenerated electrons/holes separation and utilization. The optimized s-TCS-4 photocatalyst displays the highest photocatalytic performance for glucose oxidation and hydrogen production. The glucose conversion, lactic acid selectivity, and yield on s-TCS-4 are about 95.9%, 94.3%, and 96.4%, respectively. The photocatalytic production of lactic acid for s-TCS-4 (18.5 g/L) is 2.3 times higher than the pure spherical TiO₂ photonic crystal without CdSe (s-TiO₂, 8.1 g/L), and the hydrogen production rate of s-TCS-4 is 9.4 times that of s-TiO₂. For the first time, we reveal that the photocatalytic conversion of glucose to lactic acid is a third-order and four-electron-involved reaction. This work could shed some new light on the efficient photocatalysis conversion of biomass to highly value-added products with high selectivity and yield, and simultaneously sustainable hydrogen evolution.

Utilisation of microwave-NaOH pretreatment technology to improve performance and l-lactic acid yield from vinasse

Lactic Acid as a platform chemical has broad application in various industries, especially in the production of Poly Lactic Acid (PLA) for biodegradable plastic. Empty fruit bunch (EFB), abundant by product from palm oil mill industry, is one of potential feedstock to be used in the production of lactic acid from lignocellulose biomass. EFB contains high cellulose and hemicellulose about 37– 59.7% w/w and 16–28% w/w, respectively. The aim of this paper is to study the effects of the operating conditions, such as temperature, reaction time, biomass loading, and catalyst concentration on the yield of lactic acid using barium hydroxide as alkaline catalyst. EFB pretreatment with steam explosion was applied to remove lignin content. The results showed that pretreatment reduced the lignin content from 22.66% to 9.69% w/w. Meanwhile, hemicellulose and cellulose increased from 14.40% to 16.40% w/w and 29.37% to 63.57% w/w, respectively. The highest yield of lactic acid was 21.57% C-mol, achieved by using 0.25 M Ba(OH)2 as the catalyst, with 5% w/v biomass loading, temperature 240°C, during 4 h reaction times. The yield was approximately equal to yield of lactic acid (~ 20%) compared with Pb2+ as the catalyst for EFB conversion although the later catalyst produced fewer by products during conversion.

Optimized feeding schemes of simultaneous saccharification and fermentation process for high lactic acid titer from sugarcane bagasse

Production of lactic acid from paper sludge using acid-tolerant, thermophilic Bacillus coagulan strains

Lactic acid fermentations were conducted using water hyacinth. It is known that the pretreatment and enzyme hydrolysis process optimize the potential of water hyacinth. Lactic acid produced by using lactic acid bacteria. All cells were grown at <TEX>$37^{\circ}C$</TEX> and initial pH 5.5. Lactic acid production was measured by HPLC. All Lactobacillus strains could produce lactic acid from pretreated water hyacinth. The highest lactic acid was achieved when lactic acid fermentation was carried out by L. delbrueckii for D-form and L. helveticus for L-form lactic acid production. The lactic acid concentration was 10.70 g/L by L. delbrueckii and it converted glucose in the medium to lactic acid, almost perfectly. Lactic acid production became higher when fermentation was carried out at a controlled pH 5.5. Lactic acid yield and productivity were 0.52 g/g and 0.19 g/L/h for L. helveticus, while L. delbrueckii was 0.64 g/g and 0.27 g/L/h. This study showed that water hyacinth medium could be alternative medium which can replace the complex and expensive medium for growing Lactobacillus strains in production of lactic acid.

The present study investigated the synergistic effect of nutritional supplements (amino acid and Tween 80) on lactic acid production by Lactobacillus delbruckii utilizing a sugar refinery by product (cane molasses) in a submerged fermentation process. Initially, the effect of individual factors on lactic acid yield was studied by supplementing amino acids and their combinations, Tween 80 and cane molasses at varying concentrations in production medium. A combination of l-phenylalanine and l-lysine gave a maximum lactic acid yield of 47.89 ± 0.1 g/L on a dry cell weight basis at individual factor level. Similarly, maximum lactic acid yield was obtained by supplementing the production medium with 40.0 g/L and 2.0 g/L Tween 80 and cane molasses, respectively, at individual factor level. In order to further improve the lactic acid yield, nutritional supplements were optimized by central composite rotatable design (CCRD) using Minitab 15 software. Shake flask cultivation under optimized conditions, i.e., cane molasses (32.40 g/L), Tween 80 (2.0 g/L) and l-phenylalanine and l-lysine (34.0 mg/L) gave a lactic acid yield of 64.86 ± 0.2 g/L, corresponding to 95.0 % of the predicted yield of 67.78 ± 0.3 g/L. Batch cultivation performed in 7.5 L bioreactor (working volume: 3.0 L) under optimized conditions gave maximum lactic acid yield and productivity of 79.12 ± 0.2 g/L and 3.40 g/L·h, which is higher than previous studies with reduced fermentation time. Screening of lactic acid producing bacteria and characterization of lactic acid was also done.

Continuous fermentation of clarified corn stover hydrolysate for the production of lactic acid at high yield and productivity

Tailoring non-axenic lactic acid fermentation from cheese whey permeate targeting a flexible lactic acid platform

Production of l - and d -lactic acid from waste Curcuma longa biomass through simultaneous saccharification and cofermentation