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

BackgroundEfficient conversion of lignocellulosic biomass to optically pure lactic acid is a key challenge for the economical production of biodegradable poly-lactic acid. A recently isolated strain, Thermoanaerobacterium aotearoense SCUT27, is promising as an efficient lactic acid production bacterium from biomass due to its broad substrate specificity. Additionally, its strictly anaerobic and thermophilic characteristics suppress contamination from other microoragnisms. Herein, we report the significant improvements of concentration and yield in lactic acid production from various lignocellulosic derived sugars, achieved by the carbon flux redirection through homologous recombination in T. aotearoense SCUT27.ResultsT. aotearoense SCUT27 was engineered to block the acetic acid formation pathway to improve the lactic acid production. The genetic manipulation resulted in 1.8 and 2.1 fold increase of the lactic acid yield using 10 g/L of glucose or 10 g/L of xylose as substrate, respectively. The maximum l-lactic acid yield of 0.93 g/g glucose with an optical purity of 99.3% was obtained by the engineered strain, designated as LA1002, from 50 g/L of substrate, which is very close to the theoretical value (1.0 g/g of glucose). In particular, LA1002 produced lactic acid at an unprecedented concentration up to 3.20 g/L using 10 g/L xylan as the single substrate without any pretreatment after 48 h fermentation. The non-sterilized fermentative production of l-lactic acid was also carried out, achieving values of 44.89 g/L and 0.89 g/g mixed sugar for lactic acid concentration and yield, respectively.ConclusionsBlocking acetic acid formation pathway in T. aotearoense SCUT27 increased l-lactic acid production and yield dramatically. To our best knowledge, this is the best performance of fermentation on lactic acid production using xylan as the sole carbon source, considering the final concentration, yield and fermentation time. In addition, it should be mentioned that the performance of non-sterilized simultaneous fermentation from glucose and xylose was very close to that of normal sterilized cultivation. All these results used the mutant strain, LA1002, indicated that it is a new promising candidate for the effective production of optically pure l-lactic acid from lignocellulosic biomass.

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

The lespedeza stalks with steam pretreatment were fermented to lactic acid by simultaneous saccharification and fermentation (SSF) in this study. Orthogonal design methodology was used to evaluate the optimum SSF conditions that give maximum lactic acid yield. We have investigated the following relative factors, such as temperature, loading of cellulase, calcium carbonate and concentration of substrate. The optimum operating conditions were found to be temperature of 43 °C, cellulase loading of 30 FPU/g substrate, calcium carbonate of 3 % and substrate of 6 %. Comparisons of different steam pretreated conditions on lactic acid yield from lespedeza stalks were also made. The results showed that lactic acid yields from lespedeza stalks with 4 min pretreatment at pressure of 1.0, 1.25, 1.5 and 2.0 Mpa were 41.8 %, 42.5 %, 50.6 % and 64.0 % of the theoretical, respectively. The lactic acid yield from steam pretreated lespedeza stalks was much higher than that of lespedeza stalks without pretreatment (23.9 %). It can be concluded that the lactic acid yield was remarkably improved by steam pretreatment. The yield of lactic acid from steam pretreated lespedeza stalks was 1.68 times higher than that of untreated ones. Additionally, the lactic acid yield could be further promoted from 64.0 % to 89.4 % by washing pretreated stalks with water, which suggested that water processing is a promising method to remove inhibitors in broth to improve lactic acid yield.

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.

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.

Industrial waste corn cob residue (from xylose manufacturing) without pretreatment was hydrolyzed by cellulase and cellobiase. The cellulosic hydrolysate contained 52.4 g l−1 of glucose and was used as carbon source for lactic acid fermentation by cells of Lactobacillus delbrueckii ZU-S2 immobilized in calcium alginate gel beads. The final concentration of lactic acid and the yield of lactic acid from glucose were 48.7 g l−1 and 95.2%, respectively, which were comparative to the results of pure glucose fermentation. The immobilized cells were quite stable and reusable, and the average yield of lactic acid from glucose in the hydrolysate was 95.0% in 12 repeated batches of fermentation. The suitable dilution rate of continuous fermentation process was 0.13 h−1, and the yield of lactic acid from glucose and the productivity were 92.4% and 5.746 g l−1 h−1, respectively. The production of lactic acid by simultaneous saccharification and fermentation (SSF) process was carried out in a coupling bioreactor, the final concentration of lactic acid was 55.6 g l−1, the conversion efficiency of lactic acid from cellulose was 91.3% and the productivity was 0.927 g l−1 h−1. By using fed-batch technique in the SSF process, the final concentration of lactic acid and the productivity increased to 107.6 g l−1 and 1.345 g l−1 h−1, respectively, while the dosage of cellulase per gram substrate decreased greatly. This research work should advance the bioconversion of renewable cellulosic resources and reduce environmental pollution.

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.

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.

Conversion of food wastes into lactic acid by simultaneous saccharification and fermentation (SSF) was investigated. The process involves saccharification of the starch component in food wastes by a commercial amylolytic enzyme preparation (a mixture of amyloglucosidase, α-amylase, and protease) and fermentation by Lactobacillus delbrueckii. The highest observed overall yield of lactic acid in the SSF was 91% of theoretical. Lactic acid concentration as high as 80 g/L was attainable in 48 h of the SSF. The optimum operating conditions for the maximum productivity were found to be 42°C and pH 6.0. Without supplementation of nitrogen-containing nutrients, the lactic acid yield in the SSF decreased to 60%: 27 g/L of lactic acid from 60 g/L of food waste. The overall performance of the SSF, however, was not significantly affected by the elimination of mineral supplements.

Conversion of food wastes into lactic acid by simultaneous saccharification and fermentation (SSF) was investigated. The process involves saccharification of the starch component in food wastes by a commercial amylolytic enzyme preparation (a mixture of amyloglucosidase, alpha-amylase, and protease) and fermentation by Lactobacillus delbrueckii. The highest observed overall yield of lactic acid in the SSF was 91% of theoretical. Lactic acid concentration as high as 80 g/L was attainable in 48 h of the SSF. The optimum operating conditions for the maximum productivity were found to be 42 degrees C and pH 6.0. Without supplementation of nitrogen-containing nutrients, the lactic acid yield in the SSF decreased to 60%: 27 g/L of lactic acid from 60 g/L of food waste. The overall performance of the SSF, however, was not significantly affected by the elimination of mineral supplements.

The production of value-added chemicals from the bioconversion of lignocellulose biomass has been considered a promising venture. In this study, microwave, alkali-pretreated empty fruit bunch (EFB) was used as the substrate, utilizing pelletized filamentous Rhizopus oryzae NRRL 395 and cellulolytic enzymes for lactic acid production in a fed-batch simultaneous saccharification and fermentation (SSF) process. Insoluble solids generally do not affect the SSF process until a certain concentration is exceeded. To achieve a high lactic acid concentration in the broth, a high solids loading was required to allow a higher rate of glucose conversion. However, the results revealed a decrease in the final lactic acid yield when running SSF at a massive insoluble solids level. High osmotic pressure in the medium led to poor cellular performance and caused the Rhizopus oryzae pellets to break down, affecting the lactic acid production. To improve the process performance, a fed-batch operation mode was used. The fed-batch operation was shown to facilitate higher lactic acid yield, compared with the SSF batch mode. Enzyme feeding, as well as substrate feeding, was also investigated as a means of enabling a higher dry matter content, with a high glucose conversion in SSF of cellulose-rich EFB.

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

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. 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. 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.

Fed-batch simultaneous saccharification and fermentation for valorization of sugarcane bagasse to lactic acid and evaluation of the residual solids as nutrient-rich feed ingredient

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