Lactic acid fermentation from food waste with indigenous microbiota: Effects of pH, temperature and high OLR

Lactic acid production through fermentation is an established technology, however, improvements are necessary to reduce the process costs and to decrease its market price. Lactic acid is used in many industrial sectors and its market has increased in the last decade for its use as the raw material for polylactic acid product. Using food waste as a cheap and renewable substrate, as well as fermentation at uncontrolled pH, helps to make the production cheaper and to simplify the downstream purification process. Lactic acid production at acidic conditions and the role of varying organic loading rate (OLR) and hydraulic retention time (HRT) were tested in two different semicontinuous batch fermentation systems. Reactor performances indicated that lactic acid fermentation was still possible at pH < 3.5 and even up to a pH of 2.95. The highest lactic acid production was recorded at 14-day HRT, 2.14 g VS/L·day OLR, and pH 3.11 with a maximum lactic acid concentration of 8.72 g/L and a relative yield of 0.82 g lactate/g carbohydrates. The fermentation microbial community was dominated by Lactobacillus strains, the organism mainly responsible for lactic acid conversion from carbohydrates. This study shows that low pH fermentation is a key parameter to improve lactic acid production from food waste in a semicontinuous system. Acidic pH favored both the selection of Lactobacillus strains and inhibited VFA producers from utilizing lactic acid as primary substrate, thus promoting the accumulation of lactic acid. Finally, production yields tend to decrease with high OLR and low HRT, while lactic acid production rates showed the opposite trend.

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.

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.

Lactic acid production from lactose by Lactobacillus plantarum: kinetic model and effects of pH, substrate, and oxygen

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.

In this study, we found that p-coumaric acid (p-CA), ferulic acid (FA), and condensed tannins were released from rice straw during saccharification. The presence of polyphenols prolonged the lag phase and lowered the productivity of lactic acid. p-CA was identified as a key inhibitor. Tannins had a lower inhibitory effect than p-CA; FA had little inhibitory effect. Acid, alkaline, and ball milling pretreatments elicited different levels of polyphenol release from rice straw. Due to the different levels of polyphenol release in the pretreatment step, the enzymatic hydrolysates contained different concentrations of polyphenols. Compared with fermentation with a synthetic medium, fermentation with the hydrolysates of ball-milled rice straw provided much lower productivity and yield of lactic acid due to the presence of polyphenols. Removal of these compounds played an important role in lactic acid fermentation. When rice straw was alkaline pretreated, the hydrolysates contained few phenolic compounds, resulting in high productivity and yield of lactic acid (1.8g/L/h and 26.7g/100g straw), which were comparable to those in a synthetic medium. This indicates that there is a correlation between removal of phenolic compounds and efficiency in lactic acid fermentation.

This study investigated the integrated valorization of defatted rice bran (DRB) by converting it into lactic acid (LA) and subsequently utilizing the residues from LA production for biomethane generation through anaerobic digestion (AD). Processing 480 kg of DRB resulted in the production of 70 L of pure LA and generated significant waste streams, primarily consisting of 572 kg of decanted hydrolysate pellet (Pellet DEC) and 220 kg of microfiltration retentate (Retentate MF). Exceptionally high methane yields of 374‒434 LN kgVS-1 were observed for residues from LA fermentation in biochemical methane potential tests, indicating their high potential for biogas production. During long-term semi-continuous AD, varying organic loading rates (OLRs) from 0.5‒2.5 kgVS m-3 d⁻¹ demonstrated feedstock- and OLR-dependent methane production. Reactor failure at higher OLRs was attributed to the accumulation of total ammoniacal nitrogen (TAN). The co-digestion of Pellet DEC and Retentate MF proved to be more resilient, with OLRs up to 2 kgVS m-3 d-1, mitigating TAN inhibition. Methane yields, ranging from 265‒334 LN kgVS-1 before reaching inhibitory OLR levels, were higher than those found in the literature. Process integration has emerged as a promising approach because the biogas generated from residues could effectively offset the energy demands of LA production. Supported by life cycle assessment, the integrated processes showed a 67% lower environmental impact at the midpoint and a 71% lower environmental impact at the endpoint, along with an 80% reduction in energy costs compared to the standalone LA production. Results proved a significant enhancement of the sustainability and economic viability of this integrated biorefinery approach.

This study investigated the effects of pH, total solids (TS) content, and enzymatic pretreatment on lactic acid (LA) production from food waste with indigenous microbiota. A multilevel factorial design was applied to all the essential factors for making LA production the most efficient and productive. The experimental data revealed that all the tested factors had a significant effect on the LA produced. The production of LA was progressively increased with the increase of TS content from 50 to 150 g-TS/L. With enzymatic pretreatment, the maximum production of volatile fatty acids (VFAs) and LA was, respectively, 26.17 g/L and 12.87 g/L at a pH of 6 and 150 g-TS/L. A LA yield of 0.09 g/g-TS with a productivity of 1.29 g/L day was achieved at mesophilic temperature of 37 °C and optimal operating conditions. Interestingly, the production of VFAs was 2.6-fold, and LA was 3-fold higher compared to those obtained with untreated food waste under same conditions. These results showed that enzymatically pretreated food waste at TS 15% can provide high production of VFAs and LA. The high selectivity of LA in the fermentative product, along with others, could make downstream processing economical. The multilevel factorial design predicted optimum conditions and presented a good agreement with a mean error of less than 5%.

Production of lactic acid by continuous electrodialysis fermentation with a glucose concentration controller

This study evaluated biohydrogen production in a continuous multiple tube reactor (CMTR) using a lactic acid-rich substrate derived from the co-fermentation of cassava starch wastewater (CSW) with glycerol. The process had two stages: (i) lactic acid (LA) production in an anaerobic sequential batch reactor (ASBR); and (ii) use of the LA-rich substrate in the CMTR at different organic loading rates (OLRs): 48, 72, and 96 g COD L⁻¹ d⁻¹, with a fixed hydraulic retention time of 4 h. The lactic fermentation produced a homogeneous substrate with 41% LA and 52% glycerol, suitable for hydrogen generation. CMTR performance varied with OLR: the highest OLR (96 g COD L⁻¹ d⁻¹) resulted in the greatest volumetric hydrogen production rate (1,960.3 mL H₂ L⁻¹ d⁻¹), biogas flow (9,360.9 mL d⁻¹), and COD removal (41.8%). The intermediate OLR (72 g COD L⁻¹ d⁻¹) achieved the highest hydrogen yield (8.4 mmol H₂ g⁻¹ COD), along with 95% lactic acid and 65% glycerol conversion. Metabolite profiling reinforced LA’s role as a strategic substrate in promoting efficient fermentative routes, indicating a selective shift toward the butyric pathway, where lactic and acetic acids are converted into butyric acid and hydrogen. Overall, the results demonstrate that lactic pre-fermentation of CSW and glycerol produces a viable substrate for biohydrogen production, enabling the application of elevated OLRs and maintaining a pH favourable to hydrogenogenic microbial activity. The CMTR proved to be a promising system for agro-industrial waste valorisation through sustainable hydrogen generation.

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

Characterization of inulin hydrolyzing enzyme(s) in commercial glucoamylases and its application in lactic acid production from Jerusalem artichoke tubers (Jat)

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.

Waste to wealth is a common trend in the world today. This work reports the utilization of waste fruit peels for production of lactic acid using authochthonouslactic acid bacteria. Peels of mango, orange and banana were prepared in powdered form, pretreated with HCl and added as carbon source for lactic acid production. The proximate analyses of the substrates were done. The organisms used for fermentation were isolated from spoilt banana and identified using biochemical and molecular tools. These organisms were grown using different growth factors over a period of eight days with initial pH of 6.0. Growth factors were then varied in order to optimize the yield of lactic acid. Percentage production of lactic acid was determined every 24 hours. The optimized conditions were then combined for further comparison. Isolated Lactobacillus plantarumand Lactobacillus caseiwere used for the production of lactic acid. The carbohydrate content of mango, banana and orange peels (62.48%, 55.34% and 57.06% respectively) showed that it was sufficient for use as a carbon source. The highest yield of lactic acid (27.10%) was at pH 6.0 with 2g of substrate and 1 ml inoculum at day six by Lactobacillus caseiwhile the highest yield by Lactobacillus plantarum (23.85%) was at pH 6.0, with 4g of substrate and 2 ml inoculum at day six. The highest production of lactic acid was derived when mango peels were used. The results of this study showed that lactic acid can be produced using mango, orange and banana peels.

Impact of storage duration and micro-aerobic conditions on lactic acid production from food waste