Highest Lactic Acid Yield Research Articles

Batch fermentations on synthetic mixed sugar and starch medium with amylolytic lactic acid bacteria

The green crop drying industry in Denmark uses Italian rye grass, clover, and alfalfa as raw materials for the production of green pellets. The green crop drying industry solves its energy economical problems by heating and pressing of the green crop before drying. The produced sidestream is called brown juice. Brown juice was shown to be an excellent medium for lactic acid fermentation. The aim of this study was to investigate the utilisation of brown juice in the production of polylactic acid, where wheat starch would be added to increase the lactic acid yield and, thus, the feasibility of the process. A number of amylolytic lactic acid bacteria have been identified, and in this work, six different strains were tested for their ability to produce alpha-amylase and to utilise all sugars with high lactic acid yield in a medium with a complex composition of free sugars (brown juice) and starch. Lactobacillus plantarum A6 was the only strain that showed both a good lactic acid production and utilisation of starch in this medium. The growth rate of this strain was approximately 0.4 h(-1) and the lactic acid yield was 0.7.

Production of lactic acid and byproducts from waste potato starch by Rhizopus arrhizus: role of nitrogen sources

Lactic acid was produced by Rhizopus arrhizus using waste potato starch as the substrate. The aim of this study was to identify the role of nitrogen sources and their impact on the formation of lactic acid and associated byproducts. Ammonium sulphate, ammonium nitrate, urea, yeast extract and peptone were assessed in conjunction with various ratios of carbon to nitrogen (C:N). Fermentation media with a low C:N ratio enhanced the production of lactic acid, biomass and ethanol, while a high C:N ratio favoured the production of fumaric acid. Ammonium nitrate appeared to be the most suitable nitrogen source for achieving a high and stable lactic acid yield, and minimizing the production of byproducts such as biomass and ethanol, while urea proved to be the least favourable nitrogen source. Yeast extract and peptone appeared to improve fungal cell growth. The kinetics data revealed that a high concentration of ammonium nitrate enhanced the lactic acid productivity. The maximum lactic acid concentration of 36.4 g/l, representing a yield of 91%, was obtained with addition of 0.909 g/l ammonium nitrate in 32 h.

Production of lactic acid and fungal biomass by Rhizopus fungi from food processing waste streams

This study proposed a novel waste utilization bioprocess for production of lactic acid and fungal biomass from waste streams by fungal species of Rhizopus arrhizus 36017 and R. oryzae 2062. The lactic acid and fungal biomass were produced in a single-stage simultaneous saccharification and fermentation process using potato, corn, wheat and pineapple waste streams as production media. R. arrhizus 36017 gave a high lactic acid yield up to 0.94-0.97 g/g of starch or sugars associated with 4-5 g/l of fungal biomass produced, while 17-19 g/l fungal biomass with a lactic acid yield of 0.65-0.76 g/g was produced by the R. oryzae 2062 in 36-48 h fermentation. Supplementation of 2 g/l of ammonium sulfate, yeast extract and peptone stimulated an increase in 8-15% lactic acid yield and 10-20% fungal biomass.

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

In this study, the system of electrodialysis fermentation (EDF) was improved by a glucose concentration controller (GC controller) which could control glucose concentration stable and low in fermentation broth. Under the control of the GC controller, there were little inhibitory effects of the end product and substrate on bacteria so as to result in high activity of bacteria and, further, in high productivity of lactic acid. Moreover, the low glucose concentration in the fermentation broth brought about little glucose leakage to the recovery solution and hence high yield of lactic acid. Compared with the EDFs carried out in the previous studies, the continuous EDF with a glucose concentration controller (CEDF with GC controller) was higher in productivity, yield and conversion ratio of lactic acid, indicating that it was a system more efficient to produce lactic acid.

Impurity and cost considerations for nutrient supplementation of whey permeate fermentations to produce lactic acid for biodegradable plastics

A potential application for whey permeate is to ferment it to lactic acid for use in the manufacture of biodegradable plastics. High purity lactic acid is required, thus the separation of impurities after fermentation is a major process cost. For batch fermentations, whey permeate requires nutrient supplementation, which can add to impurity levels at the end of fermentation. This work presents the results of whey permeate fermentations using L. casei , supplemented with yeast extract, whey protein hydrolysate, and malt combing nuts (MCN). There is an emphasis on investigating how little supplement needs to be added while still achieving high lactose conversion and lactic acid yield in a reasonable fermentation time. This was around 0.4% w/w for yeast extract, 5% for the hydrolysate (10% whey protein solution) and 5% for MCN. At these levels of supplement addition, the majority of the supplement is actually not utilised and just contributes to a major increase in the concentration of impurities at the end of the fermentation with a corresponding increase in separation cost, in addition to raw material cost. The ash content of regular whey permeate is another significant source of impurities that need to be separated to produce high purity lactic acid. Fermentations were performed to investigate the effect of low ash content on fermentation performance. Fermentations performed in supplemented demineralised whey permeate, with at least 70% ash reduction, showed no negative effect on fermentation performance, however fermentations conducted in a supplemented lactose solution did show a slowdown in fermentation performance. This is most likely due to mineral deficiency which should not pose a problem as minerals are usually micronutrients, and addition of very small amounts are required to restore fermentation performance.

Direct fermentation of various pure and crude starchy substrates to L(+) lactic acid using Lactobacillus amylophilus GV6

Lactobacillus amylophilus GV6 fermented a variety of pure and natural starches directly to L(+) lactic acid. Starch to lactic acid conversion efficiency was more than 90% by strain GV6 at low substrate concentrations with all starches. The strain GV6 produced high yields of lactic acid per g of substrate utilized with pure starches such as soluble starch, corn starch, and potato starch, yielding 92–96% at low substrate concentrations in 2 days and 78–89% at high substrate (10%) concentrations in 4–6 days. Strain GV6 also produced high yields of lactic acid per g of substrate utilized with crude starchy substrates such as wheat flour, sorghum flour, cassava flour, rice flour and barley flour yielding 90–93% at low substrate concentrations in 2 days and 80% or more at high substrate concentrations in 6–7 days. Lactic acid yields by L. amylophilus GV6 with pure starches were comparable when low cost crude starchy substrates were used. Lactic acid productivity by strain GV6 is higher than for any other previously reported strains of L. amylophilus.

Efficient homolactic fermentation by Kluyveromyces lactis strains defective in pyruvate utilization and transformed with the heterologous LDH gene.

A high yield of lactic acid per gram of glucose consumed and the absence of additional metabolites in the fermentation broth are two important goals of lactic acid production by microrganisms. Both purposes have been previously approached by using a Kluyveromyces lactis yeast strain lacking the single pyruvate decarboxylase gene (KlPDC1) and transformed with the heterologous lactate dehydrogenase gene (LDH). The LDH gene was placed under the control the KlPDC1 promoter, which has allowed very high levels of lactate dehydrogenase (LDH) activity, due to the absence of autoregulation by KlPdc1p. The maximal yield obtained was 0.58 g g(-1), suggesting that a large fraction of the glucose consumed was not converted into pyruvate. In a different attempt to redirect pyruvate flux toward homolactic fermentation, we used K. lactis LDH transformant strains deleted of the pyruvate dehydrogenase (PDH) E1alpha subunit gene. A great process improvement was obtained by the use of producing strains lacking both PDH and pyruvate decarboxylase activities, which showed yield levels of as high as 0.85 g g(-1) (maximum theoretical yield, 1 g g(-1)), and with high LDH activity.

Influence of whey protein hydrolysate addition to whey permeate batch fermentations for producing lactic acid

Addition of whey protein hydrolysate (WPH) to whey permeate fermentations, by Lactobacillus helveticus, to produce lactic acid was investigated. Three to four percent (w/w) supplementation with WPH solution (10% w/w protein) was required to obtain high lactose conversion and lactic acid yield in a fermentation time of 30–40 h. At this percentage supplementation, the nitrogen content of the media was 0.06–0.09% w/w. The bacteria used around 0.02% w/w nitrogen during fermentation, thus there was an abundance of unused nitrogen remaining at the end of fermentation. At 3–4% supplementation, it was calculated that around 36–47% of whey protein concentrate produced from whey would be required to supplement the whey permeate fermentation in the form of the hydrolysate.

Effect of manganese on Lactobacillus casei fermentation to produce lactic acid from whey permeate

Batch fermentations were performed to investigate the effect of manganese addition, in the form of MnSO 4·H 2O, on the performance of Lactobacillus casei for producing l-lactic acid from whey permeate supplemented with yeast extract. There was a particular emphasis on evaluating how little yeast extract and MnSO 4·H 2O is required while still obtaining high sugar conversion and lactic acid yield, as nutrient supplementation is a raw material cost and can lead to extra residual impurities remaining after fermentation. The addition of MnSO 4·H 2O had a significant beneficial affect with the fermentation time being reduced from 120 to 24 h for permeate supplemented with 0.50%w/v yeast extract. Fermentations were performed with MnSO 4·H 2O concentrations in the range of 0.001–0.03 g/l. From 0.005 to 0.03 g/l, the fermentation performance was very similar, however at the low concentration of 0.001 g/l, the fermentation was significantly slower. With MnSO 4·H 2O addition, the yeast extract concentration was reduced to 0.30%w/v while still maintaining high sugar conversion and lactic acid yield, however the fermentation was slower at 37 h. At 0.1%w/v yeast extract supplementation, the fermentation performance was poor with only 67% sugar conversion after 150 h of fermentation.

Integrated utilisation of green biomass in the green biorefinery

Grass, clover and alfalfa are used for production of fodder pellets. In the green crop drying factories in the northern countries the drying is combined with pressing of the green crops resulting in production of large volumes of plant juices, green and brown juice. In order to get rid of these enormous amounts of plant juice, representing an environmental threat, it is our aim to convert the simple drying industry to a whole crop utilisation factory, a green biorefinery, where the plant juice can be used as raw material in a fermentation process. As the plant juice is very unstable, it has been necessary to develop a method for both conservation and utilisation of the juice. The plant juice is converted to a nice universal fermentation medium by lactic acid bacteria. A number of lactic acid producing strains have been tested. Among the most productive strains, Lactobacillus paracasei ssp. paracasei P4155 is found to be the most effective in utilising fructans and citric acid. Most carbohydrates and organic acids in the juice can be converted to lactic acid by two homofermentative lactobacilli. The highest lactic acid yield and productivity is reached when using not-heat sterilised brown or green juice as the fermentation medium. The amount of free amino acids in the juice is increased and the content of vitamins and other important growth factors kept unspoiled by the lactic acid fermentation. The fermented juice can be stored as it is or evaporated to a concentrated form and used in fermentation industries for production of amino acids, organic acids, enzymes etc.

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

Batch fermentation of lactose to lactic acid was conducted using Lactobacillus plantarum under aerobic and anaerobic conditions (operation without aeration). Synthetic lactose medium was used as the culture medium and the effects of pH and substrate concentration on cell growth and lactic acid production were investigated. Lactic acid fermentation with this bacterium is found to be homolactic and primarily growth associated. Optimum pH for cell growth and acid production was found to be between 5 and 6. Anaerobic fermentation gave a higher lactic acid yield of about 2.3 times that for aerobic fermentation. Cell growth rate was about two times higher, but cell yield was only about 80% of that for aerobic fermentation. Batch fermentation studies with no pH control indicate that lactose slightly inhibits cell growth in the exponential growth phase but there are no effects in the stationary and death phases. The high lactic acid yield (0.95∼1.03 (w/w), the complete conversion rate is 1.05 (w/w)), tolerance of low pH conditions and the high cell growth rate indicate a great potential for the use of L. plantarum in lactic acid fermentations for industrial applications. Taking pH variations into account in a Monod's model, a nonlinear parameter estimation procedure using the Gaussian method and numerical integration of the differential equation by the fourth-order Runge–Kutta method are used to obtain optimal kinetic model parameters.

Fermentative production of l-lactic acid by Lactobacillus casei DSM 20011 and product recovery using ion exchange resins

In order to produce l(+)-lactic acid to be employed in poly-l-lactic acid polymer production, for biomedical applications, the strain Lactobacillus casei subsp. casei DSM 20011 was studied in a conventional batch mode using different initial concentrations of glucose. The results obtained showed that the initial glucose concentration exerts an influence on the fermentation pattern, modifying the different fermentation parameters. Nevertheless, the product yield remained at a constant value of 0.86 g·g−1. The proposed novel system of product recovery, based on the use of ion-exchange resins, gave high yields of pure lactic acid.

Lactic acid production using animal wastes as inoculum

The possibility to produce lactic acid using mixed heterogeneous inoculum found in cowdung has been demonstrated controlling physicochemical factors such as pH, temperature and the composition of the culture medium. At low pH values the principal final product was always ethanol while at higher pH values was always lactic acid, irrespective of the nitrogen source. Lactate production increased significantly when growth factors (vitamins) were added to the culture media irrespective of the nitrogen source. The results indicate that mixed cultures could be grown on media with ammonium sulphate nitrogen source obtaining high yields of lactic acid.