Acid hydrolysis of sugarcane bagasse for lactic acid production

In order to use sugarcane bagasse as a substrate for lactic acid production, optimum conditions for acid hydrolysis of the bagasse were investigated. After lignin extraction, the conditions were varied in terms of hydrochloric (HCl) or sulfuric (H₂SO₄) concentration (0.5–5%, v/v), reaction time (1–5 h) and incubation temperature (90–120 °C). The maximum catalytic efficiency (E) was 10.85 under the conditions of 0.5% of HCl at 100 °C for 5 h, which the main components (in g l⁻¹) in the hydrolysate were glucose, 1.50; xylose, 22.59; arabinose, 1.29; acetic acid, 0.15 and furfural, 1.19. To increase yield of lactic acid production from the hydrolysate by Lactococcus lactis IO-1, the hydrolysate was detoxified through amberlite and supplemented with 7 g l⁻¹ of xylose and 7 g l⁻¹ of yeast extract. The main products (in g l⁻¹) of the fermentation were lactic acid, 10.85; acetic acid, 7.87; formic acid, 6.04 and ethanol, 5.24.     

Development of a continuous cell-recycle fermentation system for production of lactic acid by Lactobacillus paracasei

Experimental devices for stimulating productivity of lactic acid fermentation were installed and an electromagnetic flow-meter and a pneumatic diaphragm pump were employed to alleviate the fouling of the membrane and to improve the durability of membrane cell-recycle bioreactors (MCRBs). In this case, the continuous fermentation using a 5 L automatic fermentor lasted stably over 150 h, and could repeat periodically with simple intermittent on-line cleaning and sterilization of the membrane filtration system. Maximum value of OD₆₂₀ of 98.7 was obtained, six times greater than that of the fed-batch fermentation. Meanwhile, maximum productivity of 31.5 g/(L h) was recorded, 10 times greater than that occurred in the fed-batch fermentation. Compared with conventional MCRBs, the MCRB system with a diaphragm pump and tangential flow-rate controlling was more stable and durable. The tangential velocity of membrane module could be monitored and controlled on-line, and the possibility of contamination due to hose rupture could be eliminated.     

Improving the lactic acid production of Actinobacillus succinogenes by using a novel fermentation and separation integration system

This work describes the development of a novel integrated system for lactic acid production by Actinobacillus succinogenes. Fermentation and separation were integrated with the use of a microfiltration (MF) membrane, and lactic acid was recovered by resin adsorption following MF. The fermentation broth containing residual sugar and nutrients was then recycled back into the fermenter after lactic acid adsorption. This novel approach overcame the problem of product inhibition and extended the cell growth period from 41 h to 120 h. Production of lactic acid was improved by 23% to 183.4 g L⁻¹. The overall yield and productivity for glucose were 0.97 g g⁻¹ and 1.53 g L⁻¹ h⁻¹, respectively. These experimental results indicate that the integrated system could benefit continuous production of lactic acid at high levels.     

Efficiency of lactic acid production by Lactobacillus helveticus in a membrane cell recycle reactor

Abstract: An economic evaluation is presented of lactic acid production in a membrane cell recycle reactor. From this evaluation it is concluded that the economic feasibility of the process is primarily limited by production capacity and product concentration and to a lesser extent by productivity. In membrane cell recycle reactor experiments and batch cultivation experiments with Lactobacillus helreticus , it is shown that the economic feasibility of the process using this organism is limited by organic acid inhibition resulting in energy uncoupling of anabolism and catabolism. Due to this inhibition, the maximum lactic acid concentration that can be obtained in the membrane reactor process is 50 g I^1—. Furthermore it is shown that not only the fermentative conversion of lactose into lactic acid but also the hydrolysis of lactose into glucose and galactose is an important process. The β-galaetosidase activity needed for the hydrolysis is generated during the exponential growth phase of Lb. helveticus     

Batch cultures of supplemented whey permeate using Lactobacillus helveticus: unstructured model for biomass formation, substrate consumption and lactic acid production

The Luedeking and Piret expression can not account for the cessation of production observed at the end of batch; so an empiric term has been previously added to this equation which accounted in a global way for possible substrate limitations. In the model developed in this work, a carbon substrate limitation appeared explicitly in the production expression. Assuming a sigmoidal variation with time of specific growth rate previously validated, the new production model matched well the entire experimental production kinetics. It has been successfully tested for a wide range of nitrogen supplementations, i.e. from an almost total coupling between growth and production for largely supplemented media, to a high decoupling in case of few available nitrogen. Since all the parameters of this model have an obvious biologic meaning, it may be an unvaluable tool for the comprehension of the phenomenon. The model accounted also well for the variation of the specific production rate versus specific growth rate, avoiding the noise due to the direct differentiation of experimental data.     

Buffering capacity and membrane H+ conductance of lactic acid bacteria

Abstract Buffering capacity and membrane conductance to H⁺ were measured in Enterococcus faecalis and Lactobacillus acidophilus by a pulse technique. The magnitude of these parameters varied between one species and another. Over the pH range studied, from pH 3.72 to 7.74, the acidophile Lactobacillus acidophilus showed higher values of buffering capacity and membrane H⁺ conductance than the neutrophile Enterococcus faecalis . These results support the idea that acidophiles have high cytoplasmic buffering capacity, which may allow them to resist changes in cytoplasmic pH.     

Lactic acid production from lignocellulose-derived sugars using lactic acid bacteria: Overview and limits

Lactic acid is an industrially important product with a large and rapidly expanding market due to its attractive and valuable multi-function properties. The economics of lactic acid production by fermentation is dependent on many factors, of which the cost of the raw materials is very significant. It is very expensive when sugars, e.g., glucose, sucrose, starch, etc., are used as the feedstock for lactic acid production. Therefore, lignocellulosic biomass is a promising feedstock for lactic acid production considering its great availability, sustainability, and low cost compared to refined sugars. Despite these advantages, the commercial use of lignocellulose for lactic acid production is still problematic. This review describes the “conventional” processes for producing lactic acid from lignocellulosic materials with lactic acid bacteria. These processes include: pretreatment of the biomass, enzyme hydrolysis to obtain fermentable sugars, fermentation technologies, and separation and purification of lactic acid. In addition, the difficulties associated with using this biomass for lactic acid production are especially introduced and several key properties that should be targeted for low-cost and advanced fermentation processes are pointed out. We also discuss the metabolism of lignocellulose-derived sugars by lactic acid bacteria.     

Direct lactic acid fermentation: Focus on simultaneous saccharification and lactic acid production

In the recent decades biotechnological production of lactic acid has gained a prime position in the industries as it is cost effective and eco-friendly. Lactic acid is a versatile chemical having a wide range of applications in food, pharmaceutical, leather and textile industries and as chemical feedstock for so many other chemicals. It also functions as the monomer for the biodegradable plastic. Biotechnological production is advantageous over chemical synthesis in that we can utilize cheap raw materials such as agro-industrial byproducts and can selectively produce the stereo isomers in an economic way. Simultaneous saccharification and fermentation can replace the classical double step fermentation by the saccharification of starchy or cellulosic biomass and conversion to lactic acid concurrently by adding inoculum along with the substrate degrading enzymes. It not only reduces the cost of production by avoiding high energy consuming biomass saccharification, but also provides the higher productivity than the single step conversion by the providing adequate sugar release.     

Recent advances in lactic acid production by microbial fermentation processes

Fermentative production of optically pure lactic acid has roused interest among researchers in recent years due to its high potential for applications in a wide range of fields. More specifically, the sharp increase in manufacturing of biodegradable polylactic acid (PLA) materials, green alternatives to petroleum-derived plastics, has significantly increased the global interest in lactic acid production. However, higher production costs have hindered the large-scale application of PLA because of the high price of lactic acid. Therefore, reduction of lactic acid production cost through utilization of inexpensive substrates and improvement of lactic acid production and productivity has become an important goal. Various methods have been employed for enhanced lactic acid production, including several bioprocess techniques facilitated by wild-type and/or engineered microbes. In this review, we will discuss lactic acid producers with relation to their fermentation characteristics and metabolism. Inexpensive fermentative substrates, such as dairy products, food and agro-industrial wastes, glycerol, and algal biomass alternatives to costly pure sugars and food crops are introduced. The operational modes and fermentation methods that have been recently reported to improve lactic acid production in terms of concentrations, yields, and productivities are summarized and compared. High cell density fermentation through immobilization and cell-recycling techniques are also addressed. Finally, advances in recovery processes and concluding remarks on the future outlook of lactic acid production are presented.     

Ethanol and lactic acid production from sugar and starch wastes by anaerobic acidification

Anaerobic conversion of carbohydrates can generate various end‐products. Besides physical parameters such as pH and temperature, the types of carbohydrate being fermented influences the fermentation pattern. Under uncontrolled pH, microbial mixed cultures from activated sludge and anaerobic digester sludge anaerobically produced ethanol from glucose while producing lactic acid from starch conversion. This trend was not only observed in batch trials. Also, continuous chemostat operation of anaerobic digester sludge resulted in the reproducible predominance of ethanol fermentation from glucose solution and lactic acid production from starch. Different feeding regimes and substrate availability (shock load versus continuous feeding) in glucose fermentation under non‐controlled pH did not affect the ethanol production as the major end product. Shifts in feed composition from glucose to starch and vice versa result in an immediate change of fermentation end products formation.     

Hyaluronic acid production and molecular weight improvement by redirection of carbon flux towards its biosynthesis pathway

Hyaluronic acid (HA) production in Streptococcus zooepidemicus competes for the carbon source along with biomass formation, lactate formation (via glycolysis) and pentose phosphate pathway (PPP). In our studies, increase in HA molecular weight was observed by redirecting the carbon flux towards HA biosynthesis pathway by partially inhibiting the glycolytic pathway. Batch bioreactor (1.2 L) studies showed that with the addition of 25 μM sodium iodoacetate, 5 g/L tryptophan and 10 g/L pyruvate, which are glycolytic inhibitors, HA molecular weight increased to 3.2, 3.2 and 3.1 MDa respectively compared to control run (2.4 MDa). Yield coefficients Y_HA/S and Y_LA/S showed inverse relationship, indicating competition for glucose between HA and lactic acid formation. Addition of 5 g/L glutamine along with 25 μM sodium iodoacetate also increased the HA concentration to 5.0 g/L from 2.0 g/L in control run. Metabolic flux analysis studies show that concentration and molecular weight of HA is increased by decreasing carbon flux towards glycolysis and PPP and increasing carbon flux towards HA precursor formation. It was observed that specific growth rate of the cells correlated positively to the specific HA production rate and negatively to the molecular weight of HA produced. Addition of antioxidant tannic acid also increased molecular weight to 3.0 MDa.     

Fermentative production of lactic acid from biomass: an overview on process developments and future perspectives

The concept of utilizing excess biomass or wastes from agricultural and agro-industrial residues to produce energy, feeds or foods, and other useful products is not necessarily new. Recently, fermentation of biomass has gained considerable attention due to the forthcoming scarcity of fossil fuels and also due to the necessity of increasing world food and feed supplies. A cost-effective viable process for lactic acid production has to be developed for which several attempts have been initiated. Fermentation techniques result in the production of either d (−) or l (+) lactic acid, or a racemic mixture of both, depending on the type of organism used. The interest in the fermentative production of lactic acid has increased due to the prospects of environmental friendliness and of using renewable resources instead of petrochemicals. Amylolytic bacteria Lactobacillus amylovorus ATCC 33622 is reported to have the efficiency of full conversion of liquefied cornstarch to lactic acid with a productivity of 20 g l⁻¹ h⁻¹. A maximum of 35 g l⁻¹ h⁻¹ was reported using a high cell density of L. helveticus (27 g l⁻¹) with a complete conversion of 55- to 60-g l⁻¹ lactose present in whey. Simultaneous saccharification and fermentation is proved to be best in the sense of high substrate concentration in lower reactor volume and low fermentation cost. In this review, a survey has been made to see how effectively the fermentation technology explored and exploited the cheaply available source materials for value addition with special emphasis on lactic acid production.     

两株乳酸菌的产酸性能及其对抗生素敏感性研究

从市售酸奶中分离出2株乳酸菌,经鉴定为嗜热链球菌(St)与保加利亚乳杆菌(Lb),并对其产酸性能及对抗生素敏感性进行了研究。结果表明:St与Lb 1∶1混合发酵效果优于单菌发酵;乳酸菌对4种抗生素类药物敏感性较弱,服用该类药物对人体肠道内乳酸菌的有益作用产生的影响较小。     

Progress and potential in the biotechnology of lactic acid bacteria

Abstract: Current activities and future prospects for the biotechnology of lactic acid bacteria are reviewed. Genetic engineering technology, including advances and limitations of plasmid vectors and chromosomal integration strategies are discussed together with the status of gene expression and the importance of in vivo gene transfer systems and transposition. Areas of biotechnological application considered include proteolysis and flavour generation, bacteriophage resistance, antimicrobials, metabolic engineering and the possible uses of lactic acid bacteria in relation to health.     

Continuous production of lactic acid from whey permeate by Lactobacillus helveticus in two chemostats in series

The effect of dilution rate on the production of lactic acid from whey permeate by Lactobacillus helveticus has been investigated. In the first chemostat of a two-stage system, total conversion (98.1%) and maximum lactic acid concentration (43.7 g l⁻¹) were obtained at a dilution rate (D_Itot) of 0.06 h⁻¹. Maximum volumetric productivities of lactic acid (8.27 g l⁻¹ h⁻¹) and biomass (1.90 g l⁻¹ h⁻¹) occurred at D_Itot of 0.40 h⁻¹. The fraction of -lactate in the product was found to increase with dilution rate and reached a maximum of 66% at the same dilution rate. The maximum specific growth rate (μ_max) on this medium was 0.7 h⁻¹. A Y_ATP (max) value of 22.4 g dry weight (mol ATP)⁻¹ and a maintenance coefficient of 8.0 mmol ATP (g dry weight h)⁻¹ were determined. The second stage, in series with the first, confirmed these results and further showed that the total residence time could be reduced by 50%, compared with a single chemostat for the same nearly complete level of substrate conversion.     

Fermentation-based biotransformation of bioactive phenolics and volatile compounds from cashew apple juice by select lactic acid bacteria

Select lactic acid bacteria (LAB); Lactobacillus plantarum, L. casei and L. acidophilus were targeted for enhancing bioactives and flavor volatiles of cashew apple juice (CAJ) that is an underutilized byproduct from cashew nut processing in Tropical countries. Results indicated the vitamin C and phenolic metabolites such as condensed tannin can be increased at certain stages such as at 12 h over the 48 h fermentation period. Whereas antioxidant activity based on DPPH and ABTS radical scavenging activity generally decreased from initial unfermented stage range of (75%–95%) to consistently in the 50% range by 48 h of fermentation and this follows the decrease in viable counts. The fermentation process increased the condensed tannin contents in CAJ whereas hydrolysable tannins decreased. In this study the changes in flavor volatile types were also analyzed over the course of CAJ fermentation. The results indicated that LAB changed the flavor profiles of fermented CAJ and overall the fruity odor decreased, but the whiskey and acid odor increased. These results provide the foundation to further target the functional benefits of LAB-induced fermented CAJ for further human, animal, and plant health applications.     

Semicontinuous production of lactic acid in a bioreactor coupled with nanofiltration membranes

The advantages of nanofiltration membranes coupled with a CSTR were demonstrated for the semicontinuous production of lactic acid from whey permeate. Lactic acid was removed from the growth medium while lactose was kept in the bioreactor with the bacterial cells; moreover, Mg²⁺ ions were also recycled in the bioreactor at 96% and the nanofiltrate color was greatly reduced. The highest volumetric productivity achieved with this device was 7.1 g l⁻¹ h⁻¹ and the lactate concentration was 55 g l⁻¹. The specific productivity was 3.54 h⁻¹. More than 99% of the membrane fouling after 44 h of fermentation was reversible. The initial permeate flux was restored easily by a water rinse. The performance of this type of membrane bioreactor was discussed.     

The physiology and biochemistry of the proteolytic system in lactic acid bacteria

Abstract: The inability of lactic acid bacteria to synthesize many of the amino acids required for protein synthesis necessitates the active functioning of a proteolytic system in those environments where protein constitutes the main nitrogen source. Biochemical and genetic analysis of the pathway by which exogenous proteins supply essential amino acids for growth has been one of the most actively investigated aspects of the metabolism of lactic acid bacteria especially in those species which are of importance in the dairy industry, such as the lactococci. Much information has now been accumulated on individual components of the proteolytic pathway in lactococci, namely, the cell envelope proteinase(s), a range of peptidases and the amino acid and peptide transport systems of the cell membrane. Possible models of the proteolytic system in lactococci can be proposed but there are still many unresolved questions concerning the operation of the pathway in vivo. This review will examine current knowledge and outstanding problems regarding the proteolytic system in lactococci and also the extent to which the lactococcal system provides a model for understanding proteolysis in other groups of lactic acid bacteria.     

Identification of lactic acid bacteria isolated from human vaginal secretions

A total of 57 lactic acid bacteria were isolated from the vaginal secretions of 259 patients. Of these strains, 37 were isolated from patients attending pre-natal clinics and the remaining strains from patients attending post-natal clinics. The strains were identified by using simple physiological and biochemical tests and their phenotypic relatedness determined by numerical analysis of total soluble cell protein patterns. The genotypic relatedness of representative strains selected from each of the protein profile clusters was determined by numerical analysis of the DNA banding patterns obtained from RAPD-PCR. The majority of lactobacilli isolated belonged to the species Lactobacillus pentosus, Lactobacillus fermentum and Enterococcus faecium. A few strains of Lactobacillus plantarum and Weissella viridescens were also isolated. One strain, TV 1029, grouped into the same protein profile cluster as E. faecium, but revealed a DNA banding pattern closer related to Enterococcus faecalis. This is the first report of W. viridescens associated with the human vagina. This revised version was published online in June 2006 with corrections to the Cover Date.