Factors affecting the fermentative lactic acid production from renewable resources1

Lactic acid was discovered in 1780 by C.W. Scheele in sour milk, and in 1881 Fermi obtained lactic acid by fermentation, resulting in its industrial production. The yearly world lactic acid production is expected to reach 259,000 metric tons by the year 2012. The interest in lactic acid is related to many aspects, among which is its relatively high added-value. In addition, such a chemical is GRAS (Generally Recognized As Safe), being recognized as harmless by the United States Food and Drug Administration, has a market with great growth potential, can be alternatively produced by fermentation or chemical synthesis and can employ a large variety of different waste materials as substrates. Lactic acid has many applications. Its existence in the form of two stereoisomers does in fact make the application of one of them or of the racemic mixture of great concern in different fields. In particular, the food and pharmaceutical industries have a preference for the isomer l (+), the only one that can be metabolized by the human body; however, the chemical industry requires one of the pure isomers or a mixture of both, according to the application. This review describes biotechnological processes to obtain lactic acid from polymeric substrates such as starchy and lignocellulosic materials. Open challenges are related to the technological optimization of the fermentation process and product purification and recovery. In addition, the opportunities and difficulties associated with using raw materials for lactic acid production are discussed.

https://maaz.ihmc.us/rid=1N4KLGGDB-C7FZZY-93H/Castillo%20Martinez%20et%20al.%20-%202013%20-%20Lactic%20acid%20properties,%20applications%20and%20productio.pdf

Lactic acid properties, applications and production: a review.

Amylolytic bacterial lactic acid fermentation - a review.

Direct lactic acid fermentation: focus on simultaneous saccharification and lactic acid production.

Aims: The overall growth kinetics of four potentially probiotic strains (Lactobacillus fermentum , Lact. reuteri , Lact. acidophilus and Lact. plantarum ) cultured in malt, barley and wheat media were investigated. The objectives were to identify the main factors influencing the growth and metabolic activity of each strain in association with the cereal substrate. Methods and Results: All fermentations were performed without pH control. A logistic-type equation, which included a growth inhibition term, was used to describe the experimental data. In the malt medium, all strains attained high maximum cell populations (8.10-10.11 log(10) cfu ml(-1) , depending on the strain), probably due to the availability of maltose, sucrose, glucose, fructose (approx. 15 g l(-1) total fermentable sugars) and free amino nitrogen (approx. 80 mg l(-1) ). The consumption of sugars during the exponential phase (10-12 h) resulted in the accumulation of lactic acid (1.06-1.99 g l(-1) ) and acetic acid (0.29-0.59 g l(-1) ), which progressively decreased the pH of the medium. Each strain demonstrated a specific preference for one or more sugars. Since small amounts of sugars were consumed by the end of the exponential phase (17-43%), the decisive growth-limiting factor was probably the pH, which at that time ranged between 3.40 and 3.77 for all of the strains. Analysis of the metabolic products confirmed the heterofermentative or homofermentative nature of the strains used, except in the case of Lact. acidophilus which demonstrated a shift towards the heterofermentative pathway. All strains produced acetic acid during the exponential phase, which could be attributed to the presence of oxygen. Lactobacillus plantarum , Lact. reuteri and Lact. fermentum continued to consume the remaining sugars and accumulate metabolic products in the medium, probably due to energy requirements for cell viability, while Lact. acidophilus entered directly into the decline phase. In the barley and wheat media all strains, especially Lact. acidophilus and Lact. reuteri , attained lower maximum cell populations (7.20-9.43 log(10) cfu ml(-1) ) than in the malt medium. This could be attributed to the low sugar content (3-4 g l(-1) total fermentable sugar for each medium) and the low free amino nitrogen concentration (15.3-26.6 mg l(-1) ). In all fermentations, the microbial growth ceased at pH values (3.73- 4.88, depending on the strain) lower than those observed for malt fermentations, which suggests that substrate deficiency in sugars and free amino nitrogen contributed to growth limitation. Conclusions: The malt medium supported the growth of all strains more than barley and wheat media due to its chemical composition, while Lact. plantarum and Lact. fermentum appeared to be less fastidious and more resistant to acidic conditions than Lact. acidophilus and Lact. reuteri . Significance and Impact of the Study: Cereals are suitable substrates for the growth of potentially probiotic lactic acid bacteria.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2672.2002.01592.x

Growth studies of potentially probiotic lactic acid bacteria in cereal-based substrates

The biosynthesis of ammonium lactate, a product of lactic acid fermentation was studied from corn and glucose at five different pH values of 5.4 to 7.8. In the glucose fermentations, a 100% conversion of substrate was obtained resulting in a maximum lactic acid production yield of 93.2%. The optimum pH for the maximum volumetric rate of lactic acid biosynthesis (1.56 g dm−3 h−1) was between 6.0 and 6.5. The corn fermentations were slower than the glucose fermentations with a resulting lactic acid yield of 67.5%. Hydrolysis of corn by enzymatic or chemical methods as well as the use of ammonium hydroxide for pH control increased both the final concentration and the rates of lactic acid production. An enhanced yield of more than 90% was finally obtained in the corn fermentations. A logistic model adequately described the kinetics of biomass growth, lactic acid production and sugar utilization in the glucose fermentations at different pH values. The dynamics of lactic acid formation in the corn fermentations were also successfully described by the developed model. The dependence of the model parameters on pH was investigated.

P. Mercier

Papers

Kinetics of lactic acid fermentation on glucose and corn by Lactobacillus amylophilus