Microbial and Physiological Characterization of Weakly Amylolytic but Fast-Growing Lactic Acid Bacteria: a Functional Role in Supporting Microbial Diversity in Pozol, a Mexican Fermented Maize Beverage

Pozol is an acid beverage obtained from the natural fermentation of nixtamal (heat- and alkali-treated maize) dough. The concentration of mono- and disaccharides from maize is reduced during nixtamalization, so that starch is the main carbohydrate available for lactic acid fermentation. In order to provide some basis to understand the role of amylolytic lactic acid bacteria (ALAB) in this fermented food, their diversity and physiological characteristics were determined. Forty amylolytic strains were characterized by phenotypic and molecular taxonomic methods. Four different biotypes were distinguished via ribotyping; Streptococcus bovis strains were found to be predominant. Streptococcus macedonicus, Lactococcus lactis, and Enterococcus sulfureus strains were also identified. S. bovis strain 25124 showed extremely low amylase yield relative to biomass (139 U g [cell dry weight]⁻¹) and specific rate of amylase production (130.7 U g [cell dry weight]⁻¹ h⁻¹). In contrast, it showed a high specific growth rate (0.94 h⁻¹) and an efficient energy conversion yield to bacterial cell biomass (0.31 g of biomass g of substrate⁻¹). These would confer on the strain a competitive advantage and are the possible reasons for its dominance. Transient accumulation of maltooligosaccharides during fermentation could presumably serve as energy sources for nonamylolytic species in pozol fermentation. This would explain the observed diversity and the dominance of nonamylolytic lactic acid bacteria at the end of fermentation. These results are the first step to understanding the importance of ALAB during pozol fermentation.     

Isolation and characterization of new amylolytic strains of Lactobacillus fermentum from fermented maize doughs (mawè and ogi) from Benin

Twelve amylolytic heterofermentative lactic acid bacteria were isolated in Benin from the fermentation processes of maize sour dough, namely ogi and mawè. Discrimination of strains was performed by DNA restriction patterns and compared with carbohydrate fermentation profiles. This allowed two new amylolytic strains, Ogi E1 and Mw2, belonging to the species Lactobacillus fermentum , to be distinguished. Strains Ogi E1 and Mw2 presented different amylolytic activities; amylase from strain Mw2 was more acidophilic and mesophilic than amylase produced by strain Ogi E1.     

Preliminary studies on chorote – a traditional Mexican fermented product

Summary The purpose of this work was to study some biochemical and microbiological changes occurring during the fermentation of chorote, an important indigenous fermented food in the Mexican state of Tabasco. The chorote solid state fermentation is similar to that for the production of pozol, though fermented and roasted cacao beans are added to the maize dough. Changes in pH, lactic acid, total and soluble protein, available lysine and tryptophan as well as in some microbial groups were recorded during a 9-day fermentation period. Microbiological analysis showed an increase in moulds, yeasts, amylolytic lactic acid and nitrogen-fixing bacteria during the fermentation. There was a decrease in pH (to 4.2) and a significant net increase in protein content. There was also an increase in soluble protein and tryptophan.     

解淀粉乳酸细菌在L-乳酸发酵生产中的应用

对解淀粉乳酸细菌及其产生的淀粉酶和发酵工艺等方面的国内外研究现状进行了综述。解淀粉乳酸细菌具有分泌淀粉酶的能力,可免去原料水解处理工序直接发酵淀粉质原料生产乳酸,可以简化生产工艺,并可节约设备投资,进而降低生产成本。解淀粉乳酸细菌主要分离自传统发酵食品,也可从有机废弃物和厨余垃圾中分离得到。介绍了解淀粉乳酸细菌直接利用淀粉质原料的机理,比较了解淀粉乳酸菌发酵生产L-乳酸的工艺。提出通过诱变育种和基因工程育种等方法获得更加高效的解淀粉乳酸细菌,并结合先进的发酵、分离技术来提高乳酸生产效率。     

Effect of pH control on lactic acid fermentation of starch by Lactobacillus manihotivorans LMG 18010T

Lactic acid fermentation of starch by Lactobacillus manihotivorans LMG 18010T, a new amylolytic L(+) lactic acid producer, was investigated and compared with starch fermentation by Lact. plantarum A6. At non-controlled pH, growth and lactic acid production from starch by Lact. manihotivorans LMG 18010T lasted 25 h. Specific growth and lactic acid production rates continuously decreased from the onset of the fermentation, unlike Lact. plantarum A6 which was able to grow and convert starch product hydrolysis into lactic acid more rapidly and efficiently at a constant rate up to pH 4.5. In spite of complete and rapid starch hydrolysis by Lact. manihotivorans LMG 18010T during the first 6 h, only 45% of starch hydrolysis products were converted to lactic acid. When pH was maintained at 6.0, lactic acid, amylase and final biomass production by Lact. manihotivorans LMG 18010T increased markedly and the fermentation time was reduced by half. Under the same conditions, an increase only in amylase production was observed with Lact. plantarum A6. When grown on glucose or starch at pH 6.0, Lact. manihotivorans LMG 18010T had an identical maximum specific growth rate (0.35 h(-1)), whereas the maximum rate of specific lactic acid production was three times higher with glucose as substrate. Lactobacillus manihotivorans LMG 18010T did not produce amylase when grown on glucose. Based on the differences in the physiology between the two species and other amylolytic lactic acid bacteria, different applications may be expected.     

Identification and functional properties of dominant lactic acid bacteria isolated at different stages of solid state fermentation of cassava during traditional <Emphasis Type="Italic">gari</Emphasis> production

Culture-based technique was used to study the population dynamics of the bacteria and determine the dominant lactic acid bacteria (LAB) during cassava fermentation. LAB was consistently isolated from the fermented mash with an initial viable count of 6.00 log c.f.u. g⁻¹ observed at 12 h. The aerobic viable count of amylolytic lactic acid bacteria (ALAB) was higher than other group of LAB throughout the fermentation up to 96 h with the highest viable count of 8.08 log c.f.u. g⁻¹. Combination of phenotypic parameters and 16S rDNA gene sequencing identified the dominant group of LAB as Lactobacillus plantarum, L. fermentum and Leuconostoc mesenteroides while the pulse field gel electrophoresis determined that the strains were genotypically heterogeneous. The sugar fermentation profile of the isolates showed that indigestible sugars such as raffinose and stachyose can be fermented by the strains. Information was also generated about the functional properties of the strains. Only strain L. plantarum 9st0 isolate at 0 h of the fermentation produced bacteriocin with antagonism against closely related indicator strains. Quantitatively, the highest amylase activity was produced by strain L. plantarum 7st12, while appreciable amylase was also produced by L. fermentum 1st96. The result of this work showed that selection of mixed starter cultures of bacteriocin- and amylase-producing L. plantarum and L. fermentum will be highly relevant as starter cultures during the intermediate and large scale gari production.     

Polyphasic study of the spatial distribution of microorganisms in Mexican pozol, a fermented maize dough, demonstrates the need for cultivation-independent methods to investigate traditional fermentations

The distribution of microorganisms in pozol balls, a fermented maize dough, was investigated by a polyphasic approach in which we used both culture-dependent and culture-independent methods, including microbial enumeration, fermentation product analysis, quantification of microbial taxa with 16S rRNA-targeted oligonucleotide probes, determination of microbial fingerprints by denaturing gradient gel electrophoresis (DGGE), and 16S ribosomal DNA gene sequencing. Our results demonstrate that DGGE fingerprinting and rRNA quantification should allow workers to precisely and rapidly characterize the microbial assemblage in a spontaneous lactic acid fermented food. Lactic acid bacteria (LAB) accounted for 90 to 97% of the total active microflora; no streptococci were isolated, although members of the genus Streptococcus accounted for 25 to 50% of the microflora. Lactobacillus plantarum and Lactobacillus fermentum, together with members of the genera Leuconostoc and Weissella, were the other dominant organisms. The overall activity was more important at the periphery of a ball, where eucaryotes, enterobacteria, and bacterial exopolysacharide producers developed. Our results also showed that the metabolism of heterofermentative LAB was influenced in situ by the distribution of the LAB in the pozol ball, whereas homolactic fermentation was controlled primarily by sugar limitation. We propose that starch is first degraded by amylases from LAB and that the resulting sugars, together with the lactate produced, allow a secondary flora to develop in the presence of oxygen. Our results strongly suggest that cultivation-independent methods should be used to study traditional fermented foods.     

Microbial community dynamics during production of the Mexican fermented maize dough pozol

The dynamics of the microbial community responsible for the traditional fermentation of maize in the production of Mexican pozol was investigated by using a polyphasic approach combining (i) microbial enumerations with culture media, (ii) denaturing gradient gel electrophoresis (DGGE) fingerprinting of total community DNA with bacterial and eukaryotic primers and sequencing of partial 16S ribosomal DNA (rDNA) genes, (iii) quantification of rRNAs from dominant microbial taxa by using phylogenetic oligonucleotide probes, and (iv) analysis of sugars and fermentation products. A Streptococcus species dominated the fermentation and accounted for between 25 and 75% of the total flora throughout the process. Results also showed that the initial epiphytic aerobic microflora was replaced in the first 2 days by heterofermentative lactic acid bacteria (LAB), including a close relative of Lactobacillus fermentum, producing lactic acid and ethanol; this heterolactic flora was then progressively replaced by homofermentative LAB (mainly close relatives of L. plantarum, L. casei, and L. delbrueckii) which continued acidification of the maize dough. At the same time, a very diverse community of yeasts and fungi developed, mainly at the periphery of the dough. The analysis of the DGGE patterns obtained with bacterial and eukaryotic primers targeting the 16S and 18S rDNA genes clearly demonstrated that there was a major shift in the community structure after 24 h and that high biodiversity-according to the Shannon-Weaver index-was maintained throughout the process. These results proved that a relatively high number of species, at least six to eight, are needed to perform this traditional lactic acid fermentation. The presence of Bifidobacterium, Enterococcus, and enterobacteria suggests a fecal origin of some important pozol microorganisms. Overall, the results obtained with different culture-dependent or -independent techniques clearly confirmed the importance of developing a polyphasic approach to study the ecology of fermented foods.     

Optimisation of media and cultivation conditions for L(+)(S)-lactic acid production by Lactobacillus casei NRRL B-441

Process variables and concentration of carbon in media were optimised for lactic acid production by Lactobacillus casei NRRL B-441. Lactic acid yield was inversely proportional to initial glucose concentration within the experimental area (80-160 g l(-1)). The highest lactic acid concentration in batch fermentation, 118.6 g l(-1), was obtained with 160 g 1(-1) glucose. The maximum volumetric productivity, 4.4 g 1(-1) h(-1) at 15 h, was achieved at an initial glucose concentration of 100 g l(-1). Similar lactic acid concentrations were reached with a fedbatch approach using growing cells, in which case the fermentation time was much shorter. Statistical experimental design and response surface methodology were used for optimising the process variables. The temperature and pH optima for lactic acid production were 35 degrees C, pH 6.3. Malt sprout extract supplemented with yeast extract (4 g l(-1)) appeared to be an economical alternative to yeast extract alone (22 g l(-1)) although the fermentation time was a little longer. The results demonstrated both the separation of the growth and lactic acid production phases and lactic acid production by non-growing cells without any nutrient supplements. Resting L. casei cells converted 120 g l(-1) glucose to lactic acid with 100% yield and a maximum volumetric productivity of 3.5 g l(-1) h(-1).     

Amylolytic bacterial lactic acid fermentation - a review

Lactic acid, an enigmatic chemical has wide applications in food, pharmaceutical, leather, textile industries and as chemical feed stock. Novel applications in synthesis of biodegradable plastics have increased the demand for lactic acid. Microbial fermentations are preferred over chemical synthesis of lactic acid due to various factors. Refined sugars, though costly, are the choice substrates for lactic acid production using Lactobacillus sps. Complex natural starchy raw materials used for production of lactic acid involve pretreatment by gelatinization and liquefaction followed by enzymatic saccharification to glucose and subsequent conversion of glucose to lactic acid by Lactobacillus fermentation. Direct conversion of starchy biomass to lactic acid by bacteria possessing both amylolytic and lactic acid producing character will eliminate the two step process to make it economical. Very few amylolytic lactic acid bacteria with high potential to produce lactic acid at high substrate concentrations are reported till date. In this view, a search has been made for various amylolytic LAB involved in production of lactic acid and utilization of cheaply available renewable agricultural starchy biomass. Lactobacillus amylophilus GV6 is an efficient and widely studied amylolytic lactic acid producing bacteria capable of utilizing inexpensive carbon and nitrogen substrates with high lactic acid production efficiency. This is the first review on amylolytic bacterial lactic acid fermentations till date.     

Culture-independent quantification of physiologically-active microbial groups in fermented foods using rRNA-targeted oligonucleotide probes: application to pozol, a Mexican lactic acid fermented maize dough

Nine phylogenetic oligonucleotide probes were used to describe at the genus level the microbial community responsible for the spontaneous fermentation of maize, leading to the production of Mexican pozol. Ribosomal RNAs of specific groups and genera, in particular, lactic acid bacteria, were quantified using a culture-independent approach. In the early stage of the fermentation, Lactococcus and Leuconostoc appeared to be the dominant genera. A contrario, these represented minor genera at the end of the fermentation when Lactobacillus dominated the process. In addition, eukaryotes seemed to play a significant role throughout the fermentation and enterobacteria could be detected by this method.     

Amylolytic activity of selected species of ruminal bacteria.

A variety of species of ruminal bacteria were screened for the ability to grow in starch-containing medium and produce amylase. Of those tested, the highest levels of amylase were produced by Streptococcus bovis JB1 and Ruminobacter amylophilus H18. Other strains that grew well on starch and produced amylase included Butyrivibrio fibrisolvens A38 and 49 and Bacteroides ruminicola 23 and B14. Varying the carbohydrate source provided for growth resulted in changes in the growth rate and level of amylase produced by these strains. All strains grew rapidly in starch-containing medium, and the rates of growth were generally more rapid than those observed for maltose-grown cultures. For S. bovis JB1, B. ruminicola 23 and B14, and B. fibrisolvens 49 and A38, amylase was produced when growth was on maltose or starch, but this activity was greatly reduced in glucose-grown cultures. The distribution of amylolytic activity between cellular and extracellular fractions was sometimes affected by the carbohydrate provided for growth. If S. bovis JB1 and B. fibrisolvens 49 were grown on starch, amylase was largely associated with cell pellets; however, if grown on maltose these strains produced activities that were almost entirely present in the extracellular fluid fractions. Although not as dramatic, a similar shift in the location of amylase activities was noted for the two B. ruminicola strains when grown on the same substrates. Growth on maltose or starch had little influence on either the predominantly cell-associated activity of B. fibrisolvens A38 or the activity of R. amylophilus H18, which was equally divided between cell pellet and extracellular fluid fractions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of cofermentation by amylolytic Lactobacillus plantarum and Lactococcus lactis strains on the fermentation process and rheology of sorghum porridge

Amylolytic lactic acid bacteria (ALAB) can potentially replace malt in reducing the viscosity of starchy porridges. However, the drawback of using ALAB is their low and delayed amylolytic activity. This necessitates searching for efficient ALAB and strategies to improve their amylolytic activity. Two ALAB, Lactobacillus plantarum MNC 21 and Lactococcus lactis MNC 24, isolated from Obushera, were used to ferment starches in MRS broth: sorghum, millet, sweet potato, and commercial soluble starch. The amylolytic activity of MNC 21 was comparable to that of the ALAB collection strain Lb. plantarum A6, while that of MNC 24 was extremely low. MNC 21, MNC 24, and their coculture were compared to A6 and sorghum malt for ability to ferment and reduce the viscosity of sorghum porridge (11.6% dry matter). ALAB and the coculture lowered the pH from 6.2 to <4.5 within 12 h, while malt as a carrier of wild starter took about 20 h. Coculturing increased lactic acid yield by 46% and 76.8% compared to the yields of MNC 21 and MNC 24 monocultures, respectively. The coculture accumulated significantly larger (P < 0.05) amounts of maltose and diacetyl than the monocultures. Sorghum malt control and the coculture hydrolyzed more starch in sorghum porridge than the monocultures. The coculture initiated changes in the rheological parameters storage modulus (G'), loss modulus (G″), phase angle (δ), and complex viscosity (η*) earlier than its constituent monocultures. The shear viscosity of sorghum porridge was reduced significantly (P < 0.05) from 1950 cP to 110 cP (malt), 281 cP (coculture), 382 cP (MNC 21), 713 cP (MNC 24), and 722 cP (A6). Coculturing strong ALAB with weak ALAB or non-ALAB can be exploited for preparation of nutrient-dense weaning foods and increasing lactic acid yield from starchy materials.     

Amylolytic activity of selected species of ruminal bacteria

A variety of species of ruminal bacteria were screened for the ability to grow in starch-containing medium and produce amylase. Of those tested, the highest levels of amylase were produced by Streptococcus bovis JB1 and Ruminobacter amylophilus H18. Other strains that grew well on starch and produced amylase included Butyrivibrio fibrisolvens A38 and 49 and Bacteroides ruminicola 23 and B14. Varying the carbohydrate source provided for growth resulted in changes in the growth rate and level of amylase produced by these strains. All strains grew rapidly in starch-containing medium, and the rates of growth were generally more rapid than those observed for maltose-grown cultures. For S. bovis JB1, B. ruminicola 23 and B14, and B. fibrisolvens 49 and A38, amylase was produced when growth was on maltose or starch, but this activity was greatly reduced in glucose-grown cultures. The distribution of amylolytic activity between cellular and extracellular fractions was sometimes affected by the carbohydrate provided for growth. If S. bovis JB1 and B. fibrisolvens 49 were grown on starch, amylase was largely associated with cell pellets; however, if grown on maltose these strains produced activities that were almost entirely present in the extracellular fluid fractions. Although not as dramatic, a similar shift in the location of amylase activities was noted for the two B. ruminicola strains when grown on the same substrates. Growth on maltose or starch had little influence on either the predominantly cell-associated activity of B. fibrisolvens A38 or the activity of R. amylophilus H18, which was equally divided between cell pellet and extracellular fluid fractions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of Streptococcus bovis from the rumen of the dromedary camel and Rusa deer

AIMS: Isolation and characterization of Streptococcus bovis from the dromedary camel and Rusa deer. METHODS AND RESULTS: Bacteria were isolated from the rumen contents of four camels and two deer fed lucerne hay by culturing on the semi-selective medium MRS agar. Based on Gram morphology and RFLP analysis seven isolates, MPR1, MPR2, MPR3, MPR4, MPR5, RD09 and RD11 were selected and putatively identified as Streptococcus. The identity of these isolates was later confirmed by comparative DNA sequence analysis of the 16S rRNA gene with the homologous sequence from S. bovis strains, JB1, C14b1, NCFB2476, SbR1, SbR7 and Sb5, from cattle and sheep, and the Streptococcus equinus strain NCD01037T. The percentage similarity amongst all strains was >99%, confirming the identification of the camel isolates as S. bovis. The strains were further characterized by their ability to utilize a range of carbohydrates, the production of volatile fatty acids (VFA) and lactate and the determination of the doubling time in basal medium 10 supplemented with glucose. All the isolates produced l-lactate as a major fermentation end product, while four of five camel isolates produced VFA. The range of carbohydrates utilized by all the strains tested, including those from cattle and sheep were identical, except that all camel isolates and the deer isolate RD11 were additionally able to utilize arabinose. CONCLUSIONS: Streptococcus bovis was successfully isolated from the rumen of camels and deer, and shown by molecular and biochemical characterization to be almost identical to S. bovis isolates from cattle and sheep. SIGNIFICANCE AND IMPACT OF THE STUDY: Streptococcus bovis is considered a key lactic acid producing bacterium from the gastrointestinal tract of ruminants, and has been implicated as a causative agent of lactic acidosis. This study is the first report of the isolation and characterization of S. bovis from the dromedary camel and Rusa deer, and suggests a major contributive role of this bacterium to fermentative acidosis.     

Engineering of Saccharomyces cerevisiae for efficient anaerobic alcoholic fermentation of L-arabinose

For cost-effective and efficient ethanol production from lignocellulosic fractions of plant biomass, the conversion of not only major constituents, such as glucose and xylose, but also less predominant sugars, such as l-arabinose, is required. Wild-type strains of Saccharomyces cerevisiae, the organism used in industrial ethanol production, cannot ferment xylose and arabinose. Although metabolic and evolutionary engineering has enabled the efficient alcoholic fermentation of xylose under anaerobic conditions, the conversion of l-arabinose into ethanol by engineered S. cerevisiae strains has previously been demonstrated only under oxygen-limited conditions. This study reports the first case of fast and efficient anaerobic alcoholic fermentation of l-arabinose by an engineered S. cerevisiae strain. This fermentation was achieved by combining the expression of the structural genes for the l-arabinose utilization pathway of Lactobacillus plantarum, the overexpression of the S. cerevisiae genes encoding the enzymes of the nonoxidative pentose phosphate pathway, and extensive evolutionary engineering. The resulting S. cerevisiae strain exhibited high rates of arabinose consumption (0.70 g h(-1) g [dry weight](-1)) and ethanol production (0.29 g h(-1) g [dry weight](-1)) and a high ethanol yield (0.43 g g(-1)) during anaerobic growth on l-arabinose as the sole carbon source. In addition, efficient ethanol production from sugar mixtures containing glucose and arabinose, which is crucial for application in industrial ethanol production, was achieved.     

Interaction of ruminal bacteria in the production and utilization of maltooligosaccharides from starch.

The degradation and utilization of starch by three amylolytic and one nonamylolytic species of ruminal bacteria were studied. Pure cultures of Streptococcus bovis JB1, Butyrivibrio fibrisolvens 49, and Bacteroides ruminicola D31d rapidly hydrolyzed starch and maltooligosaccharides accumulated. The major starch hydrolytic products detected in S. bovis cultures were glucose, maltose, maltotriose, and maltotetraose. In addition to these oligosaccharides, B. fibrisolvens cultures produced maltopentaose. The products of starch hydrolysis by B. ruminicola were even more complex, yielding glucose through maltotetraose, maltohexaose, and maltoheptaose but little maltopentaose. Selenomonas ruminantium HD4 grew poorly on starch, digested only a small portion of the available substrate, and generated no detectable oligosaccharides as a result of cultivation in starch containing medium. S. ruminantium was able to grow on a mixture of maltooligosaccharides and utilize those of lower degree (less than 10) of polymerization. A coculture system containing S. ruminantium as a dextrin-utilizing species and each of the three amylolytic bacteria was developed to test whether the products of starch hydrolysis were available for crossfeeding to another ruminal bacterium. Cocultures of S. ruminantium and S. bovis contained large numbers of S. bovis but relatively few S. ruminantium and exhibited little change in the pattern of maltooligosaccharides observed for pure cultures of S. bovis. In contrast, S. ruminantium was able to compete with B. fibrisolvens and B. ruminicola for these growth substrates. When grown with B. fibrisolvens, S. ruminantium grew to high numbers and maltooligosaccharides accumulated to a much lesser degree than in cultures of B. fibrisolvens alone. S. ruminantium-B. ruminicola cultures contained large numbers of both species, and maltooligosaccharides never accumulated in these cocultures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Direct conversion of starch to L(+) lactic acid by amylase producing Lactobacillus amylophilus GV6

Lactobacillus amylophilus strain GV6, isolated from corn starch processing industrial wastes, was amylolytic and produced 0.96?g L(+) lactic acid per gram of soluble starch. The optimum temperature and pH for growth and L(+) lactic acid production were 37?°C and 6.5, respectively. At low substrate concentrations, the lactic acid production on corn starch was almost similar to soluble starch. The strain is fermenting various naturally available starches directly to lactic acid. The total amylase activity of the strain is 0.59?U/ml/min. The strain produced 49 and 76.2?g/l L(+) lactic acid from 60?g/l corn starch and 90?g/l soluble starch, respectively. This is the highest L(+) lactic acid among the wild strains of L. amylophilus reported so far.     

Original properties of ropy strains of Lactobacillus plantarum isolated from the sour cassava starch fermentation

C. FIGUEROA, A.M. DAVILA AND J. POURQUIÉ 1997. Sour cassava starch is the result of a lactic fermentation of raw cassava starch followed by sun drying. Lactobacillus plantarum strains are commonly isolated from this fermentation. Among them, a particular group of strains has been characterized by a strong ropy phenotype, the production of a thickening factor under submerged cultures conditions, a low nutritional requirement for organic nitrogen and an absence of amylolytic activity. However, these strains have been shown to thrive on starch, through commensalistic interactions with amylolytic lactic acid bacteria. These results explain the frequent occurrence of ropy, non-amylolytic strains in sour starch fermentation, and support the hypothesis of exopolysaccharides production during this fermentation.     

Use of inexpensive nitrogen sources and starch for L(+) lactic acid production in anaerobic submerged fermentation

L(+) Lactic acid fermentation was studied by Lactobacillus amylophilus GV6 under the influence of inexpensive nitrogen sources (red lentil-RL, and Baker's yeast cells-YC) and starch by response surface methodology (RSM). Central composite rotatable design (CCRD) was employed to determine maximum lactic acid production at optimum values for process variables RL, YC and incubation period (IP) and a satisfactory fit model was realized. Lactic acid production was significantly affected by RL and IP interactions as well as by independent variables RL and YC. Maximum lactic acid production of 13.5 g/15.2g starch was obtained with RL 0.8%, YC 1% and IP of 48 h, with 92% lactic acid yield efficiency (g lactic acid produced/g substrate utilized) and 40% increase (from 50 g to 92 g/100 g starch utilized) in lactic acid production. This is the first report on response optimization in direct fermentation of starch to lactic acid using inexpensive nitrogen sources substituting peptone and yeast extract in anaerobic submerged fermentation by amylolytic lactic acid bacteria (LAB).