Characterization of a maltose-forming α-amylase from an amylolytic lactic acid bacterium Lactobacillus plantarum S21

Exploiting the Native Microorganisms from Different Food Matrices to Formulate Starter Cultures for Sourdough Bread Production

The use of sourdough for bread production involves fermentation, which is dominated by lactic acid bacteria (LAB) and yeast. Sourdough can be inoculated with a starter culture or through a food matrix containing microorganisms to initiate sourdough fermentation. Sourdough is used as leavening agent for bread making, and metabolites produced by LAB and yeast confer a specific aroma and flavor profile to bread, thus improving its sensory attributes. However, few publications report the effect of microorganisms from different food products and by-products on sourdough fermentation. This review focuses on using different starter cultures from various food sources, from wheat flour to starter cultures. Additionally, included are the types of sourdough, the sourdough fermentation process, and the biochemical transformations that take place during the sourdough fermentation process.

Efficient Secretion and Recombinant Production of a Lactobacillal α-amylase in Lactiplantibacillus plantarum WCFS1: Analysis and Comparison of the Secretion Using Different Signal Peptides

Lactic acid bacteria (LAB) have been used as starter cultures and producers of enzymes, antimicrobial peptides or metabolites that contribute to the flavor, texture and safety of food products. Lactiplantibacillus plantarum, one of the best-studied LAB, is considered as safe and effective cell factory for food applications. In this study, our aim was to use L. plantarum as the producer for high levels of a food-grade lactobacillal α-amylase, which has potential applications in food, fermentation and feed industries. The native form of an α-amylase (AmyL) from L. plantarum S21, an amylolytic LAB isolated from Thai fermented rice noodles, was expressed in L. plantarum WCFS1 using the pSIP expression system. The secretion of the α-amylase was driven by the native signal peptides of the α-amylases from L. plantarum S21 (SP_AmyL) and Lactobacillus amylovorus NRRL B-4549 (SP_AmyA), as well as by three Sec-type signal peptides derived from L. plantarum WCFS1; Lp_2145, Lp_3050, and Lp_0373. Among the tested signal peptides, Lp_2145 appears to be the best signal peptide giving the highest total and extracellular enzymatic activities of α-amylase AmyL from L. plantarum S21, which were 13.1 and 8.1 kU/L of fermentation, respectively. These yields were significantly higher than the expression and secretion in L. plantarum WCFS1 using the native signal peptide SP_AmyL, resulting in 6.2- and 5.4-fold increase in total and extracellular activities of AmyL, respectively. In terms of secretion efficiency, Lp_0373 was observed as the most efficient signal peptide among non-cognate signal peptides for the secretion of AmyL. Real-time reverse-transcriptase quantitative PCR (RT-qPCR) was used to estimate the mRNA levels of α-amylase transcript in each recombinant strain. Relative quantification by RT-qPCR indicated that the strain with the Lp_2145 signal peptide-containing construct had the highest mRNA levels and that the exchange of the signal peptide led to a change in the transcript level of the target gene.

Bioaugmentation by Pediococcus acidilactici AAF1-5 Improves the Bacterial Activity and Diversity of Cereal Vinegar Under Solid-State Fermentation

Bioaugmentation technology may be an effective strategy to improve the solid-state fermentation rate and utilization of raw materials for traditional vinegar production. The relationship between bacteria and fermentation process was analyzed to rationally design and perform bioaugmented solid-state fermentation of the Tianjin Duliu mature vinegar (TDMV). Fermentation process was highly correlated with Acetobacter, Lactobacillus, and Pediococcus contents, which were the core functional microorganisms in TDMV fermentation. Pediococcus acidilactici AAF1-5 was selected from 20 strains to fortify the fermentation due to its acidity and thermal tolerance. Bioaugmentation was performed in the upper layer of TDMV fermentation. P. acidilactici AAF1-5 colonized and then spread into the lower layer to improve the fermentation. Result showed that the fermentation period was 5 days less than that of the control. Meanwhile, the non-volatile acid, lactic acid, amino nitrogen, and reducing sugar contents in the bioaugmented TDMV increased by 53%, 14%, 32%, and 36%, respectively, compared with those in the control. Bioaugmentation with P. acidilactici AAF1-5 not only improved the utilization of starch from 79% to 83% but also increased the bacterial community diversity.

Utilizing Gelatinized Starchy Waste from Rice Noodle Factory as Substrate for L(+)-Lactic Acid Production by Amylolytic Lactic Acid Bacterium Enterococcus faecium K-1

To valorize starchy waste from rice noodle factory, bioconversion of gelatinized starchy waste (GSW) to value-added product as L(+)-lactic acid, the monomer for polylactate synthesis, was investigated using amylolytic lactic acid bacterium, Enterococcus faecium K-1. Screening for appropriate nitrogen source to replace expensive organic nitrogen sources revealed that corn steep liquor (CSL) was the most suitable regarding high efficacy for L(+)-LA achievement and low-cost property. The successful applying statistic experimental design, Plackett-Burman design incorporated with central composite design (CCD), predicted the maximum L(+)-LA of 93.07 g/L from the optimized medium (OM) containing 125.7 g/L GSW and 207.3 g/L CSL supplemented with CH₃COONa, MgSO₄, MnSO₄, K₂HPO₄, CaCl₂, (NH₄)₂HC₆H₅O₇, and Tween80. Minimizing the medium cost by removal of all inorganic salts and Tween80 from OM was not an effect on L(+)-LA yield. Fermentation using the optimized medium without minerals (OM-Mi) containing only GSW (125.7 g/L) and CSL (207.3 g/L) in a 10-L fermenter was also successful. Thinning GSW with α-amylase from Lactobacillus plantarum S21 increased L(+)-LA productivity in the early stage of 24-h fermentation. Not only showing the feasible bioconversion process for GSW utilizing as a substrate for L(+)-LA production, this research also demonstrated the efficient model for industrial starchy waste valorization.

Aislamiento e identificación de microorganismos potencialmente amilolíticos y celulolíticos de suelos de humedales de Bogotá

Las amilasas y celulasas de origen microbiano se han utilizado desde hace más de tres décadas en la industria; el aislamiento de cepas microbianas nativas productoras de enzimas es el punto de partida para aprovechar la biodiversidad microbiana para la obtención de enzimas con propiedades para la obtención de nuevos productos en la optimización de procesos industriales. El objetivo de este trabajo, fue aislar, a partir de suelo de cinco humedales en Bogotá, cepas microbianas con capacidad para producir enzimas amilolíticas y celulolíticas. Se realizó la medición de halos de hidrólisis en agar almidón y agar carboximetilcelulosa. Se determinaron las unidades enzimáticas (U/ml/min) por medio de azúcares reductores por la técnica de DNS. Se seleccionaron cuatro cepas de Bacillus subtillis amiloliquefaciens productoras de amilasas con actividades entre 752±33 y 480 ± 35 U/ml/min a 60ºC y cinco cepas celulolíticas identificadas como Bacillus subtillis amiloliquefaciens, Stenotrophomonas nitritireducens y Yersinia massiliensis, capaces de producir celulasas con actividades enzimáticas entre 19.11 ± 2.3 y 13.82 ± 2.5 UA/ml/min a 50ºC. Con estos resultados se demostró que a partir de suelos de humedales, se pueden recuperar microrganismos con capacidad de producción enzimática, como punto de partida para una posterior aplicación en procesos industriales.

Simultaneous Bioconversion of Gelatinized Starchy Waste from the Rice Noodle Manufacturing Process to Lactic Acid and Maltose-Forming α-Amylase by Lactobacillus plantarum S21, Using a Low-Cost Medium

A direct bioconversion of gelatinized starchy waste (GSW) to lactic acid by amylolytic lactic acid bacterium Lactobacillus plantarum S21 was investigated. Corn steep liquor (CSL) was selected as the most suitable low-cost nitrogen source for replacing yeast extract, beef extract, and peptone in De Man, Rogosa and Sharpe (MRS) medium. Plackett–Burman design results indicated that GSW and CSL were the two most nutrients that significantly influence lactic acid production, among eight medium components, including GSW, CSL, K2HPO4, CH3COONa, (NH4)2HC6H5O7, MgSO4, MnSO4, and Tween 80. A new low-cost medium containing only GSW (134.4 g/L) and CSL (187.7 g/L) was achieved as omitting other six components from the optimized medium had no effect on lactic acid yield. Batch fermentation at 37 °C both in 1 L and 10 L jar fermenters showed non-significantly different productivity. A by-product, maltose-forming α-amylase, was successfully achieved up to 96% recovery yield using an ultrafiltration unit equipped with a 50 kDa cut-off membrane. Crude lactic acid exhibited the additional benefit of antimicrobial activity against food and feed pathogens Salmonella enterica serovar Typhimurium TISTR 292, Vibrio cholerae TH-001, and also E. coli ATCC 25922. This study presents a promising bioprocess for the simultaneous production of lactic acid, and a value-added food enzyme, using only two industrial wastes, GSW and CSL, as the medium components.

Expression and biochemical characterization of a new alkaline tannase from Lactobacillus pentosus

Lactobacillus pentosus BA-7 and L. pentosus QA1-5 are tannin-tolerant lactic acid bacteria that were isolated from Miang, a traditional fermented tea-leaf found in northern Thailand and a tannin-rich substrate. Tannase encoding genes were isolated, cloned and overexpressed in Escherichia coli BL21(DE3). The recombinant tannase was produced with production yields of 40 and 39 KU/L for LpTanBA-7 and LpTanQA1-5, respectively. Both revealed the same molecular weight of 50 kDa as estimated by SDS-PAGE and were optimally active under alkaline pH conditions LpTanQA1-5 revealed optimal temperatures in a range of 37-40 °C as is typically found in lactic acid bacteria, while LpTanBA-7 was active at higher temperatures with an optimum temperature range of 45-55 °C. LpTanBA-7 was found to be more stable within the same range of temperatures than LpTanQA1-5. Furthermore, it was active and stable toward various organic solvents and produced 50 mg/mL of gallic acid from 100 mg/mL tannic acid. Based on the results, LpTanBA-7 is considered a new alkali-moderately thermophilic tannase obtained from lactic acid bacterium that may be capable of a feasible production capacity of gallic acid and its esters. Furthermore, tannase that is active at high temperatures could also be used in tea products in order to develop a sweet aftertaste, as well as to improve levels of antioxidant activity.

Expression and comparative characterization of complete and C-terminally truncated forms of saccharifying α-amylase from Lactobacillus plantarum S21

Lactobacillus plantarum S21 α-amylase possesses 475 amino acids at the C-terminal region identified as the starch-binding domain (SBD) and has been previously reported to play a role in raw starch degradation. To understand the specific roles of this SBD, cloning and expression of the complete (AmyL9) and C-terminally truncated (AmyL9Δ_SBD) forms of α-amylase were conducted for enzyme purification and comparative characterization. AmyL9 and AmyL9Δ_SBD were overproduced in Escherichia coli at approximately 10- and 20-times increased values of volumetric productivity when compared to α-amylase produced by the wild type, respectively. AmyL9Δ_SBD was unable to hydrolyze raw starch and exhibited substrate specificity in a similar manner to that of AmyL9, but it was weakly active toward amylopectin and glycogen. The hydrolysis products obtained from the amylaceous substrates of both enzymes were the same. In addition, AmyL9Δ_SBD showed comparatively higher K_m values than AmyL9 when it reacted with starch and amylopectin, and lower values for other kinetic constants namely v_max, k_cat, and k_cat/K_m. The results indicated that the C-terminal SBDs of L. plantarum S21 α-amylase contribute to not only substrate preference but also substrate affinity and the catalytic efficiency of the α-amylase without any changes in the degradation mechanisms of the enzyme.

Amylolytic Enzymes Acquired from L-Lactic Acid Producing Enterococcus faecium K-1 and Improvement of Direct Lactic Acid Production from Cassava Starch

An amylolytic lactic acid bacterium isolate K-1 was isolated from the wastewater of a cassava starch manufacturing factory and identified as Entercoccus faecium based on 16S rRNA gene sequence analysis. An extracellular α-amylase was purified to homogeneity and the molecular weight of the purified enzyme was approximately 112 kDa with optimal pH value and temperature measured of 7.0 and 40 °C, respectively. It was stable at a pH range of 6.0-7.0, but was markedly sensitive to high temperatures and low pH conditions, even at a pH value of 5. Ba²⁺, Al³⁺, and Co²⁺ activated enzyme activity. This bacterium was capable of producing 99.2% high optically pure L-lactic acid of 4.3 and 8.2 g/L under uncontrolled and controlled pH at 6.5 conditions, respectively, in the MRS broth containing 10 g/L cassava starch as the sole carbon source when cultivated at 37 °C for 48 h. A control pH condition of 6.5 improved and stabilized the yield of L-lactic acid production directly from starch even at a high concentration of starch at up to 150 g/L. This paper is the first report describing the properties of purified α-amylase from E. faecium. Additionally, pullulanase and cyclodextrinase activities were also firstly recorded from E. faecium K-1.

Nondairy beverage produced by controlled fermentation with potential probiotic starter cultures of lactic acid bacteria and yeast

This work aimed to develop a nondairy fermented beverage from a blend of cassava and rice based on Brazilian indigenous beverage cauim using probiotic lactic acid bacteria (LAB) and yeast. The indigenous strains Lactobacillus plantarum CCMA 0743 (from cauim) and Torulaspora delbrueckii CCMA 0235 (from tarubá), and the commercial probiotic, L. acidophilus LAC-04, were used as starter cultures in single and co-cultivations. The bacteria populations were around 8.0 log (CFU/mL) at the end of all fermentations as recommended for probiotic products. Higher residual starch contents were noted in the single LAB cultures (10.6% [w/w]) than in co-cultures (<6% [w/w]), showing that co-culture may help the digestibility. For all different assays (single and co-culture), lactic acid was the main organic acid detected (>1.6g/L) and ethanol was lower than 0.5% (w/v) consisting in a non-alcoholic beverage. The assays containing yeast showed the highest antioxidant activity (around 10% by DPPH and ABTS methods). Therefore, a nondairy fermented beverage was successfully obtained, and the co-culture of LAB and T. delbrueckii could increase the product's functional properties.

Bacterial and Archaeal α-Amylases: Diversity and Amelioration of the Desirable Characteristics for Industrial Applications

Industrial enzyme market has been projected to reach US$ 6.2 billion by 2020. Major reasons for continuous rise in the global sales of microbial enzymes are because of increase in the demand for consumer goods and biofuels. Among major industrial enzymes that find applications in baking, alcohol, detergent, and textile industries are α-amylases. These are produced by a variety of microbes, which randomly cleave α-1,4-glycosidic linkages in starch leading to the formation of limit dextrins. α-Amylases from different microbial sources vary in their properties, thus, suit specific applications. This review focuses on the native and recombinant α-amylases from bacteria and archaea, their production and the advancements in the molecular biology, protein engineering and structural studies, which aid in ameliorating their properties to suit the targeted industrial applications.