Use of Lactobacillus plantarum fermentation products in bread-making to prevent Bacillus subtilis ropy spoilage

Exploring the Inhibitory Activity of Selected Lactic Acid Bacteria against Bread Rope Spoilage Agents

In this study, a wide pool of lactic acid bacteria strains deposited in two recognized culture collections was tested against ropy bread spoilage bacteria, specifically belonging to Bacillus spp., Paenibacillus spp., and Lysinibacillus spp. High-throughput and ex vivo screening assays were performed to select the best candidates. They were further investigated to detect the production of active antimicrobial metabolites and bacteriocins. Moreover, technological and safety features were assessed to value their suitability as biocontrol agents for the production of clean-label bakery products. The most prominent inhibitory activities were shown by four strains of Lactiplantibacillus plantarum (NFICC19, NFICC 72, NFICC163, and NFICC 293), two strains of Pediococcus pentosaceus (NFICC10 and NFICC341), and Leuconostoc citreum NFICC28. Moreover, the whole genome sequencing of the selected LAB strains and the in silico analysis showed that some of the strains contain operons for bacteriocins; however, no significant evidence was observed phenotypically.

Modeling of Growth and Organic Acid Kinetics and Evolution of the Protein Profile and Amino Acid Content during Lactiplantibacillus plantarum ITM21B Fermentation in Liquid Sourdough

The application of mathematical modeling to study and characterize lactic acid bacterial strains with pro-technological and functional features has gained attention in recent years to solve the problems relevant to the variabilities of the fermentation processes of sourdough. Since the key factors contributing to the sourdough quality are relevant to the starter strain growth and its metabolic activity, in this study, the cardinal growth parameters for pH, temperature (T), water activity (a_w), and undissociated lactic acid of the sourdough strain Lactiplantibacillus plantarum ITM21B, were determined. The strain growth, pH, organic acids (lactic, acetic, phenyllactic, and hydroxy-phenyllactic), total free amino acids, and proteins were monitored during fermentation of a liquid sourdough based on wheat flour and gluten (Bio21B) after changing the starting T, pH, and inoculum load. Results demonstrated that the different fermentation conditions affected the strain growth and metabolite pattern. The organic acid production and growth performance were modeled in Bio21B, and the resulting predictive model allowed us to simulate in silico the strain performances in liquid sourdough under different scenarios. This mathematical predictive approach can be useful to optimize the fermentation conditions needed to obtain the suitable nutritional and technological characteristics of the L. plantarum ITM21B liquid sourdough.

Ropiness in Bread—A Re-Emerging Spoilage Phenomenon

As bread is a very important staple food, its spoilage threatens global food security. Ropy bread spoilage manifests in sticky and stringy degradation of the crumb, slime formation, discoloration, and an odor reminiscent of rotting fruit. Increasing consumer demand for preservative-free products and global warming may increase the occurrence of ropy spoilage. Bacillus amyloliquefaciens, B. subtilis, B. licheniformis, the B. cereus group, B. pumilus, B. sonorensis, Cytobacillus firmus, Niallia circulans, Paenibacillus polymyxa, and Priestia megaterium were reported to cause ropiness in bread. Process hygiene does not prevent ropy spoilage, as contamination of flour with these Bacillus species is unavoidable due to their occurrence as a part of the endophytic commensal microbiota of wheat and the formation of heat-stable endospores that are not inactivated during processing, baking, or storage. To date, the underlying mechanisms behind ropy bread spoilage remain unclear, high-throughput screening tools to identify rope-forming bacteria are missing, and only a limited number of strategies to reduce rope spoilage were described. This review provides a current overview on (i) routes of entry of Bacillus endospores into bread, (ii) bacterial species implicated in rope spoilage, (iii) factors influencing rope development, and (iv) methods used to assess bacterial rope-forming potential. Finally, we pinpoint key gaps in knowledge and related challenges, as well as future research questions.

Bacteriocin production and inhibition of Bacillus subtilis by Lactobacillus paracasei HD1.7 in an indirect coculture system

A broad-spectrum antimicrobial peptide named Paracin 1.7 was produced by Lactobacillus paracasei HD1.7, which was isolated from Chinese sauerkraut juice. In this study, the influence of cocultivation on the communication mechanism of L. paracasei HD1.7 and Bacillus subtilis was investigated. The two bacterial strains were grown in monoculture and indirect coculture, and the growth of both bacteria and bacteriocin production as well as the transcriptional level of luxS in L. paracasei HD1.7 and spo0A in B. subtilis were monitored. Bacteriocin production and cell numbers were increased significantly when L. paracasei HD1.7 cells were indirectly cocultured with B. subtilis, and bacteriocin-producing L. paracasei HD1.7 can prevent the growth and sporulation of B. subtilis. After indirect coculture with B. subtilis, the expression of luxS in L. paracasei HD1.7 increased in the exponential growth phase and decreased in the stationary phase compared to monoculture. The expression of spo0A in B. subtilis dropped in the indirect coculture compared to the monoculture. It indicate that the upregulation of luxS is due to a response to a secreted compound produced by B. subtilis. The results show L. paracasei HD1.7 has an amensalism on B. subtilis, while B. subtilis has a commensalism on L. paracasei HD1.7.

Effect of Amaranth and Quinoa Flours on Exopolysaccharide Production and Protein Profile of Liquid Sourdough Fermented by Weissella cibaria and Lactobacillus plantarum

Exopolysaccharides (EPSs) are known for their positive contribute to the technological properties of many foods, including bakery products. These molecules can be obtained performing piloted fermentation with lactic acid bacteria (LAB). In order to select strains able to produce EPS, a screening test in agar medium containing sucrose, fructose or glucose as carbohydrate source was performed on 21 LAB strains. Results allowed to select 8 Weissella cibaria, 2 Weissella confusa, and 2 Leuconostoc spp. strains as EPS producers only in the presence of sucrose. A further screening in liquid medium enriched with sucrose (10%) (mMRS_S) indicated the W. cibaria strain C43-11 as the higher EPS producer. The selected strain was used to develop liquid sourdoughs (LSs) with dough yield (DY) 500, fermented for 15 h and based on wheat flour and wheat gluten or pseudocereals (quinoa or amaranth) in ratio 1:1, in the presence or not of sucrose at 3% (w/w, LS weight), in comparison to Lactobacillus plantarum ITM21B, a strain not producing EPS in mMRS_S. Results indicated that the use of pseudocereals favored the EPS production. Formulations were optimized by modifying DY (500 or 250), sucrose concentration (3 or 6%) and flour ratio. LSs were characterized for the content of organic acids (lactic, acetic, phenyllactic, OH-phenyllactic), pH, TTA, EPS, viscosity, total protein degradation and protein pattern. The highest EPS production (20.79 g/kg) and viscosity (1168 mPa s) were obtained in LS (DY 250, sucrose 6%) based on quinoa flour and started with C43-11 strain. The LS was characterized by the presence of phenyllactic and OH-phenyllactic acids, protein degradation by 51.7% and proteins in the range 14-80 kDa. In these conditions, also strain ITM21B was able to produce EPS at level of 4.61 g/kg and to degrade proteins by 53.8% in LS based on wheat and quinoa flours (1:1) (DY250 and sucrose 3%). Therefore, results demonstrated that the use of selected conditions (flour type, DY, sucrose) can stimulate specific attributes of strains making them suitable for production of short fermented (15 h) LSs which can be used as bread improvers.

Profile of inhalable bacteria in PM2.5 at Mt. Tai, China: Abundance, community, and influence of air mass trajectories

Bacteria are ubiquitous in the near-surface atmosphere where they constitute an important component of aerosols with the potential to affect climate change, ecosystems, atmospheric process and human health. Limitation in tracking bacterial diversity accurately has thus far prevented the knowledge of airborne bacteria and their pathogenic properties. We performed a comprehensive assessment of bacterial abundance and diverse community in PM_2.5 collected at Mt. Tai, via high-throughput sequencing and real-time PCR. The samples exhibited a high microbial biodiversity and complex chemical composition. The dominating populations were gram-negative bacteria including Burkholderia, Delftia, Bradyrhizobium, and Methylobacterium. The PM mass concentration, chemical composition, bacterial concentration and community structure varied under the influence of different air-mass trajectories. The highest mass concentration of PM_2.5 (61 μg m^-3) and major chemical components were recorded during periods when marine southeasterly air masses were dominant. The local terrestrial air masses from Shandong peninsula and its adjacent areas harbored highest bacterial concentration loading (602 cells m^-3) and more potential pathogens at the site. In contrast, samples influenced by the long-distance air flow from Siberia and Outer Mongolia were found to have a highest richness and diversity as an average, which was also marked by the increase of dust-associated bacteria (Brevibacillus and Staphylococcus). The primary research may serve as an important reference for the environmental microbiologist, health workers, and city planners.

Assessment of Ready-to-Use Freeze-dried Immobilized Biocatalysts as Innovative Starter Cultures in Sourdough Bread Making

In the present study the effect of innovative biocatalysts as starter cultures in sourdough bread making was explored. The biocatalysts consisted of Lactobacillus paracasei K5 and Lactobacillus bulgaricus ATCC 11842 (in single and mixed form), immobilized on delignified wheat bran (DWB), and freeze dried without cryoprotectants. The parameters monitored were physicochemical characteristics, mold and rope spoilage appearance, volatile composition, and organoleptic characteristics. Results obtained showed that both biocatalysts exhibit good fermentative activity. However, the best results were achieved when freeze-dried immobilized L. paracasei K5 was applied as a single culture. In particular, the produced bread had a higher acidity (8.67 mL 0.1 N NaOH) and higher organic load (2.90 g/kg lactic acid and 1.11 g/kg acetic acid). This outcome was the main reason why this bread was preserved more regarding mold spoilage (14 days) and rope spoilage (12 days), respectively. In addition, the employment of freeze-dried immobilized L. paracasei K5 led to bread with better aromatic profile in terms of concentrations and number of volatile compounds produced as gas chromatography/mass spectrometry (GC/MS) analysis proved. Finally, no significant differences were observed through sensorial tests. Last but not least, it should be highlighted that the used microorganisms were cultured in cheese whey, minimizing the cost of the proposed biotechnological procedure.

Effect of a novel Lactobacillus paracasei starter on sourdough bread quality

The novel Lactobacillus paracasei K5 strain, recently isolated from Greek cheese, was evaluated as potential sourdough bread starter. Breads were made using different amounts of L. paracasei sourdoughs as well as traditional sourdough for comparison. Quality characteristics of the breads (acidity and rising) were examined, as well as rope spoilage through macroscopic observations and molecular analysis (PCR-DGGE). The highest acidity levels (3.15 g lactic acid and 1.13 g acetic acid per kg of bread) and better resistance to rope spoilage were observed when bread contained 30% w/w L. paracasei K5 sourdough. Spoilage in the L. paracasei K5 breads was observed at 15-16 days, 5 days later than the control breads. In addition, L. paracasei K5 sourdough improved the bread sensory properties, as reflected by consumer preference and GC/MS analysis of aroma volatiles. Therefore, L. paracasei K5 can be successfully used for sourdough bread making with good quality and extended shelf-life.

Longterm storage of post-packaged bread by controlling spoilage pathogens using Lactobacillus fermentum C14 isolated from homemade curd

One potent lactic acid bacterial strain C14 with strong antifungal activity was isolated from homemade curd. Based on morphological as well as biochemical characters and 16S rDNA sequence homology the strain was identified as Lactobacillus fermentum. It displayed a wide antimicrobial spectrum against both Gram-positive and Gram-negative pathogenic bacteria, and also against number of food spoilage, plant and human pathogenic fungi. The cell free supernatant (CFS) of the strain C14 was also effective against the fungi tested. Inhibition of radial growth of Penicillium digitatum, Trichophyton rubrum and Mucor sp. was noticed in the presence of CFS of C14 even at low concentration (1%). More than 94.3 ± 1.6% and 91.5 ± 2.2% inhibition of conidial germination of P. digitatum and Mucor sp. were noticed in the presence of 10-fold-concentrated CFS of C14. Massive deformation of the fungal mycelia was observed by SEM studies, and losses of cellular proteins and DNA are also evident upon its treatment with C14. HPLC analysis revealed the presence of phenyl lactic acid, lactic acid along with some unidentified compounds in the antifungal extract. Challenge experiment showed immense potential of the strain C14 in preventing the spoilage of bread samples caused by Mucor sp. and Bacillus subtilis. The bread samples remained fresh upto 25 days even after inoculation with Mucor sp. (3.7 × 104 spores /ml) and B. subtilis (4.6 × 104 CFU /ml). Along with the antifungal properties, the isolated lactic acid bacterial strain also showed very good antioxidant activities. Unchanged level of liver enzymes serum glutamic pyruvic transaminase and serum glutamic oxaloacetic transaminase in albino mice upon feeding with C14 also suggested non-toxic nature of the bacterial isolate.

Optimization of Aspergillus oryzae S2 α-amylase, ascorbic acid, and glucose oxidase combination for improved French and composite Ukrainian wheat dough properties and bread quality using a mixture design approach

A simplex-centroid experimental design was used for the optimization of both reducing and oxidizing improvers, namely Aspergillus oryzae S2 α-amylase (Amy), ascorbic acid (Asc), and glucose oxidase (GOD). This optimization was performed to enhance the dough and breadmaking qualities of soft French wheat flour and a composite counterpart that contained 30% Ukrainian wheat flour. Statistically significant correlations were calculated between the W index and textural parameters (e.g., dough chewiness and bread cohesiveness). The findings revealed that while the best mixture for French flour comprised 21.8% of Amy, 41.2% of Asc, and 37% of GOD, for the composite counterpart, it comprised 2.3% of Amy, 66% of Asc, and 31.7% of GOD. These optimized mixtures rearranged soft French wheat flour and its composite counterpart to a good quality and an improved flour texture, respectively. Additionally, they increased the loaf specific volumes of the breads made from soft French wheat flour and its counterpart by 25.8 and 45.43%, respectively, significantly decreased the breads' susceptibility to microbial contamination, and reclassified the breads as "good" in terms of sensory attributes.

Improvement of the antifungal activity of lactic acid bacteria by addition to the growth medium of phenylpyruvic acid, a precursor of phenyllactic acid

The aim of the current study was to improve the antifungal activity of eight lactic acid bacterial (LAB) strains by the addition of phenylpyruvic acid (PPA), a precursor of the antifungal compound phenyllactic acid (PLA), to a defined growth medium (DM). The effect of PPA addition on the LABs antifungal activity related to the production of organic acids (PLA, d-lactic, l-lactic, acetic, citric, formic and 4-hydroxy-phenyllactic acids) and of other phenylpyruvic-derived molecules, was investigated. In the presence of PPA the inhibitory activity (expressed as growth inhibition percentage) against fungal bread contaminants Aspergillus niger and Penicillium roqueforti significantly increased and was, even if not completely, associated to PLA increase (from a mean value of 0.44 to 0.93 mM). While the inhibitory activity against Endomyces fibuliger was mainly correlated to the low pH and to lactic, acetic and p-OH-PLA acids. When the PCA analysis based on data of growth inhibition percentage and organic acid concentrations was performed, strains grown in DM+PPA separated from those grown in DM and the most active strains Lactobacillus plantarum 21B, Lactobacillus fermentum 18B and Lactobacillus brevis 18F grouped together. The antifungal activity resulted to be strain-related, based on a different mechanism of action for filamentous fungi and the yeast and was not exclusively associated to the increase of PLA. Therefore, a further investigation on the unique unidentified peak in HPLC-UV chromatograms, was performed by LC-MS/MS analysis. Actually, full scan mass spectra (negative ion mode) recorded at the retention time of the unknown compound, showed a main peak of m/z 291.0 which was consistent with the nominal mass of the molecular ion [M-H](-) of polyporic acid, a PPA derivative whose antifungal activity has been previously reported (Brewer et al., 1977). In conclusion, the addition of PPA to the growth medium contributed to improve the antifungal activity of LAB strains and resulted in the production of the polyporic acid, here ascertained in LAB strains.

Study of kefir grains application in sourdough bread regarding rope spoilage caused by Bacillus spp

Sourdough breads prepared with kefir grains resulted in appearance of rope spoilage at the 15th day of bread storage, while the control samples (sourdough breads prepared with wild microflora) were spoiled approximately at the 7th day. Denaturing Gradient Gel Electrophoresis (DGGE) analysis confirmed the above macroscopic observation since Bacillus spp. were detected on sourdough breads prepared with kefir grains at the 15th day of bread storage. The content of organic acids that play synergistic role regarding the enhancement of bread self life was also determined. Lactic acid concentration of sourdough breads prepared with kefir grains were approximately 41-82% higher than the control samples, while acetic acid concentration was about 0.5-1-fold higher respectively. The concentration of some other organic acids studied was also found in higher levels (up to 0.06μg/g) than the control samples. These findings could probably explain the stability of breads prepared with kefir grains against rope spoilage.

Suitability of cereal porridges as substrate for probiotic strain Lactobacillus rhamnosus GG

The aim of this work was to find new substrates suitable for growth and metabolism of probiotic strain Lactobacillus rhamnosus GG, which would be interesting for development of new functional food. The growth and metabolic activity of Lb. rhamnosus GG in cereal (rye, barley, oat and millet) porridges were monitored during fermentation process. Cereal and porridges, were inoculated with this strain at two initial levels to obtain approximately 5 or 6 log colony form units per gram of suspension after sterilization and cooling,. Fermentation was led stationary at 37 °C for 48 hours and viable cell count, pH value, titratable acidity and organic acids were analysed. Metabolic activity of Lb. rhamnosus GG was influenced by inoculation level and by the type of cereal used. The cereals fermented by lactic acid bacteria, especially probiotic strains, might broaden the offer of probiotic products for those suffering from milk allergy.

Sourdough in gluten-free bread-making: an ancient technology to solve a novel issue?

The increasing demand for high quality gluten-free (GF) bread, clean labels and natural products is raising the need for new approaches in GF bread-making. Sourdough is the foremost fermentation used for baking purposes and it has been proven to be ideal for improving the texture, palatability, aroma, shelf life and nutritional value of wheat and rye breads. These characteristic features derive from the complex metabolic activities of the sourdough-resident lactic acid bacteria and yeasts, e.g. acidification, production of exopolysaccharides, proteolytic- amylolytic- and phytase activity, and production of antimicrobial substances. These effects have been extensively studied and well described for traditional baking, whereas little is known about the role of sourdough in GF baking. Yet, the microbiological and qualitative characterisation of local GF fermented products indicate an overlap with the microbiota of wheat/rye fermentation and suggest that the positive metabolic activities of the sourdough microbiota are still retained during fermentation of GF crops. Thus, the use of sourdough in GF baking may be the new frontier for improving the quality, safety and acceptability of GF bread.

Antifungal activity of strains of lactic acid bacteria isolated from a semolina ecosystem against Penicillium roqueforti, Aspergillus niger and Endomyces fibuliger contaminating bakery products

Thirty samples of Italian durum wheat semolina and whole durum wheat semolina, generally used for the production of Southern Italy's traditional breads, were subjected to microbiological analysis in order to explore their lactic acid bacteria (LAB) diversity and to find strains with antifungal activity. A total of 125 presumptive LAB isolates (Gram-positive and catalase-negative) were characterized by repetitive extragenic palindromic-PCR (REP-PCR) and sequence analysis of the 16S rRNA gene, leading to the identification of the following species: Weissella confusa, Weissella cibaria, Leuconostoc citreum, Leuconostoc mesenteroides, Lactococcus lactis, Lactobacillus rossiae and Lactobacillus plantarum. The REP-PCR results delineated 17 different patterns whose cluster analysis clearly differentiated W. cibaria from W. confusa isolates. Seventeen strains, each characterized by a different REP-PCR pattern, were screened for their antifungal properties. They were grown in a flour-based medium, comparable to a real food system, and the resulting fermentation products (FPs) were tested against fungal species generally contaminating bakery products, Aspergillus niger, Penicillium roqueforti and Endomyces fibuliger. The results of the study indicated a strong inhibitory activity - comparable to that obtained with the common preservative calcium propionate (0.3% w/v) - of ten LAB strains against the most widespread contaminant of bakery products, P. roqueforti. The screening also highlighted the unexplored antifungal activity of L. citreum, L. rossiae and W. cibaria (1 strain), which inhibited all fungal strains to the same or a higher extent compared with calcium propionate. The fermentation products of these three strains were characterized by low pH values, and a high content of lactic and acetic acids.