Lactobacillus paracasei: an evaluation of the flavour diversification potential of the species through genomics, metabolomics and applications

Strains of Lactobacillus paracasei are commonly isolated from numerous and diverse niches, such as dairy products, plant materials and reproductive and gastrointestinal tracts of humans and animals. In cheese, strains of L. paracasei belong predominantly to the non-starter microbiota, which is often considered to be immensely important for the development of flavour. In this project, the genetic and phenotypic diversity of L. paracasei strains and their application as adjunct cultures to support the development of flavour compounds was assessed. The bank of 310 strains investigated in this study consisted of isolates originating from cheese, yoghurt and sourdough. After genomic profiling, 99 strains were selected for future examination. The phenotypic characterisation included in vitro assessment of the key proteolytic enzyme activities, the most important factor contributing to the flavour compound development. The activities of the examined enzymes significantly differed among the analysed strains. Ten strains showing different enzyme activities were selected to compare their ability for flavour compounds production in two cheese model systems. The volatile profiles of the strains differed in both model systems, and according to the all generated results, three strains (DPC2071, DPC4206 and DPC4536) were selected as adjunct cultures for Cheddar cheese manufacture. The cheese analysis showed that although some differences existed, they were minimal and cheeses were of similar flavour characteristics. Finally, to identify and characterise specific genes that may contribute to the overall differentiation of the selected strains, genome sequencing and assembly and comparative genome analysis were performed on the three strains used in the cheese production, and a considerable level of genetic heterogeneity was observed

Symposium review: Genomic investigations of flavor formation by dairy microbiota

peer-reviewedFlavor is one of the most important attributes of any fermented dairy product. Dairy consumers are known to be willing to experiment with different flavors; thus, many companies producing fermented dairy products have looked at culture manipulation as a tool for flavor diversification. The development of flavor is a complex process, originating from a combination of microbiological, biochemical, and technological aspects. A key driver of flavor is the enzymatic activities of the deliberately inoculated starter cultures, in addition to the environmental or “nonstarter” microbiota. The contribution of microbial metabolism to flavor development in fermented dairy products has been exploited for thousands of years, but the availability of the whole genome sequences of the bacteria and yeasts involved in the fermentation process and the possibilities now offered by next-generation sequencing and downstream “omics” technologies is stimulating a more knowledge-based approach to the selection of desirable cultures for flavor development. By linking genomic traits to phenotypic outputs, it is now possible to mine the metabolic diversity of starter cultures, analyze the metabolic routes to flavor compound formation, identify those strains with flavor-forming potential, and select them for possible commercial application. This approach also allows for the identification of species and strains not previously considered as potential flavor-formers, the blending of strains with complementary metabolic pathways, and the potential improvement of key technological characteristics in existing strains, strains that are at the core of the dairy industry. An in-depth knowledge of the metabolic pathways of individual strains and their interactions in mixed culture fermentations can allow starter blends to be custom-made to suit industry needs. Applying this knowledge to starter culture research programs is enabling research and development scientists to develop superior starters, expand flavor profiles, and potentially develop new products for future market expansion

Draft Genome Sequences of Three Lactobacillus paracasei Strains, Members of the Nonstarter Microbiota of Mature Cheddar Cheese

peer-reviewedLactobacillus paracasei strains are common members of the nonstarter microbiota present in various types of cheeses. The draft genome sequences of three strains isolated from mature cheddar cheeses are reported here

Advances in the genomics and metabolomics of dairy lactobacilli: A review

The Lactobacillus genus represents the largest and most diverse genera of all the lactic acid bacteria (LAB), encompassing species with applications in industrial, biotechnological and medical fields. The increasing number of available Lactobacillus genome sequences has allowed understanding of genetic and metabolic potential of this LAB group. Pangenome and core genome studies are available for numerous species, demonstrating the plasticity of the Lactobacillus genomes and providing the evidence of niche adaptability. Advancements in the application of lactobacilli in the dairy industry lie in exploring the genetic background of their commercially important characteristics, such as flavour development potential or resistance to the phage attack. The integration of available genomic and metabolomic data through the generation of genome scale metabolic models has enabled the development of computational models that predict the behaviour of organisms under specific conditions and present a route to metabolic engineering. Lactobacilli are recognised as potential cell factories, confirmed by the successful production of many compounds. In this review, we discuss the current knowledge of genomics, metabolomics and metabolic engineering of the prevalent Lactobacillus species associated with the production of fermented dairy foods. In-depth understanding of their characteristics opens the possibilities for their future knowledge-based applications

Strains of the Lactobacillus casei group show diverse abilities for the production of flavor compounds in 2 model systems

peer-reviewedCheese flavor development is directly connected to the metabolic activity of microorganisms used during its manufacture, and the selection of metabolically diverse strains represents a potential tool for the production of cheese with novel and distinct flavor characteristics. Strains of Lactobacillus have been proven to promote the development of important cheese flavor compounds. As cheese production and ripening are long-lasting and expensive, model systems have been developed with the purpose of rapidly screening lactic acid bacteria for their flavor potential. The biodiversity of 10 strains of the Lactobacillus casei group was evaluated in 2 model systems and their volatile profiles were determined by gas chromatography-mass spectrometry. In model system 1, which represented a mixture of free AA, inoculated cells did not grow. In total, 66 compounds considered as flavor contributors were successfully identified, most of which were aldehydes, acids, and alcohols produced via AA metabolism by selected strains. Three strains (DPC2071, DPC3990, and DPC4206) had the most diverse metabolic capacities in model system 1. In model system 2, which was based on processed cheese curd, inoculated cells increased in numbers over incubation time. A total of 47 compounds were identified, and they originated not only from proteolysis, but also from glycolytic and lipolytic processes. Tested strains produced ketones, acids, and esters. Although strains produced different abundances of volatiles, diversity was less evident in model system 2, and only one strain (DPC4206) was distinguished from the others. Strains identified as the most dissimilar in both of the model systems could be more useful for cheese flavor diversification

CLINTON VS TRUMP : An investigation of how the leadership of US presidential candidates is being designed discursively in Metro and Dagens Nyheter

Abstract Title:CLINTON VS TRUMP -An investigation of how the leadership of US presidential candidates is being designed discursively in Metro and Dagens Nyheter Author: Ewelina Bosak & Sandra Stefanovic In 2016 a man and a woman competed for the first time in history in becoming the President of the United States. In 2016 one could read about the American presidential election every day in any newspaper. With this in mind, we want to examine the leadership being applied to the candidates by the news sources Metro and Dagens Nyheter. As leadership traditionally is considered a masculine feature, we apply a gender perspective to this study. The questions we intend to answer: - What discourse is construed by Metro and Dagens Nyheter regarding the leadership of Clinton and Trump? - How are Clinton and Trump being portrayed from a gender perspective? We used the method of discourse analysis, as it advocates the principle of language being the primary tool in shaping our realities. The theoretical framework we use to interpret and explain our results is based on discourse theory as well as the social construction of age and gender. Our research shows that Trump is generally being portrayed in a way not considered to be "right" in accordance to the leadership- or age norm. The discourse of Trump presents him as an inexperienced, dishonest and attempted leader with an childish behaviour. Trump is also often described through typically considered feminine features. Clinton, being perceived as almost invisible and often depicted in comparison to Trump or other male leaders, is at the same time portrayed as a successful, experienced, driven and intelligent leader. However, we have discovered that in spite of Clinton’s described leadership features she is constantly also criticised for being cold and not evoking any feelings or engagement. Clinton is not only being questioned on the basis of the masculine leadership norms, but also on the lack characteristics in line with the feminine norm

Draft genome sequence of Lactobacillus casei DPC6800, an isolate with the potential to diversify flavor in cheese

Lactobacillus casei is a nonstarter lactic acid bacterium commonly present in various types of cheeses. It is believed that strains of this species have a significant impact on the development of cheese flavor. The draft genome sequence of L. casei DPC6800, isolated from a semi-hard Dutch cheese, is reported

Comparison of two headspace extraction techniques to determine volatile profiles generated by lactic acid bacteria in a cheese model by GC-MS

Development of volatile compounds contributing to cheese flavour primarily depends on the metabolic activity of bacterial cultures used during manufacture. Gas chromatography coupled to mass spectrometry (GC-MS) preceded by volatiles extraction is widely used for volatile analysis. The volatile profiles of ten strains of Lactobacillus casei/paracasei generated using a cheese model were assessed by GC-MS using two extraction methods, headspace solid-phase microextraction (HS-SPME) with DVB/CAR/PDMS fibre and HeadSpace-Trap (HS-Trap) with Tenax® adsorbent. Chromatographic data was processed using XCMS package of R software. Numbers of total fragments detected were 1788 for HSSPME and 2073 for HS-Trap method. After annotation, 70 and 64 compounds considered as flavour contributors were successfully identified in HS-SPME and HS-Trap profiles respectively, with 40 compounds in common. HS-SPME extracted numerous alcohols, esters and acids, while HS-Trap showed higher selectivity towards short aldehydes and ketones, pyrazine derivatives and specific sulfur-containing compounds. Comparison of common volatiles revealed high correlation in extraction of long-chain ketones and alcohols, but poorcorrelation for aldehydes, sulfur compounds and acids. Principal Component Analysis highlighted similar differences between individual samples using both extraction techniques.Although two extraction techniques identified distinct compounds in the samples, they equally represented differences within the sample set

Strains of the Lactobacillus casei group show diverse abilities for the production of flavor compounds in 2 model systems

Cheese flavor development is directly connected to the metabolic activity of microorganisms used during its manufacture, and the selection of metabolically diverse strains represents a potential tool for the production of cheese with novel and distinct flavor characteristics. Strains of Lactobacillus have been proven to promote the development of important cheese flavor compounds. As cheese production and ripening are long-lasting and expensive, model systems have been developed with the purpose of rapidly screening lactic acid bacteria for their flavor potential. The biodiversity of 10 strains of the Lactobacillus casei group was evaluated in 2 model systems and their volatile profiles were determined by gas chromatography-mass spectrometry. In model system 1, which represented a mixture of free AA, inoculated cells did not grow. In total, 66 compounds considered as flavor contributors were successfully identified, most of which were aldehydes, acids, and alcohols produced via AA metabolism by selected strains. Three strains (DPC2071, DPC3990, and DPC4206) had the most diverse metabolic capacities in model system 1. In model system 2, which was based on processed cheese curd, inoculated cells increased in numbers over incubation time. A total of 47 compounds were identified, and they originated not only from proteolysis, but also from glycolytic and lipolytic processes. Tested strains produced ketones, acids, and esters. Although strains produced different abundances of volatiles, diversity was less evident in model system 2, and only one strain (DPC4206) was distinguished from the others. Strains identified as the most dissimilar in both of the model systems could be more useful for cheese flavor diversification