Characterization of Lactobacillus strains and monitoring by RAPD-PCR in controlled fermentations of “Almagro” eggplants

Dynamic interactions of lactic acid bacteria in Korean sourdough during back-slopping process

AIMS

This study aimed to clarify the cause of quality reduction in Korean sourdough after successive back-slopping.

METHODS AND RESULTS

We investigated the dynamic changes in lactic acid bacteria during the back-slopping process using genetic fingerprinting techniques. During the initial propagation phases, the dominant lactic acid bacteria were Fructilactobacillus sanfranciscensis (<5 log CFU per g sourdough), Latilactobacillus curvatus (9·5 log CFU per g sourdough) and Levilactobacillus brevis (6·5 log CFU per g sourdough). However, after the 11th propagation, F. sanfranciscensis became more prominent (>9·0 log CFU per g sourdough), whereas L. curvatus and L. brevis rapidly decreased. Monitoring these bacteria in the co-culture system revealed that acid-tolerant F. sanfranciscensis rapidly utilized maltose (1·65 g l^-1  h^-1 ) and produced large amounts of lactic acid, whereas L. brevis and L. curvatus consumed maltose slowly and L. curvatus was poorly tolerant to lactic acid.

CONCLUSION

The results indicate that competition exists between the lactic acid bacteria in sourdough during the back-slopping process, and microbial succession by acid-tolerant species results in quality reduction of sourdough.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study uncovered the cause of microbial changes during the propagation of Korean sourdough and proposed a strategy to develop starters to produce high-quality bakery products.

Influence of Environmental and Productive Factors on the Biodiversity of Lactic Acid Bacteria Population from Sheep Milk

Simple Summary

The dairy sheep sector in Spain is of great importance in the socioeconomic field. For this reason, obtaining quality milk has become a priority objective in the sector. In this context, the environment of dairy farms could affect the microbial communities present in milk, and therefore, the study of lactic acid bacteria (LAB) in this environment could be fundamental for the quality of milk and its dairy products. The objective of this study was to investigate the LAB population present in dairy sheep milk and the possible routes of contamination between the livestock environment and the milk on 12 sheep farms with different livestock practices in Castilla-La Mancha. The results showed that certain agricultural practices favour the presence of LAB in milk in addition to the fact that a significant transference between the livestock environment and bulk tank milk could exist.

Abstract

Milk is a typical and satisfactory medium for the growth of lactic acid bacteria (LAB). These microorganisms are of vital importance in the quality of the milk since they contribute to its preservation and give differential organoleptic properties to the final product. Furthermore, LABs can act as biocontrol agents in the dairy industry by inhibiting the growth of undesirable bacteria present in milk and by improving the quality of dairy products such as cheese. In this context, knowing the transfer routes used by LABs from the livestock environment to the milk is of great importance within the dairy industry. Therefore, the objectives of the present study were to expand the knowledge of the LAB population present in the milk of Manchego ewe by means of DNA sequencing techniques and to evaluate the possible transfers of LAB species based on the management of each dairy farm. Samples of bulk tank milk, air (from the milking parlour and from the livestock housing), animal feed and teat surface (taken from 10 sheep per farm) were collected in 12 traditional livestock farms in Castilla-La Mancha (Spain), where each farm presented differences regarding their farming practices. A mixed-effects model was used to evaluate the effects of livestock practices on the distribution of LAB species. Results showed that the vast majority of species identified in the milk had an isolate that was also found in other matrices, which could indicate a microbial transference via the livestock environment to the milk. In addition, the mixed model showed that the factors that positively influence the LAB count were the low-line milking system and the daily use of acid detergent in cleaning the milking machine.

Microbial Profile Antibacterial Properties and Chemical Composition of Raw Donkey Milk

The human interest in donkey milk is growing due to its nutritional, functional properties and excellent microbiological quality according to published reports. However, more research needs to be conducted to assess the above variables from various breeds. In the present study, milk samples were collected from 17 Cypriot and six Arcadian healthy Greek donkeys. The microbiological quality, somatic cell counts (SCC), chemical composition analysis, and antimicrobial activity of the samples was assessed. In addition, clustering and identification of the bacterial composition was performed by RAPD-PCR and 16S rDNA sequencing, respectively. The good microbiological quality of the samples as estimated by the total aerobic mesophilic and psychrotrophic counts, which ranged from 2.18 to 2.71 log CFU/mL and from 1.48 to 2.37 log CFU/mL, respectively, was also verified. SCC were below 4.4 log CFU/mL. However, potential pathogenic species of Staphylococcus aureus, Bacillus cereus, and Clostridium spp. were enumerated in the milk of both breeds. The gross chemical composition showed mean values for fat, protein, and lactose from 0.82% to 1.24%, 1.22% to 1.87%, and 6.01% to 6.78%, respectively. All milk samples exhibited an antimicrobial activity against St. haemolyticus and Listeria monocytogenes, although quality control measures should be taken for health and safety prior to human consumption.

Technological Feature Assessment of Lactic Acid Bacteria Isolated from Cricket Powder's Spontaneous Fermentation as Potential Starters for Cricket-Wheat Bread Production

The bacterial community profile of cricket powder highlighted the presence of four main genera: Bacteroides spp., Parabacteroides spp., Lactococcus spp., and Enterococcus spp. The spontaneous fermentation of cricket powder allowed for the isolation and characterization of seven lactic acid bacteria strains belonging to six species: Latilactobacillus curvatus, Lactiplantibacillus plantarum, Latilactobacillus sakei, Lactococcus garvieae, Weissella confusa, and Enterococcus durans. The strains were characterized and selected according to different technological properties. L. plantarum CR L1 and L. curvatus CR L13 showed the best performance in terms of general aminopeptidase activity, acidification, and growth rate in MRS broth and in dough with cricket powder and wheat flour, as well as robustness during consecutive backslopping. Thus, they were used as starter-mixed to produce sourdough to manufacture bread fortified with 20% cricket powder. The addition of cricket powder led to a significant increase of protein (up to 94%) and lipid content, from 0.7 up to 6 g/100 g of bread. Spontaneous fermentation represents a source of microbial diversity that can be exploited in order to obtain potential starters for food with innovative ingredients. Edible insects powder can be successfully added in leavened baked goods to enhance their nutritional value.

Use of Selected Lactobacilli to Increase γ-Aminobutyric Acid (GABA) Content in Sourdough Bread Enriched with Amaranth Flour

γ-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter of the central nervous system and possesses various physiological functions. GABA production can be obtained thanks to lactic acid bacteria activity in different foods such as sourdoughs. Recently, breads made from blends of pseudocereals and wheat flours have attracted much attention. Amaranth is especially interesting because of its high nutritional value, having a high protein content and containing different antioxidant compounds. Therefore, this study aimed to obtain sourdough breads enriched with GABA thanks to bacterial activity and to investigate the effect of amaranth flour addition on the antioxidant and sensorial properties of bread. Eighteen lactobacilli strains were assayed for GABA production in amaranth and wheat flour liquid sourdoughs. Two strains, Lactobacillus brevis A7 and Lactobacillus farciminis A11, demonstrated high GABA producing capability; hence, they were used to prepare breads containing 20% amaranth flour. The results confirmed the capability of the two strains to increase GABA concentrations (up to 39 mg/kg) in breads. Samples with amaranth addition showed a significantly higher total phenolic content compared to the control bread (more than 15 mg GAE 100 g^-1 dwb); sensory analysis showed that breads with amaranth were moderately acceptable. Nevertheless, their general liking evaluation was significantly lower compared to the control bread. The addition of pseudocereal to traditional wheat sourdough and selection of lactobacilli allowed the production of baked goods with enhanced GABA content and antioxidant capacity, but recipes have to be developed to increase the organoleptic acceptability of the final products.

Identification of Lactobacillus brevis using a species-specific AFLP-derived marker

A simple and specific method for the rapid detection and identification of Lactobacillus brevis was developed. A fAFLP (Fluorescent Amplified Fragment Length Polymorphisms) marker for L. brevis was used to design oligonucleotide primers for a species-specific PCR assay, targeting a 125bp fragment of the gene encoding the aldo/keto reductase of the diketogulonate-reductase family of L. brevis. This assay resulted in 100% inclusivity and exclusivity of assignment of strains to the species L. brevis. The analytical specificity of this assay was successfully tested to identify L. brevis isolates from sourdoughs.

Development of species-specific PCR primers and polyphasic characterization of Lactobacillus sanfranciscensis isolated from Korean sourdough

Lactobacillus sanfranciscensis is a bacterium used in sourdough that provides desirable properties such as better flavor and texture to the sourdough bread. Here, the intra-species diversity of L. sanfranciscensis strains isolated from Korean sourdough was studied using genotypic (multiplex-RAPD-PCR: multiplex-Randomly Amplified Polymorphic DNA-polymerase chain reaction) and phenotypic (VITEK2 Compact system) analyses. For this, a novel species-specific set of PCR primers was developed to identify L. sanfranciscensis using the recently published genome database. The primers were able to detect L. sanfranciscensis isolated from Korean sourdough with 100% accuracy. Genotyping and phenotyping analyses at the strain level demonstrated that Korean sourdough possesses various biotypes of L. sanfranciscensis strains. These strains were clustered into 5 subtypes (genotyping) or 7 subtypes (phenotyping). In summary, this strategy to construct novel primers reduced the chance of cross amplification and was able to identify the desired strain. The various strains isolated in this study can be used to develop a sourdough starter after the analysis of their fermentation characteristics.

Antifungal activity and identification of Lactobacilli, isolated from traditional dairy product "katak"

Filamentous moulds are the main spoilage microorganisms, responsible for significant economic losses and several healthy risks in human food chain. The lactic acid bacteria (LAB), especially lactobacilli could be a natural antagonist of these dangerous organisms. In Bulgaria, a very limited data exists on the antifungal activity of LAB microbiota of fermented dairy products. In the present study, four active strains were isolated from traditional fermented curd/yogurt-like product "katak", produced in Bulgaria from centuries. The new isolates KR3, KR4, KR51 and KR53 were identified by API 50 CH biochemical test and different molecular methods (species-specific PCR, RAPD-PCR and 16S rDNA sequence analysis) as Lactobacillus brevis. According to our knowledge, this is the first data on the molecular characterization of the Lactobacillus microbiota of "katak". A broad spectrum of antifungal activity of the four L. brevis KR strains against test-cultures representatives of carcinogenic, toxigenic, deteriorative and allergenic fungi from the genera Aspergillus, Fusarium, Penicillium and Trichoderma was estimated. Strains L. brevis KR3, KR4 and KR51 completely suppress the growth of Penicillium claviforme, Aspergillus awamori and Aspergillus niger. With regard to Aspergillus flavus and Trichoderma viride, a lower and strain-specific inhibitory activity was observed. The antifungal activity of our new L. brevis isolates seems to be a promising advantage of these four strains, suggesting their potential applications in different food technologies as bio-preservative agents against moulds.

A selected core microbiome drives the early stages of three popular italian cheese manufactures

Mozzarella (M), Grana Padano (GP) and Parmigiano Reggiano (PR) are three of the most important traditional Italian cheeses. In the three cheese manufactures the initial fermentation is carried out by adding natural whey cultures (NWCs) according to a back-slopping procedure. In this study, NWCs and the corresponding curds from M, GP and PR manufactures were analyzed by culture-independent pyrosequencing of the amplified V1–V3 regions of the 16S rRNA gene, in order to provide insights into the microbiota involved in the curd acidification. Moreover, culture-independent high-throughput sequencing of lacS gene amplicons was carried out to evaluate the biodiversity occurring within the S. thermophilus species. Beta diversity analysis showed a species-based differentiation between GP-PR and M manufactures indicating differences between the preparations. Nevertheless, all the samples shared a naturally-selected core microbiome, that is involved in the curd acidification. Type-level variability within S. thermophilus species was also found and twenty-eight lacS gene sequence types were identified. Although lacS gene did not prove variable enough within S. thermophilus species to be used for quantitative biotype monitoring, the possibility of using non rRNA targets for quantitative biotype identification in food was highlighted.

Typing of Lactobacillus sanfranciscensis isolates from traditional sourdoughs by combining conventional and multiplex RAPD-PCR profiles

In the present work, a rapid and reproducible molecular method, based on the combination of conventional and multiplex RAPD-PCR reactions, was developed for typing Lactobacillus sanfranciscensis isolates from traditional sourdoughs. At first, four random primers, two used singly and two combined with the primer RD1, were chosen on the basis of their differentiating capability and reproducibility. The four resulting profiles for each isolate were integrated into a unique profile to be statistically treated by cluster analysis. The method was validated on 58 L. sanfranciscensis isolates coming from three traditional Italian sourdoughs. This new RAPD method was useful for determining the genomic diversity within the L. sanfranciscensis species. In particular, the intraspecific diversity of this species seemed to be related to the sourdough origin.

Stable and non-competitive association of Saccharomyces cerevisiae, Candida milleri and Lactobacillus sanfranciscensis during manufacture of two traditional sourdough baked goods

The microbiota occurring in all the manufacturing phases of two Italian sourdough sweet-leavened baked goods (a typical Genoese dry biscuit, Lagaccio, and a soft stuffed North Italian typical cake, Panettone) were investigated over a period of three years. The two sourdough mother sponges were characterized by the stable presence of three dominant microbial species in potential competition for carbohydrates: Lactobacillus sanfranciscensis, Candida milleri, and Saccharomyces cerevisiae. Genotypic and phenotypic characterizations of microbial isolates pointed out that each mother sponge harbored its own strains, well distinguishable by molecular methods of analysis but not differing in their main metabolic properties from those known for the corresponding species. The microbial and biochemical evolution during the whole production protocol of both manufactures demonstrated that the three microbial species grew at almost the same growth rates, without exhausting any of the main carbon substrates (maltose, glucose and fructose). The quite similar growth dynamics under practical conditions and the constant presence of all fermentable carbohydrates were recognized as responsible for the stable non competitive association of maltose-positive and maltose-negative species in both sourdoughs. However, the two sourdoughs were characterized by quite different LAB to yeast ratio, with values significantly higher in Panettone than in Lagaccio. The cause of this difference could mainly be ascribed to the temperature of the mother sponge regeneration phase, that, in the case of Panettone manufacture, occurred under conditions of moderate refrigeration.

Characterization of Lactobacillus from Algerian Goat'S Milk Based on Phenotypic, 16S rDNA Sequencing and their Technological Properties

Nineteen strains of Lactobacillus isolated from goat's milk from farms in north-west of Algeria were characterized. Isolates were identified by phenotypic, physiological and genotypic methods and some of their important technological properties were studied. Phenotypic characterization was carried out by studying physiological, morphological characteristics and carbohydrate fermentation patterns using API 50 CHL system. Isolates were also characterized by partial 16S rDNA sequencing. Results obtained with phenotypic methods were correlated with the genotypic characterization and 13 isolates were identified as L. plantarum, two isolates as L. rhamnosus and one isolate as L. fermentum. Three isolates identified as L. plantarum by phenotypic characterization were found to be L. pentosus by the genotypic method. A large diversity in technological properties (acid production in skim milk, exopolysaccharide production, aminopeptidase activity, antibacterial activity and antibiotic susceptibility) was observed. Based on these results, two strains of L. plantarum (LbMS16 and LbMS21) and one strain of L. rhamnosus (LbMF25) have been tentatively selected for use as starter cultures in the manufacture of artisanal fermented dairy products in Algeria.

Diversity of lactic acid bacteria from Hussuwa, a traditional African fermented sorghum food

The diversity of lactic acid bacteria associated with Hussuwa fermentation, a Sudanese fermented sorghum food, was studied using a polyphasic taxonomical approach. Predominant strains could be well characterised based on a combination of phenotypic tests and genotypic methods such as ARDRA, rep-PCR and RAPD-PCR, as well as 16S rRNA gene sequencing of representative strains. Thus, the majority (128 of 220, 58.3%) of strains exhibited phenotypic properties typical of heterofermentative lactobacilli and of these, 100 strains were characterised more closely using the genotyping methods. The majority (97/100) strains could be characterised as Lactobacillus fermentum strains. Seventy-two of 220 strains (32.7%) showed phenotypic properties that are characteristic of pediococci. Of 41 selected strains investigated by genotyping techniques, 38 (92.7%) could be characterised as Pediococcus acidilactici strains, while three (7.3%) could be characterised as Pediococcus pentosaceus strains. The Hussuwa fermentation thus appears to be dominated by L. fermentum strains and P. acidilactici strains. For this reason, we selected representative and predominant strains as potential starter cultures for Hussuwa fermentation. These strains, L. fermentum strains BFE 2442 and BFE 2282 and P. acidilactici strain BFE 2300, were shown on the basis of RAPD-PCR fingerprinting to predominate in a model fermentation when used as starter cultures inoculated at 1 x 10(6) CFU/g and to lower the pH of the fermentation to below pH 4.0 within 48 h. These cultures should be studied for further development as starter preparations in pilot scale studies in actual field fermentations.

Evaluation of a single and combined inoculation of a Lactobacillus pentosus starter for processing cv. Arbequina natural green olives

The production of Arbequina naturally green olives is a traditional and spontaneous process in which lactic acid bacteria (LAB) and yeasts are present. To better control the fermentation of olives, strains of LAB and yeasts that had been isolated from brines were used in this study. A strain of Lactobacillus pentosus selected from an industrial olive fermentation was used as a starter culture for the traditional fermentation of Arbequina naturally green olives. Three more strains isolated from Arbequina olive brines were selected: one yeast, (Candida diddensiae), and two Lactobacillus (one L. plantarum and the other L. pentosus). The individual fermentation profile of all the strains and the co-inoculation profile of each one of the three with the first selected L. pentosus were studied in pilot-scale fermentations. The results showed that all the strains used as a starter, and particularly the yeast C. diddensiae, reduced the Enterobacteriaceae survival period in comparison with the spontaneous process. Only when a L. pentosus strain was inoculated were the LAB counts above 10(6) cfu ml(-1) throughout the process. The C. diddensiae starter failed to colonize the brine until the end of the process and no LAB were detected. Results of rep-PCR using the primer GTG(5) showed that both L. pentosus starters were able to colonize the brine by the end of the process but when they were co-inoculated only one strain was dominant. The L. plantarum starter failed to colonize the brine. In the control fermentation, various autochthonous strains of L. pentosus and L. plantarum were detected. The pH only reached desirable levels when a L. pentosus strain was inoculated. From the results of the sensory evaluation, panellists found significant differences between the different starters used for fermenting olives.

Genotypic and technological characterization of Leuconostoc isolates to be used as adjunct starters in Manchego cheese manufacture

Twenty-seven Leuconostoc (Ln.) isolates from Manchego cheese were characterized by phenotypic and genotypic methods, and their technological abilities studied in order to test their potential use as dairy starter components. While phenotypic diversity was evaluated by studying the biochemical characteristics of technological interest (i.e. acidifying and aminopeptidase activities), genotypic diversity was evidenced by using Randomly Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR). Additional technological abilities such as lipolytic, proteolytic and autolytic activities, salt and pH tolerance and production of dextran, flavour compounds and biogenic amines, were investigated. The marked differences among strains reflected the existing biodiversity in naturally fermented products. After statistically evaluating their performance, strains C0W2, belonging to Ln. lactis, and C16W5 and N2W5, belonging to Ln. mesenteroides subsp. dextranicum, revealed the best properties to be used in mixed dairy starter cultures. This study evidences the fact that natural environments can be considered as a proper source of useful strains, for the dairy industry.

Food phenolics and lactic acid bacteria

Phenolic compounds are important constituents of food products of plant origin. These compounds are directly related to sensory characteristics of foods such as flavour, astringency, and colour. In addition, the presence of phenolic compounds on the diet is beneficial to health due to their chemopreventive activities against carcinogenesis and mutagenesis, mainly due to their antioxidant activities. Lactic acid bacteria (LAB) are autochthonous microbiota of raw vegetables. To get desirable properties on fermented plant-derived food products, LAB has to be adapted to the characteristics of the plant raw materials where phenolic compounds are abundant. Lactobacillus plantarum is the commercial starter most frequently used in the fermentation of food products of plant origin. However, scarce information is still available on the influence of phenolic compounds on the growth and viability of L. plantarum and other LAB species. Moreover, metabolic pathways of biosynthesis or degradation of phenolic compounds in LAB have not been completely described. Results obtained in L. plantarum showed that L. plantarum was able to degrade some food phenolic compounds giving compounds influencing food aroma as well as compounds presenting increased antioxidant activity. Recently, several L. plantarum proteins involved in the metabolism of phenolic compounds have been genetically and biochemically characterized. The aim of this review is to give a complete and updated overview of the current knowledge among LAB and food phenolics interaction, which could facilitate the possible application of selected bacteria or their enzymes in the elaboration of food products with improved characteristics.