Thermophilic Lactic Acid Bacteria Research Articles

Thermophilic lactic acid bacteria affect the characteristics of sourdough and whole-grain wheat bread

Application of selected starter cultures for sourdough propagation may ensure stable lactic acid bacteria (LAB) diversity and defined properties of sourdough that affect quality. The impact of Lactobacillus delbrueckii ssp. bulgaricus MI, L. rossiae GL14 and L. acidophilus DSM 20079 as starter cultures were investigated for spoilage prevention and whole-grain wheat and sourdough bread properties. Whole-grain wheat sourdough propagated with these strains showed high phytase, amylase and xylanases activities. The highest phytase activity was obtained in sourdough prepared with L. bulgaricus MI. The results of gas chromatography–mass spectrometry using solid-phase microextraction showed that the compositions of volatile compounds in sourdough and whole-grain wheat bread depended on the LAB starter. In bread with L. acidophilus, 3-octen-2-ol and n-hexadecane were found, whereas those compounds were not found in other bread samples or in sourdough. Tetrahydrofurfuryl acetate was found only in bread prepared with L. bulgaricus MI sourdough. N-Pentadecane was found only in bread prepared with L. rossiae sourdough and bread prepared with spontaneous sourdough. The application of thermophilic sourdough increased bread porosity, elasticity, crumbliness and moisture content, but did not influence crumb hardness. Moreover, the fungal spoilage on the bread crust surface was suppressed using sourdough prepared with thermophilic LAB. The strain of LAB used for sourdough preparation influenced the shelf-life of bread.

Streptococcus thermophilus growth in soya milk: Sucrose consumption, nitrogen metabolism, soya protein hydrolysis and role of the cell-wall protease PrtS

Societal demand for plant-based foods is increasing. In this context, soya products fermented using lactic acid bacteria (LAB) are appealing because of their potential health and nutritional benefits. The thermophilic LAB Streptococcus thermophilus is an essential starter species in the dairy industry. However, while its physiology is well characterized, little is known about its general metabolic activity or its techno-functional properties when it is grown in soya milk. In this study, S. thermophilus LMD-9 growth, sugar production, and lactic acid production in soya milk versus cow's milk were measured. Additionally, the main metabolic pathways used by the bacterium when growing in soya milk were characterized using a proteomic approach. Streptococcus thermophilus LMD-9 growth decreased soya milk pH, from 7.5 to 4.9, in 5 h. During fermentation, acidification thus occurred in tandem with lactate production and increasing population size (final population: 1.0 × 109 CFU/ml). As growth proceeded, sucrose was consumed, and fructose was produced. The proteomic analysis (LC-MS/MS) of the strain's cytosolic and cell envelope-associated proteins revealed that proteins related to amino acid transport and nitrogen metabolism were the most common among the 328 proteins identified (63/328 = 19.2% of total proteins). The cell-wall protease PrtS was present, and an LMD-9 deletion mutant was constructed by interrupting the prtS gene (STER_RS04165 locus). Acidification levels, growth levels, and final population size were lower in the soya milk cultures when the ΔprtS strain versus the wild-type (wt) strain was used. The SDS-PAGE profile of the soluble proteins in the supernatant indicated that soya milk proteins were less hydrolyzed by the ΔprtS strain than by the wt strain. It was discovered that S. thermophilus can grow in soya milk by consuming sucrose, can hydrolyze soya proteins, and can produce acidification levels comparable to those in cow's milk. This study comprehensively examined the proteomics of S. thermophilus grown in soya milk and demonstrated that the cell-wall protease PrtS is involved in the LAB's growth in soya milk and in the proteolysis of soya proteins, which are two novel findings. These results clarify how S. thermophilus adapts to soya milk and can help inform efforts to develop new fermented plant-based foods with better-characterized biochemical and microbiological traits.

Draft Genome Sequence of Lactobacillus helveticus Lh 23, Isolated from Natural Whey Starter.

Lactobacillus helveticus is a thermophilic lactic acid bacterium that is widely employed as a starter culture for manufacturing several Swiss and Italian hard-cooked cheeses. The sequencing of L. helveticus Lh 23, which consists of 2,100,230 bp with a GC content of 36.5%, reveals industrially useful traits and interesting metabolic pathways.

Behavior of Four Main Dairy Pathogenic Bacteria during Manufacturing and Ripening of Pecorino Siciliano Cheese

Background: Consumption of raw cheese may be associated with different diseases. This study aimed to evaluate behavior of four pathogenic bacteria during manufacture and ripening of Protected Designation of Origin (PDO) Pecorino Siciliano cheese. Methods: The experimental cheese groups were inoculated with pathogenic bacteria, including Escherichia coli O157, Listeria monocytogenes, Salmonella Enteritidis, and Staphylococcus aureus. The cheese making processes were monitored from milk curdling until 3 months ripened cheeses and the levels of Lactic Acid Bacteria (LAB) and the four dairy pathogens were evaluated by plate counts. Randomly Amplified Polymorphic DNA (RAPD)-Polymerase Chain Reaction (PCR) analysis was applied to confirm that the colonies isolated during the several steps of production were the same strains added in milk. Statistical analysis was done using XLStat software. Results: The levels of mesophilic and thermophilic coccus and rod LAB in curd were comparable in both trials and reached values between 8-9 log10 Colony Forming Unit (CFU)/g in cheeses at 90 days of ripening. The four pathogenic bacteria were found in experimental curd at levels higher than those inoculated in milk and completely disappeared after 60 days of ripening. The RAPD analysis clearly demonstrated the presence of the added strain during production and confirmed the results of plate counts. Conclusion: This work showed that the production conditions of PDO Pecorino Siciliano cheese decreased growth of E. coli O157, L. monocytogenes, S. Enteritidis, and S. aureus

Selection of raw cow’s milk thermophilic lactic acid bacteria obtained from southwest Parana, Brazil, with potential use as autochthonous starter

Abstract This work aimed to isolate and identify Streptococcus and Lactobacillus species from raw cow’s milk obtained from Southwest Paraná - Brazil. We used randomly amplified polymorphic DNA (RAPD)-PCR to identify and type 58Streptococcus and 48 Lactobacillus isolates, of which 04 Streptococcus thermophilus and 02 Streptpcoccus macedonicus were confirmed by species-specific PCR and by sequencing of the 16S ribosomal RNA of 02Streptococcus lutetiensis/infantarius, 10 Lactobacillus fermentum, 03 Lactobacillus delbrueickii subspecies bulgaricus, 01 Lactobacillus rhamnosus/casei and 02 Lactobacillus helveticus. The results indicated predominance of Streptococcus thermophillus and Lactobacillus fermentum. Streptococcus thermophilus and Lactobacillus delbrueickii subspecies bulgaricus strains were tested on the basis of their acidification kinetics. Considerable variation between the Streptococcus thermophilus was observed for the maximum rate of acidification (Vm), with a maximum of -4.5 and minimum of -4.2 pH milliunits min-1. The Lactobacillus delbrueickii subspecies bulgaricus showed values between -8.4 and -7.1 pH milliunits min-1. These results suggest that strains characterized as having a high acidifying capacity, could be used as starters in cheesemaking. The ferments presented an excellent performance in the acidification process, generating adequate curves, characteristics of a starter culture.

Identifying the Diversity of Dominant LABs from Fermented Dairy Products Dahi and Yoghurt in Eastern Region of Nepal

The aim of this study was to isolate and identify lactic acid bacteria diversity from dahi/ yoghurt. Curd, also known as commercially prepared yoghurt or homemade Dahi, is formed during the slow lactic fermentation of lactose from milk by thermophilic lactic acid bacteria (LAB). Thirty-five samples of yoghurt and curd were collected from the Biratnagar and isolation and identification of bacteria were done by various microbiological techniques like MRS Agar inoculation, colony characteristics, microscopic and biochemical examination. A total of sixty-six strains of lactobacilli were isolated from curd and identification of strains was done by biochemical and carbohydrate utilization test. Lactobacillus bulgaricus, L. casei, L. fermentum, L. acidophilus, and Streptococcus thermophilus were identified from curd. pH of samples was between 3.0 to 4.0 for homemade dahi; while 4.34 to 4.5 for commercially available yoghurt. The mean colony count of lactic acid bacteria was 1.4x107–4.9x107 cfu/g. 37.9% of samples contained Streptococcus thermophilus, 30.3% had Lactobacillus bulgaricus. Forty-five isolates from 24 industrial yoghurt samples showed 37.5% of the yoghurt contained both Lactobacillus bulgaricus and Streptococcus thermophilus followed by 25% samples having S. thermophilus and L. acidophilus. Other species like L. fermentum and L. casei were less common. From 11 homemade dahi samples, 54.5% of curd possessed both S. thermophilus and L. bulgaricus; 18.2% curd had both S. thermophilus and L. fermentum. The study concludes that L. bulgaricus and Streptococcus thermophilus are prevalent potent lactic acid bacteria. This study provides an account of the diversity of lactic acid bacteria in dahi/ yoghurt which will provide useful information about the variable nature of curd in this region to future researchers.

Microbial Diversity and Sensorial Properties of Malga Cheese from Trentino (Italy) after Long-Term Ageing Period

Background: Malga cheeses are made in artisanal and seasonal dairies located in the Alps. This study was carried out to determine microbial diversity and sensorial properties of Malga cheese from Trentino (Italy) after long-term ageing period. The effects of adding the Fermalga Bacterial Pools (FBP) on microbiota biodiversity of cheese were also evaluated. Methods: Populations of Lactic Acid Bacteria (LAB), mesophilic/thermophilic lactobacilli, mesophilic/thermophilic lactococci, coliforms, Enterococcus sp., and Streptococcus sp. was evaluated by plate count in 38 cheese samples after 6 and 16 months of ageing. Sensorial analysis of cheeses was performed by a panel of 30 expert judges. Statistical analysis of the data was carried out using STATISTICA v. 8.0. Results: The total microbial count of medium-aged (6 months) cheeses was significantly (p<0.05) higher than that of long-aged (16 months) cheeses. Coliforms as well as Staphylococcus sp. were not detected in all samples. Thermophilic LAB were the relevant (45%) population in cheese made by FBP; while mesophilic LAB, mainly lactobacilli were the relevant (87%) population in the non-inoculated cheeses. The sensorial scores of 16 months-aged cheeses were significantly (p<0.05) higher than that of 6 months samples. However, there was no significant (p>0.05) difference between sensorial scores of Fermalga and non-Fermalga cheeses. Conclusion: The protection of traditional fermented foods can occur by innovative technologies, making them safe without altering their typical features. This preliminary investigation on the characteristics of Alpine Malga cheeses showed that the addition the FBP had no undesirable effect on the organoleptic characteristics of the cheeses.

Dynamics of a natural bacterial community under technological and environmental pressures: The case of natural whey starter for Parmigiano Reggiano cheese.

Natural starter cultures are undefined multiple-strains culture communities of mostly thermophilic lactic acid bacteria (LAB), in association with minor amounts of mesophilic bacteria, which structure could be affected by small changes in the parameters of the cheese/whey-making process. This study aims to investigate the complex microbiota of natural whey starter (NWS) used in Parmigiano Reggiano (PR) cheese-making, focusing on both the absolute and relative abundance of bacterial species and on the modification of the bacterial community under environmental and technological pressures. To reach this purpose a combined approach, using quantitative PCR (qPCR) and High-Throughput Sequencing (HTS), was used to investigate the bacterial dynamics of 91 whey samples collected during different steps of PR cheese-making, in one dairy, through two different lines of production, one Conventional and one Organic, over a 10 weeks period. Our results highlighted that NWS used for the production of PR cheese is a dynamic microbial community, which adapts to the different technological parameters encountered in the cheese/NWS manufacturing process, while retaining a high level of resilience of the thermophilic LAB species mainly involved in the steps of curd acidification and the early maturation process. Differences were also observed in bacterial species diversity between samples from Conventional and Organic line but, in conclusion, NWS resulted to be shaped by technological treatments, regardless of its initial different composition.

Study on molecular identification of lactic acid bacteria from fermented milks and “Smen” (a traditional steppe butter) and their enzyme producing attributes

Streptococcus thermophilus and Lactobacillus belong to a widely-knowngroup of bacteria that have been frequently used as starter bacteria in fermented dairy products. The aim of this study was to isolate, characterize andidentify of lactic acid bacteria (LAB) from raw cow’s fermented milk and‘Smen’ (a traditional steppe butter) in steppic area of Algeria to study someof their important enzyme-producing attributes. All selected strains of lacticacid bacteria (LAB) were identified and typed by phenotypic and genotypiccriteria.Six strains were identified as cocci thermophilic LAB and two of themwere selected and identified by using polymerase chain reaction (PCR) amplification for proA gene. Six strains of lactobacilli were identified as Lactobacillus genus using 16S rRNA gene. Species identification was performed by 16SrRNA gene sequencing and sequences were analysed using Basic LengthAlignment Search Tool (BLAST) programs. A phylogenetic tree based on 16SrRNA genes was constructed by the neighbor-joinin method.S. thermophilusstrains screened for their ability to produce lactic acid, titratable acidity, andpH was measured at 2h intervals, proteolytic activity in milk was examined.In another part, the four selected Lactobacillus were able to hydrolyze X-Galby production of β-galactosidase enzyme. All strains of LAB exhibited production of diacetyl. Overall, this study provides bacterial strains having potentialfor dairy industry.

Survey on the CRISPR arrays in Lactobacillus helveticus genomes.

Lactobacillus helveticus is a homofermentative thermophilic lactic acid bacteria that is mainly used in the manufacture of Swiss type and long-ripened Italian hard cheeses. In this study, the presence of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) were analysed in 25 L. helveticus genomes and identified in 23 of these genomes. A total of 40 CRISPR loci were identified and classified into five main families based on CRISPR repeats: Ldbu1, Lsal1, Lhel1, Lhel2 and a new repeat family named Lhel3. Spacers had a size between 30 and 40bp whereas repeats have an average size of 30bp, with three longer repeats. The analysis displayed the presence of conserved spacers in 23 of the 40 CRISPR loci. A geographical distribution of L. helveticus isolates with similar CRISPR spacer array profiles were not observed. Based on the presence of the signature protein Cas3, all CRISPR loci belonged to Type I. This analysis demonstrated a great CRISPR array variability within L. helveticus, which could be a useful tool for genotypic strain differentiation. A next step will be to understand the possible role of CRISPR/Cas system for the resistance of L. helveticus to phage infection. SIGNIFICANCE AND IMPACT OF THE STUDY: Lactobacillus helveticus, a lactic acid bacteria species widely used as starter culture in the dairy industry has recently also gained importance as health-promoting culture in probiotic and nutraceutical food products. The CRISPR/Cas system, a well-known molecular mechanism that provides adaptive immunity against exogenous genetic elements such as bacteriophages and plasmids in bacteria, was recently found in this species. In this study, we investigated the presence and genetic heterogeneity of CRISPR loci in 25 L. helveticus genomes. The results presented here represent an important step on the way to manage phage resistance, plasmid uptake and genome editing in this species.

Major technological differences between an industrial-type and five artisan-type Greek PDO Galotyri market cheeses as revealed by great variations in their lactic acid microbiota

Galotyri is a Greek PDO acid-curd, traditionally ripened, soft spread cheese produced from boiled (>80–90 ℃), naturally acidified ewes’ or ewes’/goats’ milk in the regions of Epirus and Thessaly. In this survey study, the microbiology of an industrial Galotyri cheese variety (11 batches) was compared with five artisan-type Galotyri cheese varieties (1–2 batches each), with emphasis on the species of lactic acid bacteria (LAB) prevailing in the final product. All market cheese samples distributed either in packaged or bulk form, were purchased from retail outlets at Ioannina, Epirus during two sampling periods, 2003–2006 and 2014–2019. A total of 366 (189 industrial and 177 artisan) cheese LAB isolates were identified by key biochemical criteria. Strains of Streptococcus thermophilus and/or Lactobacillus delbrueckii subsp. bulgaricus were isolated nearly as a pure symbiotic starter culture (97.4%) from all industrial batches, labeled as a fresh cheese combining the nutritional properties of yogurt. Conversely, the artisan-type cheeses were ripened and more diversified in terms of LAB ecology. They contained strains of <i>Lactococcus lactis</i> (19.8%), <i>Lb. plantarum</i> (16.9%), <i>S. thermophilus</i> (14.7%), <i>Leuconostoc mesenteroides</i> group (11.3%), <i>Pediococcus inopinatus</i> (7.3%), <i>Enterococcus faecalis</i> (8.5%), <i>E. faecium</i> (6.2%), <i>E. durans</i> (5.1%), <i>Lb. rhamnosus</i> (3.4%), <i>Lb. gasseri</i> (3.4%), <i>Lb. bulgaricus</i> (2.8%) and <i>Lb. acidipiscis</i> (0.6%); the prevalence of each species was cheese product batch-dependent. In conclusion: (i) the industrial Galotyri cheese technology results in a fresh yogurt-like cheese of limited (thermophilic) LAB diversity; (ii) the artisan-type Galotyri cheese technologies may vary significantly, but share a decisive ripening step that favors the predominance of mesophilic LAB species in the final market products; (iii) a regulatory distinction between fresh and ripened varieties of commercial PDO-certified Galotyri cheeses is required.

Investigation of dye removal with isolated biomasses from whey wastewater

In this work, as a new eco-friendly biosorbent, the removal of textile wastewater was carried out by biomass of mesophilic and thermophilic lactic acid bacteria (LAB), which form the natural flora of whey. Mesophilic and thermophilic LAB provide a wide variety of properties in the taste and texture of food products through the fermentation of raw materials in the production of dairy products. Whey is produced as waste after dairy products are produced. Decolorization tests of Dorasyn Red azo dye, which is widely used in the textile sector, have been carried out by obtaining biomass with LAB isolated from whey. Thus, the recovery of whey, which is accepted as waste, has been achieved. In this study, parameters affecting the dissociation reaction of different pH and biomass concentrations were investigated. The dye removal test for four different LAB biomasses (mesophilic lactobacilli and lactococci, and thermophilic lactobacilli and lactococci) was performed at ten different concentration levels (0, 0.5, 0.75, 1, 1.25, 1.5, and 5 g/L). The pH value was adjusted to pH 3 and 6.8 (original) and incubated for 3 h at 20 °C. Tested pH values were 1.5, 2, 3, 4, 5, 6, 7, 8, 9, and 10 with constant 2.5 g/L biomass concentration. Decolorization efficiencies for about 90% dye removal were obtained with mesophilic lactobacilli biomass (2.5 g/L) at pH 3 after 3-h reaction time. This study presents a report that the whey for environmental protection and paint recovery is an appropriate alternative to the decolorization of textile wastewater.

Screening of antimicrobial activity of lactic acid bacteria isolated from &lt;i&gt;anango baca&lt;/i&gt; slurry, a spontaneously fermented maize product used in Côte d’Ivoire

Anango baca is a traditional porridge-like food product made from fermented maize slurry which is widely used as a complementary food for infants in Cote d’Ivoire. The present study was conducted to assess antimicrobial activities of lactic acid bacteria (LAB) from this fermented infant’s product. Thereby, LAB were isolated into the slurry and their antimicrobial effects were examined via agar spot test and agar diffusion method prior to their identification by molecular tools. Anango baca slurry was found to be acidic (pH between 2.98 ± 0.02 and 3.75 ± 0.01). Counts of mesophilic LAB from MRS agar and thermophilic LAB varied from 6.4 ± 0.6 log UFC.g -1 to 10.9 ± 0.5 log UFC.g -1 and from 5.6 ± 2.3 log UFC.g -1 to 10.6 ± 0.5 log UFC.g -1 , respectively. Thirteen LAB produced antibacterial substances able to inhibit the growth of pathogens and foodborne spoilage indicator bacteria. They were identified as Lactobacillus fermentum (46%), L. plantarum (23%), Enterococcus faecium (23%) and Staphylococcus pasteuri (8%). Among them, E. faecium and S. pasteuri produced bacteriocins. However, these bacteria are considered sometimes to be opportunistic pathogens. Thus, fermented maize slurry production must be to do from LAB selected to improve the hygiene and safety of anango baca slurry and also children’s health. Further studies will be conducted to select LAB able to be used as starters. © 2017 International Formulae Group. All rights reserved. Keywords: Anango baca slurry, lactic acid bacteria, fermented maize porridge, antimicrobial activity, bacteriocin, molecular identification

Research into techniques for making wheat bread on hop leaven

We investigated saccharification process of scaldings depending on the parameters of their preparation and established that the largest intensity of sugar accumulation occurs within one hour of saccharification at a mass fraction of moisture in scalding of 78.0 %. The developed sourdough is recommended for the technology of rye-wheat bread with a small content of rye flour (10...12 %) or wheat bread from graded flour. It is recommended using the four-phase technique of dough preparation according to the following scheme: saccharized bitter scalding → scalding soured with the homofermentative thermophilic lactic acid bacteria L. Delbrukii‒76 → hop leaven, soured with yeast of the race S. cerevisiae L-1 and the homofermentative mesophilic lactic acid bacteria L. Plantarum-30 → dough. When using 25 % of sourdough, the acidity of dough and finished products is reduced by 2.0 degrees. That is why we recommend utilizing a given technique for making bakery products from wheat flour. This provides for the better fluffiness and state of the crumb, as well contributes to retaining the freshness of bakery products. The results of research allowed us to devise a technological scheme of production, which can be implemented at specialized lines

Promotion of Early Gut Colonization by Probiotic Intervention on Microbiota Diversity in Pregnant Sows.

The aim of this work was to design a novel mixed probiotic culture for piglets and to evaluate its beneficial effect on the piglets’ gut health. The possible mechanisms of probiotic activity, such as adhesion, competitive pathogen exclusion and influence on gut microbiota diversity were determined. Mixed probiotic starter culture is composed of three thermophilic lactic acid bacteria (LAB) strains: Lactobacillus helveticus BGRA43, Lactobacillus fermentum BGHI14 and Streptococcus thermophilus BGVLJ1-44. The strains BGVLJ1-44 and BGRA43 showed good technological properties (fast milk curdling, strong proteolytic activity). In addition, the strain BGVLJ1-44 produces exopolysaccharide (EPS), BGHI14 is heterofermentative LAB strain with significant immunomodulatory effect, while the strain BGRA43 showed strong antimicrobial activity against different pathogens and exhibited significantly higher level of adhesion to Caco-2 cells comparing to other two strains. Both lactobacilli strains BGRA43 and BGHI14 (p < 0.05), as well as probiotic combination (p < 0.01) significantly reduced the adhesion of Escherichia coli ATCC25922 to Caco-2 cells, while the strains BGVLJ1-44 (p < 0.01) and BGRA43 (p < 0.05) significantly reduced adhesion of Salmonella 654/7E (veterinary isolate). The results of farm trial revealed that treatment of sows with new fermented dairy probiotic influenced the piglets’ gut colonization with beneficial bacteria and reduced the number of enterobacteriaceae in litters from some treated sows (no significant due to high variability among animals). Finally, this is the first study reporting that the treatment of sows with probiotic combination resulted in the improved microbiota diversity in neonatal piglets.

Characterization of Exopolysaccharides Produced by Thermophilic Lactic Acid Bacteria Isolated from Tropical Fruits of Thailand.

In the present study, we have obtained two exopolysaccharide (EPS)-producing thermophilic lactic acid bacteria (LAB) that were isolated from tropical fruits of Thailand. The two strains, designated LY45 and PY45, were identified as Pediococcus pentosaceus and Lactobacillus amylovorus, respectively. Both plant-derived LAB strains, which produce neutral EPSs together with the acidic one, can grow vigorously at 45°C and even at 50°C. Hyaluronidase (EC 3.2.1.35), which catalyzes the degradation of hyaluronic acid, activates an inflammatory reaction. Interestingly, EPSs produced by the LY45 and PY45 strains were found to inhibit hyaluronidase activity at the same order of IC50 values as did sodium cromoglicate and dipotassium glycyrrhizinate, which are well-known as anti-inflammatory agents. The LY45-derived neutral EPS consists of glucose and mannose as monosaccharide components, whereas the acidic one contains mainly mannose, together with glucose and galactose. On the other hand, although Lactobacillus amylovorus PY45 also produces neutral and acidic EPSs, the main monosaccharide in both EPSs is mannose, and glucose is a minor component. Furthermore, the PY45 strain may be probiotically and industrially useful because the microorganism can utilize starch and glycogen as carbon sources.

Thermophilic Enterococcus faecium QU 50 enabled open repeated batch fermentation for l-lactic acid production from mixed sugars without carbon catabolite repression

Thermophilic lactic acid bacterium enabled homo-l-lactic acid fermentation from hexose/pentose without carbon catabolite repression, and open repeated production by immobilization.

Sensory profile development of Oaxaca cheese and relationship with physicochemical parameters

A sensory profile of Oaxaca cheese was developed. To represent both industrial and artisanal Oaxaca cheese, 3 types of cheese were manufactured under controlled conditions: 2 with pasteurized milk using a mesophilic lactic acid bacteria culture (Lactococcus lactis ssp. lactis and L. lactis ssp. cremoris) and a thermophilic lactic acid bacteria culture (Streptococcus salivarius ssp. thermophilus), and a third with naturally acidified raw milk. The cheeses were evaluated by a panel of 11 trained judges. Additionally, chemical composition and instrumental color parameters were determined, an instrumental texture profile analysis was performed, and volatile compounds were identified by solid-phase microextraction coupled with gas chromatography/mass spectrometry. The sensory profile developed includes 43 descriptors, of which 13 are discriminant among these 3 cheese types. Descriptors include visual attribute waxy; tactile (manual) attributes moist and oily; orthonasal aroma attributes empyreumatic and cow; basic taste attribute salty; mouth texture attributes chewable, gummy, adherent, fibrous, moist, and fatty; and auditory attribute squeaky. A strong correlation was found between specific sensory data and physicochemical parameters measured by instrumental and chemical methods.

Microbial community dynamics in thermophilic undefined milk starter cultures

Model undefined thermophilic starter cultures were produced from raw milk of nine pasta-filata cheesemaking plants using a selective procedure based on pasteurization and incubation at high temperature with the objective of studying the microbial community dynamics and the variability in performances under repeated (7–13) reproduction cycles with backslopping. The traditional culture-dependent approach, based on random isolation and molecular characterization of isolates was coupled to the determination of pH and the evaluation of the ability to produce acid and fermentation metabolites. Moreover, a culture-independent approach based on amplicon-targeted next-generation sequencing was employed. The microbial diversity was evaluated by 16S rRNA gene sequencing (V1–V3 regions), while the microdiversity of Streptococcus thermophilus populations was explored by using novel approach based on sequencing of partial amplicons of the phosphoserine phosphatase gene (serB). In addition, the occurrence of bacteriophages was evaluated by qPCR and by multiplex PCR. Although it was relatively easy to select for a community dominated by thermophilic lactic acid bacteria (LAB) within a single reproduction cycle, final pH, LAB populations and acid production activity fluctuated over reproduction cycles. Both culture-dependent and -independent methods showed that the cultures were dominated by either S. thermophilus or Lactobacillus delbrueckii subsp. lactis or by both species. Nevertheless, subdominant mesophilic species, including lactococci and spoilage organisms, persisted at low levels. A limited number of serB sequence types (ST) were present in S. thermophilus populations. L. delbrueckii and Lactococcus lactis bacteriophages were below the detection limit of the method used and high titres of cos type S. thermophilus bacteriophages were detected in only two cases. In one case a high titre of bacteriophages was concurrent with a S. thermophilus biotype shift in the culture.This study largely confirms previous data on the composition of undefined thermophilic starters used for the production of traditional cheeses in Italy but it is the first one to systematically address the dynamics of the cultures under a repeated reproduction regime with backslopping.

Identification, typing and functional characterization of dominant lactic acid bacteria strains from Iranian traditional yoghurt

Interest in the microbiota of traditional fermented dairy products, such as yoghurt, continues due to the need for new lactic acid bacteria (LAB) strains that can complement or replace currently-in-use starters. In this work, five traditional yoghurts and one milk sample (for making yoghurt) from different areas of the Khorasan-e-Razavi region, Iran, were subjected to microbial characterization. Among the 102 isolates recovered, which included 29 from milk, the thermophilic LAB species Streptococcus thermophilus (34) and Lactobacillus delbrueckii (36) (with similar numbers of the subsp. bulgaricus and lactis) were the majority bacteria in all samples. Wide intra-species phenotypic and genetic diversity was encountered among the isolates. The safety and technological features of 29 strains belonging to the species S. thermophilus, L. delbrueckii and Lactobacillus helveticus, all candidates for use in yoghurt-making, were examined. In culture, two S. thermophilus strains produced the biogenic amine histamine from histidine (its precursor amino acid), and five L. delbrueckii strains showed atypical resistance to tetracycline (MIC ≥ 8 μg mL−1). The remaining strains coagulated milk, producing a coagulum of good appearance and pleasant acidic aroma. None of them produced appreciable amounts of exopolysaccharides in milk under the incubation conditions. After fermentation of milk with individual and mixed strains, major yoghurt aroma volatile compounds (i.e. acetaldehyde, diacetyl and acetic acid) were detected. Also as being used in the design of commercial starters, the thermophilic LAB strains characterized in this study might be used to help improve the safety of traditional yoghurts, while maintaining their original qualitative and sensorial characteristics.