Thermophilic Lactic Acid Bacteria Research Articles

Isolation, identification, and characterization of thermophilic lactic acid bacteria isolated from whey of Kars Kashar cheeses.

Kars Kashar cheese is an artisanal pasta-filata type cheese and geographically marked in Eastern Anatolia of Turkey. The aims of this research were to determine for the first time thermophilic lactic acid bacteria (LAB) of Kars Kashar cheese and characterize the technological properties of obtained isolates. In our research, a number of 15 samples of whey were collected from the different villages in Kars. These samples were incubated at 45 °C and used as the source material for isolating thermophilic LAB. A total of 250 colonies were isolated from thermophilic whey, and 217 of them were determined to be presumptive LAB based on their Gram staining and catalase test. A total of 170 isolates were characterized by their phenotypic properties and identified using the MALDI-TOF mass spectrometry method. Phenotypic identification of isolates displayed that Enterococcus and Lactobacillus were the predominant microbiota. According to MALDI-TOF MS identification, 89 isolates were identified as Enterococcus (52.35%), 57 isolates as Lactobacillus (33.53%), 23 isolates as Streptococcus (13.53%), and one isolate as Lactococcus (0.59%). All thermophilic LAB isolates were successfully identified to the species level and it has been observed that MALDI-TOF MS can be successfully used for the identification of selected LAB. The acidification and proteolytic activities of the isolated thermophilic LAB were examined, and the isolates designated for use as starter cultures were also genotypically defined.

Antilisterial activity of raw sheep milk from two native Epirus breeds: Culture-dependent identification, bacteriocin gene detection and primary safety evaluation of the antagonistic LAB biota

Raw milk from native small ruminant breeds in Epirus, Greece, is a valuable natural source of autochthonous lactic acid bacteria (LAB) strains with superior biotechnological properties. In this study, two bulk milks (RM1, RM2) from two local sheep yards, intended for traditional Kefalotyri cheese production, were preselected for bacteriocin-like antilisterial activity by in vitro tests. Their antagonistic LAB biota was quantified followed by polyphasic (16S rRNA gene sequencing; IGS for Enterococcus; a multiplex-PCR for Leuconostoc) identification of 42 LAB (RM1/18; RM2/24) isolates further evaluated for bacteriocin encoding genes and primary safety traits. Representative isolates of the numerically dominant mesophilic LAB were Leuconostoc mesenteroides (10) in both RMs, Streptococcus parauberis (7) in RM2, and Lactococcus lactis (1) in RM1; the subdominant thermophilic LAB isolates were Enterococcus durans (8), E. faecium (6), E. faecalis (3), E. hirae (1), E. hermanniensis (1), Streptococcus lutetiensis (2), S. equinus (1) and S. gallolyticus (1). Based on their rpoB, araA, dsr and sorA profiles, six Ln. mesenteroides strains (8 isolates) were atypical lying between the subspecies mesenteroides and dextranicum, whereas two strains profiled with Ln. mesenteroides subsp. jonggajibkimchii that is first-time reported in Greek dairy food. Two RM1 E. faecium strain biotypes (3 isolates) showed strong, enterocin-mediated antilisterial activity due to entA/entB/entP possession. One E. durans from RM1 possessed entA and entP, while additional nine RM2 isolates of the E. faecium/durans group processed entA or entP singly. All showed direct (cell-associated) antilisterial activity only, as also both S. lutetiensis strains from RM2 did strongly. Desirably, no LAB isolate was β-hemolyrtic, or cytolysin-positive, or possessed vanA, vanB for vancomycin resistance, or agg, espA, hyl, and IS16 virulence genes. However, all three E. faecalis from RM2 possessed gelE and/or ace virulence genes. In conclusion, all Ln. mesenteroides strains, the two safe, enterocin A-B-P-producing E. faecium strains, and the two antilisterial S. lutetiensis strains should be validated further as potential costarter or adjunct cultures in Kefalotyri cheese. The prevalence of α-hemolytic pyogenic streptococci in raw milk, mainly S. parauberis in RM2, requires consideration in respect to subclinical mastitis in sheep and the farm hygiene overall.

Biochemical and microbiological characteristics of industrial Tsalafouti cheese

Tsalafouti is a white cheese with mild sour, acidic taste. Its spreadable texture has no gas holdings. In the present work, Tsalafouti cheese was industrially manufactured and its biochemical, organoleptic and microbiological characteristics were investigated. At 30 days of storage, the mean pH was 4.05 and moisture content was 68.06%, fat 14.9%, fat-in-dry matter 46.52%, salt 1.55%, ash 2.4%, and proteins 10.92%. Level of proteolysis remained stable during storage. The volatile compounds 3 methyl butanol, acetoin, ethanol, acetone, were found in high levels on day 30. During the organoleptic evaluation Tsalafouti was very much appreciated until day 45. Total viable counts enumerated on skim-milk containing media at 37oC remained constant within 7.5-8.0 log CFU/g from day 15 to day 90 of storage of the industrially ripened cheese. However, typical mesophilic lactic acid bacteria (LAB) increased to 8.1-8.5 log CFU/g and predominated the technological biota, whereas typical thermophilic LAB, inclusive of enterococci, remained subdominant by 1-3 log units throughout storage. Yeasts were beneficial for the sensory quality of industrial Tsalafouti from day 30 to 45 when their counts were below 6-7 log CFU/g; however, yeasts turned to be the primary spoilage agents after their counts increased to 7.5 log CFU/g with prolonged storage (day 60 to 90). All industrial cheese samples were microbiologically safe as due to their low pH (3.85 to 4.13). These data could be useful for the better recognition of traditional Greek Tsalafouti cheese.

Effect of Commercial and Autochthonous Bioprotective Cultures for Controlling Listeria monocytogenes Contamination of Pecorino Sardo Dolce PDO Cheese.

The composition and physicochemical characteristics of short-aged Pecorino Sardo PDO (Protected Designation of Origin) cheese makes it permissive to Listeria monocytogenes growth. The PDO product specification stipulates that this cheese is produced with whole sheep's milk inoculated with cultures from the area of origin. Therefore, the use of bioprotective cultures for the inhibition of pathogens in PDO cheeses is allowed only if autochthonous microorganisms are used. Furthermore, bioprotective cultures are generally used on the cheese surface to prevent the outgrowth of L. monocytogenes, the application of which can be time-consuming and require specialist technical knowledge. In this study, we examine the direct addition of bioprotective cultures to the cheese vat and compare the activity of a commercial bioprotective culture (Lactiplantibacillus plantarum) and an autochthonous lactic acid bacterium with bioprotective properties (Lactobacillus delbruekii sups. sunkii), for the inhibition of L. monocytogenes in Pecorino Sardo PDO cheese. Three types of Pecorino Sardo PDO cheese were made with bioprotective cultures added directly to the cheese milk along with the starter inoculum: PSA, with the commercial bioprotective culture; PSB, with the autochthonous bioprotective culture; and a CTRL cheese with no bioprotective culture. A challenge test was performed on each of these cheeses by artificially contaminating the cheese surface with L. monocytogenes (2 Log10 CFU/g). Three batches of each cheese type were analyzed to enumerate mesophilic and thermophilic lactic acid bacteria and to investigate the growth potential of L. monocytogenes during manufacturing, at the end of ripening, at the end of shelf-life, and after 180 days from cheese production. Both bioprotective cultures tested in this study showed inhibitory action against the pathogen with 0.3-1.8 Log10 CFU/g (colony-forming unit per gram) reduction levels. The autochthonous organism, L. sunkii, was as effective as the commercially supplied culture, and the addition of the bioprotective cultures to the cheese-making procedure offered protection against L. monocytogenes. The direct addition of bioprotective cultures to the making procedure of Pecorino Sardo PDO cheese is a potentially innovative strategy to improve the safety of this product.

Application of flow cytometry for rapid bacterial enumeration and cells physiological state detection to predict acidification capacity of natural whey starters

Natural whey starter cultures are undefined microbial communities mainly consisting of thermophilic lactic acid bacteria (LAB). The technological pressure that shapes the natural whey starter community before and during the back-slopping procedure can impact the amount and viability of the different thermophilic LAB. Traditional culture-dependent analytical methods are useful for evaluating natural whey cultures based on plate enumeration with various culture media and are commonly used as self-control procedures in dairy items. These methods have high variability and require days to obtain results. As the dairy industry has been searching for a solution to this problem for a long time, researchers must explore alternative methods for the technological evaluation of natural whey and assessment of the health status of the thermophilic acidifying bacteria community in the cheesemaking process. The flow cytometry approach has been considered an alternative to classical methods in this work sector. This study compared bacterial enumeration by plate counting and flow cytometry on natural whey samples. Flow cytometry results showed positive agreement with a tendency to overestimate, linearity, and correlation with plate counting. Other parameters have also been introduced for evaluating a natural whey starter, measuring the physiological state of the cells. Specifically, cell-wall damage and metabolic activity were also evaluated, allowing us to quantify the number of cells even in sub-optimal physiological conditions.

Comparison of Activity of Commercial Protective Cultures and Thermophilic Lactic Acid Bacteria against Listeria monocytogenes: A New Perspective to Improve the Safety of Sardinian PDO Cheeses.

Listeria monocytogenes contamination that occurs during and post-processing of dairy products is a serious concern for consumers, and bioprotective cultures can be applied to control the growth of the pathogen in sheep milk cheeses. However, to respect specifications provided for protected designation of origin (PDO) cheeses, only autochthonous microorganisms can be used as bioprotective cultures in these products. This in vitro study aimed to evaluate thermophilic lactic acid bacteria (LAB) isolated from sheep milk as bio-preservative agents to control L. monocytogenes growth in PDO cheese. Results were compared with those obtained with a commercial protective culture (cPC) composed of a Lactiplantibacillus plantarum bacteriocin producer designed to inhibit L. monocytogenes growth in cheese. The in vitro antilisterial activities of n.74 autochthonous LAB and a cPC were tested against 51 L. monocytogenes strains using an agar well diffusion assay. In addition, 16S rRNA sequencing of LAB isolates with antilisterial activity was conducted and strains of Lactobacillus helveticus, Lactobacillus delbrueckii subsp. indicus, Lactobacillus delbrueckii subsp. sunkii, Lactobacillus delbrueckii subsp. lactis and Enterococcus faecalis were identified. In this study, 33.6% (74/220) bacterial strains isolated from milk had characteristics compatible with thermophilic LAB, of which 17.6% (13/74) had in vitro antilisterial activity. These results demonstrate that raw sheep milk can be considered an important source of autochthonous thermophilic LAB that can be employed as protective cultures during the manufacturing of Sardinian PDO cheeses to improve their food safety. The use of bioprotective cultures should be seen as an additional procedure useful to improve cheese safety along with the correct application of good hygienic practices during manufacturing and the post-processing stages.

Impact of Spontaneous Fermentation and Inoculum with Natural Whey Starter on Peptidomic Profile and Biological Activities of Cheese Whey: A Comparative Study

Fermentation is a promising solution to valorize cheese whey, the main by-product of the dairy industry. In Parmigiano Reggiano cheese production, natural whey starter (NWS), an undefined community of thermophilic lactic acid bacteria, is obtained from the previous day residual whey through incubation at gradually decreasing temperature after curd cooking. The aim of this study was to investigate the effect of fermentation regime (spontaneous (S) and NWS-inoculated (I-NWS)) on biofunctionalities and release of bioactive peptides during whey fermentation. In S and I-NWS trials proteolysis reached a peak after 24 h, which corresponded to the drop out in pH and the maximum increase in lactic acid. Biological activities increased as a function of fermentation time. NWS inoculum positively affected antioxidant activity, whilst S overcame I-NWS in angiotensin-converting enzyme (ACE) and DPP-IV (dipeptidyl peptidase IV) inhibitory activities. Peptidomics revealed more than 400 peptides, mainly derived from β-casein, κ-casein, and α-lactalbumin. Among them, 49 were bioactive and 21 were ACE-inhibitors. Semi-quantitative analysis strongly correlated ACE-inhibitory activity with the sum of the peptide abundance of ACE-inhibitory peptides. In both samples, lactotripeptide isoleucine-proline-proline (IPP) was higher than valine-proline-proline (VPP), with the highest content in S after 24 h of fermentation. In conclusion, we demonstrated the ability of whey endogenous microbiota and NWS to extensively hydrolyze whey proteins, promoting the release of bioactive peptides and improving protein digestibility.

Comparative study of the physico-chemical and microbiological characteristics of raw and pasteurized camel milk

Camel milk is three times richer in vitamin C than cow's milk, it is also rich in niacin, antimicrobial factors prostaglandins and insulin. Pasteurization is an adequate option for camel milk conservation, allowing it to be consumed by people not living in arid environments. However, the obvious problem is that people prefer to consume raw camel milk for its therapeutic virtues, which they think, loses its quality after pasteurization. Therefore, the aim of this research is to study the effect of pasteurization on camel milk nutritional and hygienic quality. This work consists on analyzing four camel milk samples: a sample of raw milk and three samples of this milk , pasteurized at 63°C/30min, 72°C/15sec and at 85°C/2min under laboratory conditions. The data was subjected to Kruskal-wallis using XL-Stat software. These results show stability of the physicochemical composition (PH, acidity, density) and chemical composition (dry matter, lactose, fat, vitamine C, protein) ( p > 0.05) of camel milk pasteurized at 63°C (low pasteurization) and instability ( p < 0.05) following pasteurization high at (85°C) except the fat content which remains intact (p > 0.05). For pasteurization at (72°C) we notice a instability (p ˂ 0.05) in pH, acidity, dry matter, vitamine C and protein, a stability in the density, fat and lactose. Only low pasteurization (63°C for 30 min) can be an alternative for the conservation of
 camel milk while preserving its nutritional quality. To study its hygienic quality before and after pasteurization, the reductase test was carried out; it shows a good to fair quality for the raw milk sample and good for the pasteurized milk sample. Contaminating and original flora were counted on appropriate culture media. Results obtained shows that the pasteurization caused a total inhibition of the pathogenic flora (Halotolerants, Coliforms and Enterobacteriaceae), and partial destruction of the total aerobic mesophilic flora (TAMF), psychrotrophic and thermophilic lactic acid bacteria. This study confirms that the nutritional quality can be preserved almost intact after pasteurization at 63°C for 30min. In addition, pasteurization has an important role in camel milk sanitation by inhibiting pathogenic flora.

Microbiological Characterization of Greek Galotyri Cheese PDO Products Relative to Whether They Are Marketed Fresh or Ripened

Galotyri is the most popular traditional Greek PDO soft acid-curd cheese. This study compared the microbial numbers and types and characterized the lactic acid bacteria (LAB) biota of two artisan-type Galotyri PDO cheese varieties, one marketed fresh (Brand-K) and the other ripened (Brand-Z). Two retail batches of each cheese variety were analyzed, and a total of 102 LAB isolates were biochemically identified. LAB (7.2–9.3 log CFU/g) prevailed in all cheeses, followed by yeasts (5.8–6.8 log CFU/g). Typical starter strains of Streptococcus thermophilus and Lactobacillus delbrueckii were the most abundant species in all batches. However, the fresh Brand-K cheeses had 1–3 log units higher thermophilic starter LAB counts than the ripened Brand-Z cheeses, which contained a more diverse viable LAB biota comprising Lacticaseibacillus paracasei, Leuconostoc mesenteroides, Lentilactobacillus (L. diolivorans, L. kefiri, L. hilgardii), Pediococcus inopinatus/parvulus, few spontaneous nonstarter thermophilic streptococci and lactobacilli, and Enterococcus faecium and E. faecalis at higher subdominant levels.Conversely, the fresh Brand-K cheeses were enriched in members of the Lactiplantibacillus plantarum group; other LAB species were sporadically isolated, including Lactococcus lactis. All retail cheeses were safe (pH 3.9–4.0). No Salmonella spp. or Listeria monocytogenes were detected in 25-g samples by culture enrichment; however, Listeria innocua and coagulase-positive staphylococci (850 CFU/g) survived in one ripened batch. Gram-negative bacteria were <100 CFU/g in all cheeses. In conclusion, ripening reduced the starter LAB viability but increased the nonstarter LAB species diversity in the present Galotyri PDO market cheeses.

Cis-trans retinol isomerisation: Influence of microorganisms during the production of pasta filata cheeses

The isomerisation index, or degree of retinol isomerisation (DRI), i.e. the percentage ratio between 13-cis and all-trans retinol, could be used as process and product index in dairy products. To better investigate microbial influence on retinol isomerisation, retinol isomerisation and microbial levels have been monitored during the technological process and the storage of different “pasta filata” cheeses. In the investigated cheeses, after a saponification procedure and HPLC analysis, 13-cis retinol, all-trans retinol and other cis retinols were detected. During production, an increase of 13-cis retinol and of the DRI was found. As to their initial values, an increment in almost all microorganisms, most remarkable for lactic acid bacteria, was detected. The isomerisation index was found to be significantly correlated to the growth of thermophilic lactic acid bacteria during the production process.

Automatic Milking Systems in the Production of Parmigiano Reggiano Cheese: Effects on the Milk Quality and on Cheese Characteristics

The adoption of innovative processes, such as the automatic milking system (AMS), in the production of typical PDO cheeses, such as Parmigiano Reggiano, needs to be evaluated and tested, to verify its influence on milk quality and the typicality of the product. The present research was aimed to study the effect of the introduction of the AMS on the cheesemaking characteristics of the milk and the ripening process and the sensory properties of the Parmigiano Reggiano PDO cheese. Six cheesemaking trials were performed and, in each trial, two different separated pools of milk were submitted to the cheesemaking process in parallel, one from AMS and the other from a traditional milking parlor (TMP). AMS milk, in comparison with TMP one, showed higher content of lactose and calcium and lower contents of somatic cells, thermophilic lactic acid bacteria and chloride. Nevertheless, these changes were too small to influence the efficiency of the cheesemaking process and the cheese composition and its sensory profile. Moreover, cheeses made with AMS milk fully complied with the sensory characteristics of Parmigiano Reggiano cheese PDO, as defined by the PDO rules.

Evolution of the biochemical and microbiological characteristics of mountainous Kefalotyri cheese during ripening and storage

As artisanal cheeses are gaining recognition during the last years by consumers, efforts should be made to standardize their manufacture in order to produce safe products of high and constant quality, supporting the local economy and spreading them outside the region of origin. In this work, the biochemical and microbiological characteristics of Kefalotyri cheese produced during summer in the mountains of Pindos using an artisanal cheesemaking procedure were studied. Sheep raw cheese milk was used without starter culture addition for Kefalotyri cheese manufacture. At 90 days of ripening and storage (the date that hard cheese can be sold in the market), its moisture was 40.4%, fat 28.8%, salt 4.1% and proteins 23.3%. Butyric acid and 3methyl butanoic acid were the most abundant volatile compounds found in this cheese. Mesophilic lactic acid bacteria and cocci were dominated; high numbers of thermophilic lactic acid bacteria and cocci, enterococci and Enterobacteriaceae were also present and the microbiological data revealed a rather satisfactory hygienic sanitary condition of the cheeses.

Wagashi cheese: Probiotic bacteria incorporation and significance on microbiological, physicochemical, functional and sensory properties during storage

This study evaluated the incorporation of Lactobacillus or an Enterococcus probiotic bacteria into Wagashi cheese with a focus on their viability during production and storage, and their significance on key quality features evaluated using standard methods and a reference frame specific for Wagashi. Probiotic bacteria were added following heat treatment. Addition of probiotic strains did not affect protein content in contrary to fat, dry matter, pH and titratable activity, which were influenced by strain and storage time. Final bacteria count exceeded 7 log cfu/g suggested for probiotic cheeses. Yeast and mould counts decreased in all cheese, except for RwLc. Probiotic cheese samples, except RwLc, were similar considering their mesophilic lactic acid bacteria (LAB) counts conversely to the differences denoted for their thermophilic LAB counts. All cheeses exhibited antioxidant activity. Total phenolic content was highest in the control (Rc). Butyric, ascorbic, formic, citric, propionic, malic and lactic acid were found in the cheeses. All cheeses were scored higher than 5, and RwLp, RwLr had a significantly higher acceptability. Key cheese features were not negatively affected during storage, highlighting the suitability of Wagashi cheese as a dietary source of probiotic bacteria.

Characterization of Yeasts Isolated from Parmigiano Reggiano Cheese Natural Whey Starter: From Spoilage Agents to Potential Cell Factories for Whey Valorization.

Whey is the main byproduct of the dairy industry and contains sugars (lactose) and proteins (especially serum proteins and, at lesser extent, residual caseins), which can be valorized by the fermentative action of yeasts. In the present study, we characterized the spoilage yeast population inhabiting natural whey starter (NWS), the undefined starter culture of thermophilic lactic acid bacteria used in Parmigiano Reggiano (PR) cheesemaking, and evaluated thermotolerance, mating type, and the aptitude to produce ethanol and bioactive peptides from whey lactose and proteins, respectively, in a selected pool of strains. PCR-RFLP assay of ribosomal ITS regions and phylogenetic analysis of 26S rDNA D1/D2 domains showed that PR NWS yeast population consists of the well-documented Kluyveromyces marxianus, as well as of other species (Saccharomyces cerevisiae, Wickerhamiella pararugosa, and Torulaspora delbrueckii), with multiple biotypes scored within each species as demonstrated by (GTG)5-based MSP-PCR. Haploid and diploid K. marxianus strains were identified through MAT genotyping, while thermotolerance assay allowed the selection of strains suitable to grow up to 48 °C. In whey fermentation trials, one thermotolerant strain was suitable to release ethanol with a fermentation efficiency of 86.5%, while another candidate was able to produce the highest amounts of both ethanol and bioactive peptides with potentially anti-hypertensive function. The present work demonstrated that PR NWS is a reservoir of ethanol and bioactive peptides producer yeasts, which can be exploited to valorize whey, in agreement with the principles of circularity and sustainability.

STUDY OF PROPERTIES OF YOGHURTS MADE USING VIVO STARTER CULTURES

The article presents the results of experimental studies of qualitative indicators of milk and fermented milk products (yoghurts) made using VIVO starter cultures. VIVO starter cultures contain thermophilic lactic acid bacteria Streptococcus thermophilus, Lactobacillus delbrueckii ssp., Lactobacillus acidophilus and others.
 The determination of organoleptic and physico-chemical parameters of cow's milk and dairy products based on it was carried out according to generally accepted methods. During the organoleptic evaluation of milk and lactic acid products, the appearance and texture, smell, taste and color of milk were examined. Determination of active acidity was carried out in accordance with GOST 26781. Titratable acidity in degrees Turner was determined according to GOST 3624. The content of fat, protein, dry matter was determined according to GOST 2661: 2010.
 A study was made of the organoleptic characteristics of yogurts obtained by fermentation by using of VIVO starter cultures. The high activity of VIVO starter cultures was established, the products on the basis of which have a pleasant taste characteristic of these products.
 The results of physico-chemical analysis of yogurt samples obtained by using of VIVO starter cultures confirmed their compliance with DSTU 4343: 2004.
 Lactic acid products made with VIVO sourdough are functional products. It is recommended to use yogurts based on VIVO starter cultures to restore intestinal microflora, normalize digestion, strengthen immunity, and reduce the risk of colds and SARS.

ПЛОДОВО-ЯГОДНЫЕ НАПОЛНИТЕЛИ В ПРОИЗВОДСТВЕ КАЗАХСКИХ НАЦИОНАЛЬНЫХ КИСЛОМОЛОЧНЫХ НАПИТКОВ

This paper offers investigation of fruit and berry fillers on the rheological properties of fermented milk drinks. The research was conducted as part of a scientific research effort. Local wild plants were used as fillers. This type of research allowed expanding the range of products at the enterprise and improving the organoleptic and nutritional properties of products. The purpose of this article is to find additional local vegetable raw materials as filler for fermented milk products. The importance of the results is that the data obtained can be used by specialists of dairy farms. During the period of coronavirus infection, when there were interruptions in the supply of raw materials, such directions it sets for future research as the development and improvement new food products by using local plant raw materials were revealed. The experimental samples of fermented milk drink from goat’s milk with various fillers (tayberry, shadberry, black chokeberry and blackcurrant). The pH of the samples were measured with a pH meter (Exspert-рН, Russia). Total solids, protein, fat, ash, and titratable acidity were determined according to the methods described by the standard method. Goat's milk is subjected to ozonization for 10 minutes at an ozone concentration of 80 mg/m3 before entering the container. The pasteurized goat milk (at 37 °C) was inoculated with freeze-dried culture bacterial starter culture (thermophilic lactic acid bacteria and bifidobacteria (Breve B 10, Bifidobacterium adolescentis B 14, Bifidobacterium adolescentis B 37) in the ratio 2:1 at 5 % inoculation level. The sensory aspects were undertaken using 10 panellists. The degree of influence of the introduced bacterial starter culture on the duration of fermentation of fermented milk beverages was studied by taking into account the rheological characteristics and structural and technological parameters. A mathematical model of the dependence of the strength and acidity of a fermented milk clot on the dose of fruit and berry fillers is constructed.

Insights on biological hydrogen production routes and potential microorganisms for high hydrogen yield

Considering the present energy demand and industrial growth, finding a potential sustainable energy source is crucial. Among renewable fuels, hydrogen is considered to be the primary choice as it offers substantial benefits over other conventional fuels. Hydrogen can be generated from waste substrates, is cleaner, and has the highest energy density when compared to conventional fuels. Hydrogen production, particularly biological hydrogen production, is believed to be cost-efficient as it can be successfully performed in ambient conditions with easy operational techniques in an environmental-friendly manner. This review summarizes the different routes of biological hydrogen production including biophotolysis, indirect photolysis, dark fermentation, photofermentation, and microbial electrolysis. Further, leading microorganisms involved in biohydrogen production, such as Clostridium spp., Enterobacter spp., Bacillus spp., Escherichia coli, thermophilic lactic acid bacteria, and Klebsiella spp., along with the molecular approaches employed for the enhancement of biohydrogen production are discussed. In addition, a thorough techno-economic analysis of factors involved in the scale-up of hydrogen production is carried out.

Microbiological, physicochemical, textural and volatile characteristics of traditional kashar cheese produced in Muş

The aim of this study is to investigate physicochemical properties, microbiological qualities and volatile compound contents of traditional aged kashar cheese produced in Muş, Turkey. Vacuum packaged cheeses were purchased from six different local producers. Total aerobic mesophilic bacteria, total yeast and mold counts, mesophilic and thermophilic lactic acid bacteria populations (log CFU g-1) were in similar ranges in most samples (P>0.05). Coliform populations stayed below 1 log CFU g-1. All six samples yielded negative Salmonella spp. and positive Listeria spp. results. The average compositional properties of cheese samples in percentages (w/w) were 55.73 ± 2.47 for total solids, 27.05 ± 1.73 for protein, 25.92 ± 0.98 for fat, 4.11 ± 0.33 for salt. On average, all color parameters were different for interior and exterior parts of cheese samples. The textural hardness levels of cheese samples were between 1548.73-5727.04 g and significantly different from each other (P<0.05). A total of 17 volatile compounds were detected by GC-MS. According to the results of this study, production steps and raw materials should be standardized to minimize the diversity among products.

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.