Thermophilic Dairy Research Articles

Effects of Substrate and Processing Conditions on Nematode Suppressiveness of Anaerobic Biogas Digestates

Biogas digestates produced from anaerobically processed food or dairy manure have demonstrated some potential to suppress different pathogens and pests. In this study, digestates from these two substrates processed mesophilically (20 to 40°C) or thermophilically (>40°C) were compared for their nematode-suppressive potential. In bioassays, the suppressive potential of Heterodera schachtii or Meloidogyne incognita was tested at different amendment rates. Testing was expanded to field microplot experiments with M. incognita and greenhouse tests with Pratylenchus vulnus. In the bioassay with H. schachtii, fewer nematodes penetrated radish roots after amendment with thermophilic than with mesophilic digestates. Root penetration was lowest after treatment with digestates of food waste and thermophilic dairy manure at the highest rate. In a watermelon bioassay with M. incognita, nematode-induced galling and egg mass production were reduced after amendment with food waste digestates compared with manure digestates and after thermophilic compared with mesophilic digestates in the case of egg masses. In a greenhouse experiment with peach rootstock ‘Nemaguard’, the numbers of P. vulnus in roots were diminished after amendment with digestates at the highest rate. In microplot experiments with bell peppers, plants initially were more vigorous after amendment with thermophilic digestates than after mesophilic digestate additions. This effect was transient and was no longer measurable at harvest. In summary, food waste digestates, especially those that were thermophilically produced, had nematode suppressive and plant growth-improving properties. These effects were not long lasting and probably need additional mitigation for practical utility. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Chemical, microbiological and sensory characteristics of ‘Tsalafouti’ traditional Greek dairy product

Tsalafouti is a traditional dairy product made from sheep’s milk at the end of the lactation period. It is mainly manufactured as a farmhouse product, in high altitude mountainous areas of Southern Pindos. It has a high moisture content, creamy texture and mildly sour flavour. Its production process included the addition of salt to the milk, heating of milk to 90oC with continuous stirring, cooling and transfer to containers placed in caves under running water (around 10oC) and daily stirring for 10 to 20 days until thickening of the milk without the aid of starter cultures (i.e., natural acidification) occurred. The present work presents the physicochemical, microbiological and sensorial characteristics throughout the ageing of artisanal Tsalafouti. The acid-curd product had a pH of about 4.3 and an approximate moisture content of 79%, fat 10%, fat in dry matter 45-48%, salt 0.4% and protein 7%. Proteolysis increased during ripening at 10oC for 20 days and storage at 4 oC for additional 70 days. Ethanol, 3-methyl-1-butanol, hexanal and heptanal were the most abundant volatile compounds. The indigenous microbiota was dominated by mesophilic lactic acid bacteria (LAB) whose numbers exceeded 8 Log CFU/g on day-10 of ripening. Enterococci also increased at an approximate level of 6.5 Log CFU/g, whereas thermophilic dairy lactobacilli were not found. Growth of aerobic spoilage yeasts and moulds was suppressed below 4.5 Log CFU/g for 45 to 60 days, but afterwards, yeasts and moulds outgrew on the product surface causing spoilage. Based on the microbiological results and primarily on sensory panel evaluations, Tsalafouti can have a shelf life of 45 days when stored aerobically under refrigeration.

New advances in exopolysaccharides production of Streptococcus thermophilus.

Streptococcus thermophilus is the most important thermophilic dairy starter, and is widely used in the dairy industry. Streptococcus thermophilus exopolysaccharides received wide attention over recent decades, because they can improve the properties of the dairy product and confer beneficial health effects. The understanding of the regulatory and biosynthetic mechanisms of EPS will improve the EPS biosynthesis, increase the productivity of EPSs, and develop EPSs with desirable properties. The structure of EPSs is the focus of this study. Revealing the structure-function relationship can lead to increase the knowledge base and from there to increased research of EPS. The EPS yield is a key limiting factor in the research and utilization of EPS. In the present review, biosynthetic pathways and genetics of S. thermophilus EPSs were described and reviewed. At the same time, functional properties and applications of EPS, and strategies for enhancement of EPS production are discussed.

Formation of volatile compounds in Teleme cheese manufactured with mesophilic and thermophilic dairy starters

Teleme cheese from sheep, goat and cow milk was produced and the effect of three different starter cultures (mesophilic, thermophilic and mixed) on the formation of volatile compounds during ripening period up to 6 months was studied. Analysis of volatile compounds was performed by an automatic balance pressure headspace apparatus coupled to a GC/MS. The volatile fraction of Teleme cheeses displayed 27 volatile compounds including aldehydes, alcohols, ketones fatty acids and esters. The amount of total volatile compounds (except aldehydes) increased during ripening. The most abundant volatile compounds were butan-2-one, ethanol, butan-2-ol and acetic acid. The results indicated that the type of culture was found to affect to the formation of volatile compounds of the produced cheese. Cheeses made with thermophilic culture showed the highest mean levels of propanal, butanal, none-2-al, hexanal, heptanal, 3-methylbutanal, ethanol, butan-2-one, acetoin, acetone, diacetyl and acetic acid, while cheeses made with mesophilic and mixed cultures showed the lowest and intermediate levels, respectively. The type of milk used and the ripening time were also found to affect to the formation of volatile compounds. Sheep's milk cheese showed higher mean levels of acetaldehyde, propanal, butan-2-ol, 3-hydroxybutan-2-one and acetic acid, whereas the mean level of hexanal, acetone and 3-methylbutan-2-one were higher in goat cheese.

Growth and morphology of thermophilic dairy starters in alginate beads.

The aim of this research was to produce concentrated biomasses of thermophilic lactic starters using immobilized cell technology (ICT). Fermentations were carried out in milk using pH control with cells microentrapped in alginate beads. In the ICT fermentations, beads represented 17% of the weight. Some assays were carried out with free cells without pH control, in order to compare the ICT populations with those of classical starters. With Streptococcus thermophilus, overall populations in the fermentor were similar, but maximum bead population for (8.2 x 10(9) cfu/g beads) was 13 times higher than that obtained in a traditional starter (4.9 x 10(8) cfu/ml). For both Lactobacillus helveticus strains studied, immobilized-cell populations were about 3 x 10(9) cfu/g beads. Production of immobilized Lb. bulgaricus 210R strain was not possible, since no increases in viable counts occurred in beads. Therefore, production of concentrated cell suspension in alginate beads was more effective for S. thermophilus. Photomicrographs of cells in alginate beads demonstrated that, while the morphology of S. thermophilus remained unchanged during the ICT fermentation, immobilized cells of Lb. helveticus appeared wider. In addition, cells of Lb. bulgaricus were curved and elongated. These morphological changes would also impair the growth of immobilized lactobacilli.

Purification and molecular characterization of a tripeptidase (PepT) from Lactobacillus helveticus.

A tripeptidase (PepT) from a thermophilic dairy starter strain of Lactobacillus helveticus was purified by four chromatographic steps. PepT appeared to be a trimeric metallopeptidase with a molecular mass of 150 kDa. PepT exhibited maximum activity against hydrophobic tripeptides, with the highest activity for Met-Gly-Gly (K(m), 2.6 mM; V(max), 80.2 micromol. min(-1). microg(-1)). Some of the hydrophobic dipeptides were slowly hydrolyzed, distinguishing the Lactobacillus PepT from its counterpart in mesophilic Lactococcus lactis. No activity against tetrapeptides or amino acid p-nitroanilide derivatives was observed. The pepT gene and its flanking regions were isolated by PCR and sequenced by cyclic sequencing. The sequence analyses revealed open reading frames (ORFs) 816 bp (ORF1) and 1,239 bp (ORF2) long. ORF2 encoded a 47-kDa PepT protein which exhibited 53% identity with the PepT from L. lactis. The mRNA analyses indicated that pepT conforms a novel operon structure with an ORF1 located upstream. Several putative -35/-10 regions preceded the operon, but only one transcription start site located downstream of the first putative -10 region was identified. An inverted repeat structure with DeltaG of -64.8 kJ/mol was found downstream of the PepT-encoding region.

The effects of some herbs on the activities of thermophilic dairy cultures

In this study, the effects of some herbs (Allium sp., Thymus sp., Anhriscus sp. and Ferule sp.) on growth and acid production of thermophilic cultures (Streptococcus thermophilus and Lactobacillus bulgaricus) were determined. The herbs were sterilized with gamma radiation and added to fermentation media at concentrations of 0.5, 1, 2 and 3% (w/w). Control medium was without herb. Results showed that increasing herb concentrations stimulated acid production by Streptococcus thermophilus and Lactobacillus bulgaricus.

The effects of some herbs on the activities of thermophilic dairy cultures.

In this study, the effects of some herbs (Allium sp., Thymus sp., Anhriscus sp. and Ferule sp.) on growth and acid production of thermophilic cultures (Streptococcus thermophilus and Lactobacillus bulgaricus) were determined. The herbs were sterilized with gamma radiation and added to fermentation media at concentrations of 0.5, 1, 2 and 3% (w/w). Control medium was without herb. Results showed that increasing herb concentrations stimulated acid production by Streptococcus thermophilus and Lactobacillus bulgaricus.

Use of date products in production of the thermophilic dairy starter strain Streptococcus thermophilus

Date-coat sugar extract and date-seed hydrolysate were utilized as the main constituents of a medium for the production of a thermophilic dairy starter strain. Date-coat sugar extract was used as the carbon source, while date-seed hydrolysate was used as the nitrogen source. A suitable concentration of date-coat sugar was in the range of 50 mg sugar/ml. Addition of various amounts of date-seed hydrolysate as the sole nitrogen source in the medium showed that, in spite of a nitrogen insufficiency found in the hydrolysate, the production of the starter strain increased with date-seed hydrolysate (nitrogen) concentration, but the maximum production of biomass was less than that observed with other nitrogen sources. Therefore, various amounts of urea were added and a mixture of urea (6 mg/ml) and of date-seed hydrolysate (4.0 mg/ml) allowed an increase in the concentration of the biomass. The addition of date-seed ash as a mineral source, at a concentration of 1.0 mg/ml in the medium containing date-coat sugar extract, date-seed hydrolysate, and urea could substitute for MgSO 4, and MnSO 4 of the usual medium. This medium gave the maximum production of the thermophilic lactic acid bacteria (0.57 mg/ml) and lactic acid (2 mg/ml), very close to what was obtained with the Elliker broth medium.

Biosurfactants from thermophilic dairy streptococci and their potential role in the fouling control of heat exchanger plates

Recent work on biosurfactant release by thermophilic dairy streptococci is reviewed. There is a suggestion thatStreptococcus thermophilus isolates may release biosurfactants that stimulate detachment of already-adhering cells and leave an anti-adhesive coating on a substratum. A previously published rapid screening method is described for the identification of biosurfactant-releasing microorganisms, and growth medium supplements to enhance biosurfactant release by thermophilic dairy streptococci are reported. New experimental work described includes the isolation and purification of biosurfactants from dairy isolates by thin layer chromatography. Many compounds isolated were extremely surface-active and reduced the water surface tension to values around 30 mJ m−2 at a concentration of 10 mg ml−1. Most importantly, the thin layer chromatograms of various isolates resembled each other, and an adsorbed purified compound from one isolate retarded the deposition to glass of another isolate by a factor of two. Provided our findings implicate that these biosurfactants could also be adsorbed to heat exchanger plates in pasteurizers and thereby retard colonization by thermophilic streptococci, these compounds may have major economic implications. Further work is required, however.

Biosurfactant production by thermophilic dairy streptococci

Biosurfactant production of eight Streptococcus thermophilus strains, isolated from heat exchanger plates in the downstream side of the regenerator section of pasteurizers in the dairy industry has been measured using axisymmetric drop shape analysis by profile (ADSA-P). Strains were grown in M17 broth with either lactose, saccharose or glucose added. After harvesting, cells were suspended in water or in 10 mm potassium phosphate buffer, pH 7.0, and suspension droplets were put on a piece of FEP-Teflon. Changes in droplet profile were analysed by ADSA-P to yield the surface tension decrease due to biosurfactant production as a function of time. Surface tension decreases larger than 8 mJ·m−2 were taken as indicative of biosurfactant production. Only five strains produced biosurfactants in water, solely when saccharose was added to the growth medium. In buffer, all strains produced biosurfactants and production was generally greater than in water. Also, most strains suspended in buffer produced maximally when saccharose was added to the growth medium, whereas one strain produced maximally in buffer upon the addition of glucose. Four strains suspended in buffer produced biosurfactants when glucose was added and only two strains when lactose was added. The possible role of these biosurfactants as anti-adhesives in the dairy industry and for the survival of these strains in natural systems is discussed.

Biosurfactant production by thermophilic dairy streptococci

Biosurfactant production by thermophilic dairy streptococci

Hydrophobic and Electrostatic Cell Surface Properties of Thermophilic Dairy Streptococci

Microbial adhesion to hydrocarbons (MATH) and microelectrophoresis were done in 10 mM potassium phosphate solutions to characterize the surfaces of thermophilic dairy streptococci, isolated from pasteurizers. Regardless of whether they were grown (in M17 broth) with lactose, sucrose, or glucose added, strains were relatively hydrophilic (showing low initial removal rates by hexadecane) and slightly negatively charged. A tendency exists for cells grown with sucrose added to be more hydrophilic than cells grown with glucose or lactose added. Also, the lowest isoelectric points, i.e., the pH values for which the zeta potentials are zero, were measured for strains with glucose added to the growth medium. The isoelectric points for the strains were all rather high, between pH 3 and 5, indicative of protein-rich surfaces, although X-ray photoelectron spectroscopy did not measure excessively large amounts of nitrogen on the cell surfaces. Both MATH and microelectrophoresis were done as a function of pH. Maxima in hydrophobicity were observed at certain pH values. Usually these pH values were in the range of the isoelectric points of the cells. Thus it appears that MATH measures an interplay of hydrophobicity and electrostatic interactions. MATH measures solely hydrophobicity only when electrostatic interactions are absent, i.e., close to the isoelectric points of the cells. Considering that these thermophilic streptococci are all rather hydrophilic, a possible pathway to prevent fouling in the pasteurization process might be to render the heat exchanger plates of the pasteurizer more hydrophobic.

Assessment of Abilities of Conjugal Transfer and Stability of pAMβ1 in Dairy Lactobacilli with Emphasis on Thermophilic and Nonstarter Lactobacilli

Summary To assess the potential of horizontal gene transfer in thermophilic dairy lactobacilli and mesophilic nonstarter bacteria, a broad spectrum of strains isolated from dairy products ( Lactobacillus delbrueckii subsp. bulgaricus, L. delbrueckii subsp. lactis, L. acidophilus, L. helveticus, L. brevis, L. plantarum, L. casei subsp. casei, L. casei subsp. rhamnosus, L. fermentum, L. salivarius subsp. salicinius ) was crossed with lactic acid bacteria harbouring the broad-host-range plasmid pAMβ1 ( Lactococcus lactis subsp. lactis, Streptococcus thermophilus, Leuconostoc mesenteroides subsp. cremoris, Lactobacillus curvatus ) in agar-surface, filter-, and (milk) broth matings. A low-frequency-transfer of pAMβ1 was obtained from L. lactis subsp. lactis and S. thermophilus donors into dairy isolates of L. helveticus (transfer frequencies: 1 × 10 -7 — 8 × 10 -8 transconjugants per recipient cell) and of L. brevis (transfer frequencies: 2 × 10 -7 -5 × 10 -7 transconjugants per recipient cell) in agar-surface-matings. During non-selective successive propagation in skim milk at 37°C, a rapid decrease of plasmid stability occurred in L. brevis within the first 4 days (equivalent to 28 generations). At 30°C-culturing, a complete loss of pAMβ1 was detected after 112 generations (16 days) whilst this plasmid was still present in 10% of the L. brevis cells after 18 days of culturing at 24°C (63 generations). In contrast, growth in vegetable juices (cabbage juice, potato juice) at 30°C resulted in a remarkable stability of pAMβ1 which was still found in 80% of the cells after 77 generations (11 days).

Lactose metabolism and lactase gene sequence homologies amongst lactobacilli

A number of strains of Lactobacillus spp., including the thermophilic and mesophilic dairy species, were screened for the presence of β-galactosidase (β-gal) and phospho-β-galactosidase (pbg) enzyme activities. The majority of lactose fermenting strains exhibited β-gal rather than pbg enzyme activity with the highest levels in the thermophilic dairy species. Correlation between these enzymes and the presence of specific genetic determinants was sought using probes for β-gal and pbg genes from Lactobacillus casei ssp. casei strain 64H. Southern transfer and filter hybridization showed that the β-gal probe shared homology with one strain of Lact. casei ssp. casei only. Sequences homologous to the pbg gene were detected only in plasmid DNA from the same strain of Lact. casei ssp. casei and with plasmid DNA from an apparently unrelated strain of Lactobacillus which exhibited no pbg activity. Two other strains of Lact. casei ssp. casei appeared to show homology between their chromosomal DNA and the pbg gene probe. No other homologies were detected. Therefore, although lactase activity could be detected in many strains of Lactobacillus spp., the genetic determinants involved did not share extensive homology.

Molecular genetics ofStreptococcus thermophilus

The metabolism and genetics of Streptococcus thermophilus (presently Streptococcus salivarius ssp. thermophilus) have only been investigated recently despite its widespread use in milk fermentation processes. The development of recombinant DNA technology has allowed impressive progress to be made in the knowledge of thermophilic dairy streptococci. In particular, it has permitted a careful analysis of phenotypically altered variants which were derived from a mother strain by plasmid or chromosomal DNA reorganization. While natural phage defense mechanisms of S. thermophilus remain poorly documented, information on the bacteriophages responsible for fermentation failures has accumulated. The lysogenic state of two S. thermophilus strains has also been demonstrated for the first time. Gene transfer techniques for this species have been established and improved to the point that targeted manipulation of their chromosomal determinants is now feasible. Cloning and expression vectors have been constructed, and a few heterologous genes were successfully expressed in S. thermophilus. The first homologous genes, involved in carbohydrate utilization, have been cloned and sequenced, shedding some light on the molecular organization of key metabolic steps.

Molecular genetics of Streptococcus thermophilus

The metabolism and genetics of Streptococcus thermophilus (presently Streptococcus salivarius ssp. thermophilus) have only been investigated recently despite its widespread use in milk fermentation processes. The development of recombinant DNA technology has allowed impressive progress to be made in the knowledge of thermophilic dairy streptococci. In particular, it has permitted a careful analysis of phenotypically altered variants which were derived from a mother strain by plasmid or chromosomal DNA reorganization. While natural phage defense mechanisms of S. thermophilus remain poorly documented, information on the bacteriophages responsible for fermentation failures has accumulated. The lysogenic state of two S. thermophilus strains has also been demonstrated for the first time. Gene transfer techniques for this species have been established and improved to the point that targeted manipulation of their chromosomal determinants is now feasible. Cloning and expression vectors have been constructed, and a few heterologous genes were successfully expressed in S. thermophilus. The first homologous genes, involved in carbohydrate utilization, have been cloned and sequenced, shedding some light on the molecular organization of key metabolic steps.

Molecular cloning of lactose genes in dairy lactic streptococci: the phospho-β-galactosidase and β-galactosidase genes and their expression products

The mesophilic ( S. lactis and S. cremoris) and thermophilic ( S. thermophilus) dairy lactic streptococci, which are used in industrial dairy fermentations, contain two different lactose hydrolysing enzymes, a phospho-β-galactosidase and a β-galactosidase. The central role of these enzymes in the pathways used for lactose transport and degradation is discussed along with their properties and distributions in lactic streptococci. In addition, recent results on the cloning, expression and sequence organization of the genes for the mesophilic phospho-β-galactosidase and thermophilic β-galactosidase are reviewed. Original data are presented concerning heterologous gene expression in the study of lactose hydrolysis in lactic streptococci. These include 1) the purification of the S. lactis phospho-β-galactosidase from an overproducing Escherichia coli, and 2) the expression of the E. coli β-galactosidase ( lacZ) gene in S. lactis employing a lactic streptococcal expression vector.