Cheese starters

Probiotication of Nutritious Fruit and Vegetable Juices: An Alternative to Dairy-Based Probiotic Functional Products

Fruits and vegetables are widely known to be rich in nutrients, antioxidants, vitamins, dietary fiber, minerals, and a bioactive molecule, making them an essential component of a balanced diet with multiple documented positive effects on human health. The probiotication of plant-based juices for the production of functional and nutraceutical food serves as a healthy alternative to dairy probiotics. They are cholesterol free, lack several dairy allergens, and also encourage ingestion for people with lactose intolerance. This review highlights valuable claims regarding the efficacy of different probiotic strains on various diseases. A comprehensive nutrition comparison and the preference of plant-based over dairy probiotic drinks is also discussed, supported with updated market trends of probiotic drinks (dairy and non-dairy based). An extensive compilation of current plant-based probiotic drinks that are available in markets around the world is listed as a reference. The fermentability of carbon sources by probiotic microorganisms is crucial in addressing the development of plant-based drinks. Therefore, the pathway involved in metabolism of sucrose, glucose, fructose, and galactose in fruit and vegetable juice was also underlined. Finally, the key factors in monitoring the quality of probiotic products such as total soluble solids, sugar consumption, titratable acidity, pH, and stability at low storage temperatures were outlined.

Invited review: Crystals in cheese: More than a curiosity

Scientific interest in cheese crystals extends back more than a century. However, starting around the 1970s, industry interest, and interest on the part of cheese scientists, grew dramatically as changes in cheesemaking technology and market changes caused the presence of crystals in the marketplace to increase; advanced analytical capabilities enabled new crystalline species to be identified, their origins and causative factors to be elucidated, and their contributions to cheese texture to be better understood. It is now evident that a host of organic- and inorganic-based crystals occur in natural cheeses. Some crystals form preferentially at the surface of rindless or rinded cheeses, others in the irregular openings or spherical eyes that occur within the body of some cheeses, and still others embedded within the cheese matrix. It is also evident that crystals may profoundly influence cheese texture, both as a direct consequence of their abundance, size, shape, and hardness, and as an indirect result of cascading physiochemical events initiated by crystal formation. Consumer response to increased incidence of crystals in the marketplace has been mixed. On the one hand, surface crystals of calcium lactate pentahydrate on Cheddar cheese came to be viewed quite negatively in some markets, often being mistaken for mold growth and spoilage. This triggered industry concern and led to considerable research to determine the underlying causes and to develop strategies to limit or prevent calcium lactate pentahydrate formation. At the same time, other forms of crystallization increasingly came to be viewed as positive features in the growing market dedicated to artisanal and traditional cheeses, giving rise to a bifurcated consumer response to cheese crystals that is evident today. Traditional artisanal cheesemakers perhaps have the most to gain from advances in cheese-crystal research. Traditional artisanal cheeses rely heavily on stories that are weaved around their identity to create uniqueness and add value. A challenge and opportunity for these cheesemakers in the United States and globally will be to translate the fascinating science of their cheese crystals into engaging narratives that capture the imagination, add value to their cheese, and enhance the enjoyment of their cheese by consumers.

Effect of ripening cream with selected lactic acid bacteria on the quality of ghee

The effect of ripening cow'milk cream (40% fat) with 4 strains of lactic acid bacteria on the quality of ghee, an Indian product resembling clarified butterfat, was studied by measuring changes in titratable acidity, pH, volatile acids and diacetyl content due toStreptococcus lactis, Str. lactissubsp.diacetylactis (Str. diacetylactis), Str. thermophilusandLactobacillus bulgaricusin cream prior to conversion into ghee.L. bulgaricusproduced the maximum titratable acidity (1·25% lactic acid) followed byStr. diacetylactis(0·80 % lactic acid) after 72 h.Str. diacetylactisproduced the highest level of diacetyl (28 ppm), after 48 h.L. bulgaricusproduced no detectable diacetyl. Both of these strains produced the maximum amount of volatile acids (2·2–3·5 ml), after 72 h. The flavour and keeping quality of ghee were improved byStr. diacetylactisandStr. lactiswhilstStr. thermophilusandL. bulgaricushad no effect.

Production of concentratedStreptococcus salivariussubsp.thermophilusby coupling continuous fermentation and ultrafiltration

Continuous production of concentrated cells ofStreptococcus salivariussubsp.thermophiluswas achieved in a continuous stirred tank reactor coupled with an ultrafiltration module. A cellular productivity nine times higher than that obtained by conventional methods was observed. The viability of the cells produced was as satisfactory as that obtained by classical culture, but an increase in latency time and a slight decrease in acidification rate during downstream tests in milk were observed. Specific lactic acid productivity decreased as biomass increased. This process produced concentrated starters and lactic acid which could be purified by a downstream processing such as electrodialysis.

Thermograms ofStreptococcus thermophilusandLactobacillus bulgaricusin single and mixed culture in milk medium

Microbial thermograms have been used to investigate the growth ofStreptococcus thermophilusandLactobacillus bulgaricusin single and mixed culture in milk medium. Growth has been observed with different ratios of the strains in the inoculum and, at one ratio, the effect of the amount of inoculum. The effect of serial sub-culture both with and without pH control has been observed, and stimulation ofStr. thermophilusby cell-free fitrates ofL. bulgaricushas been examined. The development of the technique is discussed in terms of the application of microbial thermograms in selecting cultures for incorporation into mixtures and evaluating their performance.

Methods for the determination of aroma compounds in dairy products: a comparative study

Several methods used for sample preparation and for the determination of volatile flavour compounds in dairy products were tested. Steam distillation was an advantageous method for isolating volatile substances. The extraction yields for acetaldehyde, ethanol and diacetyl were >90%, and acetoin was partly separated from diacetyl. After steam distillation of the sample, gas-liquid chromatography was found to be a rapid method for the determination of acetaldehyde, ethanol and diacetyl in a wide range of concentrations corresponding to those found in dairy products. However, the lower limits for reproducible measurements were high (250, 1250 and 65 μM respectively). From the same sample, colorimetry was shown to be an accurate method for the detection of low levels of diacetyl and acetoin (12 and 57 μM respectively). Diacetyl interfered in the colorimetrie determination of acetoin. However, the interference was < 10% when the diacetyl: acetoin molar ratio was < 0·033. Dynamic head-space gas chromatography proved to be a sensitive method for acetaldehyde and diacetyl determination when a ‘purge and trap’ injector and a capillary column were used. The ranges suitable for determination lay between 25 and 100 μM for acetaldehyde and between 2·9 and 11·4 μM for diacetyl. Acetoin was analysed by HPLC on a cation-exchange column and detected by refractometry for concentrations ranging from 250 to 4000 μM.

Argentinean Lactococcus lactis bacteriophages: genetic characterization and adsorption studies

AIMS

Characterization of four virulent Lactococcus lactis phages (CHD, QF9, QF12 and QP4) isolated from whey samples obtained from Argentinean cheese plants.

METHODS AND RESULTS

Phages were characterized by means of electron microscopy, host range and DNA studies. The influence of Ca(2+), physiological cell state, pH and temperature on cell adsorption was also investigated. The double-stranded DNA genomes of these lactococcal phages showed distinctive restriction patterns. Using a multiplex PCR, phage QP4 was classified as a member of the P335 polythetic species while the three others belong to the 936 group. Ca(2+) was not needed for phage adsorption but indispensable to complete cell lysis by phage QF9. The lactococci phages adsorbed normally between pH 5 and pH 8, and from 0 degrees C to 40 degrees C, with the exception of phage QF12 which had an adsorption rate significantly lower at pH 8 and 0 degrees C.

CONCLUSIONS

Lactococcal phages from Argentina belong to the same predominant groups of phages found in other countries and they have the same general characteristics.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work is the first study to characterize Argentinean L. lactis bacteriophages.

Discovering lactic acid bacteria by genomics

This review summarizes a collection of lactic acid bacteria that are now undergoing genomic sequencing and analysis. Summaries are presented on twenty different species, with each overview discussing the organisms fundamental and practical significance, environmental habitat, and its role in fermentation, bioprocessing, or probiotics. For those projects where genome sequence data were available by March 2002, summaries include a listing of key statistics and interesting genomic features. These efforts will revolutionize our molecular view of Gram-positive bacteria, as up to 15 genomes from the low GC content lactic acid bacteria are expected to be available in the public domain by the end of 2003. Our collective view of the lactic acid bacteria will be fundamentally changed as we rediscover the relationships and capabilities of these organisms through genomics.

Characterization of mesophilic mixed starter cultures used for the manufacture of aged cheddar cheese

Seventy-one different Lactococcus lactis subsp. cremoris strains were isolated from seven mesophilic mixed starters used in the manufacture of aged Cheddar cheese in Canada. Based on plasmid profiles and growth in milk (with or without glucose, Casamino Acids or both), two mixed starters were highly heterogeneous, containing at least 18 to 24 distinct L. lactis strains. Three mixed starters were comprised of seven to nine strains, whereas two starters were relatively homogeneous, containing two or three strains. Many strains with similar plasmid profiles behaved differently during growth in milk, indicating variability in the phenotypes. Only 20% of the strains could grow in plain milk, whereas 30% could not grow in milk supplemented with glucose and Casamino Acids. Twenty-five lactococcal bacteriophages were also isolated from whey samples with single strains as hosts. Eighteen phages belonged to the 936 species and seven to the c2 species. Thirteen strains were insensitive to all 25 phages. Almost all sensitive strains were phage species-specific. The 936-like phages had a broader host range.

Gene organization in a central DNA fragment of Oenococcus oeni bacteriophage fOg44 encoding lytic, integrative and non-essential functions

The nucleotide sequence of a DNA fragment previously shown to contain the attachment site (attP) of Oenococcus oeni phage fOg44 (. Arch. Virol. 143, 523-536) has been determined. Sequence analysis indicated that this 6226bp EcoRI fragment harbours an integrase gene, in the vicinity of a direct repeat rich region defining attP, as well as genes encoding a muramidase-related lysin (Lys) and a holin polypeptide (Hol). Transcriptional studies suggested that lys and hol are mainly co-expressed, late in the lytic cycle, from a promotor located upstream of lys. Between the lytic cassette and the phage integration elements three additional open reading frames were found: orf217 and orf252 of unknown function and orf72, the putative product of which bears 32% identity with acidic excisionases from other Gram positive phages. We have established that the first two orfs, as well as the predicted promotor of orf72, are included in a 2143-bp DNA segment missing from the genome of the deletion mutant fOg44Delta2. Although lysogens of fOg44 and fOg44Delta2 exhibited similar properties, each phage produced two distinguishable types of lysogenic strains, differing in inducibility and immunity to other oenophages.

Transcriptional regulation and evolution of lactose genes in the galactose-lactose operon of Lactococcus lactis NCDO2054

The genetics of lactose utilization within the slow-lactose-fermenting Lactococcus lactis strain NCDO2054 was studied with respect to the organization, expression, and evolution of the lac genes. Initially the beta-galactosidase gene (lacZ) was cloned by complementation of an Escherichia coli mutant on a 7-kb HpaI fragment. Nucleotide sequence analysis of the complete fragment revealed part of a gal-lac operon, and the genes were characterized by inactivation and complementation analyses and in vitro enzyme activity measurements. The gene order is galK-galT-lacA-lacZ-galE; the gal genes encode enzymes of the Leloir pathway for galactose metabolism, and lacA encodes a galactoside acetyltransferase. The galT and galE genes of L. lactis LM0230 (a lactose plasmid-cured derivative of the fast-lactose-fermenting L. lactis C2) were highly similar at the nucleotide sequence level to their counterparts in strain NCDO2054 and, furthermore, had the same gene order except for the presence of the intervening lacA-lacZ strain NCDO2054. Analysis of mRNA for the gal and lac genes revealed an unusual transcriptional organization for the operon, with a surprisingly large number of transcriptional units. The regulation of the lac genes was further investigated by using fusions consisting of putative promoter fragments and the promoterless beta-glucuronidase gene (gusA) from E. coli, which identified three lactose-inducible intergenic promoters in the gal-lac operon. The greater similarity of the lacA and lacZ genes to homologs in gram-negative organisms than to those of gram-positive bacteria, in contrast to the homologies of the gal genes, suggests that the genes within the gal operon of L. lactis NCDO2054 have been recently acquired. Thus, the lacA-lacZ genes appear to have engaged the promoters of the gal operon in order to direct and control their expression.

Biotechnology of lactic acid bacteria with special reference to bacteriophage resistance

Lactic acid bacteria play an important role in many food and feed fermentations. In recent years major advances have been made in unravelling the genetic and molecular basis of significant industrial traits of lactic acid bacteria. Bacteriophages which can infect and destroy lactic acid bacteria pose a particularly serious threat to dairy fermentations that can result in serious economic losses. Consequently, these organisms and the mechanisms by which they interact with their hosts have received much research attention. This paper reviews some of the key discoveries over the years that have led us to our current understanding of bacteriophages themselves and the means by which their disruptive influence may be minimized.

Bacteriophage resistance in Lactococcus

Lactic acid bacteria are industrial microorganisms used in many food fermentations. Lactococcus species are susceptible to bacteriophage infections that may result in slowed or failed fermentations. A substantial amount of research has focused on characterizing natural mechanisms by which bacterial cells defend themselves against phage. Numerous natural phage defense mechanisms have been identified and studied, and recent efforts have improved phage resistance by using molecular techniques. The study of how phages overcome these resistance mechanisms is also an important objective. New strategies to minimize the presence, virulence, and evolution of phage are being developed and are likely to be applied industrially.

Genetics of lactose utilization in lactic acid bacteria

Lactose utilization is the primary function of lactic acid bacteria used in industrial dairy fermentations. The mechanism by which lactose is transported determines largely the pathway for the hydrolysis of the internalized disaccharide and the fate of the glucose and galactose moieties. Biochemical and genetic studies have indicated that lactose can be transported via phosphotransferase systems, transport systems dependent on ATP binding cassette proteins, or secondary transport systems including proton symport and lactose-galactose antiport systems. The genetic determinants for the group translocation and secondary transport systems have been identified in lactic acid bacteria and are reviewed here. In many cases the lactose genes are organized into operons or operon-like structures with a modular organization, in which the genes encoding lactose transport are tightly linked to those for lactose hydrolysis. In addition, in some cases the genes involved in the galactose metabolism are linked to or co-transcribed with the lactose genes, suggesting a common evolutionary pathway. The lactose genes show characteristic configurations and very high sequence identity in some phylogenetically distant lactic acid bacteria such as Leuconostoc and Lactobacillus or Lactococcus and Lactobacillus. The significance of these results for the adaptation of lactic acid bacteria to the industrial milk environment in which lactose is the sole energy source is discussed.

Sugar uptake and involved enzymatic activities by yeasts and lactic acid bacteria: their relationship with breadmaking quality

The uptake kinetics of sugars present in wheat doughs and alpha-glucosidase as well as beta-fructosidase activities were determined in different strains of yeasts and lactic acid bacteria. These strains were previously selected according to their breadmaking quality. Saccharomyces cerevisiae (P6), Candida guilliermondii (P40), Lactobacillus plantarum (B31 and La18) and L. brevis (B21) showed good performance, while Sacch. fructuum (P43), L. cellobiosus (B37) and Enterococcus faecium (B11) yielded bread of lower quality. Leuconostoc mesenteroides (B10), when used in combination with other strains led also to high quality starters. All yeast strains used assimilated glucose, fructose and maltose, exhibiting saturable kinetics. Lactic acid bacteria showed saturable kinetics only for hexoses, whereas disaccharide uptake was linear. Sacch. cerevisiae, Leuconostoc mesenteroides, L. brevis and L. plantarum (B31) displayed better sugar uptake properties. For all the strains used alpha-glucosidase and beta-fructosidase activities were detected. The highest specific activities were found for Sacch. cerevisiae, C. guilliermondii and L. plantarum (B31). These results indicate good correlation between the parameters evaluated and the breadmaking potential of the microorganisms.

A Strategy for Rotation of Different Bacteriophage Defenses in a Lactococcal Single-Strain Starter Culture System

A new strategy for starter culture rotations was developed for a series of phage-resistant clones genetically derived from a single strain of Lactococcus lactis subsp. lactis. Phage-resistant derivatives carrying different defense systems were constructed via conjugation with various plasmids encoding abortive infection (Abi/Hsp) and/or restriction and modification (R/M) systems of different specificity. The plasmids included pTR2030 (Hsp + R + /M + ), pTN20 (Abi + R + /M + ), pTRK11 (R + /M + ), and pTRK68 (R + /M + ). Selected phage-resistant transconjugants or transformants were evaluated in different rotation sequences through cycles of the Heap-Lawrence starter culture activity test in milk contaminated with phage and whey from the previous cycle. When used in consecutive sequence, derivative strains carrying the R/M systems encoded by pTN20, pTRK11, and pTRK68 retarded phage development when the initial levels of phage contamination were below 10 2 PFU/ml but not when levels were increased to 10 3 PFU/ml. Use of a derivative bearing pTR2030 (Hsp + R + /M + ) at the beginning of the rotation prevented phage development, even when the initial levels of phage contamination were high (10 6 PFU/ml). Alternating the type and specificity of R/M and Abi defenses through the rotation prevented phage proliferation and in some cases eliminated contaminating phages. A model rotation sequence for the phage defense rotation strategy was developed and performed successfully over nine cycles of the Heap-Lawrence starter culture activity test in the presence of high-titer commercial phage composites. This phage defense rotation strategy is designed to protect a highly specialized Lactococcus strain from phage attack during continuous and extended use in the dairy industry.

In vitro studies on the growth of Shigella sonnei by Lactobacillus casei and Lact. acidophilus

The inhibitory effect of lactobacilli on growth of Shigella sonnei was studied. The effect was not due to pH alone, as addition of hydrochloric, lactic or acetic acids to culture media did not inhibit the normal growth of the shigellas. The degree of inhibition was measured by disc assay and showed that the inhibitory substance(s) can be extracellular and diffusible, varying the degrees of inhibition depending on the media tested. When broth was inoculated with mixed cultures of Lactobacillus and Shigella strains, the inhibition began at 6 h and the death phase at 9 h. The higher inhibition was produced by the mixture of lactobacilli (35.5 +/- 2.5% at 6 h culture, 57.4 +/- 1.9% at 9 h and 91.2 +/- 1.2% at 14 h). The degree of inhibition was higher when the relationship pathogen : lactobacilli was 1:10(3). The specific growth rate of lactobacilli and shigella was different in pure or mixed cultures. When the lactobacillus alone was grown for 12 h and the shigellas then added, the numbers of shigellas began to decrease immediately at 37 degrees C. This work shows that the Lactobacillus strains employed in fermented milk can be used to inhibit the growth of Sh. sonnei.

Comparison of the effects of galactose and glucose on the pH responses of human dental plaque, salivary sediment and pure cultures of oral bacteria

Comparisons made in dental plaque in vivo demonstrated that galactose produces a significantly smaller decrease in pH than does glucose. In vitro studies with plaque, salivary sediment and pure cultures of oral bacteria done in the absence of intraoral factors such as flowing saliva confirmed this lesser acidogenicity of galactose. Pure culture showed that most of the bacteria tested produce a moderate to large decrease with glucose but only a few do so with galactose; most produced a moderate to little or no pH response with this sugar. This suggested that the smaller decreases in pH seen in plaque in vivo with galactose were largely due to bacterial differences, basically that resident micro-organisms individually have less galactolytic than glucolytic capability. Variance in capability was attributed to differences in membrane transport processes and metabolic pathways normally available to bacteria for galactose and glucose catabolism. In the in vitro experiments, because plaque and sediment can produce base as readily as they can produce acid, the nitrogenous substrates identified earlier as major stimulants of base formation, urea and arginine, were concurrently examined for their attenuating effects on the galactose and glucose pH responses. These showed, consistent with its lesser acidogenicity, that galactose could be countered more readily in its ability to reduce the pH by either of these two base-forming substrates than could glucose. The effects were different with urea and with arginine, urea attenuation occurred sooner and arginine attenuation later in both plaque and sediment. The corresponding acid-base pH profiles for pure cultures were different.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence and characterization of temperate bacteriophage in Streptococcus salivarius subsp. thermophilus St18

Lysogenic strains of Streptococcus salivarius subsp. thermophilus were studied using induction with mitomycin C (MC). The induction and presence of temperate phage were investigated carrying out tests on sensitive strains, electron microscopy and phage DNA analysis. Forty-five Str. salivarius subsp. thermophilus strains were subjected to induction with MC and growth of the various cultures was evaluated. Only one strain of those tested showed lysis after adding MC, thus indicating a possible lysogenic state, 0.5 micrograms MC/ml being the optimal dose. Two phi 18 phage-sensitive strains out of 45 were isolated in which this phage behaved as virulent, causing lysis of the culture in broth, but no lysis plaques on agar medium were detected. The St18 strain was cured by u.v. irradiation but no mutants sensitive to the phi 18 phage were found among the clones non-inducible by MC. The presence of phages having a hexagonal isometric head and a long non-contractile tail in the lysate obtained after inducing the St18 strain was confirmed by examination under the electron microscope. Study of the phage DNA showed a genome size of 40.9 +/- 0.5 kb without cohesive end fragments. In addition, the restriction map of the phage genome was constructed. This study has demonstrated lysogeny in Str. salivarius subsp. thermophilus and also that several phage infections of Str. salivarius subsp. thermophilus starters may have an 'endogenous' origin.

Characterization of phiLC3, a Lactococcus lactis subsp. cremoris temperature bacteriophage with cohesive single-stranded DNA ends

The temperate bacteriophage phiLC3, isolated from Lactococcus lactis subsp. cremoris, has an isometric head and a flexible tail containing 1 major protein and 8 minor proteins. Infection of a permissive L. lactis host strain yields a burst of about 50 phages per infected cell with a latent period of 60 min. A detailed restriction map of the phage chromosome was constructed by using 12 different restriction enzymes. The phage chromosome is a 33-kb linear double-stranded DNA molecule with unique cohesive ends and with a G + C content of 36.5%. Chemical sequencing of the DNA ends revealed 13-base 3' extended complementary single strands with a relatively high percentage of G + C. Pulsed-field gel electrophoretic analysis of DNA from a strain lysogenized with phiLC3 was used to localize the prophage to a 320-kb BamHI restriction endonuclease fragment from the host chromosomal DNA. This result indicates that lysogeny involves integration of the phage into the host chromosome. A spontaneous phiLC3 clear plaque mutant that was unable to give rise to lysogens was isolated.

Effect of lactic cultures on Escherichia coli in ewes' milk stored at low temperatures

The behaviour of Escherichia coli in pasteurized ewes' milk inoculated with different lactic starter cultures and incubated at temperatures in the range 4-16 degrees C for 96 h was investigated. Growth temperature of lactic starter cultures before inoculation had a significant effect on inhibition of E. coli. The growth temperature of lactic starter inoculum which resulted in the highest inhibitory activity was 24 degrees C. Size of lactic starter inoculum also significantly influenced growth of E. coli, with a higher inhibition for 1% inoculum than for 0.1% or 0.3% inocula. Single cultures of Lactococcus lactis showed a stronger inhibitory activity than single cultures of Leuconostoc cremoris or Leuconostoc dextranicum. A lactic starter culture comprising Lactococcus lactis, Leuconostoc cremoris and Leuconostoc dextranicum resulted in the strongest inhibition. Stimulation of E. coli by the lactic starter cultures was frequently recorded at 4 degrees C and 8 degrees C. However, none or a very limited growth of E. coli was seen at these temperatures.

Temperate bacteriophages and lysogeny in lactic acid bacteria

Lysogeny is widespread in the lactic acid bacteria. The majority of lysogens can be induced by UV irradiation or treatment with mitomycin C, but indicator strains which allow lytic growth of the induced phage are often not easy to identify. A few temperate phages have been shown to transduce chromosomal and/or plasmid markers. Information about the molecular biology of the temperate phages from lactic acid bacteria is sparse and needs significant supplementation in order that these potentially valuable phages might be utilized more efficiently as tools for improving existing starter strains in dairy fermentations.