Yogurt Fermentation Research Articles

Effect of Biological Materials Including Sucrose and Bacteria Ratios on the Fermentation of Goat Yogurt

Effect of biological materials including sucrose concentration and bacteria ratios on fermentation of goat yogurt was studied by measuring acidity, pH and viable counts. Sucrose concentration (v/v) was 4%, 6%, 8%, 10% and 12%. The ratios ofLactobacillus bulgaricusandStreptococcus thermophiluswere 1:3, 1:2, 1:1, 2:1 and 3:1, respectively. The results were as follows: lower or higher sucrose concentration and bacteria ratios resulted in adversely influence on overall properties of goat yogurt. The optimum sucrose concentration in goat milk was 8% and bacteria ratios were 2:1, respectively.

High genetic and phenotypic variability of Streptococcus thermophilus strains isolated from artisanal Yuruk yoghurts

Streptococcus thermophilus is a commonly used starter bacterium in dairy industry. It reduces the pH of milk rapidly and equilibrates the medium for the growth of Lactobacillus delbrueckii subsp. bulgaricus during yoghurt fermentation. Efforts to increase the diversity of artisanal yoghurt starters are not only important to bring new strains with novel and desirable characteristics, but also for the preservation of natural diversity which diminishes with the overuse and spread of industrial starters to natural resources. In the present study, 14 artisanal yoghurt samples were processed for the isolation of promising strains for yoghurt starter culture production and 66 strains were subsequently characterized. They were all identified as S. thermophilus using species-specific PCR and 16S rRNA gene sequencing. Genotypic diversity at the strain level was investigated by pulsed field gel electrophoresis (PFGE), and 22 homology groups were obtained. Further phenotypic characterization unearthed a significant phenotypic heterogeneity within homology groups, mostly with atypical novel character. Only 7 out of 66 strains showed S. thermophilus type-strain like phenotypic traits. Majority of the isolates were determined to be protease positive and fast milk acidifier to be used as yoghurt starter culture.

The effects of fish collagen on the proteolysis of milk proteins, ACE inhibitory activity and sensory evaluation of plain- and Allium sativum-yogurt

The effects of fish collagen on the acidification, milk protein proteolysis and organoleptic properties of plain- and Allium sativum-yogurt were investigated. Titratable acidity (TA%) increased (p<0.05) in the presence of fish collagen in plain-yogurt (0.87–0.95%) and in A. sativum-yogurt (0.77–0.95%) compared to in the absence of fish collagen (0.79–0.84% and 0.56–0.86%) for plain- and A. sativum-yogurt respectively. Free amino acids (FAAs) in all yogurts decreased (p<0.05) by about 1mM during yogurt fermentation. The presence of fish collagen in plain- and A. sativum-yogurts increased the FAAs by about 4.2 and 3.5mM respectively compared to their respective control 0.14 and 0.16mM for plain- and A. sativum-yogurts respectively. Effects of plain- and A. sativum-yogurts in presence or absence of fish collagen on the aggregation of milk proteins in yogurt was measured by SDS-PAGE. Some milk proteins, κ-caseins, β-lactoglobulin and α-lactalbumin were reduced as a result of fermentation both in plain- and A. sativum-yogurts. The presence of fish collagen showed further proteolysis in these proteins in plain- and A. sativum-yogurts during fermentation and refrigerated storage. However, there were little changes in the degradation of α- and β-caseins in all yogurts with or without fish collagen. The extent of proteolysis based upon OPA values was the highest on day 7 of refrigerated storage in A. sativum-fish collagen-yogurt (337.0±5.3μg/g) followed by fish collagen-yogurt (275.3±2.0μg/g), A. sativum-yogurt (245.8±4.2μg/g) and plain-yogurt (40.4±1.2μg/g). In addition, plain- and A. sativum-yogurts with or without fish collagen showed maximal inhibition of ACE-I on day 7 of storage which ranged between 55% and 80%. The addition of A. sativum reduced aroma and increased graininess of yogurt but these and overall consistency were improved in the presence of fish collagen. In conclusion, fish collagen increased FAAs content in yogurt and the enhanced proteolysis of certain milk proteins may be responsible for improving ACE inhibitory activity and organoleptic properties of A. sativum-yogurt.

H+‐ATPase‐Defective Variants of Lactobacillus delbrueckii subsp. bulgaricus Contribute to Inhibition of Postacidification of Yogurt during Chilled Storage

Continued acid production by Lactobacillus delbrueckii subsp. bulgaricus during the chilled storage of yogurt is the major cause of postacidification, resulting in a short shelf life. Two H(+) -ATPase defective variants of L. delbrueckii subsp. bulgaricus were successfully isolated and their H(+) -ATPase activities were reduced by 51.3% and 34.3%, respectively. It was shown that growth and acid production of variants were remarkably inhibited. The variants were more sensitive to acidic condition and had a significant rate for inactivation of H(+) -ATPase by N, N-dicyclohexylcarbodiimide (DCCD), along with a low H(+) -extrusion, suggesting that H(+) -ATPase is direct response for H(+) -extrusion. In addition, the variants were also more sensitive to NaCl, while H(+) -ATPase activities of variants and parent strain were significantly enhanced by NaCl stress. Obviously, H(+) -ATPase might be involved in Na(+) transportation. Furthermore, variants were inoculated in fermented milk to ferment yogurt. There was no significant difference in flavor, whereas the postacidification of yogurt during chilled storage was remarkably inhibited. It is suggested that application of L. delbrueckii subsp. bulgaricus with reduced H(+) -ATPase activity in yogurt fermentation is one of effect, economic and simple avenues of inhibiting postacidification of yogurt during refrigerated storage, giving a longer shelf life. During yogurt fermentation, continued acid production by Lactobacillus delbrueckii subsp. bulgaricus during the chilled storage of yogurt leads to milk fermentation with high postacidification, resulting in a short shelf life. In this work, 2 acid-sensitive variant strains of L. delbrueckii subsp. bulgaricus were isolated. The characteristics related to H(+) -ATPase were compared and it was observed that milk fermented by the variants had lower postacidification, giving a longer shelf life. Application of L. delbrueckii subsp. bulgaricus with reduced H(+) -ATPase activity in yogurt fermentation might be one of effect, economic and simple avenues of inhibiting yogurt postacidification during chilled storage, giving a longer shelf life.

Enhancing the oxidative resistance of yoghurt starter bacteria with heterologous catalase expression in Streptococcus thermophilus

During yoghurt fermentation, the starter bacteria often suffer oxidative damage. In this study, a heme-dependent catalase gene (katE) was isolated from Lactobacillus brevis ATCC 367 and transferred into Streptococcus thermophilus ST5. The functional expression of katE in S. thermophilus ST5 resulted in enhanced oxidative stress resistance. The survival of cells in the exponential and stationary growth phases increased 52- and 143-fold, respectively, after short-term H2O2 exposure. The long-term survival rate was also significantly improved under aerobic conditions. Furthermore, the katE expression in S. thermophilus ST5 was beneficial to Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 co-cultured in milk. The survival rates of Lb. delbrueckii subsp. bulgaricus ATCC 11842 after short-term H2O2 exposure increased 18- and 127-fold during the exponential and stationary phases, respectively. The catalase expressed in S. thermophilus eliminated H2O2 efficiently, thereby protecting the yoghurt starter bacteria from oxidative damage.

Synbiotic Potential of Yoghurt Manufactured with Probiotic Lactic Acid Bacteria Isolated from Mustard Leaf Kimchi and Prebiotic Fructooligosaccharide

In the present work, the influence of prebiotic fructooligosaccharide (FOS) on adhesion to Caco-2 cells, viability, acid and bile tolerance, antibacterial, antioxidant, enzymatic, and metabolic activities of the probiotic starters Lactobacillus acidophilus GK20 and Lactobacillus paracasei GK74, has been explored. Experiments were conducted with fermented yoghurt over a period of 7 days at . When compared to control fermentations without prebiotic, the addition of FOS was seen to significantly (p unit) and -galactosidase activities ( unit). However, FOS did not affect acid and bile tolerance, adhesion to Caco-2 cells or the antioxidant activity of the probiotics, although both L. acidophilus GK20 and L. paracasei GK74 had functionality as probiotic strains. Hence, a significant synbiotic effect was observed in fermented yoghurt after 7 days of storage at , and as a result, such synbiotic yoghurt can be said to possess synergistic actions which improve the gastrointestinal environment and promote of health.

The susceptibility of Streptococcus thermophilus 14085 to organic acid, simulated gastric juice, bile salt and disinfectant as influenced by cold shock treatment

Streptococcus thermophilus is a thermophilic lactic acid bacterium which is used as the starter organism for the fermentation of yoghurt and some cheese. In the present study, S. thermophilus BCRC 14085 was subjected to cold shock treatment by exposure at 10 °C for 2 h. The effect of cold shock on the susceptibility of S. thermophilus in subsequent lethal stress environments such as simulated gastric juice (pH 2.0–3.0), bile solution (2.0%) and various organic acids (0.75 M, pH 3.5) including propionic, lactic, acetic, citric and tartaric acid was investigated. In addition, the survival of cold-shocked and non-shocked S. thermophilus exposed to disinfectants, Clidox-S and Quatricide, were compared. Results revealed that cold shock enhanced the tolerance of S. thermophilus in the presence of simulated gastric juice (pH 2.5 and 2.8), while in bile solution, the population increase of cold-shocked cells is higher than that of non-shocked cells after 12 h of incubation. Furthermore, the susceptibility of S. thermophilus, regardless of cold shock, to organic acid varied with the kinds of organic acid examined. The cold-shocked S. thermophilus showed a significantly less survival (P < 0.05) than that of the non-shocked cells when exposed to lactic or acetic acid. Furthermore, cold shock reduced the survival of S. thermophilus when exposed to Quatricide but not Clidox-S.

Effect of Purified Oat β‐Glucan on Fermentation of Set‐Style Yogurt Mix*

Effect of oat β-glucan on the fermentation of set-style yogurt was investigated by incorporating 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% of purified oat β-glucan into the yogurt mix. It was found that levels up to 0.3% resulted in yogurts with quality characteristics similar to the control yogurt. Higher levels of β-glucan however retarded the fermentation process with noticeable difference in the characteristics of the yogurt. Examination of the morphologies of yogurt with and without β-glucan revealed that β-glucan formed aggregates with casein micelle and did not form phase-separated domains. This research demonstrated that β-glucan could be added to yogurt up to 0.3%, which meets the nutrient guidelines, to have added nutritional benefits. Yogurt is known for its beneficial effects on human health and nutrition. Yogurt production and consumption is increasing in the United States every year. However, it is lacking in β-glucans, which are recognized for their nutritional importance as functional bioactive ingredients. The main objective was to develop and characterize low-fat yogurts with added β-glucan. This research demonstrated that β-glucan could be added to yogurt up to 0.3%, which meets the nutrient guidelines for added nutritional benefits, without affecting the characteristics of yogurt significantly. This study will benefit the dairy industry by generating new products offering healthy alternatives.

CHANGES IN ISOFLAVONE GLUCOSIDE AND AGLYCONE CONTENTS OF CHICKPEA YOGHURT DURING FERMENTATION BYLACTOBACILLUS BULGARICUSANDSTREPTOCOCCUS THERMOPHILUS

Lactobacillus bulgaricus and Streptococcus thermophilus fermented chickpea yoghurt with a ratio of 1:1 (v/v) for 6–7 h at 42C. All cultures reached 109 cfu/mL of chickpea yoghurt. After 8 h, pH and titratable acidity ranged from 5.74 to 4.25 and 0.16 to 0.62%, respectively. Daidzein and genistein increased to 39.92 µg/g DW (dried weight of freeze-dried chickpea yoghurt) and 50.34 µg/g DW, respectively, after a 4-h fermentation. The amount of aglycone genistein and daidzein were more than that of glucoside daidzin and genistin. Total content of the aglycone daidzein and genistein was 90.26 µg/g DW at 4 h, which was 5.7 times of the initial fermentation (15.71 µg/g DW). Chickpea yoghurt fermentation hydrolyzed the isoflavone glucosides, and L. bulgaricus and S. thermophilus converted isoflavone glucosides to aglycones. L. bulgaricus and S. Thermophilus seemed to be effective starters for chickpea milk with more aglycones and appropriate acidity. PRACTICAL APPLICATION Chickpea is one of the oldest consumed legumes in Xinjiang, and has a significant contribution to human diet treatment. Leguminosea is the plant family most abundant in isoflavones. Furthermore, researchers have credited isoflavones in soybeans for some beneficial health effects. The addition of chickpea to milk-based products could be a good alternative for increasing the intake of chickpea. In the present study, changes in the contents of isoflavone glucosides and aglycones during chickpea yoghurt fermentation were investigated. Lactic acid bacteria were expected to effectively convert isoflavone glucosides to aglycones in chickpea milk.

Effects of Fat on Relationship between Particle Size and Physical Properties of Cross-Linking Yogurt by Purified Transglutaminase from &lt;i&gt;Streptomyces mobaraensis&lt;/i&gt; DSM 40587

The purified TGase produced by Streptomyces mobaraensis DSM 40587 from high salt medium was applied to whole and skim milk yogurt. During yogurt fermentation, no negative effect of TGase on fermentation time was found. Protein cross-linking by TGase was enhanced at varying concentrations from 0 to 5 U/g protein, resulting in a increase of apparent viscosity and decrease of syneresis. Furthermore, texture parameters were improved. However, extensive cross-linking resulted in too big size of the aggregates. The formation of these polymers resulted in a coarse texture of yogurt. Fat had no impact on the apparent viscosity and texture parameters, but significant changes in cross-linking of protein, syneresis and the sizes of the aggregates. From the range of TGase concentrations examined for properties of yogurt, the optimal level of TGase for skim milk yogurt was 1 U/g protein; however, for whole milk yogurt was 3 U/g protein.

Evaluation of probiotics properties of lactic acid bacteria isolated from breast milk and their potency as starter culture for yoghurt fermentation

Purpose: The objective of this study was to evaluate probiotic proper- ties of four LAB isolated from breast milk, i.e. Lactobacillus rhamnosus R21, L. rhamnosus B16, Pediococcus. pentosaceus A16 and L. fermentum A17 and their po- tency as starter cultures for yoghurt fermentation. Methodology: In vivo evaluation was done by feeding Sprague Dawley rats with standard diet and 10 9 cells of each LAB for 10 days. Findings: The four isolates showed good survival both in pH 2 and bile salt for 5 h, and ability to suppress the growth of pathogenic bacteria. In vivo evaluation revealed that the four isolates reduced the number of E. coli in caecum, and in- creased the number of total LAB, without potency of invasion. They also induce proliferation of splenocytes, and A16 induce secretion of IgA in blood serum. Value: R21 and B16 were potential as a single starter culture for yoghurt fermentation, while A16 have to be mixed with yoghurt starter cultures. The present finding sug- gests that the isolates are potential to be used for development of probiotic products.

Characterization of beverage obtained from symbiotic fermented milk added guava pulp and evaluation of bifidobacteria viability

Fermented milks and yogurts containing probiotics are the main products in the world with health claims, attending to a growing market demand. However, to maintain the viability of probiotic cultures during manufacture and storage of food products is a technological challenge. The main objective of this study was to evaluate the physicalchemical composition and viability of probiotics after 1, 15 and 30 days of refrigerated storage (4oC ± 1) of a beverage made with guava pulp pasteurized and fermented milk with cultured yoghurt (50/50%), mixed cultures of bifidobacteria, with and without the addition of 1.7% of prebiotics (FOS). The viability of probiotic beverages after 30 days of refrigerated storage has remained within the limit proposed by the Brazilian legislation for food with claims of functional properties with values from 10 6 to 10 7 UFC.mL -1 , even in unfavorable condition of pH ( < 4,4). The addition of 1.7% of FOS did not increase the viability of bifidobacteria. However, the addition of 1.7% FOS enables the intake of 3.4 grams of fiber in the daily portion (200 ml) which meets the recommendation for functional properties.

Development of made‐in‐transit set culture yoghurt: effect of increasing the concentration of reconstituted skim milk as the milk base

SummaryThe fermentation time, yoghurt acidity expressed as lactic acid, starter culture growth, viscosity and firmness of made‐in‐transit (MIT) set culture yoghurt produced using different concentrations of reconstituted skim milk powder (SMP) from 12% to 20% (w/v) as the milk base were investigated. All milk base formulations were ultra‐high temperature sterilised at 138 °C for 6 s. The results revealed that increasing the SMP concentration increased the viscosity and firmness of MIT set culture yoghurt. At 20% SMP, viscosity and firmness were 4650.8 cP and 1.266 N, respectively. Fermentation of MIT set culture yoghurt with 20% SMP was observed to be faster than with the other conditions. The fermentation time for a medium containing from 14% to 20% SMP could be extended to 168 h, reaching a final pH of 4.50–4.37 and at the same time improving the texture of the MIT set culture yoghurt. The SMP concentration had no influence on the total viable counts of starter bacteria in the yoghurt. The texture of MIT set culture yoghurt may be improved by increasing the concentration of SMP.

Bio-monitoring of Yogurt Fermentation Process by Near Infrared Spectroscopy

Bio-monitoring of Yogurt Fermentation Process by Near Infrared Spectroscopy

Analysis of the Cell Surface Hydrophobicity of Yoghurt Fermentation Bacteria

The cell surface hydrophobicity (CSH) of lactic acid bacteria was considered to colonization and adhesion, and playing a prebiotic function in the digestive tract. Therefore, CSH of yoghurt fermentation bacteria most commonly used was analyzed, such as Lactobacillus acidophilus, Lactobacillus bulgaricus and Streptococcus thermophilus to identify initially CSH and the influencing factors of CSH of these strains and provided a theoretical basis for the future production of high-quality dairy fermentation agents and probiotics. The method of bacterial adhesion to hydrocarbons (BATH) was utilized to determine CSH of these strains and used the different conditions to process the cell. Through this research, the results was that L. acidophilus had a strong CSH, greater than L. bulgaricus and S. thermophilus. And the influencing factors of CSH of L. acidophilus were time, temperature, pH, concentration, Ca2+ and protease. But CSH was significantly reduced by trypsin and pepsin. CSH L. acidophilus was connected with the adhesion ability. In addition, it was speculated that some substances which could mediate CSH of L. acidophilus may be a class of proteins. Therefore, in the process of dairy fermentation agent, these factors could be controlled to obtain high-quality products.

The emulsified lipid Fabuless (Olibra) does not decrease food intake but suppresses appetite when consumed with yoghurt but not alone or with solid foods: A food effect study

The lipid emulsion Fabuless (Olibra) has been shown in some studies to decrease short/medium term energy intake (EI) and prevent weight regain. The purported mechanism is the ileal brake. Whether Fabuless is efficacious under a range of dietary conditions is unknown since studies have administered the emulsion within a fermented, semi-liquid dairy yoghurt, and outcomes have been inconsistent. To determine whether Fabuless suppresses post-ingestive satiety and short-term food intake under a range of dietary conditions and forms we administered the emulsion co-presented with 185mL water, stirred into a semi-liquid dairy yoghurt, and co-presented with a solid food breakfast muffin. This was a cross-over study in 18 lean men randomised to 6 treatments: (i) lipid emulsion, LE (15g Fabuless, containing 4.2g lipid, 0.2MJ)+water, (ii) lipid control, LC (15g non-emulsified lipid/water, containing 4.2g lipid, 0.2MJ)+water, (iii) lipid emulsion+yoghurt, LE+Y (1.2MJ), (iv) lipid control+yoghurt, LC+Y (1.2MJ), (v) lipid emulsion+muffin, LE+M (1.2MJ), (vi) lipid control+muffin, LC+M (1.2MJ), each given as a test breakfast at 8.30am. Participants rated postprandial appetite sensations using visual analogue scales (VAS), and ad libitum energy intake was measured at a lunch meal 3.5h later. The lipid emulsion increased fullness compared with an energy-matched lipid control but only when administered within the semi-liquid fermented yoghurt (P<0.05). There were no effects on satiety ratings when co-presented with water or with the solid food muffin. Energy and macronutrient intake were not significantly decreased by any of the emulsion treatments. We conclude that effects are small, the format in which lipid emulsions are consumed influences postprandial satiety, and there is no evidence that this emulsion alters eating behaviour at the subsequent meal.

On-Line Monitoring of Yogurt Fermentation Using Acoustic Impedance Method

A non-contact ultrasonic system to monitor the yogurt fermentation process through a stainless steel reactor wall is described. During the process, the acoustic impedance was determined by using multiple reflections of ultrasound within the stainless steel wall. Thus, the wall was part of the measurement system. By basing on measurement multiple reflections, the instrument sensitivity is increased by the power of the reflection coefficient. Experimental results show that the acoustic impedance changes continuously while pH declines. It is very useful, especially on production scale for yogurt that the acoustic impedance measurement does not demand a liquid transparent to ultrasound. Also, this noncontact sensing method can reduce the risk of food contamination from measuring instrument, and contribute to hygienization for food manufacture industries.

Specialized adaptation of a lactic acid bacterium to the milk environment: the comparative genomics of Streptococcus thermophilus LMD-9

BackgroundStreptococcus thermophilus represents the only species among the streptococci that has “Generally Regarded As Safe” status and that plays an economically important role in the fermentation of yogurt and cheeses. We conducted comparative genome analysis of S. thermophilus LMD-9 to identify unique gene features as well as features that contribute to its adaptation to the dairy environment. In addition, we investigated the transcriptome response of LMD-9 during growth in milk in the presence of Lactobacillus delbrueckii ssp. bulgaricus, a companion culture in yogurt fermentation, and during lytic bacteriophage infection.ResultsThe S. thermophilus LMD-9 genome is comprised of a 1.8 Mbp circular chromosome (39.1% GC; 1,834 predicted open reading frames) and two small cryptic plasmids. Genome comparison with the previously sequenced LMG 18311 and CNRZ1066 strains revealed 114 kb of LMD-9 specific chromosomal region, including genes that encode for histidine biosynthetic pathway, a cell surface proteinase, various host defense mechanisms and a phage remnant. Interestingly, also unique to LMD-9 are genes encoding for a putative mucus-binding protein, a peptide transporter, and exopolysaccharide biosynthetic proteins that have close orthologs in human intestinal microorganisms. LMD-9 harbors a large number of pseudogenes (13% of ORFeome), indicating that like LMG 18311 and CNRZ1066, LMD-9 has also undergone major reductive evolution, with the loss of carbohydrate metabolic genes and virulence genes found in their streptococcal counterparts. Functional genome distribution analysis of ORFeomes among streptococci showed that all three S. thermophilus strains formed a distinct functional cluster, further establishing their specialized adaptation to the nutrient-rich milk niche. An upregulation of CRISPR1 expression in LMD-9 during lytic bacteriophage DT1 infection suggests its protective role against phage invasion. When co-cultured with L. bulgaricus, LMD-9 overexpressed genes involved in amino acid transport and metabolism as well as DNA replication.ConclusionsThe genome of S. thermophilus LMD-9 is shaped by its domestication in the dairy environment, with gene features that conferred rapid growth in milk, stress response mechanisms and host defense systems that are relevant to its industrial applications. The presence of a unique exopolysaccharide gene cluster and cell surface protein orthologs commonly associated with probiotic functionality revealed potential probiotic applications of LMD-9.

Changes in yogurt fermentation characteristics, and antioxidant potential and in vitro inhibition of angiotensin-1 converting enzyme upon the inclusion of peppermint, dill and basil

The present study investigated the effects of peppermint ( Mentha piperita), dill ( Anethum graveolens) and basil ( Ocimum basilicum) on yogurt formation, proteolysis and inhibition of angiotensin-1 converting enzyme (ACE). Herbal-yogurts had faster rates of pH reduction than plain-yogurt. All herbal-yogurts had higher ( p < 0.05) antioxidant activities than plain-yogurt, both at the end of fermentation and throughout the storage period. The o-phthalaldehyde (OPA) peptides in herbal-yogurts increased by 28–36% after 7 days of storage. All herbal-yogurts showed higher anti-ACE activity than plain-yogurt at corresponding storage periods. M. piperita yogurt had highest inhibitory effect on ACE activity throughout the storage period. Peppermint, dill and basil may be used to modify microbial fermentation of milk with the intention of producing dairy products with higher antioxidant and enhanced anti-ACE activities.

Complete Sequencing and Pan-Genomic Analysis of Lactobacillus delbrueckii subsp. bulgaricus Reveal Its Genetic Basis for Industrial Yogurt Production

Lactobacillus delbrueckii subsp. bulgaricus (Lb. bulgaricus) is an important species of Lactic Acid Bacteria (LAB) used for cheese and yogurt fermentation. The genome of Lb. bulgaricus 2038, an industrial strain mainly used for yogurt production, was completely sequenced and compared against the other two ATCC collection strains of the same subspecies. Specific physiological properties of strain 2038, such as lysine biosynthesis, formate production, aspartate-related carbon-skeleton intermediate metabolism, unique EPS synthesis and efficient DNA restriction/modification systems, are all different from those of the collection strains that might benefit the industrial production of yogurt. Other common features shared by Lb. bulgaricus strains, such as efficient protocooperation with Streptococcus thermophilus and lactate production as well as well-equipped stress tolerance mechanisms may account for it being selected originally for yogurt fermentation industry. Multiple lines of evidence suggested that Lb. bulgaricus 2038 was genetically closer to the common ancestor of the subspecies than the other two sequenced collection strains, probably due to a strict industrial maintenance process for strain 2038 that might have halted its genome decay and sustained a gene network suitable for large scale yogurt production.