Yogurt Starter Bacteria Research Articles

Duality Effect of Bee Products in Dealing with Yoghurt Starter, Probiotics and Food Borne Pathogenic Bacteria

Duality Effect of Bee Products in Dealing with Yoghurt Starter, Probiotics and Food Borne Pathogenic Bacteria

Synbiotic Yogurt Fortified with Bawang Dayak (Eleutherine palmifolia) Extract

Aims: The purpose of this research was to study the quality of yogurt symbiotic fortified with Bawang Dayak (Eleutherine palmifolia) extract.
 Study Design: This research used Completely Randomized Design (CRD) experimental method and consist of 4 treatments.
 Place and Duration of Study: Sample: Animal Product Technology Laboratory Faculty of Animal Science Universitas Brawijaya, Food Quality and Safety Testing Laboratory Department of Agricultural Product Technology, Faculty of Agricultural Technology Universitas Brawijaya, between June 2022 – December 2022.
 Methodology: The material used are skim milk, fresh milk, yogurt starter bacteria (Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophillus), and bawang dayak extract. Bawang Dayak were extracted using Microwave-Asisted Extraction (MAE) with temperature 60-700C. This research which consist of 4 treatments and 3 replications with various concentration of Bawang Dayak extract of T0 (0%), T1 (1%), T2 (4%), and T3 (6%), respectively. The samples of synbiotic yogurt with fortification of Bawang Dayak extract were analyzed for their total lactic acid bacteria, antioxidant activity, viscosity and color analysis.
 Results: Fortification of Bawang dayak extract in synbiotic yogurt results in highly significant different effects on the quality parameters of antioxidant and color (lightness, redness and yellowness) (P<0.01), but had no significant effect (P>0.05) on the total quality of lactic acid bacteria. Fortification of 6% Bawang dayak extract (T3) in yogurt produced the best quality in terms of antioxidant content and color (lightness, redness, and yellowness).
 Conclusion: The best treatment of synbiotic yogurt was achieved in T3 with the 6% of Bawang Dayak extract.

Enumeration Of Bifidobacterium Spp., Lactobacillus Acidophilus and Starter Cultures from Commercial Probiotic Yogurts and Freeze-Dried Yogurt Starter Mixes

Probiotic yogurt is a popular functional food to deliver of probiotic cells for the health-enhancing effects worldwide. The viability of probiotics in yogurt before consumption is the most important factor to providing desired effects, however, probiotic microorganisms have occasionally inadequate viability in marketable food products. In this current study, Bifidobacterium spp., L. acidophilus and yoghurt starter bacteria enumerations were made in commercial probiotic yoghurt and freeze-dried yogurt mixes. RCA 5.3 and MRS 5.2 media were used for L. delbrueckii subsp. bulgaricus counting, ST Agar and M17 Agar were used for Stretococcus thermophilus counts. While using MRS-Bile Agar and RCA-Clindamycin Agar for L. acidophilus enumeration, Bifidobacterium spp. counts were performed using MRS-NNLP medium. 5 out of yoghurt samples (A, C, D, and E) did not reveal satisfactory recovery (< 5 log CFU/g) for L. delbrueckii subsp. bulgaricus colonies on MRS 5.2 Agar while L. delbrueckii subsp. bulgaricus colony counts on RCA 5.3 Agar below 5 log CFU/g for same tested 4 samples (A, C, D, and E). The recovery rates over 9 log CFU/g were obtained in the enumerations made for all yogurt samples on both ST and M17 media. The problem of insufficient recovery rates that occurred for L. delbrueckii subsp. bulgaricus in some yogurt samples was not valid for S. thermophilus. This work indicated that high amounts of L. acidophilus were detected on both media in both of the two yoghurt samples declared as L. acidophilus on the label (F and G). On the other hand, bifidobacteria was determined above 5 log CFU/g in only 1 yoghurt sample (B) out of 7 probiotic yoghurts claimed to be Bifidobacterium spp. This study reveals relevant information on probiotic and starter counts of commercial probiotic yogurts in Turkey and discusses in detail the possible reasons for the results obtained.

Characterization of yoghurt supplemented with Lacticaseibacillus rhamnosus as a bioprotective antifungal culture

Lactic acid bacteria (LAB) play a very important role as natural bio-preservatives in foods. Accordingly, the inhibitory effect of Lactobacillus rhamnosus (L. rhamnosus) on 4 fungi species of Yarrowia, Penicillium expansum (P. expansum), Saccharomyces cerevisiae (S. cerevisiae), Aspergillus niger (A. niger), Kluyveromyces lactis (K. lactis) was investigated. Then P. expansum was selected as the most important contaminant mould in yoghurt to study the use of L. rhamnosus to reduce selective spoilage of P. expansum in yoghurt. Also, the effect of this bioprotective culture on the count of starter bacteria and some characteristics of yoghurt was determined. L. rhamnosus (106 cfu /mL) was inoculated into the milk along with yoghurt starter bacteria, so that four samples were produced T0 (L. rhamnosus = 0, P. expansum = 0), T1 (L. rhamnosus = 106 cfu/mL, P. expansum = 0), T2 (L. rhamnosus = 0, P. expansum = 105cfu/mL); T3 (L. rhamnosus = 106 cfu/mL, P. expansum = 105cfu/mL). All samples were analysed for pH, acidity, viscosity, syneresis, microbial (survival of Streptococcus thermophilus and Lactobacillus bulgaricus and P. expansum) and overall acceptability. L. rhamnosus had an inhibitory effect on the survival of P. expansum (p<0.05) but was not able to completely control it. L. rhamnosus in T3 sample had an inhibitory effect from the first day to the end of storage. Furthermore, during the storage, the survival of yoghurt starter bacteria in probiotic yoghurt samples was higher than the control (p<0.05). T3 had lower pH, viscosity and overall acceptability score compared to the control and its syneresis was higher (p<0.05). In general, the addition of 106 cfu/mL of L. rhamnosus did not have a complete inhibitory effect on P. expansum (105 CFU/mL) until the end of storage time.

The Potential of Olive Leaf Extract as a Functional Ingredient in Yoghurt Production: The Effects on Fermentation, Rheology, Sensory, and Antioxidant Properties of Cow Milk Yoghurt.

Background: Yoghurt has been traditionally consumed for its high nutritional value and health-promoting benefits. The addition of plant extracts as a source of phenolic compounds and bio-flavonoids has attracted much attention recently since milk and dairy products are deficient in these health-protecting components. Accordingly, olive leaf extract (OLE) has been considered due to the presence of bioactive compounds, primarily polyphenols. Thus, the aim of this research was to investigate the possibility of adding OLE into cow milk yoghurt as a potential functional ingredient. Methods: Yoghurts enriched with OLE (1.5, 3, and 5% v/v) were produced and compared with yoghurt without OLE. In all samples acidity, viscosity, colour, syneresis, water holding capacity (WHC), microbiological parameters, sensory properties, total phenols, and antioxidant activity (DPPH and FRAP methods) were determined. Results: The addition of OLE resulted in shorter fermentation and lower pH, but it had no adverse effect on the viability of yoghurt starter bacteria. OLE-enriched yoghurts showed increased syneresis, higher total phenols content, and antioxidant activity, while WHC and viscosity decreased. Sensory properties were slightly poorer for yoghurts containing higher OLE concentrations. Considering all of the obtained results, the addition of 1.5% OLE appeared to be optimal.

Physicochemical characteristics, sensory profile, probiotic, and starter culture viability of synbiotic yogurt.

This study aimed to envisage the effectiveness of adding three particular prebiotics (inulin, β-glucan, and Hi-maize) to synbiotic yogurt's physicochemical properties, sensory characteristics, and survivability of the probiotic and starter cultures. The yogurt's gross composition, syneresis, water-holding capacity (WHC), viscosity, sensorial properties, and probiotic and starter cell stability were analyzed. The Lactobacillus delbrueckii subsp. bulgaricus M240-5 and Streptococcus thermophilus M140-2 were employed as yogurt starter bacteria, and Lactobacillus acidophilus LA-5 as probiotic culture. The synbiotic yogurt was formulated with 5% sucrose and 0.7% artificial vanilla flavor. The findings showed that when prebiotic ingredients were added to synbiotic yogurt, it had a significant impact on its sensory qualities, WHC, syneresis, and viscosity when compared to plain yogurt samples. The prebiotics did not affect the pH and titratable acidity of the yogurt samples. Additionally, the prebiotic supplementation did not influence the protein and fat content of synbiotic yogurt (p < 0.05). Prebiotics had an impact on the probiotic cell viability and total viable count (p < 0.05) compared to the plain sample, the 2.5% β-glucan, 1.5% and 2.5% Hi-maize samples had the highest mean viability (8.95 Log CFU/ml). The starter culture ratio remained stable in response to the prebiotic levels. In summary, the production of synbiotic yogurts supplemented with Hi-maize and β-glucan at 1.5% and 2.5%, respectively, is highly advised because these supplementations provide yogurt with acceptable syneresis, viscosity, WHC, and sensory attributes.

Pullulan as a potential enhancer of Lactobacillus and Bifidobacterium viability in synbiotic low fat yoghurt and its sensory quality

Yoghurt acts as a perfect delivery system for probiotic bacteria and some functional food ingredients, thereby enhancing their viability. Pullulan (PUL), a natural exopolysaccharide produced by yeast Aureobasidium pullulans is a low-calorie food ingredient and dietary fibre with potential prebiotic properties. The main aim of the present study was to investigate the effect of 0.5%–2.0% PUL addition on pH, sensory quality and viability of the yoghurt starter and probiotic bacteria in low-fat yoghurt during 28 days of storage. PUL addition enhanced the viability of Bifidobacterium and Lactobacillus, while it did not affect S. thermophilus count. The protective effect of PUL increased with concentration and was the highest for 1.5 and 2.0% PUL supplementation. Incorporation of PUL at 1.5% and 2.0% prolonged survival of B. animalis subsp. Lactis at a concentration above the therapeutic level (<10 6 cfu/mL) for the entire storage period. All the products showed a decrease in pH during the storage period. Further, the sensory analysis revealed that PUL incorporation improved thickness, smoothness, and viscosity of low-fat yoghurts, but decreased the intensity of milk taste and aroma, contributing to a decrease in overall acceptability.

Development of novel Vitamin B12 fortified yogurts using isolated and microencapsulated Vitamin B12

AbstractAdults aged &gt; 50 years, which make up to 40% of the European population, are vulnerable to low vitamin B12 (B12) status due to age-related factors that impair digestion and absorption of protein-bound B12 from natural food sources. Older adults are recommended to meeting their dietary B12 intake through the consumption of B12-fortified foods or supplements because these products contain free B12. B12 seems most bioavailable from milk products compared to other food sources, showcasing dairy as a potential vehicle for B12 food fortification. Yogurt is a versatile, popular dairy product, making it a promising food vehicle for B12 fortification to enhance the availability of B12-fortified foods for population groups at risk of B12 deficiency. With the overall goal to develop a novel, B12-fortified dairy product, the objective of this project was to compare the shelf-life stability of different chemical forms of B12 added to yogurt either in isolated or in encapsulated form. For both fortification strategies, we compared methylcobalamin (MeCB), a naturally-occurring B12 form, and cyanocobalamin (CnCB), the synthetic form of B12. Encapsulated microparticles were created by spray-drying a maize starch-derived polymeric material (EUDRAGUARD Natural®) with 1% (w/V) MeCB or CnCB. The release of B12 from encapsulated microparticles was confirmed by in vitro simulated gastrointestinal digestion; maximum B12 release (103% recovery) was achieved under conditions simulating the small intestine, where B12 is absorbed in the human body. Yogurts were produced by incubating whole milk (3.25% milk fat) with yogurt starter bacteria at 43°C overnight; after fermentation and cooling down, isolated (I-MeCB or I-CnCB) or encapsulated B12 powders (E-MeCB or E-CnCB) in the concentration of 50μg of B12/175 g of yogurt were added, creating stirred yogurt. Yogurts were stored at 4°C for eight weeks, with intermittent sampling for B12 stability testing using RIDASCREEN immunoassay. For CnCB-fortified yogurts, I-CnCB and E-CnCB had similar B12 concentrations at baseline (48.3μg and 48.2μg, respectively) and week 8 (53.9μg and 51.4μg, respectively). Difference in B12 content between I-CnCB and E-CnCB was &lt; 5% for both time-points. For MeCB, similar concentrations were found for I-MeCB (64.1μg) and E-MeCB (65.0μg) at baseline; however, at week 8, E-MeCB remained stable (69.8μg) while a pronounced decrease in B12 was observed with I-MeCB (33.3μg). At week 8, I-MeCB B12 concentrations were 52% lower than E-MeCB. In conclusion, CnCB was shown to be the more stable fortificant throughout shelf-life. Encapsulation techniques are a viable option to increase MeCB stability in fortified yogurts.

Effect of Supplementation with Green and Black Tea on Microbiological Characteristics, Antimicrobial and Antioxidant Activities of Drinking Yoghurt

The influence of supplementation with green and black tea on microbiological properties, antimicrobial and antioxidant activities of drinking yoghurt were investigated during 21 days of storage. The samples supplemented with 2% either green or black tea had higher viable counts of both yoghurt starter bacteria than those of infused by the ratio of 4%. Both green and black tea extracts showed antimicrobial activity on E. coli, B. cereus, S. aureus and C. albicans however this effect was detected higher in samples containing green tea. The samples added green tea extract had the highest DPPH scavenging activity when compared to those supplemented with black tea extract throughout the storage. Green tea had a superior effect than black tea in terms of total phenolic content of drinking yoghurt samples.

Influence of Fortification with Inulin and Hi-maize on Acidity and Viability of Starter Culture in Probiotic Yoghurt

In this study, the effect of fortification with inulin&#x0D; and resistant starch (Hi-maize) on yoghurt starter and probiotic bacteria&#x0D; survival, as well as acidity properties of set-type probiotic yoghurt&#x0D; containing Lactobacillus acidophilus&#x0D; were investigated. Milk was fortified with inulin or Hi-maize at 2% and 4%&#x0D; ratios whereas control group had no supplement. Samples fortified with Hi-maize&#x0D; had higher lactic acid value than those fortified with same ratio of inulin.&#x0D; Lactic acid percentages increased significantly in all probiotic yoghurts at&#x0D; the end of storage in comparison to the first day (p&amp;lt;0.05). The highest&#x0D; viable counts of Streptococcus&#x0D; thermophilus were&#x0D; enumerated in the sample fortified with 2% Hi-maize during 14 days of storage.&#x0D; The control sample had as high viable counts of Lactobacillus bulgaricus as the sample fortified with 4% Hi-maize,&#x0D; except first day of the storage. The highest viability of L. acidophilus was detected in control and the sample fortified&#x0D; with 4% Hi-maize on 7th and 14th day whereas the highest&#x0D; value was reported for the control sample at the end of the storage. L.acidophilus populations ranged from&#x0D; 6.30 to 7.95 log cfu/g in probiotic yoghurts during 21 days of refrigerated&#x0D; storage. Therefore, all experimental yoghurts presented probiotic viability&#x0D; above the minimum recommended level of 6 log cfu/g suggested for beneficial&#x0D; health effects.

Formation of tyramine in yoghurt during fermentation – Interaction between yoghurt starter bacteria and Lactobacillus plantarum

This study aimed to investigate the formation of tyramine during yoghurt fermentation with the focus on interaction between Streptococcus thermophilus RSKK 04082, Lactobacillus delbrueckii subsp. bulgaricus DSM 20081 and Lactobacillus plantarum RSKK 02030. These microorganisms were used in the yoghurt fermentation as single strains or mixed cultures containing double or triple strains. The interactions between microorganisms have been also revealed by determining total free amino acids and the pH of the medium together with the microbial count of the strains. It was observed that L. delbrueckii subsp. bulgaricus DSM 20081 did not produce tyramine while S. thermophilus RSKK 04082 and L. plantarum RSKK 02030 could produce tyramine depending on the fermentation conditions. Synergistic interactions between S. thermophilus RSKK 04082 and L. delbrueckii subsp. bulgaricus DSM 20081 and, between L. delbrueckii subsp. bulgaricus DSM 20081 and L. plantarum RSKK 02030 were found in terms of tyramine production. It was observed in this study that L. delbrueckii subsp. bulgaricus DSM 20081 had indirect effect on accumulation of tyramine in the yoghurts.

Impact of honey on quality characteristics of goat yogurt containing probiotic Lactobacillus acidophilus

This study aimed to analyze the influence of adding stingless bee honey (produced by Melipona scutellaris Latrelle - uruçu) on the technological, physicochemical and sensory characteristics of goat yogurt containing probiotic Lactobacillus acidophilus La-05 during 28 days of refrigerated storage. Four formulations of goat yogurt were prepared, each varying in the added stingless bee honey amount [(0%, 5%, 10% and 15% (v/v)], but all inoculated with the probiotic L. acidophilus La-05 (0.1 g/L of goat milk). The incorporation of stingless bee honey positively affected several characteristics in goat yogurt containing L. acidophilus La-05, namely the color, syneresis, viscosity, sensory acceptance and purchase intention. All yogurt formulations presented counts of L. acidophilus La-05 above 6.0 log cfu/g by 28 days of storage, but the presence of honey increased the counts (ca. 1 log cfu/g) of L. acidophilus La-05 and yogurt starter bacteria until 21 days of storage. The results of this study presented a successful incorporation of both the probiotic L. acidophilus La-05 and the honey produced by a native Brazilian stingless bee as ingredients of a new goat dairy product with satisfactory nutritional and sensory quality and added market value because of its potential functional properties.

Feasibility Study on a Measurement Method and a Portable Measuring System to Estimate the Concentration of Cloxacillin andβ-Lactamase in Milk

Antibiotics are nowadays used and abused worldwide in common veterinary practice to treat diseases, prevent infections, and promote animal’s growth. Drug resistance occurrence is a relevant phenomenon that can inactivate the antibiotic. Moreover, antibiotics used for animals are also found in milk and it poses serious health risks to humans. Another negative effect is related to milk processors since antibiotics cause detrimental effects on cheese and yogurt starter bacteria. Given its consumption as both beverage and derivatives, milk is one of the most regulated products in food industry. Nowadays several commercial tests are available to investigate antibiotics in milk, but they generally provide a qualitative result, require bulky procedure, and are time consuming. In this paper, we investigate the use of a chromogenic cephalosporin to quantify the concentration of cloxacillin—aβ-lactam difficult to be detected by using “cowside” screenings which is the drug of choice in the method of mastitis control. The proposed measurement method and prototype have been demonstrated to be able to detect cloxacillin in milk at concentrations lower than the MRL set by the European Commission. Moreover, they are also able to detect the illegal practice of usingβ-lactamase to degradeβ-lactams in milk.

The effect of proteolytic activity of starter cultures on technologically important properties of yogurt.

In this study, the effects of proteolytic activity of yogurt starter bacteria on physicochemical and technological properties of yogurt were investigated. Moreover, impact of proteolytic activity and production of exopolysaccharide (EPS) on the performance of each strain were screened. In order to compare the textural properties of yogurt samples, four parameters were evaluated: syneresis, water‐holding capacity, cohesiveness, and hardness. Results showed that strains with high proteolytic activity had lower acidifying activity during fermentation and storage. Samples containing EPS‐producing starter cultures had low proteolytic activity except samples K, L, and M. These differences related to nature and characteristics of each strain. Counts of starter cultures in samples produced using strains with high proteolytic activity were higher than other samples. Textural analysis data showed significant differences (p < .05) among strains in the four tested parameters. Strains with high proteolytic activity showed lower texture properties than other samples. Evaluation of sensory characteristics also showed samples prepared using strains with low or medium proteolytic activity and produced with EPS‐producing strains have higher overall acceptability than other samples. Accordingly, microbial, physicochemical, and sensory properties of produced yogurts confirm that proteolytic activity is one of the most effective factors in quality of product and performance of each strain.

Developing a kinetic model for co-culture of yogurt starter bacteria growth in pH controlled batch fermentation

Streptococcus thermophilus and Lactobacillus bulgaricus are yogurt starter cultures widely used in the dairy industry. Co-culture of these bacteria leads to higher biomass yield than their separate single strain culture because of the proto-cooperation between the two species. In the present study, a kinetic model was developed for the growth and lactic acid production by these two bacteria in pH-controlled co-cultures. This model quantifies the effects of pH, temperature, lactic acid, carbon and nitrogen substrate concentrations, and the influence of each bacterium on the growth of the other. The latter effect was described by considering the calculated concentration of metabolites produced by each of the bacterium which stimulate the growth of the other. The model was validated by the experimental data obtained from a set of 12 experiments which were designed using the response surface methodology.

Plant extract enhances the viability of Lactobacillus delbrueckii subsp. bulgaricus and Lactobacillus acidophilus in probiotic nonfat yogurt.

A commercial plant extract (prepared from olive, garlic, onion and citrus extracts with sodium acetate (SA) as a carrier) was evaluated to extend the viability of yogurt starter and probiotic bacteria as a means to enhance the shelf life of live and active culture, probiotic nonfat yogurt. Yogurts prepared from three different formulas (0.5* plant extract, 0.25* SA, or no supplement) and cultures (yogurt starter plus Bifidobacterium animalis,Lactobacillus acidophilus, or both probiotics) were assessed weekly during 29 days of storage at 5°C. Supplemented yogurt mixes had greater buffering capacities than non-supplemented yogurt mixes. At the end of storage, Lactobacillus bulgaricus and L. acidophilus counts in supplemented yogurts were greater compared with non-supplemented yogurts. Supplementation did not affect Streptococcus thermophilus and B. animalis counts. Hence the greater buffering capacity of yogurt containing plant extract could enhance the longevity of the probiotics, L. bulgaricus and L. acidophilus, during storage.

Developing a detailed kinetic model for the production of yogurt starter bacteria in single strain cultures

Streptococcus thermophilus and Lactobacillus bulgaricus are the most common yogurt starter cultures used in the dairy industry. Generally, they are produced by single strain fermentation and then mixed together in appropriate proportions for the purpose of yogurt production. In the present study a kinetic model was developed for the growth and lactic acid production by these two bacteria in pH-controlled single strain batch cultures and whey based medium. The model is a function of pH, temperature, biomass, lactic acid, carbon, and nitrogen substrate concentrations. A four-parameter function was used to describe the effect of pH on the growth of each bacterium. Moreover, a modified Arrhenius law was applied in the model to describe the temperature effect. Response surface methodology was implemented to design the experiments in order to estimate the effect of pH and temperature on bacterial growth. The model was validated on a set of 12 experiments for each bacterium.

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.

Research Article: J Food Process Technol 2013, 4: 272 doi: 10.4172/2157-7110.1000272 The Newest Experience with Effervescent Tablets Containing Royal Jelly as Functional Food on Packing, Dosage and Synergistic Action in Prevention, Prophylaxis and Healing Mirjana Menkovska Abstract | Full-text | PDF | Research Article: J Food Process Technol 2013, 4: 275 doi: 10.4172/2157-7110.1000275 Predictive Model for Growth of Clostridium perfringens

This study investigates the effects of heat inactivating processing of yogurt bacteria compared with other sequential inoculation on biochemical, microbiological, and sensory characteristics of typical Iranian drink based on fermented milk (Doogh). The yogurt bacteria (Streptococcus thermophilus and Lactobacillus delbrueckiis sp. bulgaricus) were used in all treatments. Bifidobacterium animlis spp. lactis PTCC 1631 was used as probiotic bacteria. A pH, titrable acidity, redox potential, fermentation time, and viability of probiotic organisms were analyzed during fermentation and over the refrigeration storage for21 days at 5°C. Also, the sensory attributes of treatments were determined at the end of fermentation. The greatest (p<0.05) mean pH drop rate was observed in BlY-40-4.5 treatment (B. animlis spp. lactis PTCC 1631 was co-cultured with yogurt starter bacteria and incubated at 40°C until final pH 4.5).In addition, the greatest viability of bifidobacteria was observed in this treatment. The viability of bifidobacteria strains was significantly higher in heat inactivating treatments than non-heat treated treatments. This process didn’t have positive effect on sensory properties of Doogh. The most acceptability in taste, texture, and mouth feel and appearance tolerability were observed in co-culture treatment in this study.

Differential cultivation and enumeration of Lactobacillus plantarum (PTCC 1058) in the presence of yogurt starter bacteria

This study was aimed at assessing the different selective media and incubation conditions for achieving an appropriate method in the isolation and enumeration of Lactobacillusplantarum PTCC 1058, Lactobacillus delbrueckii ssp. bulgaricus and Streptococcusthermophilus in probiotic yogurt. The yogurt samples containing 1% of L. plantarum PTCC 1058 were prepared using YoFlex Express cultures (containing L. delbrueckii ssp.bulgaricus and S. thermophilus) and stored at 4°C. After 24 h, they were cultivated in seven different agar media including: de Man, Rogosa and Sharpe (MRS) agar, MRS-Bile agar, acidified MRS agar (pH = 5.2), yogurt-lactic-agar (YL), Elliker’s lactic-agar (EL), M17 medium and S. thermophilus (ST) agar as pour plate and surface plate culture, and were incubated in aerobic and anaerobic conditions at three different incubation temperatures: 15, 37 and 45°C, for 48 to 72 h. For more practical examination, L. plantarum PTCC 1058and yogurt bacteria were enumerated every week over 6 weeks. Also, the ability of L. plantarum PTCC 1058 and yogurt bacteria to grow in concentration of 0.5 to 5% of bile salts were investigated. The results indicated that both L. plantarum PTCC 1058 and L. bulgaricus could grow in low concentration (≤ 2%) of bile salts. So, MRS-Bile-agar medium was not suitable for differentiation of L. plantarum PTCC 1058 and yogurt bacteria. The best condition for differentiation of L. plantarum PTCC 1058 from yogurt bacteria was cultivation on MRS medium and incubation at 15°C for 72 h. YL and EL media and aerobic incubation at 37°C for 48 h were suitable for enumeration of L. bulgaricus, and surface plate culture in YL, M17 and ST media and aerobic incubation at 45°C for 48 h was useful for enumeration of S. thermophilus in yogurt. Key words: Lactobacillus plantarum PTCC 1058, probiotic yogurt, differential culture, yogurt starter bacteria.