Effects of fructooligosaccharide and whey protein concentrate on the viability of starter culture in reduced-fat probiotic yogurt during storage

ABSTRACT:  Viability of yogurt starter cultures and Bifidobacterium animalis was assessed during 28 d storage in reduced-fat yogurts containing 1.5% milk fat supplemented with 1.5% fructooligosaccharide or whey protein concentrate. These properties were examined in comparison with control yogurts containing 1.5% and 3% milk fat and no supplement. Although fructooligosaccharide improved the viability of Streptococcus thermophilus , Lactobacillus delbrueckii subs. bulgaricus, and Bifidobacterium animalis , the highest growth was obtained when milk was supplemented with whey protein concentrate in reduced-fat yogurt ( P < 0.05). Supplementation with 1.5% whey protein concentrate in reduced-fat yogurt increased the viable counts of S. thermophilus , L. delbrueckii subs. bulgaricus, and B. animalis by 1 log cycle in the 1st week of storage when compared to control sample. Similar improvement in the growth of both yogurt bacteria and B. animalis was also obtained in the full-fat yogurt containing 3% milk fat and no supplement. Addition of whey protein concentrate also resulted in the highest content of lactic and acetic acids ( P < 0.05). A gradual increase was obtained in organic acid contents during the storage.     

Growth, proteolytic, and ACE-I activities of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus and rheological properties of low-fat yogurt as influenced by the addition of Raftiline HP

This study investigated the influence of incorporating Raftiline HP on the pH, growth, proteolytic, and angiotensin-I converting enzyme inhibitory activities and on spontaneous whey separation, firmness, and rheological properties of low-fat yogurts during storage for 28 d at 4 degrees C. Three types of yogurts were prepared from skim milk containing 0% (YI0, control), 2% (YI2), and 3% (YI3) Raftiline HP, respectively. The incorporation of Raftiline HP improved the growth of starter organisms, particularly that of Lactobacillus delbrueckii ssp. bulgaricus, resulting in shorter fermentation time. There was a significant improvement in total proteolysis, which was highest in yogurt containing 3% Raftiline HP. The ACE inhibitory activity was maximal in YI3 compared to YI2 and YI0. Incorporation of Raftiline HP did not affect whey separation and firmness of the low-fat yogurts. All these products were more fluid like with distinct pseudoplastic properties and lesser ability to resist deformation upon applied shear.     

Use of isolated autochthonous starter cultures in yogurt production

The aim of this study was to produce yogurt from Iranian autochthonous starters. Strains of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus were isolated from autochthonous yogurts. The strains were used as starter for yogurt production. Chemical, microbial and organoleptic characteristics of products were examined. There were significant increases in acidity and acetaldehyde content, and significant decreases in pH and microbial population of samples during cold storage. There was no significant difference in organoleptic characteristics (taste, smell and texture) during cold storage. We conclude that autochthonous starters in production of yogurt can be satisfactorily used and the starters can introduce to national microbial collection.     

Effect of thermophilic lactic acid bacteria on the viability of Salmonella serovar Typhimurium PT8 during milk fermentation and preparation of buffalo's yogurt

Viability of dairy-borne Salmonella enterica ssp. enterica serovar Typhimurium PT8 was studied during the fermentation of skim milk by thermophilic lactic acid bacteria (LAB). Longer generation times of Salmonella were found in mixed cultures of skim milk containing Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus or a mixture of them (1:1), as compared with single cultures of the pathogen. Salmonella was less able to survive in mixed cultures with these LAB during prolonged incubation at 41°C and also during cold storage of the fermented milk. L actobacillus ssp. bulgaricus and its mixture with S. thermophilus were more inhibitory to the growth and survival of Salmonella than was S. thermophilus . This was associated with higher ability of L . ssp. bulgaricus and the mixture to develop acidity in milk than S. thermophilus . Examining the antibacterial activity of these LAB towards Salmonella showed that other factors including heat-resistant and heat-labile compounds were involved in inhibiting the pathogen by these cultures. The viability of the same Salmonella strain during the preparation and cold storage of buffalo's yogurt was also examined. Salmonella was found to survive longer in yogurt made with starter containing probiotic bacteria than in that prepared with the traditional starter. This was ascribed to the development of lower pH by the traditional starter.     

Effect of Versagel on the growth and metabolic activities of selected lactic acid bacteria

ABSTRACT:  In this study, the influence of a protein-based fat replacer, Versagel ^® added at 1% and 2% (w/v) to reconstituted skim milk (RSM), on the growth and metabolic activities of selected strains of yogurt starters ( Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus ) as well as probiotic organisms ( Lactobacillus casei , Lactobacillus acidophilus , and Bifidobacterium longum ) was examined. Addition of Versagel resulted in significantly improved growth of S. thermophilus and B. longum but inhibited that of L. casei , L. acidophilus , and L. delbrueckii ssp. bulgaricus . This is also reflected in the extent of reduction of pH in RSM with added Versagel by these organisms. Among the biochemical activities, proteolytic activity of all the organisms except B. longum was adversely affected by the presence of Versagel, although the angiotensin-I converting enzyme (ACE) inhibitory and α-glucosidase (α-glu) inhibitory activities were improved. Versagel at 1% level influenced the growth, while ACE inhibitory and α-glu inhibitory activities of the organisms were better at 2% level.     

Performance of Starter in Yogurt Supplemented with Soy Protein Isolate and Biotransformation of Isoflavones during Storage Period

ABSTRACT:  In this study, soy protein isolate (SPI) (4%, v/w) was supplemented to the yogurt mix to increase the amount of biologically active isoflavone in yogurt (SY). The control yogurt was without any SPI supplementation (USY). The supplementation significantly ( P < 0.05) increased the lactose metabolism by the yogurt starter including Lactobacillus delbrueckii ssp. bulgaricus ATCC 11842 (Lb 11842) and Streptococcus thermophilus ST 1342 (ST 1342) during the fermentation process by 4.7%. The starter produced more acetic acid and less lactic acid in SY than that in USY and altered the ratio of lactic and acetic acid during the entire storage period. The viability of both Lb 11842 and ST 1342 in SY was significantly ( P < 0.05) lower than that in USY from 14 d of the storage period, however, their concentration still remained high (8.11 to 8.84 log CFU/g). The starter transformed 72.8% of total inactive isoflavone glycosides (IG) to active isoflavone aglycones (IA), increasing the IA content from 1.35 to 15.01 mg/100 g sample. During the storage period, IA concentration slowly rose from 15.02 to 15.51 mg/100 g sample.     

Evaluation of the possible use of potentially probiotic Lactobacillus strains in dairy products

In the study, the ability of two potentially probiotic strains Lactobacillus plantarum 14 and Lactobacillus fermentum 4a to milk fermentation and the possibility to use them in yogurt production were investigated. The strains did not acidify milk during 24 h and 72 h fermentation at 37C, but grew well and remained at the level of 10⁸ colony-forming units (CFU)/mL during 21 days of cold storage. Their application to yogurt production along with commercial starter culture consisted on L. delbrueckii ssp. bulgaricus and S. thermophilus allowed to obtain products with typical sensory properties, pH values and numbers of potentially probiotic bacteria at desired level 10⁷ CFU/mL.     

Effect of carbon dioxide under high pressure on the survival of cheese starter cultures

A new processing method that rapidly forms curds and whey from milk has the potential to improve cheesemaking procedures if cheese starter cultures can tolerate the processing conditions. The survival of Lactobacillus delbrueckii ssp. bulgaricus, Lactococcus lactis ssp. lactis, or Streptococcus thermophilus through this new process was evaluated. Inoculated milk containing 0, 1, or 3.25% fat or Lactobacillus MRS broth or tryptone yeast lactose broth (depending on microorganism used) was sparged with CO2 to a pressure of 5.52 MPa and held for 5 min at 38 degrees C. Broth contained 7.93 to 8.78 log CFU/ ml before processing and 7.84 to 8.66 log CFU/ml afterward. Before processing, milk inoculated with L bulgaricus, L. lactis, or S. thermophilus contained 6.81, 7.35, or 6.75 log CFU/ml, respectively. After processing, the curds contained 5.68, 7.32, or 6.50 log CFU/g, and the whey had 5.05, 6.43, or 6.14 log CFU/ml, respectively. After processing, the pHs of control samples were lower by 0.41 units in broth, 0.53 units in whey, and 0.89 units in curd. The pH of the processed inoculated samples decreased by 0.3 to 0.53 units in broth, 0.32 to 0.37 units in whey, and 0.93 to 0.98 units in the curd. Storing curds containing L. lactis at 30 degrees C or control curds and curds with L. bulgaricus or S. thermophilus at 37 degrees C for an additional 48 h resulted in pHs of 5.22, 5.41, 4.53, or 4.99, respectively. This study showed that milk inoculated with cheese starter cultures and treated with CO2 under high pressure to precipitate casein-produced curds that contained sufficient numbers of viable starter culture to produce lactic acid, thereby decreasing the pH.     

Growth of Probiotic and Traditional Yogurt Cultures in Milk Supplemented with Whey Protein Hydrolysate

ABSTRACT: Growth of some probiotic bacteria was significantly improved in milk supplemented with whey protein hydrolysate (WPH). However, WPH had no effect on the growth of Lactobacillus delbrueckii ssp. bulgaricus 18, L. delbrueckii ssp. bulgaricus 10442, and Streptococcus thermophilus 1. When the probiotic bacteria were grown in combination with different yogurt cultures in milk, WPH caused significant increases in growth of Bifidobacterium longum S9, L. acidophilus O16, and L. acidophilus L-1. However, by day 28 of refrigerated storage, the populations of the probiotic cultures that had been grown in samples supplemented with WPH were similar or below those in the control samples.     

Lactoperoxidase Effects on Rheological Properties of Yogurt

A mixed culture ( Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus ) was inoculated into reconstituted skim milk and incubated. When 0.45 Unit/g or more of lactoperoxidase (LPO) was added, the yogurts had softer and smoother texture than untreated yogurt. The apparent viscosity of yogurt was also reduced by addition of LPO. The storage modulus (G') of the gel of LPO-treated yogurt decreased but the frequency-dependency remained unchanged. The amount of exopolysaccharide or degree of proteolysis in yogurt was not changed by addition of LPO.     

Short communication: effect of oxygen on symbiosis between Lactobacillus bulgaricus and Streptococcus thermophilus

Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) and Streptococcus thermophilus are traditionally used for the manufacture of yogurt. It is said that a symbiotic relationship exists between Strep. thermophilus and L. bulgaricus and this decreases fermentation time. It is well known that L. bulgaricus is stimulated by the formate produced by Strep. thermophilus, and Strep. thermophilus is stimulated by free amino acids and peptides liberated from milk proteins by L. bulgaricus in symbiotic fermentation. We found that acid production by starter culture LB81 composed of L. bulgaricus 2038 and Strep. thermophilus 1131 was greatly accelerated by decreasing dissolved oxygen (DO) to almost 0 mg/kg in the yogurt mix (reduced dissolved oxygen fermentation) and that DO interferes with the symbiotic relationship between L. bulgaricus 2038 and Strep. thermophilus 1131. We attributed the acceleration of acid production of LB81 by reduced dissolved oxygen fermentation mainly to the acceleration of formate production and the suppression of acid production of LB81 by DO mainly to the suppression of formate production.     

Viability of bifidobacteria in commercial yogurt products in North Carolina during refrigerated storage

Fifty-eight commercial yogurt products of seven brands (which claimed to include bifidobacteria) were obtained from local stores in Greensboro, North Carolina, USA. These products were examined at 0, 1, 2, 3 and 4 weeks for the viability of bifidobacteria and yogurt starter culture during refrigerated storage at 4°C. Our results showed that bifidobacteria counts were variable, ranging from 0 to 5.5 log cfu/mL. The average yogurt starter culture counts ranged from 5.20 to 8.87 log cfu/mL and 7.51–8.94 log cfu/mL for Lactobacillus delbrueckii spp. bulgaricus and Streptococcus thermophilus , respectively. Of the 58 products tested, only 44 products (76%) contained viable cultures. Viability of bifidobacteria in yogurt samples remained within the same levels during 3 weeks of storage at 4°C; however, the bacterial count started to decline during the fourth week. These results suggest optimal beneficial consumption of yogurt foods with live bifidobacteria should occur within 3 weeks of production. Results obtained from this research could be used by the industry to develop new technologies to ensure consumers receive high-quality products.     

Technical note: Development of a quantitative PCR method for monitoring strain dynamics during yogurt manufacture

Yogurt starter cultures may consist of multiple strains of Lactobacillus delbrueckii ssp. bulgaricus (LB) and Streptococcus thermophilus (ST). Conventional plating methods for monitoring LB and ST levels during yogurt manufacture do not allow for quantification of individual strains. The objective of the present work was to develop a quantitative PCR method for quantification of individual strains in a commercial yogurt starter culture. Strain-specific primers were designed for 2 ST strains (ST DGCC7796 and ST DGCC7710), 1 LB strain (DGCC4078), and 1 Lactobacillus delbrueckii ssp. lactis strain (LL; DGCC4550). Primers for the individual ST and LB strains were designed to target unique DNA sequences in clustered regularly interspersed short palindromic repeats. Primers for LL were designed to target a putative mannitol-specific IIbC component of the phosphotransferase system. Following evaluation of primer specificity, standard curves relating cell number to cycle threshold were prepared for each strain individually and in combination in yogurt mix, and no significant differences in the slopes were observed. Strain balance data was collected for yogurt prepared at 41 and 43°C to demonstrate the potential application of this method.     

Modelling the survival of starter lactic acid bacteria and Bifidobacterium bifidum in single and simultaneous cultures

The inactivation kinetics at 4 degrees C of Bifidobacterium bifidum, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, cultured alone or consociated in a laboratory medium (modified MRS broth), were modelled through the Weibull model and a second-order polynomial equation. The initial cell number of S. thermophilus and L. delbrueckii subsp. bulgaricus was approximately 6-7log (CFU/ml); the viability loss after 30 days of storage was 2.87 and 1.99log (CFU/l) for L. delbruckii subsp. bulgaricus and S. thermophilus, cultured alone, respectively; whereas the consociation of lactobacilli and streptococci with bifidobacteria reduced viability loss during storage (0.28 and 0.54log CFU/l for lactobacilli and streptococci, respectively). Finally, the consociation of lactobacilli and streptococci with B. bifidum improved their oxygen uptake.     

Behaviour of volatile compounds during the shelf life of yoghurt

The production of acetaldehyde, diacetyl and ethanol was evaluated in whole plain yoghurts manufactured with commercial starter cultures, yoghurt acquired in a local market, and milk fermented by a single culture of either Streptococcus thermophilus or Lactobacillus delbrueckii ssp. bulgaricus . The headspace technique was used for sample preparation, following identification and quantification by gas chromatography. During an 8-h incubation period, mixed cultures were the most efficient in lowering the pH (from 6.30 to 4.8), followed by S. thermophilus (from 6.30 to 5.18) and L. bulgaricus (from 6.30 to 5.8). During the storage period, however, a single culture of L. bulgaricus decreased the pH more than S. thermophilus , but still less than the mixed commercial cultures. Plain yoghurts acquired in the market, those made with commercial starter cultures, and fermented milks obtained with single cultures showed, after 21 days of storage, concentrations of acetaldehyde from 11 to 35 mg/L, and of diacetyl from 0 to 0.85 mg/L. An increasing concentration of ethanol was observed during the storage period, and its production was observed even in the incubation stage of all products. It was also observed that the acetaldehyde concentration was inversely correlated to ethanol production in some products. The combination of headspace, identification and quantification techniques by gas chromatography in this work was efficient in the identification and quantification of the major aromatic compounds and ethanol content of yoghurt.     

Growth of probiotic bacteria and bifidobacteria in a soy yogurt formulation

Soy beverage and cows' milk yogurts were produced with Steptococcus thermophilus (ATCC 4356) and Lactobacillus delbrueckii subsp. bulgaricus (IM 025). The drop in pH during fermentation was faster in the soy beverage than in cows' milk, but the final pH values were similar. Yogurts were prepared with a yogurt starter in conjunction with either the probiotic bacteria Lactobacillus johnsonii NCC533 (La-1), Lactobacillus rhamnosus ATCC 53103 (GG) or human derived bifidobacteria. The presence of the probiotic bacteria did not affect the growth of the yogurt strains. Approximately 2 log increases in both L. rhamnosus GG and L. johnsonii La-1 were observed when each was added with the yogurt strains in both cows' milk and the soy beverage. Two of the five bifidobacteria strains grew well in the cows' milk and soy beverage during fermentation with the yogurt bacteria. High pressure liquid chromatography (HPLC) analyses showed that the probiotic bacteria and the bifidobacteria were using different sugars to support their growth, depending on whether the bacteria were growing in cows' milk or soy beverage.     

嗜热链球菌和德氏乳杆菌保加利亚亚种共生关系的研究进展

嗜热链球菌和德氏乳杆菌保加利亚亚种是组成酸奶发酵剂的主要菌种,在长期共处于牛乳环境的过程中形成多种协同共生关系。这些协同共生关系赋予发酵剂菌株产酸快、黏度高、活性物质丰富等优良性能,同时对酸奶品质产生重要影响。该文旨在从营养供给、抵抗环境胁迫及酸奶品质改良等方面讨论两菌的协同共生关系,为提高发酵剂菌株活力及酸奶品质提供理论指导。     

Reactive oxygen species and lipid peroxidation product-scavenging ability of yogurt organisms.

The antioxidative activity of the intracellular extracts of yogurt organisms was investigated. All 11 strains tested, including five strains of Streptococcus thermophilus and six strains of Lactobacillus delbrueckii ssp. bulgaricus, demonstrated an antioxidative effect on the inhibition of linoleic acid peroxidation. The antioxidative effect of intracellular extracts of 10(8) cells of yogurt organisms was equivalent to 25 to 96 ppm butylated hydroxytoluene, which indicated that all strains demonstrated excellent antioxidative activity. The scavenging of reactive oxygen species, hydroxyl radical, and hydrogen peroxide was studied for intracellular extracts of yogurt organisms. All strains showed reactive oxygen species-scavenging ability. Lactobacillus delbrueckii ssp. bulgaricus Lb demonstrated the highest hydroxyl radical-scavenging ability at 234 microM. Streptococcus thermophilus MC and 821 and L. delbrueckii ssp. bulgaricus 448 and 449 scavenged the most hydrogen peroxide at approximately 50 microM. The scavenging ability of lipid peroxidation products, t-butylhydroperoxide and malondialdehyde, was also evaluated. Results showed that the extracts were not able to scavenge the t-butylhydroperoxide. Nevertheless, malondialdehyde was scavenged well by most strains.     

PROTEOLYSIS OF EWE'S CASEINS AND WHEY PROTEINS DURING FERMENTATION OF YOGURT AND STORAGE. EFFECT OF THE STARTERS USED

Yogurts are mostly produced from cow's milk and to a very limited extent from ewe's milk. Changes in the caseins and whey proteins in ovine milk subjected to different thermal treatments (63C/30 min; 73C/15 min; 85C/10 min or 96C/5 min) were followed during fermentation of yogurt, using two different starters, and during their storage up to 14 days. One starter (YC‐183) contained mixed strain culture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus at a ratio 1:1. The other starter (ABT‐3) is a well‐defined mixed‐strain culture containing Sc. thermophilus TH4, Lb. acidophilus LA5 and Bifidobacterium Bb 12 at a ratio 1:1:1. The level of free amino groups in the yogurts increased gradually during the fermentation up to a maximum after 4 or 6 h fermentation in the case of ABT‐3 and YC‐183, respectively. A large decrease in the amount of free amino groups was observed after 4–6 h fermentation. During storage of the yogurts up to 14 days, the amount of free amino groups increased with the duration of storage time up to a maximum after 7 days both in the case of YC‐183 and ABT‐3 starters. A large decrease in the concentration of free amino groups was observed in the first 24 h and between 7 and 14 days of storage in the case of yogurt made with the two starters indicating that microorganisms continue to grow in low temperatures. During the fermentation and the storage of both yogurt types, α‐lactalbumin was hydrolyzed to a slightly greater extent than β‐lactoglobulin. During fermentation and the storage, β‐casein was degraded slightly than α_S2‐ +α_S2‐caseins. Generally, a more intense heat pretreatment led to greater degradation of whey proteins and caseins during fermentation and storage. Differences in proteolytic activity between the two starters used (proteins degraded more by ABT‐3 than by YC‐183) may lead to the improvement in production and formulation of yogurts differing in their physico‐chemical and rheological properties.     

Formulations and processing of yogurt affect the microbial quality of carbonated yogurt

Carbonation, flavor, culture type, pH, and storage time were varied to investigate the effects of these variables and their interactions on the growth of both typical and nontypical yogurt cultures and some contaminating bacteria. Two types of yogurt cultures (YC-470 and YC-180) were used as the source of typical yogurt bacteria, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. In addition, Lactobacillus acidophilus (LA-K) and Bifidobacterium longum ATCC 15707 were added as nontypical yogurt cultures to make sweetened low fat (1%) Swiss-style plain, strawberry, and lemon yogurts. Samples were incubated at 43 degrees C until pH values of 5.0 or 4.2 were reached. Strawberry yogurts at low (4.2) and high (5.0) pHs were divided into three portions, which were separately inoculated with contaminating bacteria, Bacillus licheniformis ATCC 14580, Escherichia coli ATCC 11775, and Listeria monocytogenes Scott A. After incorporation of carbon dioxide (1.10 to 1.27 volume of CO2 gas dissolved in water), the yogurt was stored at 4 degrees C for a 90-d period. Carbon dioxide did not affect the growth of typical or nontypical yogurt bacteria. Also, CO2 did not inhibit the growth of undesirable microorganisms. In general, low levels of CO2 did not affect the bacterial population in yogurt. The microflora of yogurt were influenced by culture type, pH, flavor type, and storage time or their interactions.