Effects of exopolysaccharide-producing strains of Streptococcus thermophilus on technological and rheological properties of set-type yoghurt

Characterization of the Ayran Made with Commercial Probiotic Cultures for Fatty Acids, Cholesterol, Folic Acid Levels, and Anti-Oxidative Potential

Ayran is a salted drinkable fermented milk food which consumed in many countries around the world. In this study, some chemical parameters were determined to evaluate the healthy properties of ayran prepared using various commercial probiotic cultures. Four treatments of ayran were made from cow's milk and using classic yogurt culture (L. delbrueckii subsp. bulgaricus and Streptococcus thermophilus) [T1], ABT-5 culture (L. acidophilus, Bifidobacterium and S. thermophilus) [T2], exopolysaccharide producing culture (EPS-producing, L. delbrueckii subsp. bulgaricus and S. thermophilus) [T3], and EPS-producing culture + Bifidobacterium animalis subsp. lactis BB12 (mixture culture) [T4]. Treatment 1 had the highest acidity, acetaldehyde, and diacetyl values. Using probiotic [T2] or mixture cultures [T4] reduced saturated fatty acids by 1.97% and increased monounsaturated and polyunsaturated fatty acids of ayran by 4.94 and 5.72%, respectively. Also, the levels of oleic acid (omega-9), linoleic acid (omega-6), and α-linolenic acid (omega-3) increased in ayran produced using probiotic or mixture cultures. Sample T4 was highly richer in the value of antioxidant activity (27.62%) and folic acid (0.1566 mg/100 g) whereas possessed the lowest cholesterol amount (8.983 mg/100 g). Mixture culture (EPS-producing culture + Bifidobacterium animalis subsp. lactis BB12) is a good starter to improve the healthy and nutritional characteristics of bio-ayran.

Effect of whey protein isolate addition on set-type camel milk yogurt: Rheological properties and biological activities of the bioaccessible fraction

The manufacture of camel milk (CM) yogurt has been associated with several challenges, such as the weak structure and watery texture, thereby decreasing its acceptability. Therefore, this study aimed to investigate the effect of whey protein isolate (WPI) addition on the health-promoting benefits, texture profile, and rheological properties of CM yogurt after 1 and 15 d of storage. Yogurt was prepared from CM supplemented with 0, 3, and 5% of WPI and compared with bovine milk yogurt. The results show that the water holding capacity was affected by WPI addition representing 31.3%, 56.8%, 64.7%, and 45.1% for yogurt from CM containing 0, 3 or 5% WPI, and bovine milk yogurt, respectively, after 15 d. The addition of WPI increased yogurt hardness, adhesiveness, and decreased the resilience. CM yogurt without WPI showed lower apparent viscosity, storage modulus, and loss modulus values compared with other samples. The supplementation of CM with WPI improved the rheological properties of the obtained yogurt. Furthermore, the antioxidant activities of yogurt before and after in vitro digestion varied among yogurt treatments, which significantly increased after digestion except the superoxide anion scavenging and lipid oxidation inhibition. After in vitro digestion at d 1, the superoxide anion scavenging of the 4 yogurt treatments respectively decreased from 83.7%, 83.0%, 79.1%, and 87.4% to 36.7%, 38.3%, 44.6%, and 41.3%. The inhibition of α-amylase and α-glucosidase, angiotensin-converting enzyme inhibition, cholesterol removal, and degree of hydrolysis exhibited different values before and after in vitro digestion.

Differences in Aroma Metabolite Profile, Microstructure, and Rheological Properties of Fermented Milk Using Different Cultures

Texture and flavour are the key attributes determining sensory quality and are highly affected by starter cultures. A selection of phenotypic strains is needed to create diverse texture and flavour to meet consumers' preferences. In this study, the use of five lactic acid bacteria strains in the production of fermented milk, along with the metabolite profiles, microstructure, and rheological properties of the fermented milk samples, was investigated. Our results showed that Lactobacillus helveticus (LH) and Streptococcus thermophilus (ST) had a stronger acidification during fermentation but resulted in products with a coarser protein network compared to Lactococcus lactis (BL1) and Leuconostoc mesenteroides (CL3). Milk fermented by LH had the highest viscosity and exopolysaccharide concentration, while milk fermented by ST had the highest concentration of diacetyl. Although Leuconostoc pseudomesenteroides (CL3ST) had a minimal acidification capability, it produced high levels of ethyl-derived compounds associated with sweet, fruity, and floral fragrances. The results demonstrated that LH and ST could be used as starter cultures targeting fermented milks with different viscosities, while BL1, CL3, and CL3ST are suitable as adjunct cultures to impact different acidic sharpness and flavour notes.

The Role of Exopolysaccharide-Producing Streptococcus thermophilus on Physical Properties of Stirred Skim Milk Gel

The techno-functionality of exopolysaccharides (EPS) from Streptococcus thermophilus in stirred fermented milk is affected by several extrinsic (e.g., base milk composition) and intrinsic (e.g., amount and properties of EPS) factors. The aim of this study was to use skim milk models to identify the key factors that influence the physical properties of stirred fermented milk with EPS. For that, fermentation was carried out with one of three single S. thermophilus strains (intrinsic factors) at two casein:whey protein ratios of the base milk, two acidification activities of the starters, and two fermentation temperatures (extrinsic factors). The effects of the factors on the acidification kinetics, EPS amount, susceptibility to syneresis, and texture properties were then discriminated by a multivariate ANOVA-simultaneous component analysis. Strains producing ropy EPS mainly determined the texture properties, whereas the extrinsic factors primarily affected the acidification kinetics and EPS amount. When capsular EPS were also present, the syneresis was lower; however, this effect was more pronounced after enrichment of base milk with whey protein. The EPS amount did not correlate with the texture or syneresis, pointing to the importance of other factors such as the EPS location (type) and EPS–protein interactions for their functionality in stirred fermented milk.

Lacticaseibacillus rhamnosus GG Survival and Quality Parameters in Kefir Produced from Kefir Grains and Natural Kefir Starter Culture

The study aimed to determine the effect of starter cultures (kefir grains and natural kefir starter culture without grains) on Lacticaseibacillus rhamnosus GG (LGG) survival and on the quality characteristics of kefir. To this end, the viability of probiotic L. rhamnosus GG strain and the rheological properties and quality parameters of kefir beverages were tested during storage over 21 days at 4 °C. The final LGG counts were 7.71 and 7.55 log cfu/mL in natural kefir starter culture and kefir grain, respectively. When prepared with probiotic bacteria, the syneresis values of kefir prepared using natural kefir starter culture was significantly lower (p < 0.05) than that of kefir made using grains. However, the viscosity indices, hysteresis loop, and dynamic moduli were similar between kefir made with natural kefir starter culture and other kefir formulations (p > 0.05). Moreover, all samples showed shear-thinning behavior. The flavor scores for kefir prepared using natural kefir starter culture were significantly higher than for the other samples (p < 0.05), but overall acceptability was similar at the 10-day assessment across both starters (with and without grain) after the addition of probiotic bacteria (p > 0.05). Overall, the results indicate that natural kefir starter culture could be a potential probiotic carrier.

Co-Culture Strategy of Lactobacillus kefiranofaciens HL1 for Developing Functional Fermented Milk

Our previous studies indicated that Lactobacillus kefiranofaciens HL1, isolated from kefir grain, has strong antioxidant activities and anti-aging effects. However, this strain is difficult to use in isolation when manufacturing fermented products due to poor viability in milk. Thus, the purpose of this study was to apply a co-culture strategy to develop a novel probiotic fermented milk rich in L. kefiranofaciens HL1. Each of four selected starter cultures was co-cultured with kefir strain HL1 in different media to evaluate their effects on microbial activity and availability of milk fermentation. The results of a colony size test on de Man, Rogosa and Sharpe (MRS) agar agar, microbial viability, and acidification performance in MRS broth and skimmed milk suggested that Lactococcus lactis subsp. cremoris APL15 is a suitable candidate for co-culturing with HL1. We then co-cultured HL1 and APL15 in skimmed milk and report remarkable improvement in fermentation ability and no negative impact on the viability of strain HL1 or textural and rheological properties of the milk. Through a co-culture strategy, we have improved the viability of kefir strain HL1 in fermented skimmed milk products and successfully developed a novel milk product with a unique flavor and sufficient probiotics.

Bacterial exopolysaccharides for improvement of technological, functional and rheological properties of yoghurt

Exopolysaccharides (EPS) are known to have technological and functional applications in food industry including dairy based products such as yoghurt. Yoghurt is a widely consumed dairy based product due to pleasant taste and texture, as well as a source of nutrients and bioactive compounds. At the same time, structural, rheological and sensorial properties are important in the production of good quality yoghurt. Various natural hydrocolloids including EPS with stabilizing and texture enhancing properties could be useful in enhancing these desirable properties. Apart from that, EPS may enhance various other functional properties of yoghurt such as antioxidant and prebiotic potential. Based on its prebiotic property, symbiotic products could be developed by combining EPS and probiotic bacterial strains. EPS has potential to provide physical and micro structural stability, thereby enhancing the protein distribution and viscoelastic properties. Main focus of the present review is to provide an insight on the action of EPS as a functional hydrocolloid on the technological, rheological and functional properties of yoghurt and related products.

Metabolic footprint analysis of volatile metabolites by gas chromatography-ion mobility spectrometry to discriminate between different fermentation temperatures during Streptococcus thermophilus milk fermentation

Streptococcus thermophilus is widely used in the dairy industry to produce fermented milk. Gas chromatography-ion mobility spectrometry-based metabolomics was used to discriminate different fermentation temperatures (37°C and 42°C) at 3 time points (F0: pH = 6.50 ± 0.02; F1: pH = 5.20 ± 0.02; F2: pH = 4.60 ± 0.02) during S. thermophilus milk fermentation, and differences of fermentation physical properties and growth curves were also evaluated. Fermentation was completed (pH 4.60) after 6 h at 42°C and after 8 h at 37°C; there were no significant differences in viable cell counts and titratable acidity; water-holding capacity and viscosity were higher at 37°C than at 42°C. Different fermentation temperatures affected volatile metabolic profiles. After the fermentation was completed, the volatile metabolites that could be used to distinguish the fermentation temperature were hexanal, butyraldehyde, ethyl acetate, ethanol, 3-methylbutanal, 3-methylbutanoic acid, and 2-methylpropionic acid. Specifically, at 37°C of milk fermentation, branched-chain AA had higher levels, and leucine, isoleucine, and valine were involved in growth and metabolism, which promoted accumulation of some short-chain fatty acids such as 3-methylbutanoic acid and 2-methylpanprooic acid. At 42°C, at 3 different time points during fermentation, ethanol from glycolysis all presented higher levels, including acetone and 3-methylbutanal, producing a more pleasant flavor in the fermented milk. This work provides detailed insight into S. thermophilus fermented milk metabolites that differed between incubation temperatures; these data can be used for understanding and eventually predicting metabolic changes during milk fermentation.

Usage of in situ exopolysaccharide-forming lactic acid bacteria in food production: Meat products-A new field of application?

In the meat industry, hydrocolloids and phosphates are used to improve the quality attributes of meat products. However, latest research results revealed that the usage of exopolysaccharide (EPS)-forming lactic acid bacteria (LAB), which are able to produce EPS in situ during processing could be an interesting alternative. The current review aims to give a better understanding of bacterial EPS production in food matrices with a special focus on meat products. This includes an introduction to microbial EPS production (homopolysaccharides as well as heteropolysaccharides) and an overview of parameters affecting EPS formation and yield depending on LAB used. This is followed by a summary of methods to detect and characterize EPS to facilitate a rational selection of starter cultures and fermentation conditions based on desired structure-function relationships in different food matrices. The mechanism of action of in situ generated EPS is then highlighted with an emphasis on different meat products. In the process, this review also highlights food additives currently used in meat production that could in the future be replaced by in situ EPS-forming LAB.

Changes in the viscosity, textural properties, and water status in yogurt gel upon supplementation with green and Pu-erh teas

The present research was established to study the effect of green tea and Pu-erh tea (PT) additives on the mechanical and hydration properties of yogurt gels using a combination of nuclear magnetic resonance, rheological, and textural studies. Tea infusions (0-15 mL/100 mL) were added to batch milk before fermentation with yogurt culture. Obtained dairy products were analyzed for the water mobility and organization, viscosity, and texture profile. Results of the rheological and nuclear magnetic resonance studies suggested that stabilization of the yogurt gel structure was achieved upon supplementation with tea infusions. Generally, green tea fortification produced yogurts with more consolidated gel structure, tighter interacting water, and less susceptibility to shearing and temperature changes than PT treatments. In contrast, PT yogurts were more viscous and characterized by 8 to 17% lower hardness values. This knowledge can be useful for developing novel dairy products with desired structure and consistency.

Physicochemical analysis, proteolysis activity and exopolysaccharides production of herbal yogurt fortified with plant extracts

Yogurt production with starter culture at 41 °C in the presence of plant water extracts (Momordica grosvenori, Psidium guajava, Lycium barbarum or Garcinia mangostana) were studied to examine the effects on acidification, physicochemical properties, microbial growth, proteolytic activity, and exopolysaccharide (EPS) content. All plant-based yogurt reached a pH of 4.5 faster (300–330 min) than plain-yogurt (360 min). All plant water extracts stimulated Lactobacillus spp. (∼7.4 log10 CFU/mL) and Streptococcus thermophilus (8.20–8.50 log10 CFU/mL) growth except for G. mangostana which marginally inhibited Lactobacillus spp. growth (7.21 log10 CFU/mL). M. grosvenori, L. barbarum, and G. mangonstana were significantly affected proteolysis of milk proteins (46.2 ± 0.8, 39.9 ± 0.5, & 35.8 ± 0.1 µg/mL; respectively) compared to plain-yogurt (26.3 ± 0.4 µg/mL). The presence of G. mangostana and L. barbarum resulted in an increase (p < 0.05) of total solids content (∼15.0%) and water holding capacity in yogurt (28.1 ± 1.2 & 26.5 ± 0.3%; respectively; p < 0.05). In addition, M. grosvenori water extract enhanced (p < 0.05) syneresis of yogurt (1.78 ± 0.30%). L. barbarum yogurt showed the highest EPS concentration (220.9 ± 12.4 µg/L) among yogurt samples. In conclusion, the presence of plant water extracts positively altered yogurt fermentation, enhanced proteolysis of milk protein, and induced EPS production.

Optimization of stabilized probiotic Doogh formulation by edible gums and response surface methodology: assessment of stability, viability and organoleptic attributes

In this study the effect of gelan, xanthan and quince seed gum (QSG) on stability, probiotic viability and qualitative properties of Doogh using response surface methodology was determined. Three gums were used at three levels of 0, 0.25 and 0.5%. The results showed that the effect of QSG on viscosity and serum separation was significant (P < 0.05). The effect of QSG on viability of B. bifidum was significant (P < 0.05). Sensory evaluation showed that effect of using of QSG was significant and the score of taste, odor and overall acceptance increased by increasing of concentration of QSG. At the optimum point, the stability, viscosity pH, probiotic load and overall acceptance were 92.24%, 11.852 mPa s, 3.87, 8.37 log cfu/mL and 4.42, respectively. Using of combination of gums at the optimal concentration prevented phase separation and maintained the probiotic viability of Doogh. Therefore, the optimization of formulation can be used for production of stabilized probiotic Doogh in dairy industry.

Structural characterization of exopolysaccharide from Streptococcus thermophilus ASCC 1275

In this study, we purified and characterized exopolysaccharide (EPS) produced by a high-EPS-producing dairy starter bacterium, Streptococcus thermophilus ASCC 1275. Crude EPS was extracted from S. thermophilus ASCC 1275 and partially purified using dialysis. Further purification and fractionation of exopolysaccharide was conducted using HPLC on a Superose 6 column (Cytiva/Global Life Sciences Solutions, Marlborough, MA). Glycosyl composition analysis, linkage analysis along with 1-dimensional and 2-dimensional nuclear magnetic resonance spectroscopy were performed to deduce the structure of EPS. Three fractions (F) obtained from gel permeation chromatography were termed F1 (2.6%), F2 (45.8%), and F3 (51.6%) with average molecular weights of approximately 511, 40, and 5 kDa, respectively. Monosaccharide composition analysis revealed the dominance of glucose, galactose, and mannose in all 3 fractions. Major linkages observed in F3 were terminal galactopyranosyl (t-Gal), 3-linked glucopyranosyl (3-Glc), 3-linked galactofuranosyl (3-Galf), and 3,6-linked glucopyranosyl (3,6-Glc) and major linkages present in F2 were 4-Glc (48 mol%), followed by terminal mannopyranosyl (t-Man), 2- + 3-linked mannopyranosyl (2-Man+3-Man), and 2,6-linked mannopyranosyl (2,6-Man; total ∼28 mol%). The 1-dimensional and 2-dimensional nuclear magnetic resonance spectroscopy revealed that F2 comprised mannans linked by (1→2) linkages and F3 consisted of linear chains of α-d-glucopyranosyl (α-d-Glcp), β-d-glucopyranosyl (β-d-Glcp), and β-d-galactofuranosyl (β-d-Galf) connected by (1→3) linkages; branching was through (1→6) linkage in F3. A possible structure of EPS in F2 and F3 was proposed.

Structural characterization and prebiotic potential of an acidic polysaccharide from Imperial Chrysanthemum

A novel water-soluble polysaccharide, named ICP-1, was isolated and purified by Sephadex G-200 after extracting the crude polysaccharide (ICP) from Imperial Chrysanthemum. The structural characterization of ICP-1 was determined by physical and chemical methods, FT-IR, NMR, SEM, HPGPC, periodate oxidation, Smith degradation, methylation and Congo red test. Then, acid production and proliferation of lactic acid bacteria and the tolerance tests of simulated gastrointestinal fluid were measured to investigate the activity of prebiotic potential. The results showed that ICP-1 was an acidic hetero-polysaccharide with an average molecular weight of 2.98 × 10³ kDa and a specific optical rotation of +155°. The glycosyl residues of ICP-1 were composed of (1→), (1→4) and (1→6) glucose, (1→5) arabinose, (1→4) galacturonic acid and (1→3,6) mannose. Besides, ICP-1 can speed up the acid production of lactic acid bacteria and promote the growth and proliferation of lactic acid bacteria effectively.

Development of probiotic yogurt: effect of strain combination on nutritional, rheological, organoleptic and probiotic properties

Seven combinations of yogurt; C1 [yogurt starter culture (YSC)], T1, [YSC + Lactobacillus acidophilus (LA)], T2 [YSC + Bifidobacterium bifidum (BB)], T3 [YSC + Lactobacillus plantarum (LP)], T4 [YSC + Lactobacillus casei (LC)], T5 [YSC + LA + BB] and T6 [YSC + LP + LC] were developed. Nutritional [proximate and minerals], rheological [total soluble solids (TSS), pH, titratable acidity (TA), water holding capacity, synersis, viscosity] organoleptic and probiotic properties [viability, acid tolerance, bile salt tolerance] were assessed with standard methods. Nutritional composition differed significantly among samples except for the iron and zinc (P < 0.05). Yogurt containing LP as single or in combination with LC resulted in significantly higher ash, protein, calcium and phosphorous level. Probiotic combination also significantly affected the rheological properties of yogurts (P < 0.05). Yogurt with LP and LC as single or in combination lead to significantly higher TSS and viscosity while significantly low syneresis, whereas yogurt with LA as single or in combination resulted in low pH and high TA (P < 0.05). Interestingly, combination of LA and BB increased TSS, reduced pH and syneresis as compare to these bacteria as single probiotic source. Panel experts found yogurt with LP more flavourful. Combination of multi-strain and multi-species probiotic resulted in improved texture but we found no significant difference in overall acceptability. Combination of probiotic strains also resulted in better probiotic potential with multi-species combination found to be even more effective. BB seemed more stable than three other probiotic strains. The present study can be helpful to dairy industry in developing new probiotic products and may provide a rational for selecting a combination of probiotic strains.

Consumer rejection threshold, acceptability rates, physicochemical properties, and shelf-life of strawberry-flavored yogurts with reductions of sugar

BACKGROUND

There is an increasing demand for reduced-sugar products due to the worldwide prevalence of obesity, diabetes, and cardiovascular diseases. The aim of this study was to evaluate the effects of sugar (sucrose) reductions on the acceptability, preference, and quality of strawberry-flavored yogurts. A consumer rejection threshold test and an acceptability test (N = 53) were conducted using six yogurt samples with decreasing concentrations of sugar (12-5/100 g). Additional physicochemical tests (pH, °Brix, water-holding-capacity, viscosity, and color) were conducted to examine the quality and shelf-life of strawberry-flavored yogurts with reductions of sucrose during 28 days of storage at 4 °C.

RESULTS

Reduction of sucrose affected the acceptability and physicochemical characteristics of yogurts. The consumer rejection threshold showed that sucrose in strawberry-flavored yogurts could be reduced to 5.25/100 g from an initial concentration of 12/100 g without affecting the preferences of consumers. The 71%-sucrose (8.50/100 g of yogurt) was perceived as the most liked (6.27 using a nine-point hedonic scale) and the most preferred (rank sum = 127.50) yogurt sample. For the physicochemical properties of yogurts, the viscosity (3263-5473 cP) decreased, and the color lightness (80.98-85.44) increased during 28 days of storage at 4 °C.

CONCLUSION

Physicochemical properties and preferences were affected by the reduction of sugar. The consumer rejection threshold analysis showed that sucrose can be reduced to less than half of the initial concentration. These findings are useful to understand consumers' acceptability and shelf-life of yogurts with reduced-sugar formulations in the developing of new products. © 2020 Society of Chemical Industry.

Effect of faba bean and chickpea mucilage incorporation in the structure and functionality of kefir

This investigation aimed to investigate the viability of kefir enrichment with mucilage extracted from faba bean and chickpea. Four formulations of kefir were studied: fermented milk (control), milk with 3% of faba bean mucilage, milk with 3% of chickpea mucilage and milk with 3% of inulin from artichoke (as prebiotic control). Kefirs were evaluated during 28 days’ storage time at refrigerated temperature. Microbial viability, physicochemical properties (total titratable acidity, syneresis and pH), rheological properties (flow and dynamic shear rheology) and consumer’s acceptability were evaluated. The number of bacteria significantly increased during storage period in all the formulations. The pH decreases during storage whereas total titratable acidity increased as was expected. Kefir supplemented with mucilage showed slightly lower but not significantly different sensory acceptability scores in comparison to the control. The novel mucilage ingredients could be prebiotic source for improving kefir quality.

The N-terminal domain of rhamnosyltransferase EpsF influences exopolysaccharide chain length determination in Streptococcus thermophilus 05-34

Glycosyltransferases are key enzymes involved in the assembly of repeating units of exopolysaccharides (EPS). A glycosyltransferase generally consists of the N-terminal and the C-terminal domain, however, the functional role of these domains in EPS biosynthesis remains largely unknown. In this study, homologous overexpression was employed to investigate the effects of EpsF_N, a truncated form of rhamnosyltransferase EpsF with only the N-terminal domain, on EPS biosynthesis in Streptococcus thermophilus 05-34. Reverse transcription qPCR and Western blotting analysis confirmed the successful expression of epsF_N in 05-34 at the transcription and translation level, respectively. Further analysis showed that the monosaccharide composition and yield of EPS were not affected by the overexpression of epsF_N, whereas the molecular mass decreased by 5-fold. Accordingly, the transcription levels of genes involved in EPS biosynthesis, including chain-length determination gene epsC, were down-regulated by 5- to 6-fold. These results indicated that the N-terminal domain of EpsF alone could influence the molecular mass of EPS, probably via lowering the concentration of sugar precursors, which may lead to decreased expression of genes responsible for chain-length determination.

Ability of a Wild Weissella Strain to Modify Viscosity of Fermented Milk

Despite the fact that strains belonging to Weissella species have not yet been approved for use as starter culture, recent toxicological studies open new perspectives on their potential employment. The aim of this study was to evaluate the ability of a wild Weissella minor (W4451) strain to modify milk viscosity compared to Lactobacillus delbrueckii subsp. bulgaricus, which is commonly used for this purpose in dairy products. To reach this goal, milk viscosity has been evaluated by means of two very different instruments: one rotational viscometer and the Ford cup. Moreover, water holding capacity was evaluated. W4451, previously isolated from sourdough, was able to acidify milk, to produce polysaccharides in situ and thus improve milk viscosity. The ability of W4451 to produce at the same time lactic acid and high amounts of polysaccharides makes it a good candidate to improve the composition of starters for dairy products. Ford cup turned out to be a simple method to measure fermented milk viscosity by small- or medium-sized dairies.

Screening and Identification of New Types of Exopolysaccharides-Producing Lactic Acid in the Inner Mongolia Dairy Products

Exopolysaccharides (EPS) is a type of polysaccharide produced by lactic acid bacteria (LAB) that can be directly used in foods to make the products more excellent. Therefore, batch studies were performed to explore the effect of different LAB on the production of EPS and antioxidant activity. Five strains with high EPS yield and antioxidant activity were screened out from 66 strains isolated from Tibetan dairy products. The results show that EPS produntion of the five strains (B55, B62, B30, 7830 and K2) were 110.66, 145.48, 132.78, 122.11 and 111.72 mg·L−1, respectively, and they have a higher DPPH free radical scavenging activity (56.29, 66.43, 62.94, 68.71, 61.87%). Five LAB strains were identified and classified based on screening, purification and 16S rDNA sequences. Molecular characterization based on partial sequence 16S rDNA homology confirmed the initial identification as Lactobacillus fermentum (B55, B62), Lactobacillus plantarum (7830), Pediococcus acidilactici (B30) and Lactobacillus helveticus (K2).

Comparative Genomics of Streptococcus thermophilus Support Important Traits Concerning the Evolution, Biology and Technological Properties of the Species

Streptococcus thermophilus is a major starter for the dairy industry with great economic importance. In this study we analyzed 23 fully sequenced genomes of S. thermophilus to highlight novel aspects of the evolution, biology and technological properties of this species. Pan/core genome analysis revealed that the species has an important number of conserved genes and that the pan genome is probably going to be closed soon. According to whole genome phylogeny and average nucleotide identity (ANI) analysis, most S. thermophilus strains were grouped in two major clusters (i.e., clusters A and B). More specifically, cluster A includes strains with chromosomes above 1.83 Mbp, while cluster B includes chromosomes below this threshold. This observation suggests that strains belonging to the two clusters may be differentiated by gene gain or gene loss events. Furthermore, certain strains of cluster A could be further subdivided in subgroups, i.e., subgroup I (ASCC 1275, DGCC 7710, KLDS SM, MN-BM-A02, and ND07), II (MN-BM-A01 and MN-ZLW-002), III (LMD-9 and SMQ-301), and IV (APC151 and ND03). In cluster B certain strains formed one distinct subgroup, i.e., subgroup I (CNRZ1066, CS8, EPS, and S9). Clusters and subgroups observed for S. thermophilus indicate the existence of lineages within the species, an observation which was further supported to a variable degree by the distribution and/or the architecture of several genomic traits. These would include exopolysaccharide (EPS) gene clusters, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs)-CRISPR associated (Cas) systems, as well as restriction-modification (R-M) systems and genomic islands (GIs). Of note, the histidine biosynthetic cluster was found present in all cluster A strains (plus strain NCTC12958^T) but was absent from all strains in cluster B. Other loci related to lactose/galactose catabolism and urea metabolism, aminopeptidases, the majority of amino acid and peptide transporters, as well as amino acid biosynthetic pathways were found to be conserved in all strains suggesting their central role for the species. Our study highlights the necessity of sequencing and analyzing more S. thermophilus complete genomes to further elucidate important aspects of strain diversity within this starter culture that may be related to its application in the dairy industry.

Comparison of the Effects of the Alcalase-Hydrolysates of Caseinate, and of Fish and Bovine Gelatins on the Acidification and Textural Features of Set-Style Skimmed Yogurt-Type Products

Commercial caseinate and two gelatins from bovine and fish skin were hydrolyzed by alcalase, and used at 2 g/kg in skimmed bovine milk that was then fermented with a commercial direct vat set starter, to clarify different effects of these hydrolysates on acidification and textural attributes of set-style yogurt samples. Compared with the fermentation of the yogurt sample without hydrolysate addition, the two gelatin hydrolysates in the yogurt samples endowed lower titratable acidity but higher pH values and thus delayed yogurt fermentation, while the caseinate hydrolysate showed an effect opposite to the two gelatin hydrolysates. The two gelatin hydrolysates induced worse quality attributes for the resultant yogurt samples, including higher syneresis extent, smaller hysteresis loop areas, and lower values in these textural indices like hardness, adhesiveness, apparent viscosity, elastic and viscous moduli. However, the caseinate hydrolysate led to improved quality attributes. Moreover, bovine gelatin hydrolysate always had a greater negative effect than fish gelatin hydrolysate on yogurt acidification and texture. It is concluded that these gelatin hydrolysates could confer the yogurt with intended bio-activities of gelatin hydrolysates but negatively impact yogurt acidification and texture, while the caseinate hydrolysate might be helpful for yogurt processing by shortening fermentation time and improving yogurt texture.

Functional Genomic Analyses of Exopolysaccharide-Producing Streptococcus thermophilus ASCC 1275 in Response to Milk Fermentation Conditions

Exopolysaccharide (EPS) produced from dairy bacteria improves texture and functionalities of fermented dairy foods. Our previous study showed improved EPS production from Streptococcus thermophilus ASCC1275 (ST1275) by simple alteration of fermentation conditions such as pH decrease (pH 6.5 → pH 5.5), temperature increase (37°C → 40°C) and/or whey protein isolate (WPI) supplementation. The iTRAQ-based proteomics in combination with transcriptomics were applied to understand cellular protein expression in ST1275 in response to above shifts during milk fermentation. The pH decrease induced the most differentially expressed proteins (DEPs) that are involved in cellular metabolic responses including glutamate catabolism, arginine biosynthesis, cysteine catabolism, purine metabolism, lactose uptake, and fatty acid biosynthesis. Temperature increase and WPI supplementation did not induce much changes in global protein express profiles of ST1275 between comparisons of pH 5.5 conditions. Comparative proteomic analyses from pairwise comparisons demonstrated enhanced glutamate catabolism and purine metabolism under pH 5.5 conditions (Cd2, Cd3, and Cd4) compared to that of pH 6.5 condition (Cd1). Concordance analysis for differential expressed genes (DEGs) and DEPs highlighted down-regulated glutamate catabolism and up-regulated arginine biosynthesis in pH 5.5 conditions. Down regulation of glutamate catabolism was also confirmed by pathway enrichment analysis. Down-regulation of EpsB involved in EPS assembly was observed at both mRNA and protein level in pH 5.5 conditions compared to that in pH 6.5 condition. Medium pH decreased to mild acidic level induced cellular changes associated with glutamate catabolism, arginine biosynthesis and regulation of EPS assembly in ST1275.

Fermented soymilk and soy and cow milk mixture, supplemented with orange peel fiber or Tremella flava fermented powder as prebiotics for high exopolysaccharide-producing Lactobacillus pentosus SLC 13

BACKGROUND

A high exopolysaccharide-producing Lactobacillus pentosus SLC 13 strain was isolated from mustard pickles and showed the characteristics of a probiotic. Orange peel fiber powder (OPFP) and Tremella flava fermented powder (TFP) were shown to be potential prebiotics for L. pentosus SLC 13. The present study aimed to further develop new symbiotic fermented lactic acid beverages using SLC 13 with different proportions of cow milk and soymilk as food substrates, as well as with OPFP or TFP as prebiotics.

RESULTS

Acidification rate (soymilk groups, 3.02-4.37 mU min^-1 ; soymilk/milk mixture groups, 1.33-2.84 mU min^-1 ) and fermentation time (soymilk groups, 7.09-9.25 h; soymilk/milk mixture groups, 12.51-27.34 h) indicated that soymilk represents a suitable substrate for SLC 13-mediated fermentation. Moreover, OPFP and TFP induced a higher exopolysaccharide production of SLC 13 and a higher water holding capacity of fermented beverages. Sensory evaluations suggested that soymilk groups fermented with 10 g kg^-1 OPFP (SF-1.0P) and that with 5 g kg^-1 TFP (SF-0.5T) and also soymilk/milk mixture groups fermented with 5 g kg^-1 OPFP (HSMF-0.5P) and that with 10 g kg^-1 TFP (HSMF-1.0T) represent potential fermented drinks. Additionally, SF-1.0P and SF-0.5T products could be preserved for at least 21 days at 4 °C, with high viable cell counts (> 8.8 log₁₀ CFU mL^-1 ) and water holding capacity.

CONCLUSION

In the present study, we developed SF-1.0P and SF-0.5T products as a new symbiotic fermented lactic acid beverages. However, in the future, consumer acceptability could be improved by properly regulating the ratio of sugar to acid or seasoning. © 2019 Society of Chemical Industry.

Clustering of Streptococcus thermophilus Strains to Establish a Relation between Exopolysaccharide Characteristics and Gel Properties of Acidified Milk

In situ produced extracellular polysaccharides (EPS) from lactic acid bacteria are generally known to affect the texture of fermented dairy products; however, the interplay between EPS and product properties is still poorly understood. The aim of this study was to establish a relationship between concentration and properties of EPS, and gel formation of milk analysed by noninvasive Multispeckle Diffusing Wave Spectroscopy. Twenty Streptococcus thermophilus strains were classified with respect to EPS concentration (8-126 mg GE/kg) and ropiness (thread length: 15-80 mm). Five groups identified by cluster analysis demonstrate the high strain-to-strain variability even within one species of lactic acid bacteria. Results from acidification and gelation experiments averaged per cluster indicate that fermentation time and gel stiffness is higher for strains that produce ropy EPS. A further increase in gel stiffness was detected for strains that also produced cell-bound EPS, which underlines the importance of both ropy and cell-bound EPS for improving acid gel properties. The results may be helpful for a proper selection of EPS-producing starter cultures.