Acidification Properties Research Articles

Isolation and identification of high viscosity-producing lactic acid bacteria from a traditional fermented milk in Xinjiang and its role in fermentation process

Forty-four lactic acid bacteria (LAB) isolated from traditional Sayram ropy fermented milk (SRFM) in southern Xinjiang of China. Further two strains were selected based on their high viscosity-producing activity. Based on the API 50 CHL strip and 16S rDNA sequence analysis, strain MB 2-1 was a Gram-positive, rod-shaped Lactobacillus helveticus and strain MB 5-1 was identified as Streptococcus thermophilus. Both the two LAB strains were grown in the milk fermentations for pure and mixed cultures and were evaluated for their growth, acidification properties, EPS production, and ability to increase the apparent viscosity of fermented milk, respectively. L. helveticus MB 2-1 displayed a high increasing in viable cell counts and the acidifying capacity in pure cultures, whereas the relatively high EPS production and viscosity-producing capacity detected in pure culture with S. thermophilus MB 5-1 as starter culture. In addition, the mixed culture of the two strains showed a higher cell growth, EPS production, and high viscosity-producing capacity at 37 °C. Values of apparent viscosity were 4.03- and 2.41-fold higher in mixed culture than for pure cultures of L. helveticus MB 2-1 and S. thermophilus MB 5-1, respectively. There was a positive correlation between the viscosity and high molecular weight EPS production with pure and mixed cultures. Our data showed two strains combination, with high viscosity-producing and acidifying capacity, can be used in mixed cultures for the manufacture of fermented milk with improved functional properties.

Screening human intestinal Bifidobacterium strains for growth, acidification, EPS production and viscosity potential in low-fat milk

Bifidobacterium strains of human origin were screened for their ability to grow in milk and produce exopolysaccharides (EPS). Bifidobacterium strains were grown in low-fat UHT milk and were evaluated for their growth, acidification properties, EPS production and ability to increase the viscosity of fermented milk. The strains that grew well in milk were strains of Bifidobacterium breve and Bifidobacterium longum and B. longum subsp. longum. Among the 22 strains, EPS was produced by Bifidobacterium bifidum ALM 35, B. breve NCIMB 8807 (UCC 2003), B. longum subsp. infantis CCUG 52486 and Bifidobacterium infantis NCIMB 702205 at concentrations ranging from 25 to 140 mg L −1. The molecular mass and the composition varied considerably, depending on the strain. Analysis of the correlation between the apparent viscosity of the fermented milk and pH indicated that the EPS produced during the acidification of milk possibly contributed to the viscosity of the milk products.

Diversity of Lactobacillus sakei strains investigated by phenotypic and genotypic methods

The diversity of 10 strains of Lactobacillus sakei, a commercially important species of lactobacilli, was characterized by studying food isolates. Growth characteristics varied among the strains when examined after growth in a complex medium and a defined medium with either glucose or ribose. A commercial starter culture strain showed the fastest growth rates and high biomass formation on all media, while two of the strains hardly grew on ribose. Based on acidification properties in a meat model, some of the strains had the ability to compete with the indigenous microbiota of the meat batter in addition to being fast acid producers. Carbohydrate-fermentation abilities revealed a relatively wide variation, clustering the strains into two phenotypic groups. The isolates were analyzed using different genetic fingerprinting techniques, demonstrating a distinction between two genetic groups, a grouping consistent with previous studies dealing with L. sakei strains. Comparative genome hybridization (CGH) was introduced for clustering the strains and the same division into two genetic groups was observed. Chromosomal sizes of the strains were estimated by pulsed field gel electrophoresis (PFGE) and were found to vary from 1884 to 2175 kb. The genetic groups did not correlate with the clustering obtained with carbohydrate-fermenting abilities or with chromosomal sizes.

Bio-hydrogen production from food waste and sewage sludge in the presence of aged refuse excavated from refuse landfill

In this work, the aged refuse (AR) excavated from a typical refuse landfill with over 10 years of placement was used for the enhancement of bio-hydrogen production from food wastes. Firstly, the food wastes taken from a university dining hall were inoculated with sewage sludge (SL) pre-treated by 15 min heating at 80 °C. It was found that below 0.4% of hydrogen concentration could be detected in the biogas produced due to its severe acidification properties. However, the addition of AR (50% in weight) can considerably increase the hydrogen concentration in the biogas to over 26.6% with pH ascending from 4.36 to 5.81, in comparison with 4–6% using activated carbon as additive with pH descending from 4.43 to 3.91. Meanwhile, it was also found that the hydrogen content in the biogas decreased drastically to 3.3% when the AR was sterilized by heating at 160 °C for 2 h and then used as additive for bio-hydrogen production from food wastes, indicating that the AR may chiefly function as a microbial inoculum instead of a porous material like activated carbon. Statistical analysis showed that the ultimate hydrogen production potential ( H p), hydrogen production rate ( R max) and lag-phase time ( λ) were found to be 193.85 mL/gVS, 94.35 mL/(h gVS), 15.28 h, respectively, in the presence of 50% AR, and the optimal mixing ratios were 100:50 (wet weight) for food wastes to AR and 100:30 (dry weight) for food wastes to sewage SL, respectively.

Critical Role of Electrostatic Interactions of Amino Acids at the Cytoplasmic Region of Helices 3 and 6 in Rhodopsin Conformational Properties and Activation

The cytoplasmic sides of transmembrane helices 3 and 6 of G-protein-coupled receptors are connected by a network of ionic interactions that play an important role in maintaining its inactive conformation. To investigate the role of such a network in rhodopsin structure and function, we have constructed single mutants at position 134 in helix 3 and at positions 247 and 251 in helix 6, as well as combinations of these to obtain double mutants involving the two helices. These mutants have been expressed in COS-1 cells, immunopurified using the rho-1D4 antibody, and studied by UV-visible spectrophotometry. Most of the single mutations did not affect chromophore formation, but double mutants, especially those involving the T251K mutant, resulted in low yield of protein and impaired 11-cis-retinal binding. Single mutants E134Q, E247Q, and E247A showed the ability to activate transducin in the dark, and E134Q and E247A enhanced activation upon illumination, with regard to wild-type rhodopsin. Mutations E247A and T251A (in E134Q/E247A and E134Q/T251A double mutants) resulted in enhanced activation compared with the single E134Q mutant in the dark. A role for Thr(251) in this network is proposed for the first time in rhodopsin. As a result of these mutations, alterations in the hydrogen bond interactions between the amino acid side chains at the cytoplasmic region of transmembrane helices 3 and 6 have been observed using molecular dynamics simulations. Our combined experimental and modeling results provide new insights into the details of the structural determinants of the conformational change ensuing photoactivation of rhodopsin.

Conversion of Lactococcus lactis cell envelope proteinase specificity by partial allele exchange

To determine whether conversion of lactocepin substrate binding regions by gene replacement can alter lactocepin specificity in Lactococcus lactis starter bacteria without affecting other important strain properties. We utilized two-step gene replacement to convert substrate-binding determinants in the L. lactis prtP genes encoding group h (bitter) lactocepin in two industrial strains into the corresponding group b (nonbitter) variant. Analysis of lactocepin activity toward alpha(s1)-casein (f 1-23) by reversed-phase high-pressure liquid chromatography demonstrated enzyme specificity among isogenic derivatives had been altered in a manner that was consistent with predicted amino acid substitutions in substrate binding regions. Milk acidification properties of some mutants were not statistically different (P > 0.05) from wild-type parent strains, and strain propensity for autolysis was also not significantly (P > 0.05) changed. Conversion of lactocepin substrate binding regions by allele exchange can effectively alter lactocepin specificity in industrial strains of L. lactis without significantly affecting other important strain properties. Methodology outlined in this study can be used to alter lactocepin specificity in commercial starter cultures with a propensity for bitter flavour defect, and prtP derivatives developed by this approach should be suitable for commercial application.

The Influence of Starter Cultures on Barley Contaminated with Fusarium Culmorum TMW 4.0754

This study investigates the effects of lactic acid bacteria (LAB) added concomitantly to barley infected with fungal spores or mycelia of Fusarium culmorum TMW 4.0754. The trials were performed in a micromalting plant simulating an industrial malting program. Malt samples were compared with those of nonacidified barley, disinfected nonacidified barley, chemically acidified barley, and barley with additional modified DeMan-Rogosa-Sharpe 4 medium. All control samples had fungal spores and fungal mycelia added. Bacterial cultures were chosen as a result of their enzymatic (proteolytic/amylolytic) activity level or their good acidification properties. The effects of the LAB and Fusarium-infected malts on wort characteristics were investigated. Characteristics such as pH, extract, color, viscosity, total soluble nitrogen (TSN), free amino nitrogen (FAN), apparent fermentability, and lautering performance of the resultant worts were determined. Results showed that spores of F. culmorum TMW 4.0754 do not affect the quality of malt or wort. The quality of wort was reduced when mycelia of F. culmorum were applied in the presence of LAB or chemical lactic acid leading to slower filtration rates, lower extract, fermentability, TSN, and FAN yields along with higher viscosity levels. These effects seemed to depend mainly on the presence of mycelia together with the content of lactic acid present.

Study of the behaviour of Lactobacillus plantarum and Leuconostoc starters during a complete wheat sourdough breadmaking process

The acidification properties, metabolic activity and technological performance of four individual Lactobacillus plantarum or Leuconostoc freeze-dried starters were investigated during a complete wheat sourdough breadmaking process including 0.2 g/100 g baker's yeast. Microbiological contents (lactic acid bacteria and yeasts), acidification characteristics (pH and total titratable acidity), soluble carbohydrates (maltose, glucose and fructose) and fermentative end-products (lactic and acetic acids, ethanol) contents were evaluated during both sourdough and corresponding bread dough fermentation. Biochemical and technological analysis of the resulting bread products are also presented. Some differences among strains in acidification properties and soluble carbohydrates availability were outlined both in sourdough and bread dough. Each individual Leuconostoc or Lb. plantarum starter was able to produce a characteristic fermentation and was found to ensure the production of breads with overall satisfactory acceptance.

RESPONSE

To the Editor: We appreciate the comments from Dr. Parmar regarding his concern over the use of urine alkalinization [e.g., tricitrates (oral Polycitra)] for patients receiving combination therapy with both the ketogenic diet and carbonic anhydrase inhibitors. Although theoretically the acidification of the diet and alkalinization of carbonic anhydrase inhibitors could counteract each other, they do not seem to do so clinically. Should this have been the case, one would have expected a decreased risk, lower than even the 2–4% reported for topiramate or zonisamide alone. As mentioned in our study, we found an almost identical risk of kidney stones with this combination to that with the use of the ketogenic diet alone. We therefore suspect that the acidification properties of the diet are the predominant influence on kidney stone formation. For years, oral polycitrates have been very beneficial in our ketogenic diet patients when this occurs. We acknowledge the lack of data to prove the benefit of polycitrates for combination therapy patients. We hope this will improve. We agree with Dr. Parmar against routinely recommending polycitrate use, because a lack of risk without evidence of gain is not a valid reason to start a daily medication. In our discussion, however, we did not recommend its use for these patients routinely, but only for those with higher risk for stones (either a family history of kidney stones or prior urologic abnormalities). In these patients, we strongly support the prophylactic use of oral polycitrates when combination therapy is started.

Modelling of rheological, microbiological and acidification properties of a fermented milk product containing a probiotic strain of Lactobacillus paracasei

Abstract The simultaneous effect of fermentation temperature (FT, 36.7–43.4°C), milk total solid level (TS, 11.3–14.7%, w/v) and total inoculum concentration (TI, 2.16–3.84 v/v) on the acidification process and the rheological properties of fermented milk products with Lactobacillus paracasei ssp paracasei B117, Lactobacillus delbrueckii ssp bulgaricus Y 6.15 and Streptococcus thermophilus Y 4.10 was explored by means of response surface methodology. Maximum storage modulus (G′max), minimum loss tangent (tan δmin), rate of gelation (IE) and onset of gelation were the rheological parameters studied. Maximum acidification rate (Vm), time at which maximum acidification rate was observed (Tm), and time to reach the end of fermentation (Te) characterized the kinetics of acidification, whereas the increase in the number of the three bacteria at the end of fermentation was chosen as the microbiological parameter of the system. The growth/survival of microorganisms and the organic acid profile during cold storage as well as the overall product acceptability by a consumer panel were also assessed. TS strongly affected G′max and tan δmin; high TS resulted in large increase in G′max and decrease in tan δmin. Increasing fermentation temperature gave a decrease in the onset of gelation, Vm, Tm and Te, and an increase in the gelation rate (IE). Under conditions of relatively low FT (37–40°C), high TS (about 14%) and high TI (3–4%), relatively high gelation and low acidification rates were observed, fermentation took a longer time to finish, but the formed gels were firmer, showing higher G′max and lower tan δmin values. Low FT (36–38°C) enabled higher increase in the number of L. paracasei B 117. The probiotic strain showed good compatibility with the S. thermophilus Y 4.10 and L. bulgaricus Y 6.15, and satisfactory levels of all bacteria were found during fermentation and storage at 4°C for 21 days. No major differences in lactic and uric acid contents were seen between the control (probiotic strain-free product) and the probiotic fermented milk, whereas the latter contained slightly higher amounts of citric, pyruvic and orotic acids. Moreover, the probiotic fermented milk was graded by the consumer panel with a similar acceptability score as the control product.

Free‐Flow Electrophoretic Analysis of Endosome Subpopulations of Rat Hepatocytes

Endosomes constitute a functionally, morphologically, and biochemically heterogeneous population of intracellular organelles that play a major role in sorting of incoming ligands, receptors, membrane, and lumenal content. This unit provides protocols for labeling and isolation of endosomes of polarized rat hepatocytes. By application of free-flow zone electrophoresis functional endosomal subcompartments involved in transports to lysosomes and transcytosis are resolved from each other. Methods to analyze the protein composition or acidification properties of these highly purified endosomes are also described.

The production of freeze-dried immobilized cultures of Streptococcus thermophilus and their acidification properties in milk.

The aim of this study was to prepare alginate-immobilized freeze-dried cultures of Streptococcus thermophilus and to compare the acidifying activities of these rehydrated cultures with classical free cell liquid inoculants. Streptococcus thermophilus BT1 grew in alginate beads and the population reached 10(10) cfu g(-1) after 6 h incubation. Re-inoculation of the beads in fresh medium with a further 6 h incubation did not improve the biomass level, but extending the incubation at 42 degrees C to 24 h caused significant death. The rehydrated immobilized cell technology (ICT) starter contained 13% free cells. In acidifying activity tests, the ICT culture had a similar acidification curve to that of a classical milk-grown free cell culture, except that it reached lower final pH values. Although the differences between the ICT and liquid cultures were not important, there were significant effects of inoculation level on lag time, maximum acidification rate and on the pH and time at which the acidification rate was at its highest.

Acidification of Grape Musts bySaccharomyces cerevisiaeWine Yeast Strains Genetically Engineered to Produce Lactic Acid

Engineered <i>Saccharomyces cerevisiae</i> strains over-expressing a bacterial lacticodehydrogenase (LDH) have been described to perform mixed lactic acid-alcoholic fermentation under laboratory conditions The acidification properties of these strains might be of great value for fermented beverages and especially in enology to solve problems of insufficient acidity in hot regions. To assess the relevance of this model during alcoholic fermentation under enological conditions, eight wine strains expressing the LDH gene on a multicopy plasmid were constructed. The level of L(+) lactic acid produced and the resulting acidification were shown to be influenced by the strain and to a greater extent by the grape must composition. Wines obtained by lactic acid-alcoholic fermentation of seven grape musts contained 2.6 to 8.6 g/L of L(+) lactic acid. In comparison with classic alcoholic fermentation, lactic acid-alcoholic fermentation resulted in a decrease of 0.2 to 0.35 pH units in wines containing 5 to 8 g/L of lactic acid. Two grape musts with moderate or low acidity levels (pH 3.36 and pH 3.75) were acidified effectively (50% increase in total acidity, 0.17 and 0.27 pH unit decrease) by the production of 5 g/L of L(+) lactic acid by an engineered wine yeast strain. A reduction of 0.25 percent (vol/vol) of alcohol was also observed as a result of the diversion of carbon towards L(+) lactic acid. The volatile acidity was unchanged in the wine obtained with the engineered strain compared to the control strain. Despite a slower fermentation rate, the ability to ferment grape musts and the growth characteristics were not affected.

Effect of leavening microflora on pizza dough properties.

Fourteen different starter cultures containing one strain of Saccharomyces cerevisiae with and without individual or combinations of lactic acid bacteria (Lactobacillus plantarum, Lact. sanfrancisco, Enterococcus faecium, Leuconostoc mesenteroides) were employed to investigate the role of leavening microflora on the properties of pizza doughs. Microbiological, chemical and physical characteristics of doughs prepared with the same flour and under the same processing conditions were determined. Leavening times and acidification properties depended on the microbial association used. The proportions of lactic and acetic acid produced by lactic acid bacteria were consistent with the metabolic properties of the strains employed. The bacteria/yeast ratios arising from microbial counts at the end of the leavening process were always lower in comparison to sour- or bread-doughs. The size of the yeast population did not change much, while bacteria showed from one to four duplications. Rheologically, the fermented doughs could only be significantly distinguished from the control dough with regard to the elastic modulus. Principal Component Analysis was applied to the acidimetric data. The scattergram of the two principal components effectively discriminated 13 of the 14 pizza dough types.

Effect of processing conditions on acidification properties of wheat sour doughs

The pH, total titratable acidity (TTA) and lactic and acetic acids production have been investigated for wheat sour doughs with and without yeast addition, inoculated with two strains of Lactobacillus plantarum (B33, B39). To study the effect of flour extraction rate (0.54, 11.11 and 1.68% ash content), dough yield (DY) (160, 200 and 240 of sour dough/100 g flour), and fermentation temperature (25, 30 and 35°C) a response surface regression, factor analysis and K-means clustering analysis were used. • Results from factor analysis point out that the extraction rate of flour governs TTA and acetic acid content; this factor accounts for the 53% of variability of the data. Dough yield is highly correlated with lactic acid content, explaining 27% of the total variance. Finally, temperature explains the remaining 16% of variation, but it is not related to any analytical variable. From K-means clustering analysis, flour extraction rate of 1.68% ash content leads to the highest TTA and acetic acid values, whereas DY of 240 g sour dough/100 g flour gives the greatest lactic acid content, and DY of 160 leads to the lowest levels of TTA and organic acids .

Microbial Sour Doughs Influence Acidification Properties and Breadmaking Potential of Wheat Dough

ABSTRACTBreads from sour doughs were started with Lactobacillis plantarum (L‐73, or B‐39) or Lactobacillus brevis (L‐62)‐, and incorporated at 10, 17.5, or 25%. Lactic and acetic acid production depended on bacterial starter and yeast. Started doughs had longer mixing time, stability, more softening with time; lower resistance to extension; shorter fermentation, less stability, and greater oven rise. Breads had greater volume, lower density, softer crumb and higher slice height. Interactive effects between inoculum and microbial composition of starter were reflected in sensory scores. Adequate sour dough inoculum was lower for heterofermentative strains (10%, L‐62) than for homofermentative strains (17.5%, B‐39; 25%, L‐73), due to deleterious effects on rheological properties.

Microflora and acidification properties of yogurt and yogurt-related products fermented with commercially available starter cultures

Yogurts and yogurt-related milk products were produced using 44 commercially available starter cultures from 8 suppliers. The yogurt starters consisted of the classical yogurt microflora and the yogurt-related cultures containing Lactobacillus acidophilus and/or Bifidobacterium spp. instead of or in addition to the yogurt bacteria. The counts of lactobacilli in the fresh yogurts varied between 5.5 × 10 7 and 6.5 × 10 8 CFU/ml, and the counts of streptococci varied from 3.5 × 10 7 to 1.2 × 10 9 CFU/ml. About 80% of the yogurts had higher counts of cocci than rods. During storage of the products for 2 weeks at 6°C the stability of the microflora differed markedly among the cultures. In the fresh yogurt-related products the L. acidophilus counts ranged from 4.0 × 10 5 to 2.6 × 10 8 CFU/ml; bifidobacteria were found at levels between 4.0 × 10 6 and 2.6 × 10 8 CFU/ml. In most products reduced viable counts of these bacteria were observed after 2 weeks. Titratable acidity increased on average by 22.3% in the yogurts, and by 14.9% in the yogurt-related products during storage. In most products a higher amount of L(+)- than D(−)-lactic acid was found.

Effects of parathyroid hormone and calcium and their interrelationship on urinary acidification in the rat.

1. The influence of thyroparathyroidectomy on renal function and specifically on acid excretion was studied in rats with or without oral supplementation of calcium. 2. Thyroparathyroidectomy caused a significant decrease in glomerular filtration rate, in the urinary/plasma inulin ratio and in overall acid excretion. These changes were not corrected by calcium supplementation. 3. Rates of proximal tubular acidification were studied by means of double-barrelled resin/reference microelectrodes. Acidification half-time was significantly increased in both thyroparathyroidectomized and calcium-supplemented thyroparathyroidectomized rats (8.38 s and 7.40 s, respectively) compared with control rats (5.44 s). 4. When 10(-6) mol/l A23187, a calcium ionophore, was added to the luminal bicarbonate solution, the acidification half-time returned to 3.97 s in the thyroparathyroidectomized rats, whereas no significant changes were detected in the properties of acidification in the control rats. 5. These data show that parathyroid hormone and cellular calcium are important factors involved in proximal tubular H+ secretion, which appears to be largely dependent on a well-defined concentration range of these agents.

Trehalose, a cryoprotectant for Lactobacillus bulgaricus

The cryoprotective effect of trehalose in the freezing-thawing process was assayed in two strains of Lactobacillus bulgaricus. The viability and acidification properties before and after the process were compared. At a concentration of 0.3 M, trehalose was able to preserve the viability and the acidification power. The degree of protection is dependent on the strain and those compounds present in the medium. This effect is more noticeable in water an culture medium than in milk. However, the milk supplied with trehalose has the highest effectiveness.

Acidification properties of lactic acid bacteria in rye sour doughs

The acidification properties of 33 different sour dough bacteria and starter cultures, one spontaneously generated sour dough and one commercial sour dough starter, a ‘Reinzuchtsauer’ from West Germany, were characterized. The bacteria were tested in three different sour dough processes, the Berliner short-sour-process, the Detmolder one-stage-process and the recently developed Lönner one-stage-process. The Lönner one-stage-process showed a number of advantages in comparison with the other processes. The organisms produced their lowest pH-values and their highest acid equivalents in this process. The rates of pH-decrease were also higher as well as the fermentation quotients. Some of the organisms previously isolated from sour doughs, showed very good properties of acidification. Among the homofermentative organisms, Lactobacillus acidophilus, L. alimentarius, L. plantarum and the unidentified organisms Lactobacillus spp. I and f showed the best properties. Among the heterofermentative organisms the best properties were displayed by L. brevis ssp. lindneri I and II and the unidentified Lactobacillus spp. e, g, h, k and n.