1,720,997 research outputs found
Use of dairy and non-dairy Lactobacillus plantarum, Lactobacillus paraplantarum and Lactobacillus pentosus strains as adjuncts in cheddar cheese
Full text linkLactobacilli have been used as adjunct cultures in the manufacture of different cheeses with the objective of accelerating ripening and/or improving cheese quality, but no studies have been conducted with strains from non-dairy origins. A miniature cheddar-type cheese model was used to screen ten dairy and non-dairy Lactobacillus plantarum, Lactobacillus paraplantarum and Lactobacillus pentosus strains for their performances as adjuncts in cheese manufacture. All strains were able to grow and survive in the cheese environment and produced only minor, although statistically significant, changes in gross cheese composition. Adjuncts affected secondary proteolysis causing differences in the levels of free amino groups, total free amino acids and reversed-phase HPLC (RP-HPLC) profiles of pH 4.6-soluble extract. Three strains were selected on the basis of differences in proteolysis pattern and used in a pilot-plant production of cheddar cheese, which was ripened for 180 days. The results confirmed that use of L. plantarum adjuncts significantly affected secondary proteolysis as measured by free amino acid production with minor impact on gross composition and primary starter performance, but the impact on RP- HPLC profiles of pH 4.6-soluble extracts was not statistically significant. The use of a strain originally isolated from olive brine fermentation, L. plantarum P1.5, resulted in significantly improved preference scores over the control
Partial purification and characterization of an X-prolyl dipeptidyl aminopeptidase from Lactobacillus sanfranciscensis CB1
No full textAn X-prolyldipeptidylaminopeptidase (PepX) from LactobacillussanfranciscensisCB1, a key sourdough lactic acid bacterium, was partially purified by five chromatographic steps. As estimated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration, the enzyme appeared to be a 49.2–56 kDa monomer. Optimal activity occurred at pH 6.0 and 30 °C, with Km of 0.6 mM and Vmax of 99.6 nmol mg−1 min−1. The D value, calculated at 45 °C, was ∼5.46 s. The enzyme hydrolyzed (almost exclusively) substrates with a X-Pro N-terminal sequence. It did not possess prolidase, aminopeptidase or endopeptidase activities. No hydrolysis of the Pro-rich 33-mer epitope (a potent inducer of gut-derived human T-cell lines in celiac patients) was found when it was treated with PepX alone. When the general aminopeptidase type N was combined with PepX, the hydrolysis of 33-mer peptide (0.2 mM) was complete after 24 h of incubation at 30 °C. Leucine and glutamine residues were liberated from the Pro-rich 33-mer peptide by aminopeptidase type N, thus favouring the subsequent PepX activity. PepX was inactivated by p-chloromercuribenzoate, 3,4-dichloroisocoumarin and phenanthroline which exerted a competitive mode of inhibition. Among divalent cations, only Zn2+, Hg2+ and Mn2+ markedly decreased the enzyme activity. Quadratic response surface methodology was used to study the individual and interactive effects of temperature, pH and NaCl on the PepX activity. The enzyme maintained considerable activity under the environmental conditions which characterize the sourdough fermentation
Acid production, proteolysis, autolytic and inhibitory properties of lactic acid bacteria isolated from pasta-filata cheeses: a multivariate screening study.
No full textPurification and characterization of an intracellular family 3b-glucosidase from Lactobacillus sanfranciscensis CB1
No full textRP-HPLC peptide profiling of cheese extracts: a study of sources of variation, repeatability and reproducibility
No full textPeptide profiling of cheese extracts by RP-HPLC is widely used to study cheese quality and authenticity. Repeatability, reproducibility and the contribution of differences in sample/treatment, extraction, and the effect of the chromatographic run was studied. Chromatograms (108) of pH 4.6-soluble extracts from 180 d Cheddar cheeses were used to evaluate the precision of the method and to quantify the effect of treatment and replicate cheese trial. Repeatability and reproducibility coefficient of variations of peaks/RT classes varied widely and no clear correlation was found between peak size and reproducibility. ANOVA of Principal Component scores identified significant differences among cheeses and a trial effect. Partial Least Square Discriminant Analysis identified variables related to cheese treatment. Statistical process control methods were used to study the variability of replicate injections over the life of a single column showing the discriminatory power of RP-HPLC and gaving possibilities to improve both process control and process optimizatio
Contribution of proteolytic activity associated with somatic cells in milk to cheese ripening
No full textThe effect of proteolytic enzymes from somatic cells on cheese quality was studied. In preliminary experiments, milk and two
sodium caseinate systems (pH 6.5 and pH 5.2, the latter in the presence of 5% NaCl) were used as substrates to investigate the proteolytic activity of somatic cells recovered from mastitic milk. Urea-polyacrylamide gel electrophoretograms of hydrolysates suggested that somatic cell extracts contributed directly to proteolysis both in buffer and in milk, but that such activity was reduced by batch pasteurisation (63 1C for 30 min). Sodium caseinate was readily hydrolysed by somatic cell extracts; hydrolysis of as1-casein was greater at pH 5.2 and increased with level of somatic cells, suggesting that somatic cells contain proteolytic enzymes which are more active at acidic pH values. Subsequently, miniature Cheddar-type cheeses were made from batches of milk to which somatic cells were added (at levels of levels of 3x105 or 6x105 cellsmL_1), either before or after pasteurisation. Proteolysis during ripening of cheese (as measured by levels of pH 4.6-soluble nitrogen) increased with somatic cell addition, although this effect was reduced by pasteurisation after cell addition. Somatic cells may also have directly influenced cheese moisture content, which has been established as a principal indicator of quality of Cheddar-type cheese. Proteolytic enzymes of somatic cells from milk were shown to contribute directly to proteolysis in milk and cheese
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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