Effect of calcium on the physical properties of stirred probiotic yogurt.

The effect of calcium on the viscosity, firmness, and smoothness, as determined by extent of nodulation, of stirred probiotic yogurt produced by bacterial fermentation was investigated. Standardized milk for yogurt manufacture was prepared, and calcium was added or removed from the system. Calcium was added as Ca(2+) in the form of CaCl(2) (up to 13.6 mM) or nonionic calcium as Gadocal-K (calcium potassium citrate; up to 49.8 mM). Calcium was removed by chelating with sodium citrate (up to 16 mM) or by cation exchange with Amberlite IR-120 plus (sodium form) resin (up to 10 g/L). Calcium chloride and sodium citrate were added either before or after heat treatment of milk, and nonionic calcium was added before heat treatment. Calcium removal by ion exchange was performed before heat treatment. Neither Ca(2+) addition nor removal by chelation with citrate resulted in stirred yogurt with viscosity, firmness, and smoothness superior to those of the control yogurt, whereas addition of 49.8 mM nonionic calcium and removal of calcium (5.6 mM or ~10% of total calcium) by cation exchange improved the firmness and viscosity without affecting yogurt smoothness. The study identified Gadocal-K as a possible source of calcium fortification of stirred yogurt without loss of texture.

Preliminary characterization of wild lactic acid bacteria and their abilities to produce flavour compounds in ripened model cheese system.

AIMS: The aim of this work was to preliminary characterize wild lactic acid bacteria (LAB), previously isolated during artisanal Pecorino Siciliano (PS) cheese-making for technological and flavour formation abilities in a model cheese system. METHODS AND RESULTS: Twelve LAB were studied for the ability to grow at 10 and 45 degrees C, to coagulate and acidify both reconstituted skim milk and ewe's milk. Moreover, the capacity of the strains to generate aroma compounds was evaluated in a model cheese system at 30- and 60-day ripening. Flavour compounds were screened by sensory analysis and throughout gas chromatography (GC)-mass spectrometry (MS). Most of the strains were able to grow both at 10 and 45 degrees C and exhibited high ability to acidify and coagulate ewes' milk. Sensory evaluation revealed that the wild strains produced more significant flavour attributes than commercial strains in the 60-day-old model cheese system. GC-MS data confirmed the results of sensory evaluations and showed the ability of wild lactobacilli to generate key volatile compounds. Particularly, three wild lactobacilli strains, belonging to Lactobacillus casei, Lb. rhamnosus and Lb. plantarum species, generated both in 60- and 30-day-old model cheeses system, the 3-methyl butan(al)(ol) compound, which is associated with fruity taste. CONCLUSIONS: The present work preliminarily demonstrated that the technological and flavour formation abilities of the wild strains are strain-specific and that wild lactobacilli, which produced key flavour compounds during ripening, could be used as tailor-made starters. SIGNIFICANCE AND IMPACT OF THE STUDY: This study reports the technological characterization and flavour formation ability of wild LAB strains isolated from artisanal Pecorino cheese and highlights that the catabolic activities were highly strain dependent. Hence, wild lactobacilli could be selected as tailor-made starter cultures for the PS cheese manufacture.

Bacterial population in traditional sourdough evaluated by molecular methods.

AIMS: To study the microbial communities in artisanal sourdoughs, manufactured by traditional procedure in different areas of Sicily, and to evaluate the lactic acid bacteria (LAB) population by classical and culture-independent approaches. METHODS AND RESULTS: Forty-five LAB isolates were identified both by phenotypic and molecular methods. The restriction fragment length polymorphism and 16S ribosomal DNA gene sequencing gave evidence of a variety of species with the dominance of Lactobacillus sanfranciscensis and Lactobacillus pentosus, in all sourdoughs tested. Culture-independent method, such as denaturing gradient gel electrophoresis (DGGE) of the V6-V8 regions of the 16S rDNA, was applied for microbial community fingerprint. The DGGE profiles revealed the dominance of L. sanfranciscensis species. In addition, Lactobacillus-specific primers were used to amplify the V1-V3 regions of the 16S rDNA. DGGE profiles flourished the dominance of L. sanfranciscensis and Lactobacillus fermentum in the traditional sourdoughs, and revealed that the closely related species Lactobacillus kimchii and Lactobacillus alimentarius were not discriminated. CONCLUSIONS: Lactobacillus-specific PCR-DGGE analysis is a rapid tool for rapid detection of Lactobacillus species in artisanal sourdough. SIGNIFICANCE AND IMPACT OF THE STUDY: This study reports a characterization of Lactobacillus isolates from artisanal sourdoughs and highlights the value of DGGE approach to detect uncultivable Lactobacillus species.

Identification of Pichia anomala isolated from yoghurt by RFLP of the ITS region.

Several packs of swollen retailed plain and flavoured yoghurt were examined. The most commonly found species was Pichia anomala, identified both by physiological tests and RFLP analysis of the rDNA internal transcribed spacer (ITS) region. The isolated strains did not ferment lactose and were positive for galactose fermentation, confirming the hypothesis that galactose-fermenting yeast could be the cause of spoilage in yoghurt.

[IgM ISAGA test in the diagnosis of acute acquired Toxoplasma infections]. / Il test IgM ISAGA nella diagnosi di infezione toxoplasmica acuta acquista.

An immunoglobulin M immunosorbent agglutination assay (IgM ISAGA) was tested in 1804 outpatients' samples. The test was negative in all 1091 sera from individual negative in the total indirect immunofluorescence antibody (IFA tot) test and in the passive hemagglutination (HA) test and in 15 sera with inconclusive results in these two tests. The 698 sera positive in the IFA tot and HA tests were also tested with direct IgM enzyme-linked immunosorbent assay (IgM ELISA). The 74 sera positive in the IgM ISAGA and/or IgM ELISA were also tested in the IgM immunofluorescent (IgM IFA) test. These sera belong to 42 individuals, 26 of whom were followed for previous positive results in the IgM ELISA test. 51 samples (68.9%) were found positive in both IgM ISAGA and IgM ELISA tests. Only 13 (25.5%) of these 51 samples were found positive in the IgM IFA. 9 samples (12.2%) were positive only in the IgM ISAGA test. Conversely another 9 samples (12.2%) were positive only in the IgM ELISA test, performed on serum as well as on chromatographic IgM fraction. Finally five samples (6.7%) yielded false positive results in the IgM ELISA test, and three of them were found false positive also in the IgM IFA test. All these five samples in fact were found negative on IgM chromatographic fraction in both tests. In conclusion, IgM ISAGA appears to be more specific than direct IgM ELISA or IgM IFA test for the detection of Toxoplasma gondii IgM. Sensitivity of IgM ISAGA test seems to be as good as in the direct IgM ELISA and better than in the IgM IFA test for the diagnosis of acute acquired toxoplasma infection.