The problem of flow-induced crystallization (FIC) of polymer melts is addressed via a microrheological approach. In particular, the Doi−Edwards model with the so-called independent alignment approximation (DE−IAA) is used to calculate the flow-induced change of free energy. Subsequently, the crystallization induction time, i.e., the nucleation characteristic time, is calculated in isothermal steady shear and uniaxial elongational flows. Asymptotic, analytical expressions for the induction time are also derived in the limit of low and high Deborah number (the product of the deformation rate and the polymer relaxation time). The DE−IAA model is found to give more realistic predictions than those of simpler, dumbbell-like models already proposed in the literature. When compared to existing FIC experimental data in shear flow, good quantitative agreement is found with the polymer relaxation time as the only adjustable parameter of the model.

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Using rheological techniques, we investigate the evolution of the microstructure evolution during the early stages of quiescent crystallization of poly(1-butene). In performing the measurements, use is made of an innovative experimental protocol, called “inverse quenching”, which allows stopping the crystallization process and producing a stable biphasic (crystalline/amorphous) system. In this way, very low frequency measurements at fixed degrees of crystallization are made possible. We find that crystallization, evidenced as a liquid-to-solid transition (LST) under isothermal conditions, with characteristics of critical gel behavior, takes place at surprisingly low degrees of crystallinity (below 1.5%). The critical gel properties, which are found to depend on both crystallization temperature and molecular weight, can be reduced to a single master curve when the gel strength is plotted as a function of the relaxation exponent. More importantly, the LST is preceded by the development of a long relaxation process. This latter process, although not fully understood, brings analogies to the slow dynamics observed in hybrid colloid−polymer systems (block copolymer micelles or multiarm star polymers) as well as the recently suggested presence of dormant nuclei. It is clear, however, that the connectivity among crystallites, apparently via the amorphous segments, plays a key role in this new process.

Aims: The microbial community of different types of unripened Pasta Filata cheese was investigated by culture-independent methods with the aim of rapidly achieving knowledge about cheese microbiota and discriminating traditional and industrial cheeses. Methods and Results: The microbial DNA extracted directly from the samples was used as a template in PCR experiments to amplify the 16S±23S rDNA spacer region and the V3 region of the 16S rDNA. Conventional electrophoresis of the ampli®ed spacers allowed known classes of these DNA fragments belonging to genera and species of lactic acid bacteria to be distinguished. Denaturing gradient gel electrophoresis analysis of V3 amplicons was supported by reference cultures of LAB used as markers. Conclusions: Both molecular approaches furnished the expected information about microbial diversity and were quite valid for discriminating industrial, semi-artisanal or traditional cheeses, characterized by increasingly complex DNA pro®les. Signi®cance and Impact of the Study 1 : Both methods could be used for legal purposes when products obtained through prescribed manufacturing regulations are to be analysed.

The composition of 16 natural whey cultures from 3 different Mozzarella chee se plants was investigated. They consisted mainly of lactic acid bacteria, coliform bacteria and yeasts. Micrococci, butyric and propionic acid bacteria only occurred occasionally. Lactobacillus lactis was the most common species of Lactobacillus while Streptococcus lactis and Str. thermophilus were the most common species of Streptococcus. Enteropathogenic Escherichia coli were always present. Different species of Leuconostoc and yeasts belonging to the genera Candida, Kluyveromyces, Debaryomyces and Brettanomyces were also isolated. Acidifying and proteolytic capacity of the strains showed that these activities were widely affected by tempe rature and type of milk (cow or waterbuffalo milk). Streptococci were the most active acid pro du cers at the cheese vat temperature (37 oC).

Streptococci from different collections and dairy materials were characterized by conventional and molecular methods. After amplification of the 16S-23S rDNA spacer region, all the strains referable to the genus Streptococcus exhibited a single polymerase chain reaction (PCR) product, allowing their differentiation from enterococci. Cleaving this PCR product with Hae III, two different restriction patterns could be observed, allowing Streptococcus salivarius DSM 20560T, Strep. thermophilus NCDO 822 and two strains of Streptococcus spp. to be gathered in one group and all the other strains in another. In order to achieve strain typing, all the cultures were investigated by random amplified polymorphic DNA (RAPD)-PCR analysis employing two selected primers. The results were treated by cluster analysis, appearing significantly consistent with both the taxonomic position and the origin of the strains. Pulsed-field gel electrophoresis (PFGE) of Sma I digests of the genomic DNA from 11 representative strains with decreasing levels of RAPD similarity allowed their diversity to be confirmed, even though RAPD-PCR proved to be less discriminating than PFGE analysis. The results are discussed with reference to the capability of the analytical procedures used to aid both identification and strain typing of streptococci, as well as the taxonomic structure of the species Strep. thermophilus.

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