Identification of Lactococcus lactis ssp. and Streptococcus thermоphilus virulent bacteriophages isolated in dairy processing plants of Ukraine. Methods. The morphology of the viral particles was studied by transmission electron microscopy. Identification of structural proteins of phage was carried out by SDS-PAGE. The taxonomic position of phages was determined by multiplex PCR. Results. We presented results of the study of biological properties of 21 lactic acid bacteria phages isolated in dairy processing plants of Ukraine during 2007-2017. It was shown that phages had long, noncontractile tails, and therefore were classified to Caudovirales order, Siphoviridae family. Phages of L. lactis ssp. differed by head shape: phages with isometric heads of B1 morphotype and phages with prolate heads of B2 morphotype were detected. All analyzed S. thermophilus phages displayed specific morphology for B1 morphotype. Some of them had atypical shorter tails of 133-137 nm in length, with basal plates without globular appendages. Lytic activity spectrum of various phages was investigated and it was defined an absence of correlations between the indices of phages lytic activity and viral particles morphology. Phages of L. lactis ssp. were very heterogeneous on the basis of protein composition and formed three groups. Thus, с2 phages species differed by the fact that contained major proteins with greater molecular weights-30, 55 and 72 kDa. Phages of S. thermoрhilus contained two or three major proteins with the molecular weights of 33 and 27 kDa; 42, 26, and 15 kDa, respectively. Conclusions. Bacteriophages of L. lactis ssp. according to their morphology, protein profile and PCR results were identified to species: 1) 38.1 % of phages belong to species 936; 2) to the species P335-9.5 %; 3) to the species c2-19.0 %. Phages S. thermophilus were identified to three groups: 1) the group of cos-type amounted to 14.3 % of the total; 2) the group of pac-type-9.5 % аnd 3) 987 group-9.5 % of phages.
Bacteriophage-insensitive Streptococcus thermophilus mutants (BIMs) were obtained by treating the phage-sensitive industrial strains with virulent phages. Five BIMs acquired resistance to S. thermophilus phages of two (cos and pac) main groups selected at Ukrainian dairy processing enterprises. In addition, the valuable biotechnological properties of BIMs were characterised. During fermentation, they formed fermented milk curds with a homogeneous, dense consistency, with pleasant taste and flavour. The BIMs were identified as S. thermophilus by phenotypic and species-specific PCR methods. The BIMs could be used as starters to stabilise the fermentation process under phage infection conditions.
Investigation of the appearance and elimination of “pinking” phenomenon in white wines is presented in the paper. Several factors that can cause pinking were analyzed: the degree of grapes ripeness and enzymatic treatment. The effect of fining agents based on polyvinylpolypyrrolidone (PVPP) on the elimination of “pinking” was determined. It was proved that pinking in wines decreases with an increase in the sugar content in grape. This is explained by a decrease in the content of anthocyanins at the end of technical ripeness of grape. Experimental studies confirmed that the use of pectolytic enzymes with cellulase, hemicellulase, β-glucanase activities increases the intensity of straw color and the appearance of body tones, but does not affect pinking. Such treatment contributed to a slight increase in the content of phenolic compounds in wine materials, but did not affect the content of anthocyanins and “pinking” susceptibility. Treatment of wine materials with complex PVPP-based agents including sorbents and flocculants, is an effective way to eliminate the “pinking” phenomenon. This reduces “pinking” in wine materials from 70…90 % to 1…2 %. This is due to the presence of sorbents and flocculants in the fining agents, which react with phenolic substances that cause “pinking” in white wines, and remove them from the system. So, there are reasons to argue that processing grape at the end of technical ripeness will contribute to a lower “pinking” susceptibility of wine materials; pectolytic enzymes did not affect the appearance of this phenomenon in white wines, and PVPP-based fining agents together with bentonite, activated carbon, gelatin or casein, are an effective way to reduce the “pinking” susceptibility of wine.
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