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Cross-linking reaction with transglutaminase (m-TG) was used to obtain yoghurt produced with YO-MIX TM 511 yoghurt starter (Danisco). The use of two different temperatures (37 and 42°C), the presence of m-TG and the storage time (28 days) of the yoghurt were the factors that influenced the immunoreactive and sensory properties. The ELISA results obtained during the reaction of yoghurt proteins with a specific antibody against individual milk proteins (b-lactoglobulin, a-lactalbumin, a-casein, b-casein and j-casein) indicated differences on the level of immunoreactivity of individual proteins. The b-lg immunoreactivity of yoghurt produced at 37°C was not detectable in any of the samples whereas during the process conducted at 42°C the presence of this protein at low level was observed (1.00 and 3.33% without and with m-TG, respectively). The lack of j-casein was detected in the storage yogurt sample prepared during fermentation at 42°C. The samples were subjected to sensory evaluation using quantitative descriptive analysis (QDA). A trained personnel (n = 6) rated the yogurts for smell, taste and texture. The data obtained from QDA (16 attributes and 4 yoghurts) were subjected to a principal component analysis (PCA). The results (QDA and PCA) proved that the addition of the m-TG enzyme had significant impact on the sensory quality of the samples. Four principal components (PC1-PC4) determined 96.05% of the total variance of the samples.

We present here the results of an exploration of the bacteriophage content of dairy wheys collected from milk plants localized in various regions of Poland. Thirty-three whey samples from 17 regions were analyzed and found to contain phages active against L. lactis strains. High phage titer in all whey samples suggested phage-induced lysis to be the main cause of fermentation failures. In total, over 220 isolated phages were examined for their restriction patterns, genome sizes, genetic groups of DNA homology, and host ranges. Based on DNA digestions the identified phages were classified into 34 distinct DNA restriction groups. Phage genome sizes were estimated at 14-35 kb. Multiplex PCR analysis established that the studied phages belong to two out of the three main lactococcal phage types--c2 and 936, while P335-type phages were not detected. Yet, analyses of bacterial starter strains revealed that the majority of them are lysogenic and carry prophages of P335-type in their chromosome. Phage geographical distribution and host range are additionally discussed.

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Kefir is a dairy product popular in many countries in Central Europe, especially in Poland and other countries of Eastern and Northern Europe. This type of fermented milk is produced by a complex population of symbiotic bacteria and yeasts. In this work, conditions for DNA extraction, involving disruption of kefir grains and a cascade of cell lysis treatments, were established. Extraction procedure of total microbial DNA was carried out directly from fresh kefir grains. Using different lysis stringency conditions, five DNA pools were obtained. Genetic diversity of DNA pools were validated by RAPD analysis, which showed differences in patterns of amplified DNA fragments, indicating diverse microbial composition of all the analysed samples. These DNA pools were used for construction of genomic DNA libraries for sequencing. As much as 50% of the analysed nucleotide sequences showed homology to sequences from bacteria belonging to the Lactobacillus genus. Several sequences were similar to sequences from bacteria representing Lactococcus, Oenococcus, Pediococcus, Streptococcus and Leuconostoc species. Among homologues of yeast proteins were those from Candida albicans, Candida glabrata, Kluyveromyces lactis and Saccharomyces cerevisiae. In addition, several sequences were found to be homologous to sequences from bacteriophages.

The aim of the study was to find a way to recover the quality of kefir grains that had been subjected to the following treatments: homogenisation, rinsing the grains with water, freeze‐drying and milling, freezing in liquid nitrogen and then frozen storage, and cool storage. The grains were studied in respect of their later replication in milk, their size and their microbiota composition. The daily transfer of treated kefir grains, except freeze‐dried ones, into fresh milk was effective in respect of the recovery of their growth dynamics, size and microbiota balance. The growth dynamics of grains in milk seems to be a very good indicator of their vital and technological functions.

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