Milk Biotech

Cover illustration: Girl drinking glass of milk. Milk processing is the focus of this special issue of Biotechnology Journal, edited by Professor Knut Heller (Kiel, Germany). In spite of centuries of research on milk processing, this topic still requires and justifies intensive research: in this issue we demonstrate that recent knowledge on bioactive peptides, bacteriophages and healthy milk bioprocessing allow to make the nutritive and health potential of milk fully available to the consumers. Image: Corbis Digital Stock     

Variations of Human Milk Protein Preparations from Individual Milk Samples

The acid coagulability of casein from 54 individual human milk samples and the variation of coagulability of their casein preparations by rennin were examined. The casein and whey protein preparations from individual human milk samples were also compared by polyacrylamide gel electrophoresis (PAE). Casein coagulated distinctly from 22 human milk samples when the pH was adjusted to 4.6 with acid, but it did not from other 32 samples. Twenty-two samples of casein preparations coagulated distinctly by rennin in the presence of calcium ions but 19 samples just became turbid. When the classification of human casein based on PAE pattern of major six bands was applied in our preparations, type A appeared most often and type C did least. Any regular relationship was not found between variation of the PAE pattern of casein preparations from individual human milk samples and that of acid coagulability or rennin coagulability.     

Relation of Milk Production Loss to Milk Somatic Cell Count

Milk production loss was studied in relation to increased somatic cell count (SCC). Available data were weekly test-day milk yields and SCC (in 1,000 cells/ml), and mastitis incidences. In total, 18,131 records from 274 cows were used. Production loss was determined for test-day kg milk, kg protein, and kg energy-corrected milk. Least-squares analysis of variance was used to estimate the direct effect of Log10(SCC) on production. The recorded measures of production were first corrected for fixed effects, with adjustment factors estimated from a healthy data-set. The average daily milk yield was 19.7 kg/day in first lactation and 22.0 in later lactations. The geometric mean of SCC was 63.1 in first lactation and 107.2 in later lactations. The incidence of clinical mastitis treated by a veterinarian was 19.8% of the lactations-at-risk. Linear relationships were found between the production parameters and Log10(SCC). Quadratic and cubic effects were evaluated, but were found to contribute little to the overall fit of the models. The individual milk yield loss was 1.29 kg/day for each unit increase in Log10(SCC) for cows in first lactation. Milk yield decreased by 2.04 kg/day per unit Log10(SCC) for older cows. Corresponding values for protein yield were 0.042 and 0.067 kg/day for first and later lactations, respectively.