Abstract

The number of somatic cells in milk increases when cows are sick or the rules of their milking are violated. This leads to the unfavorable changes in the composition and properties of raw-milk as well as to the biochemical and microbiological issues during its processing. The significance of changes is determined by how sick the animals are. The objective of this work was to study the influence of somatic cells number in raw milk on its ability to be fermented by the starter cultures and on the quality of the final product. The authors also determined the maximum concentration of somatic cells in the milk which can be processed to produce fermented drinks. The work was carried out in the laboratories of ITMO University (St. Petersburg) and some analyses were made in a dairy plant laboratory. The authors were using standard techniques during the experiments. The obtained data showed that the ability of milk to be fermented by lactic acid bacteria during fermented drinks production decreases when the number of somatic cells in raw milk increases. The starter cultures growth inhibition took place when the number of somatic cells was more than300 thousand/см3 and it became significant when its value was above 400 thousand/см3. When the number exceeded 500 thousand/см3 the period of milk fermentation by Streptococcus thermophilus increased 2 times and by mixed cultures - about1.5 times, which is unacceptable. Streptococcus thermophilus is less stable than mixed cultures containing Streptococcus thermophiles and Lactobacillus bulgaricus to the increased number of somatic cells. The increase of somatic cells number in raw milk has negative effect on the quality of such fermented drink as curdled milk. The decrease in curdled milk quality took place when the number of somatic cells was more than 300 thousand/см3. When the authors used milk with more than 500 thousand/см3 somatic cells this led to the decline in organoleptic properties of the drink. The quality of curdled milk produced from milk when the number of somatic cells was more than 500 thousand/см3 was low. This became evident due to the insufficient number of lactic acid bacteria, too viscous and slimy consistency, whey separation, strange aftertaste and flavor. To ensure high quality of fermented drinks it is necessary to take raw milk with somatic cells number not more than 300CFU/g. The usage of milk having more than 400 thousand/см3 somatic cells can lead to the production of the dairy product of unacceptable quality.

Keywords

Raw milk, milk somatic cells, raw milk technological properties

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