The mechanism of urea action in milk on the fermentation activity of lactic cultures
1994
Lukasova, J. (Vysoka Skola Veterinarni a Farmaceuticka, Brno (Czech Republic))
The increased content of urea in milk influences its processing to fermented products and to cheese. The effect of urea in milk (40-60 mmol/l) on yoghurt and sour cream cultures was investigated. A higher content of urea had negative impacts on the activity of yoghurt culture. The concentration higher than 6 mmol/l decreased the counts of lactobacilli, which induced an adverse ratio of streptococci and lactobacilli. This resulted in poor fermentation, low acidity and increased content of ammonia in the product. The presence of urea in sour cream culture evokes intensive multiplication, and this leads to overfermentation of products. No inhibitory effects on the particular strains of lactic bacteria were observed, nor on Lactobacillus delbrueckii subsp. bulgaricus. The compound which negatively influences the activity of lactic cultures is presumably not urea but ammonia produced by enzymatic breakdown of urea.
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