Lactococcus lactis
Lactococcus lactis is a Gram-positive lactic acid bacteria that is widely present in nature and holds an important position in the fields of food fermentation, biotechnology and medicine.
Taxonomic status: It belongs to the genus Lactococcus and was once classified under the genus Streptococcus. Later, due to differences in genetic and physiological characteristics, it was independently classified as the genus Lactococcus. The type species is Lactococcus lactis subsp. lactis.
Morphology and staining: Spherical or oval, often arranged in pairs or short chains, Gram-positive, no spores, no flagella, and immobile.
Facultative anaerobic bacteria mainly produce lactic acid (mainly L-lactic acid, and some strains produce D-lactic acid) by fermenting carbohydrates (such as lactose), and are typical "homomorphic fermentation lactic acid bacteria".
The nutritional requirements are complex, requiring growth factors such as amino acids, vitamins, and nucleotides, and are often used in the optimization research of culture media.
Growth conditions: The optimal temperature is 30-32℃. It has strong acid resistance (pH 5.5-6.5) and can grow slowly in a refrigerated environment. It is suitable for low-temperature storage after food fermentation.
The core role in food fermentation
Acid production and antibacterial: The lactic acid produced during fermentation lowers the pH of the environment, inhibits the growth of spoilage bacteria and pathogenic bacteria (such as Listeria), and extends the shelf life of food.
Flavor and texture improvement: It breaks down lactose to produce lactic acid, while secreting proteases, peptidases, etc., to degrade milk protein and generate flavor substances (such as aldehydes and ketones), and promotes the coagulation of whey protein, endowing fermented dairy products (such as cheese and yogurt) with a unique taste.
Probiotic potential
Some strains (such as Lactococcus lactis subsp. cremoris) can colonize in the intestinal tract, regulate the balance of flora, and inhibit harmful bacteria (such as Escherichia coli).
It can stimulate intestinal mucosal immunity and enhance the body's immunity, especially playing a role in the intestinal development of infants and young children.
Fundamentals of Biotechnology Application
As a genetically engineered model strain, it is used to express exogenous proteins (such as vaccines and cytokines) due to its clear genetic background, easy culture and high safety. For instance, through genetic modification, anti-inflammatory factors (such as IL-10) can be produced for research on the treatment of intestinal inflammation.
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