pediococcus is a facultative anaerobic bacterium, which means that they can grow under anaerobic and oxygen conditions, and their tolerance to oxygen levels varies depending on species and strains. The growth and acid production of certain species and strains (including individual strains of P. damnosus) may be inhibited by oxygen, while certain species and strains will grow better and produce more acid (microaerobic) in the presence of oxygen. The strains found in beer have hops tolerance. Due to the continuous metabolism of long-chain polysaccharides, the acid production will increase with the prolongation of storage time. Streptococcus can form a thin film on the surface of beer.
The position of pediococcus in the biological classification system: Bacterium kingdom, Firmicutes phylum, Bacillus class, Lactobacillus order, Lactobacillus family, Streptococcus genus. Currently, there are 11 recognized species of Streptococcus genus. They are P.acidilacii, P.argentinicus, P.cellicola, P.claussenii, P.damnosus, P.ethanolidurans, P.inopinatus, P.parvulus, P.pentaaceus (subspecies pentaaceus and intermedium), P.siamensis, and P. stilesii.
pediococcus belongs to the same type of lactic acid bacteria (lactic acid bacteria can be divided into three major categories according to fermentation type, namely, same type of lactic acid fermentation, heterotype of lactic acid fermentation, and facultative heterotype of lactic acid fermentation. Homotype fermentation refers to glucose passing through the EMP pathway, only producing lactic acid as a metabolic product; During heterotypic fermentation, only lactic acid is generated, and CO2 and ethanol or acetic acid are also generated, When fermenting glucose, lactic acid is produced, and except for P.dextrinicus, other species do not produce carbon dioxide. Does not produce alcohol and acetic acid. All strains of Streptococcus can ferment and utilize fructose, mannose, and cellobiose. Most strains can ferment galactose and maltose, while most strains cannot ferment rhamnose, melibiose, rosin, raffinose, and inulin.
Streptococcus can also produce bacteriocins, such as lactococcin. The main species that can be produced are P. acidilactici (Lactococcus lactis), P. damnosus (Harmful Streptococcus), and P. pentosaceus (Pentosaceus pentosaceus). These strains are not only similar in phylogeny, but also have many similar biochemical characteristics. Streptococcus suis is considered a conditional pathogen due to its association with certain human infections.
pediococcus can improve or damage fermented foods, including beer, wine, and cider. They also play an important role in the fermentation of some pickled Chinese cabbage, meat and cheese. It is the main sourness microorganism in the brewing of Lambik. Some species have also been isolated from plants, fruits, and fermented plant materials. In wine, P Parvulus is the most common species, and in beer, P. damnosus is the most common. P. Pentosaceus is often more sensitive to hops than P.damnosus.
P. Lactilactici
Lactococcus lactis can grow at pH 4.2-8, and the final pH on MRS medium is 3.5-3.8. The most suitable growth temperature is 40 ℃, and the maximum growth temperature is 53 ℃. It has a certain degree of heat resistance, but it can also die after being treated at 70 ℃ for 10 minutes. It cannot be distinguished from Streptococcus pentosus based on cell morphology, cultural characteristics, and physiological characteristics, and genetic technology is needed to distinguish it. Phenologically, strains of Lactococcus lactis can produce a bacteriocin called Pa-1/AcH, which can be used in animal experiments to treat constipation, diarrhea, reduce stress, and enhance immune function. It can be isolated from fermented vegetables, fermented dairy products, and fermented meat, with the standard strain isolated from barley.
P. Pentosaceus
It can grow in an aerobic environment, and colonies will appear when cultured on a solid medium at 30 ℃ for 24 hours. The optimal growth pH is 6-6.5, but it can also grow at pH 8. On MRS liquid culture medium, the final pH will be lower than 4. The optimal growth temperature for different strains varies, usually between 28-32 ℃ and stagnant at 39-42 ℃. Without Lactococcus lactis, it has good heat resistance and can die after 8 minutes of treatment at 65 ℃. Many strains can produce bacteriocins, which are sensitive to hops and isolated from dry beer yeast in the United States.