3. Native antimicrobial compounds of milk Flashcards
Native antimicrobial compounds of milk
- milk is healthy food source of energy, proteins, vitamins and minerals
- contains also some physiologically active substances
- a number of proteins found in milk under various conditions exhibit anti-microbial activity
Major anti-microbial proteins
- 3 main ones:
- lactoferin
- lysozyme
- lactoperoxidase
Function
- in protecting neonates from infection until their own immune system has developed - present in colostrum, in very high concentration
- neonates need these to prevent infection of GIT or of the organism
- impact on shelf life of fresh raw milk:
- these subtances are present in fresh raw milk
- can inhibit or kill the bacteria present in milk
- fresh raw milk has longer shelf life due to this
- but the activity of these substances depends on the concentration and on the temperature of
the milk after milking - involved in prevention of mastitis:
- present in the mammary gland during dry period —> protecting the mammary gland against infection as the concentration is very high at this moment
- involved in protecting the consumer
1) Lactoferin
- iron binding glycoprotein
- a member for the transferrin family:
- a group of proteins that bind specifically to iron
- closely related to transferrin (present in blood)
- also related to an iron chelating protein found in hen egg white, ovotransferrin
- these proteins are distinct molecules, and behave differently in biological systems - lactoferrin has the highest binding ability
Lactoferin - Occurence
Occurence
- produced by mucosal epithelial cells in various mammalian species: humans, cows, goats, horses, dogs, several rodents
- present in mucosal secretions: tears, saliva, vaginal fluids, semen, nasal and bronchial secretions, bile, GIT secretions, urine, milk and colostrum (highest)
- also found in blood plasma and amniotic fluid
- considerable amount in secondary granulophilic neutrophils
Lactoferin - Biological importance
- exhibit strong anti-microbial activity against broad spectrum of bacteria, fungi, yeasts, viruses, parasites
- promote the growth of beneficial bacteria e.g. lactobacillus, bifidobacterium
- also exhibits anti-inflammatory and anti-carcinogenic activities - has several enzymatic functions
- plays a key role in maintaining cellular iron levels in the body
Lactoferin
Antimicrobial activities
Antibacterial activity:
- has both bacteriostatic and bactericidal functions
- bacteriostatic:
- due to its ability to take up the Fe3+ ions: bind free iron which is essential for the growth of bacteria
- iron is also an important factor of virulence of many pathogens
- lack of iron —> inhibits growth of iron dependent bacteria e.g. E. coli, Klebsiella, Salmonella,
Proteus, Pseudomonas, Bacillus, Listeria, Candida albicans
- bactericidal:
- not iron dependent, and may be mediated though more than one pathway
- has been attributed to its direct interaction with bacterial surfaces
- G- bacteria:
- LF bind to lipid A of LPS —> liberation of this lipid —> damage to cell membrane - change the permeability of the cell membrane of bacteria
- resulting in lysis of the bacteria
- G+ bacteria:
- LF bound to negatively charged molecules on the cell membrane e.g. lipoteichoic acid
- neutralising wall charge, allowing the action of antibacterial compounds such as lysozyme
Lactoferin
Antiviral activity:
- prevents DNA and RNA viruses
- prevention of virus attachment by interaction with cell surface glycosaminoglycans and low
density lipoproteins receptors - has been demonstrated to inhibit in vitro the multiplication of different viruses
Lactoferin
Anti-fungal activity:
- both hLF and bLF as well as lactoferricin
- especially towards C. albicans and C. krussei - by altering the permeability of the cell surface
Lactoferricin
- produced after enzymatic activity of pepsin inside GIT
- pepsin low molecular type
- has higher anti-bacterial properties than LF
- effective against a large number of G+ and G- bacteria: Str. bovis, E. coli, Salmonella enteritidis,
Pseudomonas aeruginosa, etc - derived from the N terminal region of lactoferrin
- 2 forms:
- lactoferricin H from human - lactoferricin B from bovine
2) Lysozyme
- also called muramidase: catalyses the hydrolysis some linkages in the bacterial wall
- types:
- chicken-type (c-lysozyme):
- typically found in egg white of birds
- also purified from various tissues and secretions of mammals — milk, saliva, tears, urine,
respiratory and cervical secretions - g-type: derived from the egg white of domestic goose
- h-type: from plant
- i-type: invertebrates
- b-type: from bacteria (bacillus)
- v-type: from viruses
Lysozymes in milk
- Lc and Lg differ in their aa sequence, molecular mass and extinction coefficiton
- Ho, camel and Eq milk lysozymes are considered to be c type due to identical molecular mass
- can divide the milk into 2 groups:
- milks which have high levels of lysozyme, human, equine, camel - milks with lower levels of lysozyme: bovine, sheep, goats
Lysozymes
Anti-microbial activities and other activities
- catalyses the hydrolysis of 1.4-beta linkages between N-acetylmuramic acid and N-acetyl D- glucosamine residues in peptidoglycan, a constitute of bacterial cell walls
- susceptibility of bacteria to lysozyme depends on a number of factors
- stimulates synthesis of interleukins and α and γ interferons
- modulates generation of TNFα
- induces phagocytising cells
- prevents excess generation of free radicals
Lysozymes
Applications
- pharmaceutical industry:
- prophylactically for dental caries
- lozenges for sore throat
- in contact lens decontamination solutions and eye drops
- creams for topical reparation of certain dystrophic and inflammatory lesions of skin and soft
tissues - cosmetics
- food industry:
- as preservative in food
- food packaging biofilm: extends shelf-life of non-sterile or minimally processed foods e.g.
poultry, meat, sausage - added to infant formula
- cheese industry:
- inhibits the growth of clostridium tyrobutyricum, added into milk during cheese production:
clostridium can damage the cheeses during the ripening, causes late-blowing and undesirable
flavours - hastens ripening of cheese
- wine industry: due to its lytic action on G+ lactic acid bacteria, good alternative to sulphites
3) Lactoperoxidase
- peroxidase activity occurs in various exocrine gland secretions: saliva, tears, bronchial, ansal, intestinal secretions as well as in milk
- peroxidase in milk = lactoperoxidase
- glycoprotein containing also iron
- anti-bacterial activity:
- lactoperoxidase alone has very low antibacterial activity
- need presence of hydrogen peroxide and thiocyanate (SCN)
- catalyses oxidation of SCN to hypothiocyanate = responsible for anti-microbial activity by inhibiting bacterial metabolism
- activity of this system is also used in countries where it is not possible to cool the milk immediately after milking
- adding hydrogen peroxide into the milk can support the activity of this system
- the fresh milk has longer shelf life
- but in CZ, it is not possible to use this system and to add the hydrogen peroxide into the milk - only in developing countries
