Among different intrinsic factors which help microbial growth on a particular food, one is the redox potential of food. Can anyone explain me the basic mechanism of this process.
Dear Shabir Ahmed,
I have prepared for you a summary about the EFFECT OF REDOX POTENTIAL ON MICROBIAL GROWTH.
Redox or oxidoreduction potential is defined as the sum of all the oxidizing (dissolved oxygen, free radicals, hydrogen peroxide, some oxidized metal ions…) and reducing (some vitamins, some reduced metal ions, thiol-containing molecules, hydrogen…) couples found in the medium. This means when the concentration of oxidizing molecules increases the redox potential value of the medium increases (determined in millivolts or volts) but when the concentration of the reducing molecule increases the redox value of the medium decreases. For simplifying the term of redox, we can say that it expresses the concentration of mobile electrons (that can move from molecule to another) in the medium, whereas the pH value expresses the concentration of protons (H+) in the medium.
Now how can the redox potential affect the growth of microorganisms?
To respond to this question we must keep in the head the relationship between the oxygen as oxidant found in the atmosphere and the redox potential. When a microorganism is found in aerobic medium (containing dissolved oxygen) it means this medium is favorable for the growth of aerobic microorganisms which can use the oxygen as a final acceptor of electrons produced from the substrate via the metabolism.
It is important to indicate here also that every microorganism possesses a favorable value of redox for growth (this behavior likes that found for pH, water activity and temperature; and a microorganism found in a medium “swims” to a location with a favorable redox value. Furthermore, it was reported that the redox potential value affects the pH intracellular of a microorganism, which forms a component of the proton-motive force. This effect of the redox on the pH intracellular was attributed to the change of the permeability of the cellular membrane, which increased by the decrease of the redox value of the medium. Other studies reported the effect of redox potential on the surface properties of the cellular membrane such as the hydrophobicity and the character of donor/acceptor of electrons. The ability of redox potential of the medium on the toxin production capacity and spore germination in some microbial strains was also reported. It is important here to remind that the bacterial membranes have an essential function in energy conservation as the location about which a proton motive force is generated. This proton motive force (also called electrochemical gradient) forms a source of energy for bacteria.
We can summarize the mechanism of the effect of redox potential on the growth of microorganisms as follows:
1) Its effect on the structural composition of some sensitive-components/molecules found on the surface of the cell. These redox-sensitive components/molecules could be enzymes located in the surface of the cell, which its protein part (Apoenzyme) could be composed of sulfur-containing amino acids making it sensitive to the redox potential of the medium. Furthermore, the cofactors of these enzymes such as Fe, Zn, Mg and Cu could be found in oxidized or reduced form, which means the susceptibility of these metal ions to the redox potential of the substrate or/and the medium.
By the same manner, we can discuss the effect of redox potential on several redox-sensitive molecules located in the surface of the cell such as proteins, phospholipids, saturated and unsaturated fatty acids, which could be affected directly by the redox potential of the medium. The modification in the structural or the composition of these molecules affects different cellular systems such as the transport and energetic ones.
2) If the energetic system of the cell (proton motive force) changes the ATP content of the cell will change which can affect many essential functions of the cell.
Best Reading
Duried Alwazeer
Dear Shabir Ahmed,
I have prepared for you a summary about the EFFECT OF REDOX POTENTIAL ON MICROBIAL GROWTH.
Redox or oxidoreduction potential is defined as the sum of all the oxidizing (dissolved oxygen, free radicals, hydrogen peroxide, some oxidized metal ions…) and reducing (some vitamins, some reduced metal ions, thiol-containing molecules, hydrogen…) couples found in the medium. This means when the concentration of oxidizing molecules increases the redox potential value of the medium increases (determined in millivolts or volts) but when the concentration of the reducing molecule increases the redox value of the medium decreases. For simplifying the term of redox, we can say that it expresses the concentration of mobile electrons (that can move from molecule to another) in the medium, whereas the pH value expresses the concentration of protons (H+) in the medium.
Now how can the redox potential affect the growth of microorganisms?
To respond to this question we must keep in the head the relationship between the oxygen as oxidant found in the atmosphere and the redox potential. When a microorganism is found in aerobic medium (containing dissolved oxygen) it means this medium is favorable for the growth of aerobic microorganisms which can use the oxygen as a final acceptor of electrons produced from the substrate via the metabolism.
It is important to indicate here also that every microorganism possesses a favorable value of redox for growth (this behavior likes that found for pH, water activity and temperature; and a microorganism found in a medium “swims” to a location with a favorable redox value. Furthermore, it was reported that the redox potential value affects the pH intracellular of a microorganism, which forms a component of the proton-motive force. This effect of the redox on the pH intracellular was attributed to the change of the permeability of the cellular membrane, which increased by the decrease of the redox value of the medium. Other studies reported the effect of redox potential on the surface properties of the cellular membrane such as the hydrophobicity and the character of donor/acceptor of electrons. The ability of redox potential of the medium on the toxin production capacity and spore germination in some microbial strains was also reported. It is important here to remind that the bacterial membranes have an essential function in energy conservation as the location about which a proton motive force is generated. This proton motive force (also called electrochemical gradient) forms a source of energy for bacteria.
We can summarize the mechanism of the effect of redox potential on the growth of microorganisms as follows:
1) Its effect on the structural composition of some sensitive-components/molecules found on the surface of the cell. These redox-sensitive components/molecules could be enzymes located in the surface of the cell, which its protein part (Apoenzyme) could be composed of sulfur-containing amino acids making it sensitive to the redox potential of the medium. Furthermore, the cofactors of these enzymes such as Fe, Zn, Mg and Cu could be found in oxidized or reduced form, which means the susceptibility of these metal ions to the redox potential of the substrate or/and the medium.
By the same manner, we can discuss the effect of redox potential on several redox-sensitive molecules located in the surface of the cell such as proteins, phospholipids, saturated and unsaturated fatty acids, which could be affected directly by the redox potential of the medium. The modification in the structural or the composition of these molecules affects different cellular systems such as the transport and energetic ones.
2) If the energetic system of the cell (proton motive force) changes the ATP content of the cell will change which can affect many essential functions of the cell.
Best Reading
Duried Alwazeer
A book chapter will be published in the next time about the concept of oxidoreduction potential and its measurement and effects on microorganisms, and its applications in food industries.
Dear Shabir,
Redox potential is a measure of potential difference in a system on food. IN redox, loss of electron is a reducing agent and gain of electron is a electron acceptor. Potential of Oxidized range is +mV and Reducing range is -mV. The redox potential of a food is influenced by its chemical composition, specific process condition given and storage reduction in relation to air. Fresh food of plants and animal origin in a reduced stage due to presence of reducing substances such as sugars, ascorbic acids and sulphydryl group of protein. Diffusion of oxygen into these fresh food substances can change the redox potential of the food. Processing food heating can also alter the Eh(Reduced or Oxidized). The presence of oxygen in the environment is important in the growth of microorganism. The ranges of Eh can be changed in the Aerobes and Anerobes, -250 mV to 500 mV. The presence of oxygen is responsible to grow microorganism and redox potential can be easily measured using the EMF cell principle one as a cathode and one is anode.
Hope it is helpful for you.
Ashish
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