Utilization
The inhibitory effect of nisin is restricted to pathogenic gram-positive microorganisms and all spore forming microorganisms. For example, lactic acid bacteria, Streptococci, Bacilli and Clostridia. However, yeast and moulds are not inhibited by nisin. This heat resistant peptide is applied to suppress anaerobes in cheese and cheeses products, especially in hard cheese and processed cheese to inhibit butyric acid fermentation.
Mechanisms of action
The action of nisin is directed against the cytoplasmic membrane right after the germination of the spore. Its action is pronounced against spores rather than vegetative cells.
4.PHB-esters
It was found in “chicken and mushroom pastry”.
Properties
They are the alkyl esters of p-hydroxybenzoic acid and are stable. The solubility in water decreases with increasing alkyl chain length.
Utilization
The esters are mostly antifungal agents. They are effective against yeasts but less so against bacteria, especially those gram-negative bacteria. The uses of PHB-esters are governed by 3 properties: action dependent on the pH value, very low water solubility and particular organoleptic characteristics.
Mechanisms of action
Its mode of action is very similar to that of benzoic acid. The parabens dissolve in or through the cell membrane, interfering with the membrane-related processes or structures. In addition to that, paraben has been found to inhibit both growth and isolated uptake systems for amino acids.
5.Sodium Ascorbate (C6H7NaO6)
It was found in the “smoked reformed ham of Italiano ham and cheese tortellini”.
Properties
It is the salt of ascorbic acid (vitamin C). It is soluble in water. In water, it readily reacts with atmospheric oxygen and other oxidizing agents.
Utilization
Na ascorbate is used as an antioxidant due to its high affinity for oxygen. Furthermore, it is also functions as a colour preservative. It is used as a reducing agent in curing of meat for a good pink colour. In addition, it helps to retard the browning reactions in fruits and vegetable products.
Mechanisms of action
In this context, Na ascorbate is included in the curing-salt mixtures to reduce the amount of residue nitrite. As a reducing agent, it influences the rate of key reducing reaction in the formation of nitrosyl myoglobin (MbNO). MbNO is responsible for the read pigment of the uncooked bacon and ham. As a result, lower levels of nitrites or nitrates could be used in pickles. At the mean time, it also hinders the nitrosation reaction.
6.Sodium Benzoate
It was found in “marmalade”.
Properties
It is the salt of benzoic acid. It occurs in the form of white crystalline powder. Its solubility is 200 times greater than benzoic acid.
Utilization
The inhibition activity of sodium benzoate is mainly against yeasts and moulds. Bacteria are only partially inhibited. It is used for preservation of sour foods, which has a pH of 4-4.5 or lowers, as they can tolerate at acidic pHs. The usual quantity applied is 0.05-0.1%
Mechanisms of action
The undissociated part of benzoic acid is the effective agent. Its action is pH dependent because it has to penetrate the cell wall of the microorganisms in order to develop its action. Generally, it has been discovered to influence the enzyme controlling acetic acid metabolism and oxidative phosphorylation. Moreover, the preservative also intervene at various points in the tricarboxylic cycle, especially where the dehydrogenases of α-ketoglutaric acid and succinic acid are involved.
7.Sodium Nitrite (NaNO2)
It was found in the “ honey roast sandwich ham ”.
Properties
It is the salt of nitrous acid. It is a white to pale yellowish granular powder with salty taste. It has a high solubility in water.
Utilization
It is used primarily to preserve the red colour of meat. Apart from this, sodium nitrite also demonstrates antimicrobial activity. It is particularly effective against outgrowth of Clostridium botulinum, which can produce the deadly toxin, botulin.
Mechanisms of action
The nitrite oxidises the iron ( ) state of the muscle myoglobin to the iron ( ) state.
Fe 2+ + No2- + H+ ---------- Fe3+ + NO + OH-
The myoglobin (Mb) is converted to metamyoglobin (MMb). The resulting nitrogen oxide will react with the iron MMb to form nitrosyl metmyoglobin (MMbNO). The respiratory system of the muscle tissue will reduce MMbNO to nitrosyl myoglobin, MbNO, which is the red pigment of the uncooked bacon and ham.
The antimicrobial effect, which is termed as “ Perigo effect ”, is related to the residual nitrite in ham. During cooking of the ham, much of the residual nitrite is broken down to nitrogen oxide. NO has an inhibition effect on at least one enzyme (namely pyruvate:ferrodoxin oxidoreductase), which plays an important role in the energy metabolism. Interfering activity of NO includes inhibiting oxygen uptake, oxidative phosphorylation and H+ dependent active transport. Furthermore, the uncoupler also causes collapse of proton gradient. As a result, the growth and toxin production of Clostridium botulinum is severely affected.
Apart from NaNO2, Sodium nitrate is used in curing of meat to supply the nitrite. This is due to the reason that nitrite is the effective agent.
NO3- + 2[H] --------- NO2- + H2O
8.Sorbic acid (C6H8O2)
It was found in “cheese”.
Properties
It is a white monocyclic crystal with a specific odour and sour taste. It will melt at 132 to 135 0C. The solubility increases with temperature. It is effective over a broad range of pH but ineffective above pH 7.
Utilization
It is effective against mould and yeast but only marginally effective against bacteria. This makes it very suitable as a cheese preservative because it permits the fermentation action of lactic acid bacteria.
Mechanisms of action
The activity of sorbic acid is very pH dependent. The un-dissociated acid constituent, which is antimicrobial, will penetrate the cell wall in order to develop action in the cell. Its action includes inhibition of various enzymes such as enolase and lactate dehydrogenase and others. One of the ways is by forming covalent bonds between its own double bonds and the SH groups of enzymes.
9.Sulphur dioxide (SO2)
It was found in ''ready to eat apricot dried fruits".
Properties
SO2 is a colourless, non-combustible gas with a pungent odour. It dissolves in water to yield sulphurous acid. The density of SO2 is twice higher than that of air.
Usage
It is widely used in many foods and beverages as preservatives and antioxidants.
Its functions include prevention of oxidation, inhibition of chemical and enzymatic reactions and the inhibition of the growth of yeasts, moulds and bacteria. It is commonly used in the form or sodium hydrogen sulphite, sodium metabisulphite, potassium metabisulphite and calcium hydrogen sulphite.
Mechanisms of action
In the production of dehydrated fruits, SO2 provides protection against oxidative, enzymatic and non-enzymatic browning reactions. Moreover, it also helps to delay colour changes or acts as bleaching agent.
SO2 prevents enzymatic browning by inactivating the phenolases, which are mainly found in fruits and vegetables. These enzymes facilitate the conversion of colourless phenolic compounds to highly coloured quinones.
Fig 1
Fig 2
In non-enzymatic browning, SO2 inhibits discoloration by blocking compounds with reactive carbonyl groups, the nonreactive hydroxy sulphonate sugar derivatives.
Although SO2 itself is successful in many systems in very low concentration, combinations with other preservatives such as sorbic acid, sorbates and ascorbic acid may be more effective for browning prevention in certain foods and beverages.
10.Vitamin E
It was found in “vegetable fat spread”.
Properties
It is a group of derivatives of 6-hydroxychroman carrying a phytyl side chain. There are two main groups of compound, which have vitamin E activity, the tocopherols and tocotrienols. The vitamin E content of foods is expressed as mg α- tocopherol. Therefore, vitamin E is sometimes labelled as tocopherols in the product.
Utilization
It functions as an antioxidant in oily and fatty foods. Rancidity of foods resulted from autoxidation of the unsaturated fatty acid is prevented.
Mechanisms of action
As an antioxidant, vitamin E blocks the free-radical chain reactions of lipid peroxidation. The propagation process it blocked by donating the a hydrogen atom to a free radical such ROO ,
AH + ROO ---------- ROOH + A
The antioxidant free radicals are stabilised by resonance and couldn’t continue to with the reaction chain. They appear to enter termination reaction such as
A + A ------ A-A and A + ROO ------- ROO-A
However, the antioxidants do not reduce the ultimate degree of rancidity. In fact, they lengthen the induction period in rough proportion of their concentration.
References
1. Belitz, H.D. and W. Grosch (1999) Food Chemistry, (2nd edition), Springer-Verlag Berlin Heidelberg, Germany.
2.Coultate, T.P. (1996), Food: The Chemistry of Its Components, (3rd edition), Royal Society of Chemistry Paperback, Cambridge, p239-241, 247-257.
3.. Luek, E. (1980) Antimicrobial Food Additives, Springer-Verlag Berlin Heidelberg, Germany.
4.Russell, N.J and Gould, G.W (1991), Food Preservatives, Blackie and Son Ltd, UK.
5.Schroeter, L.C. (1966), Sulfur Dioxide Applications in Foods, Beverages and Pharmaceuticals, Pergamon Press, London, p200-203.
6. Lecture notes of Food Commidities by Dr. David Gray.
