Antimicrobials will undoubtedly continue to be needed to provide the food supply that will be demanded in the future. The global economy in which we live will result will be demanded in the future. The global economy in which we live will result in foods being transported throughout the world. If foods are arriving in the condition expected, preservatives will be needed. Many chemical compound, either present naturally or formed during processing or legally added as ingredients, are capable of killing microorganisms or controlling their growth in foods. They are designated as antimicrobial inhibitors. A preservative is defined as any substance, which is capable of inhibiting, retarding, or arresting the growth of microorganism, of any deterioration of food due to microorganism or of masking the evidence of any such deterioration. Antimicrobial compound add to products during manufacturing process to reduce bacterial or fungal growth.
According to PFA Act, (1951)
A substance which when added to food is a capable of inhibiting, retarding, or arresting the process of fermentation, acidification or other decomposition of food.
Antimicrobial food additives are
Ø An efficient
Ø Cost effective
Ø Only effective way to control fungal growth in foods.
Occurrence
Ø Naturally occurring in certain foods
Ø Added to foods during processing.
Classified according to quantity used for preservation of the foods.
Class I - More than 0.5 %
Ø Common salt
Ø Sugar
Ø Dextrose
Ø Glucose syrup
Ø Wood smoke
Ø Spices
Ø Vinegar or acetic acid
Ø Honey
Class II : Less than 0.5%
§ Benzoic acid including its salts
§ Sulphurous acid including its salts
§ Nitrates or nitrities of sodium or potassium
§ Sorbic acid including its sodium, potassium andlactic acid and calcium, phosphate
§ Nisin
§ Sodium and calcium propionate
The ideal antimicrobial preservative is :
Ø Have a wide range of antimicrobial activity.
Ø Nontoxic to human beings or animals.
Ø Economical.
Ø No effect on the flavour, taste, or aroma of the original food.
Ø Not encourage the development of resistant strains
Ø Kill rather than inhibit microorganism.
Mechanism of microbial inhibitors :
Ø By interfering with the genetic mechanism of cell division or interference with cell membrane permeability.
Ø Interference with the enzyme systems of the microbe by competing with the substrate for place on the active enzyme surface.
Ø By inhibition of biosynthesis of vitamins
Ø By the formation of complexes with heavy metal ions.
Benzoic Acid
Ø Also called phenylformic acid or benzenecarboxylic acid
Ø Occur as colourless or white needless and its salt highly soluble in water
Ø Occurs in cranberries, prunes, plumes, cinnamon, ripe clove and also in apples, strawberries
Mechanism :
Undissociated molecules responsible for antimicrobial activity as it taken up by cells.
Interfering with the permeability of the microbial cell membrane.
General Effectiveness :
Most active against yeasts, bacteria, less active against molds
Effective pH : 2.5 to 4.5
Metabolism : Conjugated with glycine to produce hippuric acid which is excreted
Application : Carbonated, non carbonated beverages, purees, concentrate, Jams, Jellies, preserves, Pie filling, Salad dressings, Pickles, Olives, Relishes.
Parabens
Ø First described by Sabalitschka in 1924
Ø Alkyl esters of p-Hydroxybenzoic acid
Ø Stable in air and resistant to cold and heat
Ø Solubility increases from methyl to heptyl in ethanol
Ø More active against mold and yeasts than bacteria
Ø Effective pH- Below 7.0 the parabens are weakly effective
Application -
Carbonated beverages and other soft drinks - a ratio of 2 methy to 1 propyl used
Beer - 12 ppm of n heptyl ester of p hydroxybezoic acid
Baked Goods – Used in fruit product, flavour extracts, pickles, olives, artificially sweetened James, jellies and preserve.
Acetic Acid and Acetates
General Effectiveness : Most effective against yeasts and bacteria and less extent against molds. Diacetate effective against rope and mold in bread.
Effective pH : From 3.5 to 5.5
Application :
Meals : Pickled sausages and pigs feet. Vinegar packed sausages required minimum 3.6% acetic acid.
Bakery Products : High concentration required. However, Sodium diacetate used in small concentration in bread and rolls. Traditional concentration 0.4 part to 100 part of flour.
Acid tasting Products : Used in catsup, mayonnaise, pickles, salad dressing.
Propionic Acid and Propionates
History : Antimicrobial properties were noted in 1913.
Physical Property : It is corrosive acid with strong odour.
Effectiveness : More effective against moulds but not effective against yeasts and bacteria.
Effective pH : 5.0 or 6.0
Mechanism : Accumulates in cells
Inhibities the enzyme of metabolism
Competing with Alanine and other amino acids
Application :
Cheese : 8% Propionic Acid solution used in cheddar cheese
Butter : Propionate treated parchment wrappers provide protection
Bakery Products : Increase mold free life of bread by 8 days. Prevent rope formation in bread s even at pH level 6.0. Sodium salt used in cake and unleavened goods, and calcium salt in bread.
Sulfur Dioxide and Sulfites
Historical records indicates that burning of sulfur was used by ancient, Egyptians and Romans in connection with their wine making
Physical Property : A colourless, non flammable gas has a suffocating odour and effect.
Effective pH : As the pH decrease, the proportion of H2SO3 increase and the bisulfite (HSO3- ) ion concentration decrease .
Action : A broad spectrum antimicrobial agents, inhibiting yeasts, moulds, and bacteria
Mechanism of microbial inhibition by Sulphur Dioxide :
1. Inhibiting carbohydrate metabolism
2. Reduction of bisulphate bond (S-S) in enzyme proteins.
3. Inhibition of respiratory mechanism by halting the reaction involving nicotinamide dianucleotide.
Application - In dehydrated fruits, and vegetables, fruit juices, syrups, concentrates, purees and in wine making industry.
Fruit juices, syrups, Concentrates, Purees- 350-600 ppm
Wines- During fermentation 50-100 ppm required
During bulk storage 50-75 ppm required.
Fruit and vegetables for dehydration
Fruits exposed to SO2 at 43oC to 49o C
Vegetable dipped in solution of neutral Sulfites and Bisulfites
Apricot, peaches – 2000 ppm
Pears- 1000 ppm
Raisins 1500 ppm
Apples - 800 ppm
Carrot and potatoes 200 to 250 ppm
Meat and fishes- Help in eliminating black spot formation in shrimp.
Nitrates
Ø Nitrite salt soluble in water but not in ethanol
Ø Add directly or lipuid ingredient or produced by the action of nitrate reducing bacteria on a source of nitrate in the food
Ø Effective pH- 5.0-5.5
Ø 150-200 ppm of nitrate inhibit clostridia in canned comminuted and cured meat.
Hexamine
Ø Acts as a preservative by slow breakdown to formaldehyde.
Ø Used in canned fish and many other popular semi preserved specialties in Scandinavian countries and in the continent.
Dehydroacetic Acid
Ø Insoluble in water, but soluble in the sodium salt.
Ø Effective at all pH values and application is many perishable foods.
Ø Effective at low pH concentration.
Ø Used to control ripening in U.S.A.
Carbon Dioxide
Gas at ambient temperature and solidifies at –78.5 Co.
Effective - Effective against mould, and gram negative psychotropic bacteria
Mechanism : By exclusion of oxygen
Acidification of the cell interior
Interference with cellular enzyme
Used : Evolved by meat products in gas permeable films.
In MAP for beef, pork, poultry , and other food product.
Hydrogen Peroxide
Mechanism : > Antimicrobial effect is due to its oxidative properties.
> Bactericidal and sporicidal
> Bactericidal and sporicidal
Application : Increase keeping quality of milk, cheese milk, cultured buttermilk, sour cream, egg and fish products.
Fatty Acid Ester
Ø Certain fatty acid esters have antimicrobial activity in food.
Ø Most effective is Glyceryl Monolaurate (monolaurin).
Ø Effective against gram positive bacteria, molds, and yeasts.
Ø Less effective against Gram negative.
Ø Efficiency increase in presence of EDTA and inhibit Gram negative bacteria.
Glucose Oxidase
§ Produce hydrogen peroxide by catalyzing the oxidation of glucose to Gluconic Acid.
§ Present in honey responsible for production for H2O2 as an inhibitory agents.
§ Inhibit bacteria include acinetobacter, Bacillus cereus, Salmonella etc.
Lactoperoxidase System
Ø Molecular weight – 7,83,000 Daltion.
Ø Glycoprotein with one heme group and 9.9-10.2% carbohydrates.
Ø Present in raw milk, colostrums, saliva and other biological secretion.
Ø Form antimicrobial compound reacting with Pseudohalogen Thiocyanate and Hydrogen Peroxide.
Ø Disrupts cell function.
Ø Damage the sugar and amino acid transport system.
Ø Inhibits viruses, gram positive and gram negative bacteria, fungi.
Limitation :
Ø Adhere to surfaces such as glass.
Ø Inactivated by reducing compound and enzyme such as Horseradish Peroxidase.
Ø Enzymes competing for H2O2 can reduce the inhibitory activity of LPS.
Ø Inhibited by Suofhydryl containing compound (Cysteine) and by skim milk that received serve heat treatment.
Ovotransferrin
Ø Albumen constituent of egg white
Ø Have two iron binding sites each bound by anion
Ø Effective ph - 9.5
Ø Mechanism : functions by sequestering available ferric ion
Avidin
Chemical Nature : Water soluble Glycoprotein
Source : Egg albumin
Structure : Made up of four identical Polypetides subunits
Mechanism : > Bacteriostatic agent
> Binds biotin
Application : Pharmaceuticals
Conalbumin
Source : About 10-12% of the total egg white solids.
Mechanism :
- Binding of iron
- Retard the growth of microorganism
- Extend the lag phase of growth
- Decrease the rate of multiplication
Property : Sensitive to heat and 80% of the activity is lost with heating to 70-79o C for 3 min.
Effectiveness : Gram positive are more effective than gram negative bacteria.
Indirect Antimicrobial
Compounds that are added to foods for purposes other than their antimicrobial effects.Vanillic Acid : Vanillic Acid and its ester used in fruits, bread and cheese spreads.
Used to wash vegetables, whole fruits such as oranges.
Boric Acid
Ø Antimold
Ø Used in treating citrus products which are to be shipped as fresh.
Ø Application involve treating with 8% solution before Waxing.
Borax (Sodium Tetraborate) :
Phosphoric Acid :
Used in some soft drinks e.g. Cola.
Antibiotics are secondary metabolite produced by microorganism than inhibit or kill a wide spectrum of other microorganism.
Limitations
Sugar
Mechanism : Make water unavailable to organisms and to their osmotic effect.
Application :
- Sweetened condensed milk, fruit in syrups.
- Requires about six times more Sucrose than NaCl.
- Pies, Cakes is stable due to high concentrations of sugar.
Sodium Chloride
Mechanism :
- Reduce water activity and create unfavorable condition for microbial growth.
- Causes high osmotic pressure and hence plasmolysis of cells.
- Dehydrate foods by drawing out moisture.
- Ionizes to yield the chlorine ion.
- Reduce the solubility of oxygen in the moisture.
- Sanitizes the cell against carbon dioxide.
- Interferes with the action of proteolytic enzymes.
- Relatively low concentration stimulates microbial growth whereas high concentration inhibits growth.
- Inhibit pathogenic bacteria, toxic producing fungi.
Flavouring Agents
> More antifungal than antibacterial.
> Non lactic, gram positive bacteria are most sensitive.
> Diacetyl is most effective flavouring agents.
Propylene Glycol
Ø Also called 1,2 propanediol.
Ø Prepared by propylene with chlorinated water to form the Chlorohydrin
Mechanism :
- Reduce water activity.
- Alters the permeability of the cell membrane.
Spices
Ø Whole spices are more effective than spice extracts.
Ø The antimicrobial activity of spices is due to presence of essential oils.
Ø Gram positive organism more sensitive than gram negative organism.
Ø Cinnamon, clove, and mustard are strong inhibitors while black pepper, red pepper and ginger are weak inhibitors.
Ø Onions contains two Phenolic Compound : Protocatechuric Acid and Catechol.
Ø Inhibition of microbial spoilage in mayonnaise based delicatessen salads with onion extract was demonstrated.
Ethanol
Ø A colourless liquid, miscible in water and have boiling point of 78o C.
Ø Bactericidal but not sporicidial.
Ø Denature protein in the cytoplasm at high concentration.
Ø Reduce water activity at low concentration.
Ø Used in sweet wines.
Ø Approved for use as a direct antimicrobial in pizza crust not exceed 2% by product weight.
Chitosan
Ø A polycationic polymer obtained by alkaline hydrolysis of chitin from the shells of Crustaceae.
Ø Destabilize the cell wall and cell membrane functions.
Ø Effective against bacteria, yeasts and molds.
Ethyl Formate
Ø A flammable liquid (C3H6O2, -74)
Ø Soluble in water about 10 parts.
Ø Decompose into alcohol and free formic acid.
Ø A yeast and mould inhibitor in nuts, dried fruits and cereals.
Ø Permissible levels is 15 to 200 ppm.
Methyl Formide
Ø Also known as Bromomethane.
Ø Colourless gas (CH3Br, m.w. 94.95).
Ø Free soluble in ethanol.
Ø Fumigant and fungistat for dates.
Ø Permissible level is 100 ppm.
Chlorine Dioxide
Ø Has the odour of chlorine.
Ø Unstable in light.
Ø Solubility in water is 3 g/l.
Ø Hydrolysis to Chlorous and Chloric Acid.
Ø Less than 1 ppm apply to decontaminate meat carcasses.
Ø Sodium and Potassium Nitrite used in curing of meat alongwith Sodium Erythorbate or Sodium Ascorbate.
Ethylene Diaminetetracetate
§ Have no much antimicrobial effect.
§ Destabilize the barrier functions of the outer membrane of the Gram negative bacteria and also of Gram positive bacteria.
§ Enhance the antibacterial action of membrane acting chemicals like antioxidants, bacteriocins.
§ Inhibit germination of C. Botulinin’s spore.
§ Limitation : Divalent cations reduce the effectiveness of EDTA.
Bipehenyl
Ø Used to control the decay of citrus fruit by Penicillia for long distance shipment
Ø Generally impregnated into fruit wraps or sheets between fruit layer.
Benomyl
Ø Applied uniformly over the entire surface of fruits
Ø Applied at concentration of 0.5 to 1.0 g/l .
Medium Chain Fatty Acid
Ø Medium chain fatty acids containing 12-18 carbons atoms are most effective.
Ø Primarily bacteriostatic rather than bacteriocidal.
Ø Lauric, Myristic and Palmitic effective against bacteria.
Ø Capric and Lauric Acid effective against yeasts.
Ø Inhibitory activity increase with the increase in double bonds in unsaturated fatty acids.
Ø Undissociated form responsible for antimicrobial activity.
Antibiotics
Wood Smoking
Ø Smoke generated by burning hardwood such as oak, walnut etc.
Ø May be bacteriostatic or bactericidial and slight antifungal.
Ø Contain volatile compound like Formaldehyde, phenols, cresols. May contain Aldehyde, waxes, Ketones, Acetaldehyde, resins, Guaiacol, and its methyl and propyl isomers, Catechol, Methyl Catechol, and Pyrogallol and its methyl ester.
Ø More effective against vegetative cells than bacterial spores.
Ø Used mainly for meat.
Ø Liquid smoke similar in chemicals but has little preservative effect.
Limitation :
- Contain carcinogenic chemicals like Benzopyrene and Dibenzanthracene so take little consumption of foods treated with smoke to reduce colon cancer.
- It improve colour and have a tenderizing action on meats.
Limitations
Ø Toxicological data for natural antimicrobial are lacking and are as expensive to assemble as data for chemical compounds.
Ø With the exception of Nisin, Natamycin and Lysozyme, no isolated naturally occurring antimicrobial are approved for use in foods by regulatory agencies.
Ø Some of the chemicals used as preservatives are controversial in terms of the health risk involved and the benefits of extending the shelf life of the food.
Ø The antimicrobial activity range of most known bacteriocins is narrow and does not extend to the Gram negative bacteria.
Ø The amount of bacteriocin produced when a producing LAB is added to a food, is quite low due to insufficient growth of the LAB and absorption of the bacteriocin onto the food matrix.
Ø The genetic information allowing for bacteriocin production in some cases is not stable.
Trends in Future
Ø Vogler et al suggested a future preservatives that these consists of combinations of amino acids and fatty acids and are claimed to breakdown to their components which are readily digested in the usual way without any toxicity to the consumer.
Ø Attempts are being made to replace the controversial chemicals with new antimicrobials or combinations of safe chemicals.
Ø A proper study on the use of spices as antimicrobials agents will be helpful in avoiding or reducing the risk associated with the addition of chemical preservatives to foods.
Ø Current research trends in food microbiology and food technology focus on mild, physical preservative techniques and the use of natural antimicrobial compounds.
Conclusions
The naturally present antimicrobials and organic acids exhibit good inhibitory properties.
