Food Preservation- Chemical Preservatives with Types, Examples

Chemical preservatives are intentional food additives incorporated into food to prevent or retard food spoilage caused by microbiological, enzymological, or chemical reactions.

These chemical preservatives should be nontoxic to humans or animals.
Chemical preservatives come under the food additives generally recognized as safe (GRAS).
Chemical preservatives can also be termed antimicrobials.
The main purpose of using chemical preservatives is to inhibit the growth and activity of foodborne pathogens and spoilage microorganisms.
Chemical preservatives used in food can have both bacteriostatic and bactericidal properties per the concentration used.

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How food can get chemical preservatives?

Intentional addition during food production, processing, or packaging
Chemical migration from the packaging materials
Due to a chemical reaction occurring in food
Residues of pesticides, herbicides, and fungicides on raw food materials
Migration of disinfectants used on utensils or equipment into foods

Role of chemical preservatives

Interferes with the cell wall, cell membrane, enzymatic activity, nucleic acids, etc., to prevent microorganisms’ growth and activity.
Retard, prevent or control undesirable changes in flavor, color, texture, or consistency of food and nutritive value of food.
Control natural spoilage of food

Chemical Preservatives as Food Preservation

Classification of chemical preservatives

Class I: Traditional preservatives (natural)
Class II: Chemical preservatives (Artificial)

Class I: Traditional Preservatives: These include preservatives like wood, smoke, sugar, honey, salt, spices, alcohol, vinegar, vegetable oil, spices, etc which are commonly used in our kitchen in past. These chemical preservatives are not restricted to use and there is no imposed limitation on their use. These naturally occurring preservatives are regarded as safe for human health.

Class II: Chemical preservatives: These are synthetic chemical preservatives that are made in the laboratory. For e.g nitrites, propionates, parabens, benzoates, acetates, sorbates, sulfur dioxide, etc.

Microbial preservatives: These include antimicrobial preservatives like bacteriocins (e.g. nicin) which are produced by some strains of lactic acid bacteria and inhibit the growth of food spoilage or pathogenic bacteria. E.g nisin, produced by lactococcus lactis inhibits the growth of Clostridium tyrobutyricum, C. botulinum, and, listeria monocytogenes in cheese, other dairy products meats, fish, etc. Using bacteriocins like microbial preservatives help reduce the use of chemical preservatives like nitrates, sorbates, and benzoates which consumers consider bad.

Ideal properties of chemical preservatives

Some food preservatives and their acceptable daily intake

Chemical preservatives with their ADI quantities (mg/kg BW). E (Europe) number refer to code for substance used as food additives. The E numbers for preservatives range from E200 to E399.

Table1: According to EU regulation, chemical food additives with their ADI quantities.

S.N.	Chemical preservative	E number	ADI (mg/kg BW)
1	Sorbic acid	E200	25
2	Sodium sorbate	E201	25
3	Potassium sorbate	E202	25
4	Benzoic acid	E210	5
5	Sodium benzoate	E211	5
6	Parabens	E214-E219	10
7	Sulfur dioxide and Sulfites	E220-E228	0.7
8	Potassium nitrite	E249	0.07
9	Sodium nitrite	E250	0.1
10	Sodium nitrate +	E251 +	3.7
11	Potassium nitrate	E252	3.7
12	Acetic acid	E260
13	Propionic acid and propionates	E280- E289	5

Source: Adding Molecules to Food, Pros, and Cons: A Review on Synthetic and Natural Food Additives. Marcio Carocho, Maria Filomena Barreiro, Patricia Morales, and Isabel C.F.R. Ferreira.

Factors affecting the effectiveness of chemical preservatives

Chemical preservative properties

Solubility
Toxicity

Microbial factors

Microbial inherent resistance to chemical preservatives
Initial microbial load
Growth rate and phase of microorganisms
Stress reaction of microorganisms
Homeostasis ability of microorganisms
Use of additional preservative methods

Intrinsic factors of food

pH of the food
Water activity of food

Extrinsic factors

Storage time and temperature
Gas composition
Atmosphere and relative humidity

Different chemical preservatives and their application in the food industry

S.N	Chemical preservatives	Targeted microorganisms	Mode of action	Advantages	Disadvantages	Applications
1	Sulfur dioxide (SO₂)	Yeast, mold	Increase pH and imbalance cellular metabolic process, alter the enzymatic system,	Antioxidant properties, prevent browning, preserve color, cheaper and easily available	The intense pungent odor and corrosive property makes it unuseful in canning	Beverages, fruits products, heat-sensitive foods, effective for low pH foods
2	Sorbates(Sodium sorbate and Potassium sorbate)	Yeast, Mold, Bacteria	Disturb enzyme system, inhibit many enzymes involved in TCA cycle			Beverages; juices, wines, cheese, fish meat bakery items,
3	Benzoic acid and benzoates	Yeast, molds	Disturb enzymatic system	Most active against yeasts and molds. Used to preserve colored fruit juices	Risk of respiratory disease	High acid foods, fruit drinks, cider, carbonated beverages, pickles, jams, salad dressings, soy sauce
4	Parabens (p-hydroxybenzoic acid)	Yeast, Mold, bacteria	Destroy complex structure of the cell and denature protein inside the cell			Soft drinks, fish products, salad dressing
5	Propionic acid	Mold, yeast, and a few bacteria	Disturb enzyme system			Low acid foods, processed cheese preservation
6	Nitrate and nitrite	Anaerobic bacteria (Clostridium botulinum), other pathogenic microbes	Inhibit metabolic enzyme	Preserve the color of red meat by forming nitrosomyoglobin	The formation of carcinogenic nitrosamines is triggering extensive research	Used in cured meats, better at low pH foods
7	Phosphates	More against gram-positive bacteria (Bacillus, clostridium)	Chelating metal ions
8	Sulfites	More Bacteria, less effective to yeast and mold	Target to the cytoplasmic membrane, DNA replication, protein synthesis, and enzymatic actions	Acts as antioxidants and inhibit enzymatic browning		Fruits and vegetable products, wine
9	Sodium chloride (NaCl)	Bacteria	Osmotic shock to Plasmolysis	Better preservation if used as a pretreatment before canning, pasteurization, or drying	Weak against Staphylococcus and listeria monocytogens	Salting of meats and fish
10	Wood smoke (Traditional method)	Bacteria, fungi	The release of different phenolic compounds, ketones, aldehyde, and alcohol, which serves as an antimicrobial preservative	Easy to use		Meat, sausage, ham, bacon, fish
11	Nisin	Clostridium botulinum and other bacteria				Cheese, cooked meat, poultry

The working mechanism of organic acids on the bacterial cell

Organic acids like Acetic acid, benzoic acid, lactic acid, propionic acid, sorbic acid, etc., are effective as preservatives for foods with a pH of less than 5. So, they are the best for preserving acidic foods.

At acidic pH, protonated or uncharged organic acid crosses the cell membrane and enters the cytoplasm.
In neutral cytoplasmic pH, organic acids dissociate and release the proton that acidifies the cytoplasm.
This cell uses ATP to pump protons out of the cell to deacidify the cytoplasm, which makes energy unavailable for their growth.

Table: Guidelines for using chemical preservatives in food by DFTQC, Nepal 2075 B.S. (2018 A.D.)

S.N.	Food	Preservatives	PPM
1	Sausage meat containing raw meat, Cereals, spices	Sulfur dioxide	450
2	Undried fruits: Cherries, Strawberries, and raspberries. Other fruits	Sulfur dioxide	2000 1000
3	Concentrated fruit juice	Sulfur dioxide	1500
4	Dried fruits	Sulfur dioxide	1500
5	Apricots, peaches, apples, pears	Sulfur dioxide	2000
6	Sugar, dextrose, jaggery, refined sugar	Sulfur dioxide	70
7	Beer	Sulfur dioxide	70
8	Cider	Sulfur dioxide	200
9	Alcoholic wine	Sulfur dioxide	450
10	Dried ginger	Sulfur dioxide	2000
11	Squash, fruit syrups, barley water	Sulfur dioxide, or benzoic acid	350 600
12	Pickles	Sulfur dioxide, or benzoic acid	250 100
13	Jam, marmalade, fruit jelly	Sulfur dioxide, or benzoic acid	40 200
14	Coffee extract	Benzoic acid	120
15	Tomato or other juices	Benzoic acid	750
16	Pickled meat, bacon, canned meat	Sodium nitrite or potassium nitrite	200
17	Cheese or processed cheese	Sorbic acid or Sodium sorbate or potassium sorbate	3000
18	Paneer	Sorbic acid or Sodium sorbate or potassium sorbate	2000
19	Flour confectionery	Sorbic acid or Sodium sorbate or potassium sorbate	1500
20	Baking flour	Sodium diacetate, Propionates, Methyl propyl hydroxybenzoate	2500 3200 500

Do you know?

Nitrite and nitrate preservatives should not be used in infant foods.
The use of titanium dioxide (E171) is fully banned as a food additive in the EU.

“Preservatives can be used to extend the expiration dates of food but unfortunately not of people.”

References

Potter NP (1987), Food Science, CBS Pub, India
Rahman MS (1999), Handbook of Food Preservation, Marcel Dekker, Inc, NY
Desrosier EN (1963), The Technology of Food Preservation, AVI Publishing Company, New York
Thomas J. Montville, Food microbiology an introduction (third edition), ASM Press, Washington, DC
PAȘCA, C., COROIAN, A., & SOCACI, S. (2018). Risks and Benefits of Food Additives – Review. Bulletin Of University Of Agricultural Sciences And Veterinary Medicine Cluj-Napoca. Animal Science And Biotechnologies, 75(2), 71. DOI: 10.15835/buasvmcn-asb:2018.0026.
Department of Food Technology and Quality Control (DFTQC), 2075 guideline