What are Chemical preservatives?

• Chemical preservatives are substances that are added to food intentionally to prevent or slow down food spoilage caused by various factors such as microorganisms, enzymes, or chemical reactions. They are classified as food additives and are generally recognized as safe (GRAS) for consumption by humans and animals.
• The primary function of chemical preservatives is to inhibit the growth and activity of foodborne pathogens and spoilage microorganisms. By doing so, they help to extend the shelf life of food products and maintain their quality and safety. Chemical preservatives can have both bacteriostatic and bactericidal properties, depending on the concentration used. Bacteriostatic preservatives inhibit the growth of bacteria, while bactericidal preservatives kill or destroy bacteria.
• Chemical preservatives are carefully selected to ensure they are effective against specific types of microorganisms and do not pose a risk to human health. Common examples of chemical preservatives include benzoates, sorbates, sulfites, nitrites, and propionates. These preservatives can be added to various food products, including baked goods, beverages, dairy products, meat products, and canned foods.
• It is important to note that the use of chemical preservatives in food is subject to regulations and guidelines set by food safety authorities. The permitted levels of preservatives in food are determined based on extensive research and safety evaluations. Consumers should always read food labels to be aware of the presence of chemical preservatives and their specific usage in different food products.
• While chemical preservatives play a valuable role in food preservation, it is also important to consider alternative methods such as natural preservatives and good manufacturing practices to ensure the safety and quality of food without relying solely on chemical additives.

How Foods Get Chemical Preservatives?

Food can acquire chemical preservatives through various means:

1. Intentional addition during food production, processing, or packaging: Food manufacturers may deliberately incorporate chemical preservatives into their products to enhance their shelf life and prevent spoilage. These preservatives are carefully selected and added in specific amounts to ensure their effectiveness and safety.
2. Chemical migration from packaging materials: Some packaging materials, such as plastic containers or cans, may contain chemicals that can migrate into food over time. These chemicals can act as preservatives and help prolong the shelf life of the packaged food. However, food safety regulations set limits on the amount of migration allowed to ensure consumer safety.
3. Chemical reaction occurring in food: In certain cases, chemical reactions can naturally occur within the food itself, resulting in the formation of compounds with preservative properties. For example, the fermentation process in certain foods produces organic acids that act as natural preservatives.
4. Residues of pesticides, herbicides, and fungicides on raw food materials: Agricultural practices often involve the use of pesticides, herbicides, and fungicides to protect crops from pests and diseases. Some residues of these chemicals can remain on the harvested produce. While these residues are regulated and controlled, they can contribute to the preservation of the food by inhibiting the growth of spoilage microorganisms.
5. Migration of disinfectants used on utensils or equipment into foods: During food preparation and processing, disinfectants and sanitizers may be used to clean utensils, equipment, and food contact surfaces. If not rinsed off thoroughly, traces of these chemicals can end up in the food, potentially acting as preservatives.

Role of chemical preservatives 

Chemical preservatives play a crucial role in food preservation by performing several functions:

1. Inhibition of Microbial Growth: Chemical preservatives interfere with the cell wall, cell membrane, enzymatic activity, nucleic acids, or other essential components of microorganisms. By doing so, they prevent the growth and activity of bacteria, yeasts, molds, and other microorganisms that can cause food spoilage and foodborne illnesses. This inhibition of microbial growth helps to extend the shelf life of food products and maintain their safety.
2. Preservation of Quality Attributes: Chemical preservatives are employed to retard, prevent, or control undesirable changes in the flavor, color, texture, or consistency of food. They help to maintain the sensory attributes of food products and prevent or delay the development of off-flavors, discoloration, texture degradation, and other quality defects that can occur during storage.
3. Retention of Nutritive Value: Chemical preservatives can also contribute to preserving the nutritive value of food. By inhibiting microbial growth and enzymatic activity, they help to slow down the degradation of essential nutrients, such as vitamins, minerals, and proteins. This retention of nutritive value ensures that the food remains nutritious and provides essential nutrients even during extended storage periods.
4. Control of Natural Spoilage: Chemical preservatives are effective in controlling the natural spoilage processes that occur in food. They inhibit the growth of spoilage microorganisms that can lead to the deterioration of food quality, including off-flavors, odors, and texture changes. By controlling natural spoilage, chemical preservatives help to maintain the freshness and overall quality of food products.

Classification of chemical preservatives

Chemical preservatives can be classified into different categories based on their nature and origin. Here are three common classifications of chemical preservatives:

1. Class I: Traditional Preservatives (Natural): These preservatives include naturally occurring substances that have been used for centuries to preserve food. Examples of traditional preservatives include salt, sugar, honey, vinegar, vegetable oil, spices, smoke, and alcohol. These preservatives are derived from natural sources and have been traditionally used in various cultures for their antimicrobial and antioxidant properties. Class I preservatives are generally regarded as safe for human consumption, and there are no specific limitations on their use.
2. Class II: Chemical Preservatives (Artificial): Chemical preservatives in this category are synthetic compounds that are manufactured in laboratories. They are specifically designed to inhibit microbial growth and extend the shelf life of food products. Examples of Class II preservatives include nitrites, propionates, parabens, benzoates, acetates, sorbates, and sulfur dioxide. These preservatives are widely used in processed foods, beverages, and food products that require longer shelf life and improved safety. The use of Class II preservatives is regulated by food safety authorities to ensure their safety and to establish acceptable levels of use.
3. Microbial Preservatives: Microbial preservatives are a special category of preservatives that utilize naturally occurring antimicrobial compounds produced by certain microorganisms. Bacteriocins, such as nisin produced by Lactococcus lactis, are examples of microbial preservatives. Bacteriocins have antimicrobial activity against specific bacteria and are used to inhibit the growth of food spoilage or pathogenic bacteria. The use of microbial preservatives can reduce the reliance on chemical preservatives and offer an alternative for food preservation, particularly in the dairy industry.

Examples of Some food preservatives and their acceptable daily intake

Here are some food preservatives commonly used in the food industry, along with their E numbers and acceptable daily intake (ADI) quantities:

1. Sorbic acid (E200): ADI of 25 mg/kg BW
2. Sodium sorbate (E201): ADI of 25 mg/kg BW
3. Potassium sorbate (E202): ADI of 25 mg/kg BW
4. Benzoic acid (E210): ADI of 5 mg/kg BW
5. Sodium benzoate (E211): ADI of 5 mg/kg BW
6. Parabens (E214-E219): ADI of 10 mg/kg BW
7. Sulfur dioxide and Sulfites (E220-E228): ADI of 0.7 mg/kg BW
8. Potassium nitrite (E249): ADI of 0.07 mg/kg BW
9. Sodium nitrite (E250): ADI of 0.1 mg/kg BW
10. Sodium nitrate + (E251 +): ADI of 3.7 mg/kg BW
11. Potassium nitrate (E252): ADI of 3.7 mg/kg BW
12. Acetic acid (E260): No specific ADI mentioned
13. Propionic acid and propionates (E280-E289): ADI of 5 mg/kg BW

It’s important to note that the ADI represents the amount of a specific food additive that can be consumed daily over a lifetime without any appreciable health risk. These ADI values are established based on scientific assessments conducted by food safety authorities and are subject to ongoing evaluation and revision as new data becomes available. The ADI quantities mentioned here are specific to European Union regulations and may vary in other countries or regions.

Factors affecting the effectiveness of chemical preservatives 

The effectiveness of chemical preservatives in food is influenced by various factors. Here are some key factors that can affect their effectiveness:

1. Chemical preservative properties:
   • Solubility: The solubility of the preservative in the food matrix affects its distribution and availability to inhibit microbial growth.
   • Toxicity: The concentration and toxicity of the preservative can determine its effectiveness in controlling microorganisms.
2. Microbial factors:
   • Microbial inherent resistance: Some microorganisms may naturally possess resistance mechanisms against specific preservatives, which can reduce their effectiveness.
   • Initial microbial load: The initial population of microorganisms in the food can influence the efficacy of preservatives. Higher initial load may require higher concentrations of preservatives.
   • Growth rate and phase: Microorganisms in different growth phases may respond differently to preservatives, with actively growing cells being more susceptible.
   • Stress reaction: Microorganisms can activate stress response mechanisms to counteract the effects of preservatives, reducing their effectiveness.
   • Homeostasis ability: Some microorganisms have the ability to maintain internal pH or ion concentrations, which can affect their susceptibility to preservatives.
   • Use of additional preservative methods: The combined use of multiple preservatives or preservation techniques can enhance overall effectiveness.
3. Intrinsic factors of food:
   • pH of the food: The acidity or alkalinity of the food can impact the antimicrobial activity of preservatives. Certain preservatives are more effective in acidic or alkaline conditions.
   • Water activity: The water activity level in food affects microbial growth. Preservatives may be more effective in low water activity environments.
4. Extrinsic factors:
   • Storage time and temperature: Extended storage time and improper temperatures can compromise the effectiveness of preservatives, allowing microbial growth.
   • Gas composition: The presence of certain gases, such as oxygen or carbon dioxide, can influence the growth of specific microorganisms and affect preservative efficacy.
   • Atmosphere and relative humidity: The surrounding environment, including atmospheric conditions and humidity, can impact the growth and survival of microorganisms.

Examples of Different chemical preservatives and their application in the food industry

Different chemical preservatives are used in the food industry to inhibit the growth of microorganisms and extend the shelf life of food products. Here are some commonly used chemical preservatives, along with their target microorganisms, mode of action, advantages, disadvantages, and applications:

1. Sulfur dioxide (SO2):
   • Targeted microorganisms: Yeast, mold
   • Mode of action: Increase pH and imbalance cellular metabolic processes, alter the enzymatic system
   • Advantages: Antioxidant properties, prevents browning, preserves color, easily available
   • Disadvantages: Intense pungent odor, corrosive properties, unsuitable for canning
   • Applications: Beverages, fruit products, heat-sensitive foods, effective for low pH foods
2. Sorbates (Sodium sorbate and Potassium sorbate):
   • Targeted microorganisms: Yeast, mold, bacteria
   • Mode of action: Disturbs the enzyme system, inhibits many enzymes involved in the TCA cycle
   • Advantages: Effective against a wide range of microorganisms
   • Disadvantages: None significant
   • Applications: Beverages (juices, wines), cheese, fish meat, bakery items
3. Benzoic acid and benzoates:
   • Targeted microorganisms: Yeast, molds
   • Mode of action: Disturbs the enzymatic system
   • Advantages: Most active against yeasts and molds, used to preserve colored fruit juices
   • Disadvantages: Risk of respiratory disease
   • Applications: High acid foods, fruit drinks, cider, carbonated beverages, pickles, jams, salad dressings, soy sauce
4. Parabens (p-hydroxybenzoic acid):
   • Targeted microorganisms: Yeast, mold, bacteria
   • Mode of action: Destroys the complex structure of the cell and denatures proteins
   • Advantages: Effective against a variety of microorganisms
   • Disadvantages: None significant
   • Applications: Soft drinks, fish products, salad dressings
5. Propionic acid:
   • Targeted microorganisms: Mold, yeast, and a few bacteria
   • Mode of action: Disturbs the enzyme system
   • Advantages: Effective against molds and yeast
   • Disadvantages: None significant
   • Applications: Low acid foods, processed cheese preservation
6. Nitrate and nitrite:
   • Targeted microorganisms: Anaerobic bacteria (Clostridium botulinum), other pathogenic microbes
   • Mode of action: Inhibit metabolic enzymes, preserve the color of red meat
   • Advantages: Preserves meat color, prevents botulism
   • Disadvantages: Formation of carcinogenic nitrosamines
   • Applications: Cured meats, especially at low pH
7. Phosphates:
   • Targeted microorganisms: More effective against gram-positive bacteria (Bacillus, Clostridium)
   • Mode of action: Chelating metal ions
   • Advantages: None significant
   • Disadvantages: None significant
   • Applications: Various food products
8. Sulfites:
   • Targeted microorganisms: More effective against bacteria, less effective against yeast and mold
   • Mode of action: Targets the cytoplasmic membrane, DNA replication, protein synthesis, and enzymatic actions
   • Advantages: Acts as antioxidants, inhibits enzymatic browning
   • Disadvantages: May cause allergic reactions in some individuals
   • Applications: Fruits and vegetable products, wine
9. Sodium chloride (NaCl):
   • Targeted microorganisms: Bacteria
   • Mode of action: Osmotic shock, plasmolysis
   • Advantages: Better preservation if used as a pretreatment, enhances flavor
   • Disadvantages: Weak against Staphylococcus and Listeria monocytogens
   • Applications: Salting of meats and fish
10. Wood smoke (Traditional method):

• Targeted microorganisms: Bacteria, fungi
• Mode of action: Release of antimicrobial phenolic compounds, ketones, aldehydes, and alcohols
• Advantages: Easy to use, imparts unique flavors
• Disadvantages: None significant
• Applications: Meat, sausage, ham, bacon, fish

11. Nisin:

• Targeted microorganisms: Clostridium botulinum and other bacteria
• Mode of action: Disrupts cell wall synthesis
• Advantages: Effective against specific bacteria, natural preservative
• Disadvantages: Limited range of activity
• Applications: Cheese, cooked meat, poultry

These are just a few examples of chemical preservatives used in the food industry. Each preservative has specific characteristics and applications, allowing food manufacturers to select the most suitable option based on their desired preservation goals and specific food products.

The working mechanism of organic acids on the bacterial cell

Organic acids, such as acetic acid, benzoic acid, lactic acid, propionic acid, and sorbic acid, have antimicrobial properties and are commonly used as preservatives for acidic foods. Here is the working mechanism of organic acids on bacterial cells:

1. Entry into the cell: At acidic pH, the protonated or uncharged form of organic acids can easily cross the bacterial cell membrane and enter the cytoplasm.
2. Acidification of the cytoplasm: Once inside the cytoplasm, in a neutral pH environment, the organic acids dissociate and release protons (H+ ions), thereby lowering the cytoplasmic pH and creating an acidic environment.
3. Energy depletion: The acidic cytoplasm triggers the bacterial cell to utilize ATP (adenosine triphosphate) to pump protons out of the cell, aiming to deacidify the cytoplasm. This process consumes energy, depriving the bacteria of the required energy for growth and survival.

By disrupting the intracellular pH homeostasis and depleting energy resources, organic acids effectively inhibit the growth and survival of bacteria. They interfere with essential metabolic processes and enzyme activities, ultimately leading to the inhibition of microbial growth and the preservation of food.

It is important to note that the effectiveness of organic acids as preservatives is influenced by various factors such as the concentration of the preservative, pH of the food, temperature, and the specific microorganisms targeted. The recommended usage levels of chemical preservatives, including organic acids, may vary depending on the food product, as indicated in the guidelines provided in the table. These guidelines help ensure the safe and effective use of chemical preservatives in food production and processing.

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