Lecture 10 Preservatives

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Food Chemistry Lecture 10: Preservatives

Transcript of Lecture 10 Preservatives

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Food Chemistry

Lecture 10: Preservatives

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Introduction

A preservative is a natural or synthetic chemical that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes

Why add preservatives to food? To prevent lipid and fat oxidation – taste and smell bad and

harmful for consumption To prevent molds & bacteria from growing.

Difference between food additives and food preservatives Food Additives – any substances that becomes part of a

food product when added through processing, storage or packaging

Food Preservatives – any additives that extend a food's freshness or shelf life and keep it from spoiling or oxidizing

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Type of Preservatives

Preservative food additives can be used alone or in conjunction with other methods of food preservation

Synthetic Preservatives Common anti-microbial preservatives include

• Calcium propionate• Sodium nitrate• Sodium nitrite• Sulphites (sulfur dioxide, sodium bisulfite, potassium hydrogen

sulfite, etc.)• Disodium EDTA

Antioxidants • BHA and BHT

Other preservatives (non-food)• Formaldehyde• Glutaraldehyde• Methylchloroisothiazolinone

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Type of Preservatives

Natural PreservativesOrganic acid

• Citric acid• Benzoic acid• Sorbic acid• Propionic acid• Acetic acid

Vitamin CTocopherols

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Food Additives

Acids  Food acids are added to make flavors "sharper", and also act

as preservatives and antioxidants. vinegar, citric acid, tartaric acid, malic acid, fumaric acid, lactic acid

Acidity regulators  Acidity regulators are used to change or otherwise control the

acidity and alkalinity of foods. Citric, acetic and lactic acids Anticaking agents 

Anticaking agents keep powders such as milk powder from caking or sticking. Calcium carbonate, Magnesium Carbonate

Antifoaming agents  Antifoaming agents reduce or prevent foaming in foods. Silicone

derivatives Antioxidants 

Antioxidants such as vitamin C act as preservatives by inhibiting the effects of oxygen on food, and can be beneficial to health.

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Food Additives

Bulking agents  Bulking agents such as starch are additives that increase the bulk

of a food without affecting its nutritional value. Food coloring 

Colorings are added to food to replace colors lost during preparation, or to make food look more attractive.

Color retention agents  In contrast to colorings, color retention agents are used to preserve

a food's existing color: Ascorbic acid Emulsifiers 

Emulsifiers allow water and oils to remain mixed together as in mayonnaise, ice cream, and homogenized milk: Lecithin

Flavors  Flavors are additives that give food a particular taste or smell, and

may be derived from natural ingredients or created artificially

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Food Additives

Humectants Humectants prevent foods from drying out: Glycerine

Preservatives  Preservatives prevent or inhibit spoilage of food due to fungi,

bacteria and other microorganisms: Nitrites Stabilizers 

Stabilizers, thickeners and gelling agents, like agar or pectin (used in jam for example) give foods a firmer texture. While they are not true emulsifiers, they help to stabilize emulsions

Sweeteners  Sweeteners are added to foods for flavoring. Sweeteners other

than sugar are added to keep the food energy (calories) low: Table sugar

Thickeners  Thickeners are substances which, when added to the mixture,

increase its viscosity without substantially modifying its other properties: Guar gum, xanthan gum

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Calcium Propionate

Calcium propionate or calcium propanoate is the calcium salt of propionic acid

As a food additive, it is listed as E number 282 in the Calcium propionate is used as a preservative in a wide

variety of products, bread, other bakery goods, processed meat and other dairy products

In agriculture, it is used, amongst other things, to prevent milk fever in cows and as a feed supplement

Propionates prevent microbes from producing the energy they need, like benzoates do.

However, unlike benzoates, propionates do not require an acidic environment.

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Calcium Propionate

Calcium propionate is used in bakery products as a mold inhibitor

Mold contamination is considered a serious problem amongst bakers, and conditions commonly found in baking present near-optimal conditions for mold growth

A few decades ago, mold was a serious problem but today's improved sanitary practices in the bakery, have virtually eliminated this form of spoilage – Calcium propionate and sodium propionate are effective against mold

According to the Pesticide Action Network North America, calcium propionate is slightly toxic

Calcium propionate can be used as a pesticide

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Sodium Nitrate

Sodium nitrate is the chemical compound with the formula NaNO3

This salt, also known as "Chile saltpeter" (to distinguish it from ordinary saltpeter, potassium nitrate), is a white solid which is very soluble in water

Sodium nitrate is used as an ingredient in fertilizers, explosives as well as in glass and pottery enamels; the compound has been mined extensively for those purposes

Sodium nitrate is also synthesized industrially by neutralizing nitric acid with soda ash

Sodium nitrate has antimicrobial properties when used as a food preservative. It is found naturally in leafy green vegetables

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Sodium Nitrite

As a food additive, it serves a dual purpose in the food industry: Enhance the color of preserved fish and meats Prevents growth of Clostridium botulinum, the bacteria which

causes botulism In the European Union it may be used only as a mixture with salt

containing at most 0.6% sodium nitrite. It has the E number E250 While this chemical will prevent the growth of bacteria, it can be

toxic for mammals. For this reason, sodium nitrite sold as a food additive is dyed bright pink to avoid mistaking it for something else

Principal dangers of using sodium nitrite as a food additive is the formation of carcinogenic nitrosamines by the reaction of sodium nitrite with amino acids in the presence of heat in an acidic environment – cooked meats

Recent studies have found a link between high processed meat consumption and colon cancer, possibly due to preservatives such as sodium nitrite

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Sulfites

Sulfites are sometimes added to foods to act as enhancers or preservatives. They may come in various forms, such as: Sulfur dioxide Potassium bisulfite or potassium metabisulfite Sodium bisulfite, sodium metabisulfite or sodium sulfite

Some humans are allergic to sulfites. It is an undeclared allergen that may cause breathing difficulty within minutes after eating a food containing sulfites

Asthmatics and people with allergies to aspirin (also known as salicylate sensitivity) are at an elevated risk for reaction to sulfites

FDA prohibits the use of sulfites in foods that are important sources of thiamin (vitamin B1), such as enriched flour, because sulfites destroy the nutrient.

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Sulfites

Sulfur dioxide Main product from the combustion of sulfur

compounds is often described as the "smell of burning sulfur" but is not responsible for the smell of rotten eggs

Sulfur dioxide is sometimes used as a preservative for dried apricots and other dried fruits due to its antimicrobial properties

The preservative is used to maintain the appearance of the fruit and prevent rotting. Its presence can give fruit a distinctive chemical taste

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Sulfites

Potassium bisulfite or potassium metabisulfite A white crystalline powder with a pungent sulfur odour The main use for the chemical is as an antioxidant or

chemical sterilant. Potassium metabisulfite is a common wine additive,

where it forms sulfur dioxide gas (SO2) This prevents most wild microorganisms from

growing, and it acts as potent antioxidant, protecting both the color, and delicate flavors of wine

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Sulfites

Sodium bisulfite, sodium metabisulfite or sodium sulfite Used in almost all commercial wines, to prevent oxidation

and preserve flavor In fruit canning, sodium bisulfite is used to prevent browning

(caused by oxidation) and to kill microbes In the case of wine making, Sodium bisulfite releases sulfur

dioxide gas when added to water or products containing water. The sulfur dioxide kills yeasts, fungi, and bacteria in the grape juice before fermentation

When the sulfur dioxide levels have subsided (about 24 hours), fresh yeast is added for fermentation.

It is later added to bottled wine to prevent oxidation (which makes vinegar), and to protect the color of the wine from oxidation, which causes browning.

The sulfur dioxide displaces oxygen in the bottle and dissolved in the wine.

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Disodium EDTA

EDTA is a widely-used abbreviation for the chemical compound ethylenediaminetetraacetic acid

EDTA refers to the chelating agent with the formula (HO2CCH2)2NCH2CH2N(CH2CO2H)2.

EDTA forms especially strong complexes with Mn(II), Cu(II), Fe(III), and Co(III)

In food application disodium EDTA is added as preservative to prevent catalytic oxidation by metal ions or stabilizer and for iron fortification

Approved by the FDA as a preservative in packaged foods, vitamins, and baby food

Oral exposures (and inhalation) have been noted to cause reproductive and developmental effects

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BHA

Butylated hydroxyanisole (BHA) is a phenolic antioxidant Phenolic antioxidants prevent rancidity of fats and oils in food by protecting

against lipid oxidation. BHA is able to stabilize free radicals by acting as free radical scavengers,

further free radical reactions are prevented When the food additives amendment was enacted (1958), BHA and BHT

were listed as common preservatives considered generally recognized as safe (GRAS). GRAS regulations limit BHA and BHT to 0.02 percent or 200 ppm of the fat or oil content of the food product.

Both BHT and BHA have been removed from the GRAS list and subjected to tolerances

BHA is also used as a preservative for dry foods, such as cereals. FDA limited BHA to 50 ppm of the total product.

Studies have suggested that at very high levels in the diets of laboratory animals, BHA could cause tumors in rats, mice and hamsters, and liver tumors in fish.

The National Institutes of Health considers BHA reasonably anticipated to be a human carcinogen.

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BHT

Butylated hydroxytoluene (BHT) is a phenolic antioxidant Oxygen prefer to react with BHT rather than lipid itself – protecting

against lipid oxidation. Although not toxic itself, BHT may interact with other substances:

Protects against toxicity in some cases Potentiates toxicity in others For example, in animal studies BHT was demonstrated to be

protective against mutagens such as benzopyrene and carcinogens when given during or before exposure to benzopyrene, but enhances toxicity when given after exposure.

Some beneficial health effects of BHT: There are reports that BHT inhibits formations of some types of

tumors. Protective against carbon tetrachloride poisoning. There is some evidence that it slows aging in mice Research is underway concerning the use of BHT in AIDS

treatment

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Formaldehyde

An aqueous solution of formaldehyde can be useful as a disinfectant, as it kills most bacteria and fungi (including their spores)

It is also used as a preservative in vaccinations. In medicine, formaldehyde solutions are applied topically to dry the skin, such as in the treatment of warts

The International Agency for Research on Cancer (IARC) has determined that occupational exposure to formaldehyde causes nasopharyngeal cancer in humans

Formaldehyde has been banned in cosmetics in both Sweden and Japan

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Glutaraldehyde

Glutaraldehyde is a colorless liquid with a pungent odor used to disinfect medical and dental equipment – solution of 0.1% to 1.0% concentration may be used for system disinfection and as a preservative for long term storage

Also used to kill insect – as insecticide It is also used for industrial water treatment and as a

chemical preservative However, it is toxic, causing severe eye, nose, throat

and lung irritation, along with headaches, drowsiness and dizziness

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Methylchloroisothiazolinone

Methylchloroisothiazolinone is a preservative with antibacterial and antifungal effects

It is effective against gram-positive and gram-negative bacteria, yeast and fungi

It is found in many water-based personal care products and cosmetics

It is also used in glue production, detergents, paints, fuels and other industrial processes

It was first used in cosmetics in the 1970s In high concentrations it can cause chemical burns

and it is a skin and membrane irritant and so it was largely removed from most cosmetic products except for those with only short duration skin contact such as rinse-offs

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Natural Preservatives

Organic Acids These have been used for a long time as food preservatives

and are antimicrobial in nature They are primarily used to prevent mold growth Organic Acids are readily available, easy to use and are

very inexpensive Basically, the ability of an Organic Acid to prevent the

growth of micro-organisms depends upon the pH of the foodstuff

Therefore, some food products use a combination of organic acids so that the food will not grow fungi over a range of pHs

Organic Acid preservatives may affect food pH slightly Organic acid do not have any toxic, carcinogenic, estrogen

mimic or mutagenic properties

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Natural Preservatives

Citric Acid Found in citrus such as oranges, lemons and limes,

Citric Acid is sour tasting.  It is added to some food stuffs such as candy and soft drinks to make them sour.  So not only is it used as a preservative, it's also a flavoring agent.  It is also used to adjust pH.

Benzoic Acid (BA) First isolated from Styrax benzoin, a tropical tree,

many types of fruits including strawberries & drupes have Benzoic Acid in them

BA is also found in cheese, spices such as cinnamon, clove & nutmeg, teas, cocoa, mushrooms and honey.

Like other organic acids, BA is used to prevent the growth of fungi & bacteria.  It is added to fruit juices, soft drinks, pickles and other similar foodstuffs.

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Natural Preservatives

Sorbic Acid Originally isolated from Mountain Ash (Sorbus sp.) berries, Sorbic

Acid is used to prevent the growth of molds in cheese, wine, fish, margarine

Another name for Sorbic Acid is "sorbates". Propionic Acid

Fermented products such as Swiss cheese & yogurt may have a high concentration of Propionic Acid

Propionic acid is produced naturally in the digestive tract and is a natural component of sweat

Propionic Acid is typically used in bakery goods, breads, meat, meat products and pizza.  It is not used in many other foodstuffs due to it's strong odor.

Acetic Acid The simplest organic acid, this is primarily used to adjust pH.  Most people know Acetic Acid as vinegar.  Acetic acid is a byproduct of fermenting fruits and grains

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Natural Preservatives

Vitamin C (Ascorbic Acid) Not only a necessary nutrient, Vitamin C is also an

inexpensive food preservative Ascorbic Acid is water soluble and is a good anti-oxidant

and anti-fungal compound It is also tart or sour and is used as a flavor enhancer  Humans, primates and other animals have lost their ability

to synthesize their own Vitamin C, and this is why it is an essential vitamin. 

Obviously, this is a very safe food & feed preservative. DID YOU KNOW? 

• Vitamin C and Vitamin E work together in the body.  Vitamin C 'recharges' Vitamin E, so that Vitamin E can work again as an antioxidant quenching free radicals which protects cells from damage

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Natural Presevatives

Tocopherols (Vitamin E) There are four tocopherols:  Alpha, Beta, Delta & Gamma Alpha Tocopherol accounts for 80% of the activity of

Vitamin E but Gamma Tocopherol is also biologically active Most Alpha Tocopherol on the market is chemically

synthesized Natural tocopherols are all of the D or biologically active

form, whereas synthetics are a 50:50 mix of D:L and therefore only have half the activity of natural E Vitamins. 

Tocopherols preserve food by preventing oxidation and oils from going rancid

Typically, when used as a food preservative (versus using tocopherols for vitamin nutrition), the mix will contain little Alpha Tocopherol and more of the other Tocopherols