Chemical Food Preservation

• Chemical preservation involves the inhibition of microorganisms without necessarily destroying them.

Introduction to Chemical Preservation

• Preservatives are substances that either delay microbial growth or prevent quality deterioration during manufacture, distribution, and storage under certain conditions.
• Preservatives can be of natural or synthetic origin.
• Preservatives are added in very low quantities without significantly altering the food's organoleptic and physico-chemical properties.
• Chemicals are added to preserve food after processing and before packaging.

Mechanisms of Action

• Destroy cell membranes of microorganisms.
• Affect enzyme activity or genetic mechanisms of microorganisms.

Traditional Chemical Food Preservatives

• Sugar
• Salt

Salt as a Preservative

• Salt preserves food by increasing osmotic pressure to prevent microorganism development.
• Leads to osmotic dehydration
• Water migrates out of the cells by osmotic pressure, resulting in cell shrinkage and some membrane damage.
• Cell growth of microorganisms is inhibited.
• Salt binds water, reducing available water for microbial growth by decreasing water activity (aw).
• Salting is one of the oldest methods for preserving food, including fish products and meat such as bacon and ham.
• A disadvantage of using salt is the strong taste, making it unsuitable for every food.

Sugar as a Preservative

• Sugar's effect is similar to salt.
• Sugar increases osmotic pressure and lowers water activity (Aw.)
• Sugar concentration of 60% in the liquid phase assures food preservation.
• Sugar is used to preserve fruits (jams, syrups, candied fruits), vegetables (candied ginger), and condensed milk.

Acidic Preservatives

• Benzoic acid
• Sorbic acid (Potassium sorbate)
• Lactic acid

Benzoic Acid

• Constitutes one of the most common chemical food preservatives mostly in the form of its sodium salt.

• Sodium benzoate is commonly used in acid or acidified foods like fruit juices, syrups, sauerkraut, pickles, fruit cocktails, and mustards.

• Yeasts are more inhibited by benzoate than molds and bacteria.

Sorbic Acid and Potassium Sorbate

• Sorbic acid and its salts are tasteless and odorless in foods.
• Considered non-toxic and metabolizes in the body.
• Sorbates are used for mold and yeast inhibition across a variety of foods, these include fruits and vegetables, fruit juices, pickles, sauerkraut, syrups, jellies, jams, and dehydrated fruits.
• Potassium sorbate is a white powder that is very soluble in water.
• It is also known as "wine stabilizer”
• It is used to prevent undesirable refermentation(sweet wines, sparkling wines, ciders)
• Inhibits molds and yeasts in cheese, wine, yogurt, dried meats, apple cider, soft drinks, fruit drinks, and baked goods.

Lactic Acid

• Lactic acid is the main product of food fermentations, formed by microbial degradation of sugars in products like sauerkraut and pickles.
• The pH decreases to a level unfavorable for the growth of spoilage organisms, such as putrefactive anaerobes and butyric-acid-producing bacteria.
• Yeasts and molds that can grow can be controlled by other preservatives like sorbate and benzoate.

Other Chemical Preservatives

• Sulphur dioxide and sulphites
• Carbon dioxide
• Nitrates (NO3-) and Nitrites (NO2-)

Antioxidants in Food Preservation

• Antioxidants are added when appropriate methods are not possible or satisfactory.
• Antioxidants protect foods against auto-oxidation.
• Antioxidants inhibit oxidation by reacting with free radicals
• Free radicals are unstable molecules seeking electrons, contributing to aging and the onset of various diseases
• Antioxidants slow oxidation by donating an electron to oxygen free radicals.

Synthetic Antioxidants

• Include BHT, di-tert-butylhydroxytoluene, BHA, tert-butylhydroxyanisole, DBHQ, di-tert-butylhydroquinone PG, propyl gallate, OG, octyl gallate, and DG, tert-dodecyl gallate.
• Are used for food stabilization because of strict safety regulations.

Natural Antioxidants

• Consumers commonly prefer products stabilized with natural antioxidants
• Almost all plants, fungi, microorganisms, and animal tissue contains antioxidants of various types
• Best application of natural antioxidants occur when used in natural food components (cereals, nuts, vegetables, and fruits) as these are regarded as safe.
• Natural food ingredients can be spices for the application of antioxidants.

Natural Antioxidant Examples

• Tocopherols:
• The most common and are present mostly in plant-based foods.
• Antioxidants from Oilseeds
• Palm fruit - Tocopherols
• Olive fruit - Oleoeuropein aglycone
• Sesame seed - Sesamol
• Cottonseed - Gossypol
• Rapeseed - Sinapic acid
• Flaxseed - Lignans
• Rice bran - Oryzanol
• Antioxidants from Cereals and Grain Legumes
• Contain several types of phenolic

Antioxidants in Fruits and Vegetables

• Citrus: Flavonoids, carotenoids
• Plums: Phenolics
• Persimmon: Procyanins, catechins
• Red wine: Anthocyanins
• Pineapple: Flavanols
• Onion: Sulfur compounds
• Garlic: Sulfides, disulfides
• Green pepper: Flavonoids
• Carrots: Carotenoids, flavonoids
• Betel: Oleoresins, eugenol, hydroxychavicol
• Legume: Flavonoids
• Green olives: Anthocyanins
• Mustard: Phenolics, isothiocyanates
• Oak (wood): Phenolic acids, lignins

Natural Antimicrobials for Food Preservation

• Plant origin
• Animal origin
• Microbial origin

Antimicrobials of Plant Origin

• Spices and herbs are known to inhibit bacteria, yeasts, and molds and are used for food preservation and medicinal purposes.
• Plants produces antimicrobial through enzymatic action to boost protection against stress, and to fight against microorganism and animals.
• Plants contain preformed mixture of antimicrobial components in active form while some are produced after physical injury.
• Allicin only gets produced when an onion is physically hurt.
• Includes Phytoalexins, Phenolic Compounds, Essential oils, and Organic Acids.

Antimicrobials of Animal Origin

• Animals produce several antimicrobial compounds, as first line of defense, which are also found in, milk and eggs
• Chitosan - crustacean shells, used in coatings and edible antimicrobial films
• Lactoferrin - is commonly present in milk
• Lactoperoxidase - is a native enzyme in animal secretions such as saliva, and milk
• Lysozyme - hen's egg

Fermentation as a Method for Food Preservation

• Fermentation preserves food by eliminating microorganisms or controlling their growth.
• A process in which microorganisms change the sensory (flavor, odor, etc.) and functional properties of a food to produce a desirable end product.
• Fermentation, along with salting, cooking, smoking, and sun drying, is an ancient tradition used to extend storage time.
• Raw animal and plant ingredients have been fermented for thousands of years.
• Can extend shelf life of foods by relatively low costs.
• Used in developing communities with limited facilities

Fermentation uses includes

• Minimizing the level of microbial contamination in the food.
• Inhibiting the growth of the contaminating microflora.
• Killing the contaminating microorganisms.
• Microorganisms can improve their own competitiveness by changing the environment.

Benefits of Fermented Foods

• The acceptability is based mainly on sensory properties.
• Developed by many cultures for two main reasons:
• To preserve harvested or slaughtered products.
• To improve sensory properties.

Microorganisms Used in Food Fermentations

• Lactic Acid Bacteria
• Acetic Acid Bacteria
• Yeasts
• Molds

Lactic Acid Bacteria (LAB)

• LAB performs an essential role in the preservation and production of healthy foods.
• Examples of are fermented vegetables (sauerkraut, pickled cucumbers, radish), fermented milk (yogurt, kefir, cheeses), sourdough breads, and fermented sausages
• Growing in most foods to produce acid which lowers pH rapidly, inhibiting competing organisms.

Acetic Acid Bacteria

• Acetic acid is one of the oldest known chemicals, named after the Latin word "acetum."
• Acetic acid bacteria are aerobes, acid tolerant, and grow well at pH levels below 5.
• They derive energy from the oxidation of ethanol to acetic acid.
• Their most desirable action occurs in the production of vinegar, where oxygen is available.
• Alcohol to acetic acid is an undesirable change during fermentation when producing wine due to a vinegary off-flavor.

Yeasts

• Yeasts are widely distributed in natural habitats that are rich in carbohydrates such as fruits and plant nectars.
• They are rarely toxic or pathogenic and widely accepted to consumers.
• Saccharomyces cerevisiae is the most frequently used strain.
• Also used to produce ethanol, CO2, flavor, and aroma.

Molds

• Molds are important to the food industry as preservers of foods, particularly in fermentations for flavor development.
• The genus Penicillium is associated with the ripening and distinctive flavor of Roquefort, blue cheeses, and Camembert cheeses, and some sausage.
• Other molds (Aspergillus oryzae, Rhizopus oligosporus) are used in fermentations of soybeans to make miso, soy sauce, and tempeh.
• Tempeh: a traditional soy product from Indonesia produced by a natural culturing (Aspergillus or Rhizopus) and controlled fermentation process that binds soybeans into a cake form.

Fermented Products

• Alcoholic Beverages: – Beer and wine
• Distilled Spirits
• Lactic Acid Products: – Dairy Products (Yogurt, Cheese) – Fermented Vegetables – Fermented Animal Products (Fermented Sausages, Fermented Fish)
• Other Fermented products: – Bread, Sourdough, and Vinegar
• Oriental Fermented Products (Soy Sauce, Tempeh)

Drying and Food Preservation

• Drying foods is the most common method of preservation used by humans and the food processing industry.
• Dehydration is considered one of the most important achievements in human history because it makes humans less dependent on a daily food supply.
• Drying times depended on the sun , however now sophisticated types of equipment and methods are used to dehydrate foods.
• USDA lists dehydrated foods as having no more than 2.5% water (dry basis), while dried foods have more than 2.5% water (dry basis).

Drying Modes of Preservation

• Drying reduces water activity which preserves foods by inhibiting microbial growth and deteriorative chemical reactions
• Higher temperatures degrade microorganisms and the activity of enzymes
• It is necessary to maximize microorganism and enzyme inactivation to prevent spoilage.
• Thermal drying is effective for removing heat
• Thermal drying is one of the most widely used methods of drying foods
• Industrial drying of food is one of the most energy-intensive processes.

Factors to Consider Before Drying

• The type of product to be dried
• Desired properties of the finished product
• Allowable temperature tolerance
• The product's susceptibility to heat
• Pretreatments required
• Capital and processing costs (rentability)
• Environmental factors (temperature, pH...)

Thermal Drying Methods

• Sun Drying
• Solar Drying
• Convection Air Drying
• Explosive Puff Drying
• Spray Drying
• Vacuum Drying
• Freeze Drying
• Heat Pump Drying
• Smoking

Sun Drying

• Only used for drying in the earlier days
• Foods are exposed by placing it on land or hanging in the air
• Main disadvantages includes contaminations from the environment, insects, birds, floor space requirements, difficulty controlling the process large space for high input, and high labor inputs
• Sun drying is the cheapest method of drying foods.

Solar Drying

• Is an extension of sun drying that uses radiation energy from the sun
• Asorbing surface collects sun light and converts it to heat
• Solar drying is a non-polluting processes and uses renewable energy
• Dehydration of various agricultural products
• Product is dried in closed space which protects agaisnt weather, mechanical impurities, insects, and pests
• Solar drying's limit is its use in large scale production.

Convection Air Drying

• This dries by using an enclosed and heated chamber.
• Hot air is allowed to pass over the product, which has been placed in open- air
• Is regularly accomplished by passing air at regulating air and humidity by passing or through the food dryer
• Important factors- Temoerature (hotter the air, fastest rate), humidity (lower air, higher rate), air velocity (velocity increases rate), product composition(product structue and composition).

Explosive Puff Drying

• Explosive puff drying uses a combination of high temperature and high pressure, and a sudden release of the pressure to flush out the water out.
• Creates easy rehydrate products
• Breakfast cereals

Spray Drying

• Used to remove water from a liquid mixture, transforming it into powder form (dry soup, milk powder, coffee, cocoa...).
• The size of the equipment is very large.
• Oily materials might require special preparation to remove excessive levels of fat before atomization.
• A fluidized to be dried is first atomized by pumping it by a nozzel or a rotary atomizer to form small droplets with large surface are.
• The fluid is then rapidly evaporated while minimizing contact time and heat damage.

Vacuum Drying

• Vacuum drying can be a useful tool for solid, heat-sensitive products such as fruit powders.
• Vacuum allows water to vaporize at a lower temperature.
• Improves color, texture, and flavor of vacuum-dried products compared with air dried products.

Freeze Drying

• Freeze by freezing the material and then reducing surrounding pressure to allow frozen water to sublimate
• Use for high quality dry product with heat sensitive and components (vitamins, antbiotics) Frozen material subjected to pressure below Triple point (0%, 610%) and heated to cause ices sublimation to vapor.

Heat Pump Drying

• Heat pump is further extension from conventional
• Dry heated air to suoolied continuously to the product to pick up moisture more effectively Advantages – higher energy effiency – better product quality – independent from ambient conditions – zero enviromental inpsct – condensate is recovered
• The heat pump operates at low temperatures to reduce aroma, colors degredation.

Schematic diagram of the operation of a typical heat pump dryer

• (1)vapor-sealed and insulated structure
• (2)Humidifier
• (3)overheat vent
• (4)external condenser
• (5)heat pump dehumidifier
• (6)condensate
• (7)product tray
• (8)primary air circulation fan
• (9)air distributor

Smoking in Food Preservation

• Smoking is an ancient process used by many communities.
• Heat generation with smoke also causes drying effect
• Smoking is considered a pretreatment rather than the drying process itself.
• Mainly used for meat and fish

The main purposes

• Desirable flavor and colors to foods
• Some of the compounds formed have a preservative effect.
• Prevent lipid oxidation in meat and fish effects.

Smoke- Chemical Composition

• It's a slow process and hard to control.
• Wood smoke is complex with over 400 Volcannes
• Nitrogen oxides responsible for the characteristics color
• Polycyclic aromatic hydrocarbon and phenolic compounds unique to test and the chemicals or are also some most controversial for a health process.
• Oak and beech will produce smoke with sensory properties.

Risk of Smoking Food

• Concentration can reach hazardous levels
• Proceed under controlled condition.

Smoking Methods

• Involves Passing Hot smoke in a range of woods over officials to partially draw it 1M part flavor Aroma a smoke hot that Smoking apply it at smoke products cooking temp. Is at least .8°
• Cold Smoking is only applied the smoke products and temperatures below 35 degree Celsius
• Both both hard and code smoked fish are preserved primarily by salt and moisture Smoke deposition effective and only control of surface spoilers or more modern medicine smoking is used for formulation liquids to reduce risk.