Food preservation is the science of extending the shelf life of food, maintaining as much as possible its nutritional quality and avoiding the growth of unwanted microorganisms.

FOOD PRESERVATION INTRODUCTION

Food spoilage refers to undesirable changes occurring in food due to the influence of air, heat, light, moisture, which foster the growth of microorganisms. Foods are spoilt by the action of: (1) Microorganisms (2) Enzymes and (3) Insects.

BACTERIA FUNGI PROTOZOA VIRUS

Main causes of food spoilage

Bacterial infections can be transmitted from man to man, from man to animal and from animal to man (zoonoses). • INFECTION, invasion of body tissues by bacteria that cause damage proportional to their invasive capacity and quantity, and the immune capacity of the affected body. • INTOXICATION (or poisoning) caused by the ingestion of chemicals produced by bacteria, called bacterial toxins as botulinum, tetanus and staphilococcus toxins.

FOOD PRESERVATION

In the majority of food-borne bacterial diseases the presence of bacteria and their toxins are closely related and the disease presents at the same time character of an infection and intoxication. The clinically healthy subjects that host pathogens in their body without being affected by the disease are called "carriers".

Problems of healthy carriers among those involved in the processing of foods, as they may inadvertently contaminate food, thus transmitting the pathogen to other people. FOOD POISONING

Cross contamination is one of the most common causes of food poisoning. It happens when harmful germs are spread onto food from other food, surfaces, hands or equipment.

• Don't let raw meat, poultry or unwashed raw vegetables touch other foods. • Never prepare ready-to-eat food using a chopping board, utensil or knife that you have used to prepare raw meat, poultry or unwashed raw vegetables unless they have been washed and disinfected thoroughly first. • Clean worktops and utensils with hot water and detergent and remember to disinfect those surfaces that have come in contact with raw meat, poultry and unwashed raw vegetables.

CROSS CONTAMINATION OF FOOD

BACTERIA can be: USEFUL: they are found in cheese, yogurt, various sausages, preventing other dangerous bacteria to develop. SPOILAGE: bacteria of putrefaction; they can multiply in the presence of moisture, high temperature, variation of pH and too long storage times. DANGEROUS: or pathogenic bacteria, i.e. those ones that cause diseases (infections or poisoning), either directly or through the production of toxic substances called "toxins".

MICROORGANISMS CLASSIFICATION

TIME: In 20 hours the single cell can develop five billion cells. MOISTURE: Foods with a higher moisture content are the ones that most easily allow bacterial growth (eg. broths). TEMPERATURE: The ideal temperature for their development is between 10-60 °C. The temperature which they prefer is very close to that of the human body (37 °C).

Low temperatures stop their reproduction, which resumes when favorable temperature conditions are restored. Only high temperatures ensure the death of pathogenic germs. MICROORGANISMS GROWTH

.... other conditions that affect microbial growth: OXYGEN: some species of bacteria can live only in the presence of oxygen (aerobic), while others can live even in its absence (anaerobic). Some bacteria cause of poisoning may live and multiply even in hermetically sealed containers, and then deprived of oxygen, if they have not been killed by an appropriate heat treatment (Botulin toxin). ACIDITY: most of the bacteria is spread mainly in products neither too acidic nor too alkaline. The ideal pH for growth is between 6 and 8.

MICROORGANISMS GROWTH

Anaerobic, spore formed in canned or vacuumpacked.

Growth conditions

Food

Frequence

Growth temperature 10 and 45°C. Spores are destroyed at 121°C and toxins by boiling at 100°C for 15 minutes.

Food improperly sterilized. Homemade preserves.

Rare

FOOD SOURCE: preserved vegetables, homemade sausages and vacuum products in oil, smoked fish.

Growth conditions

Food

Frequence

Growth and toxin production between 10-40°C. Bacteria are destroyed from 63°C, toxins are heat resistant.

Egg-based products.

Very frequent.

FOOD SOURCE: ice cream, confectionery, dairy products, foods made with raw milk.

Salmonella Typhi and Paratyphi Growth conditions

Food

Frequence

Growth in preserved food between 10 and 40°C. Bacteria are destroyed by the heating at 63°C for 30 minutes.

Poorly processed and lightly cooked protein foods. Foods that come in contact with faecal material of animal origin.

Very frequent.

Salmonella are bacteria that live in intestines of humans and animals, even in healthy carriers. Salmonellosis is transmitted through the ingestion of food contaminated with feces of infected animals. FOOD SOURCES: poultry, raw meats, eggs, raw milk.

Growth conditions

Food

Frequence

Growth in food kept between 10 and 40°C. Some strains are resistant to boiling process. Spores are destroyed at 121°C.

Meat and sauces (especially if prepared a lot of time in advance).

Very frequent in catering.

Anaerobe, is found in feces and meats, survives heat and dehydration. FOOD SOURCES: poultry, meat, heated foods, spices, vegetables and soups.

Growth conditions

Food

Frequence

Does not multiply at a pH less than 4. Not resistant to pasteurization.

Potentially present in Rare. all foods, but especially in cheeses, meats and vegetables.

FOOD SOURCES: Ready-to-eat deli meats and hot dogs. Refrigerated pâtés or meat spreads. Unpasteurized (raw) milk and dairy products Soft cheese made with unpasteurized milk, such as queso fresco, Feta, Brie, Camembert. Refrigerated smoked seafood.

Listeria is unlike many other germs because it can grow even in the cold temperature of the refrigerator. Listeria is killed by cooking and pasteurization.

Nematodes (worms) are commonly present in fish caught in the wild, most frequently in the liver and belly cavity, but can also occur in the flesh.

Anisakiasis is an uncommon disease because the parasite is killed by heating (55°C for 1 min), and by freezing (−20°C for 24 h). There is a risk of illness from fishery products consumed raw, for example sushi, or after only mild processing, such as salting at low concentrations or smoking. Many countries (also Italy) now require that fish used for these mildly processed products must be frozen before processing or before sale.

RAW MATERIALS:

ENVIRONMENT:

MANUFACTURING PRACTICES:

SOURCES OF FOOD CONTAMINATION

Any food processed to retain its nutritional and sensory profile can be considered "preserved“ - stored products: those packed in containers that are maintained for a long time at room or low temperatures (frozen, dried, canned, lyophilized, etc.). - semi-preserved products: those that are kept for a limited time and who have suffered less drastic procedures (pasteurized, chilled, etc.). - processed products: those that have undergone deep transformations of their original structure (fermented products, salted, seasoned, smoked etc.). PRESERVED FOOD

PHYSICAL: temperature control, water content control, oxygen content control in the packaging, exposure to radiations CHEMICAL: use of natural preservatives, use of chemical food additives BIOLOGICAL: fermentation (Yougurt)

FOOD PRESERVATION METHODS METHODS CLASSIFICATION

Refrigeration slows down the biological, chemical, and physical reactions that shorten the shelf life of food.

FOOD PRESERVATION BY PHYSICAL METHODS

REFRIGERATION

The refrigeration temperatures range from -1 to +8 °C, the choice depending on the type of food. There are two categories of refrigerated products: - refrigerated during transport and storage but sold at room temperature (fruit, vegetables, etc.) -

distributed, stored and sold T-fridge these include: food as livestock meat, milk, dairy products, fresh fish products; pre-cooked meat and fish, fresh meats and sausages, delicatessen products, salads and fresh pastries.

REFRIGERATION

Postharvest life of fruits can be extended by both refrigeration and CONTROLLED ATMOSPHERE (CA) storage in which oxygen is kept at about 5 percent and CARBON DIOXIDE at 1 to 3 percent, while temperature is held at a level best suited to the particular fruit. So-called CA storage is common today for apples and pears and is being adapted to other fruits.

REFRIGERATION UNDER CONTROLLED-ATMOSPHERE

For most of microbial contaminants the presence of oxygen is necessary, therefore the first goal of this technology will be the reduction of O2 percentage in contact with the food. Carbon dioxide (CO2), nitrogen (N2) or their mixtures are the most widely used gases to create a modified atmosphere. Mechanisms of action: removing the oxygen, the microbial growth is slowed hydrating in water lowers the pH of the medium and the acid pH creates an unfavorable environment to germs (only for CO2) inhibition of different enzymes of the tissue metabolism (fruit ripening and rotting meat slow)

REFRIGERATION UNDER CONTROLLED-ATMOSPHERE

Only one exception, where OXYGEN presence is favorable to improve food storage: •

oxygenates myoglobin (red pigment of fresh meat) improving the red color of the meat

In all the other cases, the presence of OXYGEN is detrimental to food storage for the following reasons: •

promoter of enzymatic and chemical oxidations

•

activates the degradation of beta-carotene

•

is the substrate of respiration of plant and microbial cells

REFRIGERATION UNDER CONTROLLED-ATMOSPHERE

PACKAGING

Because packaging helps to control the immediate environment of a food product, it is useful in creating conditions that extend the storage life (shelf life) of a food.

Modified - Atmosphere Packaging (MAP)

barrier properties Packaging materials such as polyvinyl chloride (PVC), and polypropylene (PP) offer low moisture permeability. Similarly, packaging materials with low gas permeability are used for fatty foods in order to minimize oxidation reactions. Because fresh fruits and vegetables respire, they require packaging materials, such as polyethylene (PE), that have high permeability to gases.

REFRIGERATION UNDER MODIFIED-ATMOSPHERE

The packaging in modified atmospheres widely used in the United States and in the European Countries is allowed in Italy for some products established by law (fresh pasta, baked goods, meats, fresh cut fruits etc.). The packing material must be compatible with the gas used on the casing and must include the following information:

“PRODOTTO CONFEZIONATO IN ATMOSFERA MODIFICATA O PROTETTIVA” "PRODUCT PACKAGED IN A MODIFIED OR PROTECTIVE ATMOSPHERE" REFRIGERATION UNDER MODIFIED-ATMOSPHERE

When pressure is below the atmospheric value, a vacuum packaging is made with the aim to prolong the product preservation through the elimination of the oxygen. Storage in "CRYOVAC" provides refrigeration of food under vacuum in a plastic and waterproof wrap (eg. sausages, ham, cold cuts, etc.).

The bags are firstly sealed under vacuum, then, the package is immersed for a few seconds in water at 90°C: the heat-labile film perfectly adheres to the food.

UNDER VACUUM PACKAGING

Flash freezing is a process in which food is very quickly frozen at extremely cold temperatures (more nutrients, more flavor). The freezing point of a food is a function of its composition (freezing point is usually between -0.5°C and -4°C). Enzymatic reactions are stopped in a product in which 100% of the water is solidified.

FOOD PRESERVATION – PHYSICAL METHODS

FREEZING

Industrial flash freezing process allows reaching quickly temperatures below -18°C. This quick process forms very small ice crystals in the cells and no damage is caused to the structure of the food. Deep-freezing, instead, is a slower process. Therefore it forms bigger ice crystals that can break the cell walls. When the product is thawed, cells lose liquid and consequently nutritive principles get lost and the organoleptic qualities of the product can decrease.

FREEZING

Flash freezing refers to the process in various food industries to quickly freeze perishable food items. This rapid freezing is done by submerging the sample in liquid nitrogen or a mixture of dry ice and ethanol. Then, the flash freezing differs from freezing depending on the cooling time: by the law, a frozen product undergoes a rapid freezing, such that at the end of the process, which lasted up to 4 hours, the temperature is lower than or equal to -18°C throughout the mass and the same temperature is maintained throughout the process of preservation. FLASH FREEZING

1. CONTACT WITH PLATES: the product is pressed between two plates at -40°, -50°C (cubes of spinach) 2. FORCED AIR: bulk foodstuffs are subjected to a jet of air to -40°, -50°C in a tunnel or freezing cells. Ex. Freezers fluid bed (eg. peas, green beans, carrot cubes, etc.) 3. IMMERSION IN NON-FREEZABLE LIQUIDS: the product, sealed in waterproof packaging, is immersed in solutions that freeze at very low temperatures (poultry) 4. DIRECT USE OF THE FREEZING AGENT : the food is treated with liquid nitrogen (-196°C) or carbon dioxide (-80°C), which does not leave any residue on the food.

METHODS OF FLASH FREEZING

The COLD CHAIN extends from the raw material supplier (e.g. onfarm cooling of milk) through to the consumers’ refrigerator/freezer, and all the steps in between.

COLD CHAIN

The vegetables are subjected to "BLANCHING" or burn, a very short cooking that inactivates the enzymes that could alter the food quality.

BLANCHING • • • • •

Slows or stops enzymatic action, preserving flavor, color and texture cleanses the surface of dirt, bacteria, molds and other organisms brightens the color helps retard loss of vitamins softens vegetables and makes them easier to pack and less susceptible to freezer burn

BLANCHING VEGETABLES BEFORE FREEZING

The action of the heat prevents the processes of fermentation and putrefaction that the development of the bacterial flora usually causes at room T. Pasteurized food must be stored in such conditions as to limit the development of microorganisms. Generally, the pasteurization is combined with other preservation methods such as refrigeration, the addition of chemicals and under vacuum packaging.

FOOD PRESERVATION – PHYSICAL METHODS METHODS WITH HIGH TEMPERATURE

The microorganisms are particularly sensitive to high temperatures, especially when coupled with humidity. The moist heating, which acts by coagulating the proteins, has an effect more energetic and rapid than the dry heat, which oxidizes the chemical components of the cell. For exposure to moist heating most of the vegetative forms succumbs to 60-70°C in 5-10 min. A food preservation process that heats liquids to 70-75°C for 15 seconds, or 60-65°C for 30 minutes, in order to kill bacteria, yeasts, and molds. The term pasteurization derives from Pasteur, who in 1860 discovered that heating the wine at 60°C and maintaining this temperature for a few minutes, the wine could be stored longer.

Dr. Pasteur

METHODS WITH HIGH TEMPERATURE

PASTEURIZATION TYPE

T (°C)

TIME

FOOD

LOW

60 - 65

30 min

Wine, beer, milk for cheese making

HIGH

70 - 75

2-3 min

For milk now substituted by HTST

FAST or HTST High Temperature Short Time

70 - 75

15-20 sec Applied to liquid food flowing in a thin layer between two metal heated walls (or plates)

Normally, pasteurization is followed by a rapid cooling of the product that maintains almost unaltered its original quality, but it can not be stored for long.

PASTEURIZATION

The milk is pushed via pumps into a hollow space between two thin plates in steel, in contact with heat exchangers filled of water at 70°C (HTST). The milk reaches the same temperature for a few seconds. In cheese making, the heat pasteurization destroys the lactic acid bacteria (Lactobacillus acidophilus). These bacteria are essential for the subsequent stages of processing, so, they are necessarily added after pasteurization for lactose fermentation.

MILK PASTEURIZATION

All microbial forms, including spores are destroyed. Canning products are not completely aseptic Temperatures and exposure times for: COMMERCIAL STERILIZATION The sterilization temperatures are related to the acidity of the food: with pH lower than 4.5 a temperature of 100°C is enough; with a pH higher than 4.5, a temperature of 115-120°C is needed for at least 20 minutes.

CANNING (Food Sterilization)

Heat treatment of such products must be intensive enough to inactivate the most heat resistant bacterial microorganisms (spores of Clostridium). In practice, the meat products filled in sealed containers are exposed to temperatures above 100°C in pressure cookers. Temperatures above 100°C, usually ranging from 110121°C depending on the type of product, must be reached inside the product.

A compromise has to be reached in order to keep the heat sterilization intensive enough for the microbiological safety of the products and as moderate as possible for product quality reasons.

CANNING

In order to reach temperatures above 100°C, the thermal treatment has to be performed under P in pressure cookers, also called autoclaves or retorts. In the autoclaves, high temperatures are generated either by direct steam injection, by heating water up to temperatures over 100°C or by combined steam and water heating.

vertical autoclaves

pressures up to 5.0 bar.

CANNING

Larger autoclaves are usually horizontal and loaded through a front lid. Horizontal autoclaves can be built as single or double vessel system. The double vessel systems have the advantage that the water is heated up in the upper vessel to the sterilization temperature and released into the lower (processing) vessel, when it is loaded and hermetically closed. AUTOCLAVE OR RETORT

Using the two–vessel system, the heat treatment can begin immediately without lengthy heating up of the processing vessel and the hot water can be recycled afterwards for immediate use in the following sterilization cycle.

CANNING

- Indirect UHT (Ultra High Temperature) : 140-150°C for a few seconds, carried on the food packaged plunged in water or in an autoclave; - Direct UHT : 140-150°C for a few seconds, carried out by the injection of superheated steam in the bulk product. Followed by cooling and aseptic packaging in sterile containers (multi-layer cartons flexible or TETRAPAK).

The sterilized foods can also be subjected to methods of aseptic packaging (mild technology). The process consists in the continuous sterilization of food in bulk, followed by cold-aseptic packaging, in sterile containers. Technology introduced on a large scale in 1960 with the introduction of the Tetra Pak packaging (milk, fruit juice, instant soups, tomato pulp, etc..).

Foods that undergo this treatment have superior nutritional and organoleptic properties to the classical sterilized, but they have a shorter duration (3 or more months versus 2-5 years).

ASEPTIC PACKAGING

The food packaging can be sanitized on the surface by using vapors of hydrogen peroxide (H2O2). All the online manufacturing are carried out safely in a clean room maintained in over Pressure, eliminating the risks related to the presence of residual sterilizing agents in contact with the product.

All the sterilizing vapor is recovered via catalyst, and split into O2 and H2O ensuring an eco-friendly process.

ASEPTIC PACKAGING

Paper (75%)

2 4 5

PE (20%)

1

Aluminum (5%) 3

Tetra Packs are constituted by a multilayer structure of paper, plastic (polyethylene), and aluminum. The paper represents more than 75% of the total.

ASEPTIC PACKAGING

The presence of liquid water is essential for the life of microorganisms and the enzyme activity. Its elimination, even partial, creates a hostile environment to microbial growth and enzymatic activities and, therefore, constitute a tool for the preservation of food products. The percentage of water to be eliminated depends on the nature of the food: it must be almost total (eg. Milk, cereal grains) or can also be partial (eg. Tomato concentrates, fruit juices about 60 ÷ 70%).

DEHYDRATION

DEHYDRATION CAN BE CARRIED OUT EITHER BY HOT OR COLD METHODS.

HOT DEHYDRATION consists in the evaporation of water in a current of hot air or in special evaporators. Because a prolonged heating under vacuum may also cause a loss of nutrients, actually, the process of concentration can be performed by reverse osmosis or by microwave heating. Industrially, the dehydration of the goods is obtained in industrial ovens. Long Shelf life. Significant reduction of volume and weight. Lower transport costs.

Drying Oven

CLASSICAL DRYING

In the drying process the initial content of water is lowered up to 5%. It can also be done via microwaves, electromagnetic radiation with λ = 1 cm; considerably used in food industry, for the property to quickly penetrate in the food reducing the heating time.

Tunnel Oven

DRYING

The main goal of the food's concentration is to reduce its volume and weight, in the case it is destined to a direct consumption or must be processed by industries, making its transportation and storage easier and less expensive. The partial elimination of the water enhances the preservation of the food, but is not sufficient to keep it so long, and must be combined with other preservation treatments, as the addition of chemicals (eg. sugar or salt), or “hot methods” as pasteurization or sterilization. The milk, as an example, is concentrated under reduced pressure by heating to 50-60°C.

CONCENTRATION

The concentration of a food product can be achieved by using different technologies, based on different physical principles. It is important to identify for each type of food the more suitable process to preserve the nutritional, organoleptic characteristics and physical appearance. The main techniques are the followings: 1. Concentration by evaporation 2. Cryoconcentration 3. Concentration by membrane technologies

FOOD CONCENTRATION

Concentration by evaporation It is the classic and most common method, also used at domestic level: water is removed by evaporation heating the food, to increase the speed of the process. A disadvantage of this method can be the altering of food’s characteristics for such nutrients sensitive to high temperatures, and for volatile components loosed in significant amounts with a consequent decrease of the aroma. It is used for fruit juices, canned tomatoes, etc. CONCENTRATION BY EVAPORATION

CRYOCONCENTRATION

This technique exploits the properties of a solution to lower its congelation point with respect to the pure water (eg. orange juice 11% freezes at -2°C; 50% freezes at -9°C). When it drops below 0°C, pure water is separated from the rest of the solution in the form of ice. The ice can be then removed and the remaining liquid solution becomes more concentrated as it has lost some of the water. This technique allows to maintain the nutritional and organoleptic characteristics of foods, avoiding the loss of such components sensitive to high temperatures, in orange juice, wine, beer (which is only concentrated for an easier transport), coffee, vinegar, milk, tea.

CRYOCONCENTRATION

These techniques utilize semipermeable membranes. They can be considered special sieves that have a tight weave that allows the retention of larger particles and pass the smaller ones. Depending on the size of the pores of the membrane, there are the following processes: traditional filtration, microfiltration, and ultrafiltration. These methods are worth of noting and poorly expensive; moreover, they do not alter the characteristics of the food and are important for obtaining nutraceuticals and food supplements (eg. whey proteins extracted by ultrafiltration). CONCENTRATION BY MEMBRANE TECHNOLOGIES

The concentration of a rich in water food can also be obtained using the technology of REVERSE OSMOSIS, using a semipermeable membrane, which allows the passage of water, but not of the substances dissolved in it.

Applying to the solution which has to be concentrated, a pressure higher than its OSMOTIC PRESSURE, there will be a flow of water from the solution itself to the less concentrated (usually drinking water or pure water) with further concentration of the first solution (fruit juices and so on).

CONCENTRATION BY MEMBRANE TECHNOLOGIES

Lyophilization or freeze drying is a process by which very different biological materials may be preserved undamaged for extended periods. Freeze-dried products may be kept at room temperature, with low weight, and their properties are restored after rehydration. LYOPHILIZATION is carried out using a simple principle of physics called SUBLIMATION = transition of a substance from the solid to the vapor state, without firstly passing through an intermediate liquid phase.

1-2% residual moisture Food regenerated by addition of H2O Conservation guaranteed for 3 years

FREEZE-DRYING process or LYOPHILIZATION

The lyophilization is obtained by rapid freezing of the food at temperatures of -30, -40°C, and subsequent dehydration by sublimation under vacuum at low T.

water phase diagram

FOOD PRESERVATION – PHYSICAL METHODS LYOPHILIZATION

FREEZE-DRYER SCHEME

To extract water from foods, the process of LYOPHILIZATION consists of: FREEZING: The product is frozen. VACUUM: After freezing, the product is placed under vacuum (frozen water in the product vaporize without passing through the liquid phase = sublimation). HEAT: Heat (25-30°C) is applied to the frozen product to accelerate sublimation. CONDENSATION: Low-temperature condenser plates remove the vaporized solvent from the vacuum chamber by converting it back to a solid.

LYOPHILIZATION

The product to be treated is placed in a chamber in which vacuum is rapidly produced. As pressure in the chamber drops, temperature also drops and the water contained in the product freezes. Next, still under vacuum, the product is heated and ice sublimation occurs (water turns into vapor without passing through the liquid phase). Conventional industrial installations produce vacuum by means of a combination of vacuum pumps and cold traps which operate at -40 or -50°C, to freeze water to be extracted from the product and to reduce the pressure within the freeze-drying chamber. The large mechanical vacuum pumps and freezing equipment require specialized labor to run and maintain - which increases cost.

LYOPHILIZATION PLANT

The freeze-dried food must be packaged in pouches resistant to oxygen and moisture, usually aluminum and polyethylene, but also glass. Food Types Suitable For Freeze Drying • Coffee • Fruit and juice • Vegetables • Meat • Fish and Seafood • Eggs • Dairy The packaging of these products is a crucial manufacturing process, and must be accomplished in vacuum or in CONTROLLED ATMOSPHERE LYOPHILIZATION

RADIANT ENERGY HAS DIFFERING WAVELENGTHS AND DEGREES OF POWER. Light, infrared heat and microwaves are forms of radiant energy. The radiation of interest in food preservation is IONIZING RADIATION, also known as irradiation. These shorter wavelengths are capable of damaging microorganisms such as those that contaminate food or cause food spoilage and deterioration. Method of food preservation since 1950.

IRRADIATION

The preservation technique that employs ionizing radiation has been used for the first time in the USA in 1943 to sterilize hamburgers.

It consists in subjecting the food to the action of electromagnetic radiations, such as:

• X rays • γ rays • UV radiation

IRRADIATION

HOW IRRADIATION IS USED:

• Sterilization of medical equipment (instruments, surgical gloves, alcohol wipes, sutures, etc.) • Sterilization of consumer products (adhesive bandages, contact lens cleaning solutions, cosmetics, etc.) • Foods for immune-compromised hospital patients (e.g., AIDS, cancer, or transplant patients) • Some foods for astronauts, who cannot risk foodborne illness • Spices and seasonings used in products such as sausage and certain baked goods.

IONIZING RADIATION

The treatments can: 1. reduce the microbial load of some foods increasing shelf life 2. destroy parasites and insects as an alternative to chemical pesticides 3. inhibit the germination of tubers and bulbs TO NORMAL STRENGTH (DOSE OF RADIATION) IS A SURFACE STERILIZATION RESIDUAL RADIOACTIVITY DOES NOT REMAIN IN FOOD

IONIZING RADIATION

Two things are needed for the irradiation process: • a source of radiant energy • a way to confine that energy The radiation can only be made in authorized buildings, using radioactive sources such as the 60Co and 137Cs. The products subjected to radiation must have a symbol on the box to mark it.

IONIZING RADIATION

Salting is used because most bacteria, fungi and other potentially pathogenic organisms cannot survive in a highly salty (NaCl) environment, due to the hypertonic nature of salt. Any living cell in such an environment will become dehydrated through osmosis and die or become temporarily inactivated. DRY SALTING: by rubbing the salt on the surface of solid food or overlapping layers, where the salt is generally mixed with spices. The salt must quickly penetrate into the tissues of the food. This method of salting is suitable for long aging products and long shelf life (fish, sausages). WET SALTING: action is slower and less intense. It is used for food that need other treatments such as smoking, refrigeration or cooking. It is performed using saline solutions at different concentrations. The wet salting can be carried out by immersion or injection of saline solutions (cheese).

FOOD PRESERVATION – CHEMICAL METHODS SALT (NaCl)

SALTING

Sugar exerts its preservative action in a similar way to the salt, by dehydrating microorganisms by osmosis, thus making them inactive. The sucrose must be present in the food in a concentration not less than 50%, as lower percentages favoring fermentative phenomena. Sugar can be used in the crystalline state or as a syrup, which means sugar and water at different concentrations. Nevertheless, there are osmophilus microorganisms not hampered by high concentrations of sugar. This method can also be combined with heat treatment for the preservation of fruit, such as jam or jelly.

SUGAR

USE OF NATURAL PRESERVATIVES

Both olive and seed oils are used to protect food from air's contact and, thus, prevent the development of aerobic microorganisms. In contrast, the anaerobic organisms can be rather easily develop, such as Clostridium botulinum, responsible for a toxin that can be lethal. To avoid this contamination, the method can be combined with other processes, such as salting, acidification, dehydration and pasteurization. This method is often used for fish or vegetables.

Vegetal oils

USE OF NATURAL PRESERVATIVES

Vinegar is the product of the acetic fermentation of wine. It must contain no more than 6% of total acidity expressed as acetic acid, and a residual amount of alcohol no higher than 1.5%.

The preservative action is due to the acetic acid content and the consequent lowering of the pH. The vinegar is used in the preservation of many plants and as adjuvant in other techniques. The pickle, like oil, must undergo advance other conservation processes, such as salting and pasteurization.

FOOD PRESERVATION – CHEMICAL METHODS VINEGAR

USE OF NATURAL PRESERVATIVES

Used at high concentrations (around 70%) ETHYL ALCOOL is lethal against vegetative forms while at the same dose is ineffective for bacterial spores. Bacteria are more sensitive than yeasts. The antimicrobial action of alcohol is due to several factors: • Denaturation of protoplasmic proteins • Dehydration of cells

Ethanol is present as a preservative in some bakery products (bread box) to prevent mold growth due to moisture in the product.

FOOD PRESERVATION – CHEMICAL METHODS

CH3CH2OH

USE OF NATURAL PRESERVATIVES

SMOKED SALMON

Smoking, in food processing, concerns the exposure of cured meat, fish and dairy products to smoke of aromatic woods for the purposes of preserving food and increasing their palatability by adding flavour and imparting a rich brown colour. Preservation technique used by man since ancient times.

The drying action of the smoke tends to preserve the meat, though many of the chemicals present in wood smoke (e.g., formaldehyde and certain alcohols) are natural preservatives as well.

FOOD PRESERVATION – CHEMICAL METHODS

FOOD SMOKING

The practice attained high levels of quality in several cultures, notably the smoking of fish in Scandinavia and northwestern North America and the production of smoked hams in Europe and US There are two types of smoking: Cold smoking the food is heated to a temperature between 20°C and 45°C, and the treatment is prolonged for days or weeks Hot smoking the food is heated to a temperature between 50°C and 90°C for a short period of time, generally a few hours The smoking process is often preceded by salting, which increases the dehydration, inactivates microorganisms and gives more flavor. The smoke has antiseptic, antioxidant and antimicrobial properties. Food's aspect and taste is extensively modified in a characteristic and functional way.

FOOD SMOKING

Food most frequently submitted to smoking: 1. MEAT (sausages, frankfurters, sausages, Prague ham, bacon) 2. FISH (salmon, herring, mackerel, swordfish) 3. CHEESES (mozzarella, ricotta, provolone). The smoked food has more concentrated nutrients than the fresh food: 100 grams of smoked salmon provide 25.4 grams of protein compared with the same weight of fresh that provide 18.5 grams. Smoking is a discussed treatment for the action of the substances present in the smoke (phenol and volatile compounds).

FOOD SMOKING

To avoid these harmful substances, which can be present in the smoke, such as benzopyrene, considered a carcinogen, the food industry has looked for other solutions, such as the use of smoke flavorings or liquid smoke. LIQUID SMOKE is produced by condensing wood smoke created by the pyrolysis of sawdust or wood chips followed by removal of the carcinogenic polyaromatic hydrocarbons. The main products of wood pyrolysis are phenols, carbonyls and organic acids which are responsible for the flavor, color and antimicrobial properties of liquid smoke.

LIQUID SMOKE

SOLPHYTES (E221-228) SORBIC ACID (E200) NITRATES E NITRITES (E249-252) BENZOIC ACID AND SALTS (E210-213) ASCORBIC ACID (E 300)

FOOD PRESERVATION – CHEMICAL METHODS CHEMICAL PRESERVATIVES