Food Preservation PDF

# Food Preservation ## Principles of Food Preservation: - Food preservation by delay of microbial decomposition. - Food preservation by prevention of microbial decomposition. - Food preservation by asepsis (sterilization, filtration and controlling of microbial growth and activity). - Removal of m...

# Food Preservation ## Principles of Food Preservation: - Food preservation by delay of microbial decomposition. - Food preservation by prevention of microbial decomposition. - Food preservation by asepsis (sterilization, filtration and controlling of microbial growth and activity). - Removal of microorganisms. - Maintenance of anaerobic conditions. The principle of food preservation includes prevention against microbial decomposition, prevention of self-decomposing foods, and prevention against the various chemical, physical and mechanical damage of the food. ## 1. Prevention or delay of microbial contamination. ### How to prevent or delay microbial contamination in food: 1. Wash hands regularly with soap and water (especially after eating, drinking, or using the toilet). 2. Ensure staff are adequately trained and the food preparation and storage areas are clean and hygienic. 3. Keep the working environment sanitized as intervention strategies. 4. Foodborne pathogens can spread fast through dirty hands, utensils, equipment, and food. ## 2. Prevention or delay of self-decomposition of the food. ### How to prevent or delay self-decomposition of the food: 1. Damage self-enzyme of food that causes self-decomposition. For example, damaging the ripening enzyme of fruits by washing it in hot water. 2. Prevent purely chemical reactions occurring in food that damage the food. For example, prevention of oxidative rancidity of lipid by addition of anti-oxidant. 3. Create a hostile environment for fungi and bacteria by increasing the sugar, salt, or acid content of the food. Candying, salt curing, and pickling are methods commonly used to preserve food. 4. Activate enzymes in food by means such as salting, picking sugaring, etc. 5. Remove pro-oxidants making use of antioxidants. ## Preventing food spoilage ### How to prevent food spoilage: 1. Follow the four steps to food safety: clean, separate, cook, and chill. 2. Store fruits and vegetables according to their different requirements. 3. Refrigerate dairy products and other perishable foods. 4. Organize your food according to the date of expiry and don't stock up. 5. Store dry foods in a dry, moisture-free environment. 6. Remove spoiled food and separate foods to avoid cross-contamination. 7. Dry, pickle, or can your food to remove water and prevent bacterial growth. 8. Eat leftovers within a few days or freeze them. 9. Don't wash fresh produce before storing as it can introduce moisture and bacteria. 10. Don't freeze already contaminated food, as it can still spoil when thawed. ## Methods of Food Preservation ### A. Preservation by use of high temperatures: High-temperature preservation is based on the destructive effect of heat on microorganisms, thereby extending the shelf life of foods. High temperature refers to any temperature higher than ambient temperature applied to food. Preservation of foods by heat treatment can be done by two methods viz. pasteurization and sterilization. ### Factors influence the thermal resistance of microbial cells or spores: 1. **The relationship between temperature and time:** The time of killing cells or spores under a certain group conditions decrease with increasing temperature. 2. **Initial concentration of spores (or cells):** The higher the number of spores or cells, the greater the number of spores heat treatment is necessary to kill them all. 3. **The previous history of the vegetative cells or spores:** The conditions in which the cells live, they have grown and produced spores, and their processing affect their heat resistance. 4. **Phases of growth or age:** Bacterial cells know their greatest resistance during the late lag phase but almost as great resistance during their maximum stationary phase, followed by a decline in resistance. ### Heat treatments employed in processing foods: - Heating below 100°C (pasteurization). - Heating at about 100°C (boiling). - Heating above 100°C (sterilization). #### 1. Pasteurization: Pasteurization a heat treatment that kills parts but not all the microorganisms present and involves the application of temperatures below 100°C. It is commonly used in the dairy industry to kill bacteria that can cause spoilage and disease. Heating may be by steam, hot water, dry heat, or electric currents. Products are cooled promptly after the heat treatment. Pasteurization is used: 1. When more rigorous heat treatments might harm the quality of the product. 2. To kill pathogens in milk. 3. When the main spoilage organisms are not very heat resistant (Ex Yeasts in fruit juices). 4. When competing microorganisms are to be killed, allowing the desired fermentation. #### Preservative methods used to supplement pasteurization include - Refrigeration Ex: Milk - Keeping out microorganisms Ex: Packaging - Addition of high concentrations of sugar. Ex: Sweetened condensed milk - Presence or addition of chemical preservatives. Ex: Organic acids on pickles. #### Methods of pasteurization: 1. **High-temperature short-time (HTST):** - In this method, high temperature is employed for a short time. - The temperature is 71.7°C, and the time is 15 seconds. 2. **Ultra-high temperature (UHT):** - Earlier pasteurization temperature was set based on pathogenic organism present in milk Mycobacterium tuberculosis. This bacterium killed at 61.7°C. 3. **LTLT Method: (Low-temperature long time):** - In this method, low temperature is employed for a longer time. The temperature is 62.8°C, and the time is 30 minutes. #### 1- Ultra pasteurization: - In this method, the temperature applied is 137.8°C for at least 2 seconds. #### 2- Boiling: - This treatment was sufficient to kill everything but bacterial spores in the food and it is sufficient to preserve even low and medium acid foods. - Many acid foods can be processed successfully at 100°C or less. 100°C temperature is obtained by boiling a liquid food or by immersion the container of food in boiling water or exposure to steam. It is the incipient or gentle boiling with a temperature about 100°C. #### 3- Sterilization: - Temperatures above 100°C usually are obtained using steam under pressure in steam pressure sterilizers or retorts (autoclaves). The temperature in the retorts increases with rising steam pressures. - Ex: Milk can be heated to temperatures up to 150°C by use of steam injection or steam infusion followed by flash evaporation of the condensed steam and rapid cooling. Processes such as this for milk have been referred to as ultrahigh temperature or Ultra Heat Temperature (UHT) processes. - To detection of the efficiency of the food sterilization process, the presence of Clostridium botulinum is detected because it has great resistance to high heat. ### Thermal Destruction of Microorganisms: 1. **Thermal death time (TDT):** - This is the time necessary to kill a given number of microorganisms at a specified temperature. 2. **The thermal death point (TDP):** - This is the temperature necessary to kill a given number of microorganisms in a fixed time (10 minutes). 3. **D Value (the decimal reduction time):** - This is the time required to destroy 90% of the microorganisms. ### B. Preservation by use of Low temperatures: Low temperatures are used to retard chemical reactions and action of food enzymes and to slow down, or stop the growth and activity of microorganisms in food. ### Growth of Microorganisms at low temperatures: - Freezing prevents the growth of most foodborne microorganisms, and refrigeration temperature slows growth rates. - Clostridium botulinum type E has a minimum temperature for growth of about 3.3°C. - Yersinia enterocolitica grow at temperatures 0-3°C. ### Temperatures employed in low-temperature storage: 1. **Common or cellar storage:** - The temperature in common or cellar storage usually lower than 15°C. Root crops, potatoes, cabbage, celery, apples stored for limited periods. The deterioration of such fruits and vegetables by their own enzymes and by microorganisms, is not prevented, but is slower than at atmospheric temperatures. Low humidity in the storage cellar results in losses of moisture from the stored food and too high humidity favors spoilage by microorganisms. 2. **Chilling or cold storage:** - Chilling storage is at temperatures not far above freezing and usually involves cooling by ice or mechanical refrigeration. Eggs, dairy products, meats, seafood, vegetables and fruits may be held in chilling storage for a limited time. Enzymatic and microbial changes in the foods are not prevented but are slowed considerably. Chilling temperature is selected on the basis of the kind of food and the time and conditions of storage. Ex: Banana stored and keeps best at 13.3–16.7°C. Sweet potatoes keep best at 10-12.8°C. - Relative humidity in the chilling storage varies with the food stored and with environmental factors such as temperature, composition of the atmosphere, and ray treatments. - Changes in humidity, as well as in temperature during storage, may cause "sweating" or precipitation of moisture on the food. A moist surface favors microbial spoilage. - Ventilation or control of air velocities of the storage room is important in maintaining a uniform relative humidity throughout the room, removing odors, and preventing the development of stable odors and flavors. - The amounts and proportions of gases in the storage atmosphere influence preservation by chilling. Stored plant foods continue to respire, using oxygen, and giving off carbon dioxide. - In "Gas storage" of foods, where the composition of the atmosphere has been controlled by the introduction of CO2, Ozone, or other gas, or the removal of CO2. Gas storage ordinarily is combined with chilling storage. In the presence of optimal concentrations of carbon dioxide or ozone, the following advantages are present. A food will remain unspoiled for a longer period. Higher relative humidity can be maintained without harm to the keeping quality of certain foods. Higher storage temperature can be used without shortening the keeping time of the food. - 2.5% CO2 to be best for eggs - 10.0% CO2 for chilled beef - 100% CO2 for Bacon. - Combination of U.V. irradiation with chilling storage helps preserve some foods, and may permit the use of a higher humidity or storage temperature than with chilling along. U.V. lamps have been installed in rooms for the storage of meat and cheese. 3. **Freezing or frozen storage:** - The storage of foods in the frozen condition has been an important practice for centuries. Under frozen storage, microbial growth is prevented, and the action of food enzymes is greatly retarded. The lower the storage temperature, the slower will be any chemical or enzymatic reactions. - Fruits and vegetables are selected on the basis of their suitability for freezing and their maturity, and are washed, trimmed, cut or otherwise pretreated as desired. Vegetables are scalded or blanched. Fruits are packed in syrup. Most foods are packaged before freezing, but strawberries are frozen before packaging. Scalding or blanching of vegetables is done with hot water or steam and has the following advantages: - Inactivation of most of the plant enzymes which cause toughness, change in colour, mustiness, loss in flavour, softening, and loss in nutritive valve. - Reduction in the numbers of microorganisms on the food. - Enhancement of the green color of vegetables such as spinach. ### Types of freezing: 1. **Quick Freezing:** - The temperature of foods is lowered to about -20°C within 30 minutes. - Small ice crystals formed (intracellular ice crystals). - Blocks or suppresses metabolism. - Brief exposure to a concentration of adverse. - No adaptation to low temperatures. - Thermal shock. - No protective effect. 2. **Slow Freezing:** - Temperature is achieved within 3–72 hours. - Large ice crystals formed (extracellular crystals) - Breakdown of metabolic rapport - Longer exposure to adverse or injurious factors - Gradual adaptation - No shock effects - Accumulation of concentrated solutes with beneficial effects. ### Advantages of Quick Freezing over slow freezing: 1. Smaller ice crystals are formed; hence there is less mechanical destruction of intact cells of the food. 2. There is a shorter period of solidification of ice 3. There, is more prompt prevention of microbial growth 4. There is more rapid slowing of enzyme action. 5. Quick frozen foods are supposed to bring to the room temperature before cooking or consumption. This process is called thawing. Ex: Vegetables, meat. ### Effect of Freezing on Microorganisms: - Bacteria differ in their capacity to survive during freezing, with cocci being generally more resistant than Staphylococcus aureus or vegetative cells of Clostridium sp. - Endospores and food-poisoning toxins are unaffected by low temperatures. - Occurrence of low-temperature-induced changes in fatty acid composition, it is known that an increase in the degree of unsaturation of fatty acids in lipids leads to a decrease in the lipid melting point that increased the synthesis of unsaturated fatty acids at low temperatures which led to highly resistant to low temperature. ### Changes during preparation for Freezing: - The rate and kind of deterioration of foods before freezing will depend on the condition of the food at harvesting or slaughter and the methods of handling. The temperatures at which the food is held and other environmental conditions will determine the kinds of microorganisms to grow and the changes to be produced. - The condition of the food at the time of freezing will determine the potential quality of the frozen food. ### C. Preservation by Drying: - The preservation of foods by drying has been practiced for centuries. Drying usually is accomplished by the removal of water, but any method that reduces the amount of available moisture i.e. lowers the aw in a food is a form of drying. Ex: dried fish are heavily salted to remove moisture. - Grains after harvest dried to minimum moisture levels. Sugar is added to sweetened condensed milk to reduce the amount of available moisture. - **Sun-dried food:** Moisture removed by exposure to the sun's rays without any artificially produced heat and controlled temperatures, and air velocities. - **Dehydrated food:** Dehydrated food has been dried by artificially produced heat under controlled conditions of temperature, and airflow. Condensed usually implies that moisture has been removed from liquid food. Evaporated may have a similar meaning or may be used synonymously with the term dehydrated. ### Methods of Drying: 1. **Solar Drying:** Solar drying is limited to climates with a hot sun and a dry atmosphere certain fruits such as raisins, prunes, figs, apricots, nectarines, pears, and peaches are dried by solar. Fish, rice, and other grains are also dried. 2. **Mechanical drying:** Artificial drying involves the passage of heated air with controlled relative humidity over the food to be dried. The simplest dryer is the evaporator or kiln, sometimes used in the farm home. This method is considered the best method of drying food. 3. **Forced-draft drying:** Using systems employ currents of heated air that move across thefood usually in tunnels. The alternative method is moving the food on the conveyor belt or trays in carts through the heated air. Liquid foods like milk, juices, and soups may be evaporated by the use of low temperature and vacuum. 4. **Drum drying:** Is the passage of food over a heated drum with or without vacuum. 5. **Spray drying:** Is spraying the liquid into a current of dry, heated air. ### Factors in the control of Drying: 1. The temperature employed 2. The relative humidity of the air. 3. Velocity of the air 4. Time of drying. Improper control of the factors may cause case hardening resulting from more rapid evaporation of moisture from the surface than diffusion from the interior. It results in hard, horny, impenetrable surface film that hinders further drying. ### D. Using food additives - A food additive is a substance, or mixture of substances, other than a basic food substance, that have been specifically added to prevent spoilage or food decomposition is referred to as preservatives, whether they are natural or chemical substances. #### Ideal Antimicrobial preservative: 1. Have a wide range of antimicrobial activity. 2. Non-toxic to human beings or animals. 3. Economical. 4. Don't have an effect on the flavor, taste, or aroma of the original food. 5. Don't inactivated by the food or any substance in the food. 6. Encourage the development of resistant strains. 7. Kill rather than inhibit microorganisms. #### Factors that influence the effectiveness of preservatives: 1. Concentration of the preservatives. 2. Kind, number, age, and previous history of the microorganism. 3. Temperature. 4. Time. 5. The chemical and physical characteristics of the substrate in which the microorganism is found. #### a) Nitrites and Nitrates: - Combinations of these various salts have been used in curing solutions and curing mixtures for meats. Nitrites decompose to nitric acid which forms nitrosomyoglobin when reacts with the pigments in meats and thereby forms a stable red colour. Nitrites can react with secondary and tertiary amines to form nitrosamines, which are known to be carcinogenic. Nitrites are currently added in the form of sodium nitrite, potassium nitrite, sodiumnitrate, and potassium nitrate. Inhibits Clostridium botulinum in meat products. #### b) Sugar and salt: - These compounds lower water activity (aw) and harmful microorganisms. Sodium chloride is used in brines and curing solutions or applied directly to the food. Enough may be added to slow down or prevent the growth of microorganisms. - Salt has the following effects: 1. It causes high osmotic pressure and hence plasmolysis of cells. 2. It dehydrates foods by drawing out and typing up moisture as it dehydrates microbial cells. 3. It ionizes to yield the chlorine ion. 4. It reduces the solubility of oxygen in the moisture 5. It sensitizes the cell against CO2. 6. It interferes with the action of proteolytic enzymes. - Sugar such as glucose or sucrose has the ability to make water unavailable to organisms by osmotic effect. #### c) Alcohol: - Ethanol, a coagulant, and denatures of cell proteins are most germicidal in concentrations between 70 95%. Flavoring extracts e.g., vanilla and lemon extracts are preserved by their content of alcohol. Beer, and wine contain alcohol which retards microbial growth. #### d) Wood smoke: - Smoking foods usually has two main purposes: - Adding desired flavors and Preservation effect. - Improvement in the color of the inside of meat - Gloss of the outside and a tenderizing action on meats. - The smoking process helps preservation by impregnating the food near the surface with chemical preservatives from the smoke. - Wood smoke contains a large number of volatile compounds that may have a bacteriostatic and bactericidal effect. Formaldehyde is considered the most effective with phenols and cresols. - Smoking temperatures for meat vary from 43 71°C and the smoking period lasts from a few hours to several days. ### E. Food Preservation by Radiation: - Low-frequency, long-wavelength, low-energy radiation ranges from radio waves to infrared. Conversely, the high-frequency, shorter-wavelength radiations have high quantum energies and excite or destroy organic compounds and microorganisms without heating the product. - Microbial destruction without the generation of high temperatures suggested the term "cold sterilization." - Radiations of higher frequencies have high energy contents and are capable of actually breaking individual molecules into ions, hence the term ionizing irradiation. ### Factors Influencing Effectiveness - Direct rays are effective unless they come from special reflectors, and even then their effectiveness is reduced. The factors that influence the effectiveness of ultraviolet rays are as follows: - **Time.** The longer the time of exposure to a given concentration, the more effective the treatment. - **Intensity.** Within the short distance (Ex: industrial uses) the intensities of the rays vary inversely with distance from the lamp. - **Penetration.** The rays affect only the outer surface of most irradiated foods directly exposed to the lamp and do not penetrate to microorganisms inside the food. The lamps reduce the number of viable organisms in the air surrounding the food.