Food Preservation MIC 204 Unit 4 PDF

# Food Preservation ## MIC 204 ## UNIT 4 ### Principles of Food Preservation 1. Prevention or delay of microbial decomposition 2. Prevention or delay the self-decomposition of the food 3. Prevent damage caused by insects, animals, mechanical, etc. ### Applications of Microbial Growth Curve to...

# Food Preservation ## MIC 204 ## UNIT 4 ### Principles of Food Preservation 1. Prevention or delay of microbial decomposition 2. Prevention or delay the self-decomposition of the food 3. Prevent damage caused by insects, animals, mechanical, etc. ### Applications of Microbial Growth Curve to Food Preservation - Microbial decomposition of foods will be prevented if all spoilage organisms are killed, and recontamination is prevented. - Predict microbial growth of food spoilage. Example: Salmonella - Control at any course. Example: Growth rate, lag time, generation time - Hindering the growth of microorganisms by merely stopping multiplication does not necessarily prevent decomposition because viable organisms or their enzymes may continue to be active. ### Methods of Food Preservation - Asepsis — Keeping out microorganisms - Removal of microorganisms - Maintenance of anaerobic conditions - Use of high temperature - Drying and Smoking - Use of Chemical Preservatives - Irradiation ### Bioburden - **Kinds of microorganisms:** Present, whether any spoilage or pathogenic microorganisms - **Number of microorganisms:** Spoilage organisms, food spoilage, difficult to preserve **Aim:** To measure the total number of viable microbes (total microbial count) on a food prior to its final sterilization before use. ### Maintenance of Anaerobic Conditions - Anaerobic conditions can be achieved by a complete fill, replacement of air by CO2 or N2, and others. - Spores are resistant to heat and may survive in canned food but they are unable to germinate in the absence of oxygen. ### Use of High Temperatures - Temperature and time used in heat processing will depend on: - The effect of heat on the food - Other preservation methods employed | Heat Treatment | Microorganisms | | --- | --- | | ↑ | ↓ | **Classification of heat treatments used on foods:** 1. **Pasteurization:** Below 100 °C 2. **Heat at 100 °C:** 3. **Heat > 100 °C:** #### *a. Pasteurization* - Heat treatments that kills most but not all microorganisms - Examples: - Milk 63 °C, 30 minutes; 72 °C, 15 minutes - Juice 77 °C, 30 minutes; 88 °C, 30 seconds - Pasteurized products are cooled promptly after the heat treatment. **Pasteurization is important when:** 1. Heat treatment will not harm the quality of product. 2. Main spoilage microbes are not very heat resistant. Example: Yeast in fruit juices. 3. To kill pathogens. 4. Any surviving organisms will be treated with other preservative methods. 5. Competing organisms are to be killed, allowing a desired fermentation. **Preservative Methods used to supplement Pasteurization:** 1. Refrigeration 2. Keeping out microorganisms by packaging 3. Maintenance of anaerobic conditions 4. Addition of high concentration of sugar. 5. Presence of chemical preservatives #### *b. Heating at about 100 °C* - Sufficient to kill all microbes but not spores - Many acid foods are successfully preserved at 100 °C. - **Methods:** - Boiled - Immersion - Baking - Simmering - Roasting - Frying - Blanching - Exposure flowing steam #### *c. Heating above 100 °C* - Obtained by means of steam under pressure - Steam pressure ↑ Temperature ↑. - 121 °C, 1 ATM - **Commercial sterility:** Includes heating foods at high temperatures for a short time, such as in ultra-heat treatment - All commercially sterile foods should be stored in cool, dry places to prevent any viable thermophilic spores from germinating and causing spoilage to the foods. - **Ultra Heat Treatment:** Treatment of milk by heating at 150 °C by steam injection followed by "flash evaporation" of the condensed steam. **Objective of heating foods:** 1. To destroy pathogens and spoilage microorganisms. 2. To destroy toxins present in foods. 3. To destroy vegetative cells and spores of yeast, bacteria, and molds. 4. To destroy undesirable enzymes. This can affect the quality of foods. 5. To control the growth of surviving microorganisms 6. To retain the acceptance and nutritional quality of foods 7. To reduce competition ### Canning Process - Preservation of foods in sealed containers followed by the application of heat treatment. - Canning - Also known as "hermetically sealed containers" is done in tin cans, glass containers, aluminum, and plastic pouches. ### Flowchart of Canning Process The process of canning pears is shown in the attached flowchart. ### Spoilage of Canned Food - Spoilage of canned food can be divided into 3 types: 1. Microbial spoilage 2. Chemical spoilage 3. Enzymatic spoilage - In general, microbial spoilage can occur due to under processing and/or leakage after processing. ### Types of Spoilage in Canned Food - Types of spoilage in canned food depend on the type of microorganisms involved: 1. **Thermophilic Bacteria and Spores** - These bacteria can cause 3 types of spoilage, especially when cans are kept at > 43° C. - "Flat-sour" spoilage - Thermophilic Anaerobe Spoilage - Sulphide stinker spoilage 2. **Mesophilic Bacteria** - Bacillus spp. - Clostridium spp. Example: C. sporogenes. 3. **Non-spore-forming Bacteria** - Example: Streptococcus, micrococcus, etc. Which will produce acid and gas. 4. **Moulds and Yeasts** - Can be killed by mild heat ### Use of Low Temperature - Low temperatures reduce the activity of microorganisms by reducing the chemical reaction and action of enzymes. - Low temperatures will prevent the growth of microorganisms, allowing only small metabolic activity. - Hence, less microbial growth and spoilage is delayed/prevented. #### *A. Chilling Temperature* - Temperature of 6°C can prevent the growth of food poisoning microorganisms, except Clostridium botulinum type E and retard the growth of spoilage microorganisms. - Chilling temperature is the main method for temporary preservation of food. - Psychrotroph are microorganisms which can grow at low temperatures. Example: Flavobacterium spp. and Pseud. Alcaligenes, but they have a low growth rate. #### *B. Freezing Temperature* - Causes a reduction in the number of viable microorganisms but does not sterilize the food. - The percentage of microorganisms killed during freezing and storage varies depending on: - Substrate (kind of food) - Type of freezing - **Advantages of fast freezing:** - Smaller ice crystal forms - less mechanical destruction to food. - Short period of solidification - sudden death to microorganisms and quick inactivation of enzymes. - Food quality after thawing is better. ### Drying and Smoking #### *A. Drying* - Methods which lowers the water content of food to a point where the activities of enzymes and food spoilage and food poisoning microorganism are destroyed/inhibited. - The lower the water activity of food, the greater is inhibition. - If Aw is between 0.75 - 0.70, the spoilage is delayed. If Aw is 0.65, the spoilage is most unlikely to occur for 2 years. - Moulds and yeasts are more important in spoilage dried foods since bacteria require higher water content for growth. - Example: - Streptomyces rouxii Aw 0.65 - Aspergillus glaucus Aw 0.60 - **Types of drying:** - Sun drying - Spray drying - Free drying - Smoking - **Treatment before drying (to reduce the number of microorganisms):** - Washing - Dipping food in alkaline solution. - Treatment with SO2 (1000 - 3000 ppm) - Blanching/scalding - **Effects of drying upon foods:** - Desiccated foods are subjected to certain chemical changes which can cause undesirable products. - Dried food that contains fat and oxygen can cause oxidative rancidity to occur. - Dried food which contains reducing sugar can undergo a color change called the Maillard reaction. Carbonyl groups of reducing sugar react with amino groups of proteins and amino acids followed by a series of complex reactions. The browning is undesirable because of the unnatural color and bitter taste imparted to the food. - Loss of vitamin C - Discoloration - Toughness - **Methods of minimizing chemical changes in dried food:** - Keep moisture content as low as possible. - Reduce the level of reducing sugar as low as possible. - Reduce serial blanching in the same water. - Use SO2 to retain vitamin C and avoid browning. #### *B. Smoking* - Heating foods using smoke from various types of wood to preserve foods. - The smoke produces heat which kills some microorganisms on the surface. - Heat also reduces Aw. - Smoke also contains antimicrobial compounds, such as formaldehyde, which can inhibit the growth of some microorganisms. - The presence of aromatic compounds also give a distinctive flavor to the food. - This will make the foods taste better and more tender - such as smoked fish. - Woodsmoke is more effective against vegetative cells than against bacterial spores. ### Chemical Preservatives - **Food Additives/Preservatives:** - "A substance or a mixture of substance which are specifically added to prevent deterioration or decomposition of a food." - **Deterioration may be caused by:** - Microorganisms - Food enzymes - Chemical reactions - **Chemical preservatives are used mainly to inhibit the growth and activity of microorganisms by:** - Interfering with their cell membranes - Their enzymes activity - Their genetic mechanisms ### Other Preservative Methods #### *a. Filtration* - Although fruit juices can be preserved by chemical preservatives, now we can get products without any preservatives added. - Fruit juices are subjected to filters with steam sterilize methods for 10-20 minutes. The sterile products are filled aseptically in sterile bottles or cartons. #### *b. Radiation* - Gamma ray is the cheapest form of radiation for food preservation. - X-rays essentially have the same character as gamma rays but are produced differently. **Factors affecting radiation:** - **Types and species of microbes:** Spores are generally radioresistant - **Number of microbes:** The more cells present, the less effective is a given dose of radiation. - **Composition of medium:** Cells in protein media are more resistant. Proteins exert a protective effect against radiation. - **Presence or absence of oxygen:** Resistance is reportedly increased when oxygen is absent. - **Physical state of food:** Dried cells are more resistant to damage from radiation than moist cells. - **Age of cells:** Cells in lag phase are more resistant than in other phases of growth. #### *c. Antibiotics* - Antibiotics such as aureomycin, terramysin, and chloromycetin were found to be effective in lengthening the storage time of raw food, especially meats, fish, and poultry at chilling temperatures. - Niasin has been used to suppress anaerobes in cheese and cheese products. - Natamycin has been tested in orange juice, fresh fruits, sausage, and cheese. - **Some problems in the use of antibiotics:** - Effect of antibiotics on microorganisms vary with the species. - Organisms can be adapted to increasing concentrations of an antibiotic, so that resistant strains finally develop. - Other organisms which are not significant food spoilers but have acquired resistance, will eventually be important in food spoilage. - The effect the antibiotic will have on the consumer.