Food preservation F.6 Chemical Project 1.Introduction 2.The need to preserve food 3.Main principles of food preservation 4.Technical principles of food preservation 5.Common techniques of food preservation If there is no food preservation, Then……... 10% Food Spoiled Food Used 90% Food spoilage owing to microbial activities Caused by yeasts,fungi or bacteria either toxic in nature or produce toxic chemical eg.bread mould Food spoilage owing to chemical changes Oxidation of glycerides-> peroxide Oxidation of phenols-> browning of apple Reasons: Microbial activities caused by yeast, fungi, bacteria etc.. Chemical and biochemical changes in food How do the micro-organisms spoil the food? The micro-organisms are toxin in nature. They produce toxin chemicals when they act on the food. Examples of micro-organisms that spoiled food: Mould on bread Lactic acid bacteria in the souring mild Clostridium botulinum on meat. Principles of browning of apple: The phenols in apple is oxidized into diquinounes The diquinones will undergo polymerization and finally a brown products were formed 1.Killing of micro-organisms -micro-organisms found everywhere -rapid growth in damp & warm environment -Produce toxic substances ,harmful to man 2.Inhibition of microbial growth -reproduce by simple cell division -necessary to keep food in conditions that are not favourable for microbial growth 3.Retardation of chemical or biochemical changes -food undergo chemical or biochemical in storage even the absence of micro- organisms -Removal of air or water from food, and the inhibition of enzyme activities are common methods used to read the chemical or biochemical changes in food. Providing a favourable condition for the growth of micro-organisms Advantages of increasing or decreasing the pH value Extreme pH condition will inhabit the growth of the micro-organism Examples: The use of vinegar in pickling ,use of lactic acid in yogurt Since the micro-organism require a minimum a moisture content of 20% to growth Decreasing the moisture content inside the cells by increasing the solute concentration of food,would inhabit the microbial growth Principle:Water potential of the micro-organism is higher than that in the surroundings ,as water flow from higher water potential to lower water potential ,the cells run dry Advantages:Micro-organism would not capable to grow Examples:Putting the food into concentrated salt or Providing a favourable conditions microbial growth in food and leading to hydrolytic reaction during which food is spoiled. Advantages of the removal of water: Slowing down the microbial growth rate.Suppressing chemical and biochemical changes . Examples:Drying and dehydration Providing a favourable condition for microbial growth in food Advantages of decreasing temperature Retarding the growth of micro-organism Advantages of increasing temperature a.Destroying the bacterial cells and the spores b.Killing the micro-organisms Examples:Heat treatment,freezing Since many chemicals can inhabit the microbial growth,the use of chemical , such as Anti-oxidant can be used to reduce the amount of dissolved oxygen in food .It can retard the chemical and biochemical changes Principle: Heat kills micro-organisms, destroys enzyme activity of micro-organisms in food. Length of storage: It depends on the heat treatment and upon the type of food Changes in quality: The quality of food is maintained E.g. the dried food products such as biscuits, vegetables, fruit, fish,shrimp and milk Principle: Water is unavailable for reactions to occur, and for micro-organisms to grow. Length of storage: This varies with the product, storage conditions and the final moisture content Changes in quality: Often the reconstituted or rehydrated food is comparable to fresh food Principle: Radiation destroys enzymes and micro-organisms inside the food Length of storage: It significantly increases the storage of any food in comparison to its preservation by conventional methods Changes in quality: Nutrient destruction is no greater than hat by conventional methods Principle: Chilling slows down microbial activities and chemical changes resulting in spoilage Length of storage: After which time undesirable off- flavours slowly develops Changes in quality: Freezing promotes the retention of nutrients and does not destroy nutrients In jam, fruits in heavy sugar syrup.Food is kept in a strong sugar solution. Principle: Water available for enzyme action and microbial growth is removed by osmosis. Length of storage: When properly bottled or canned, these fruits may be stored a year or more. Changes in quality: these foods contain more calories than fresh fruit. Salt Fish Principle: Water essential for enzyme action and microbial growth is removed by osmosis. Length of storage: Most product can be stored three weeks to several months. Changes in quality: Its greater the loss in food value, including loss of vitamins and minerals Principle: Cooking destroys enzymes and micro- organisms. Length of storage: It can keep well for more than one year when properly canned Changes in quality: 1. Colour and texture often different from fresh product 2. No practical effect on proteins, carbohydrates and fats 3. Vitamin C and B are often destroyed. Principle: Most micro-organisms do not grow well in acidic solutions Length of storage: Picking alone is not enough for long term storage. Changes in quality: It adds an appealing flavour to the food Principle: Sodium chloride ties up the water otherwise used as a growth medium by micro-organism Length of storage: It mainly depends on the amount of chemicals used and the food product. Changes in quality: The quality of food is generally maintained Principle: The added substances inactivate or kill micro-organisms, retard chemical spoilage. Length of storage: It depends on the nature of chemical used and the formed product. Changes in quality: Quality is maintained or enhanced.
Pages to are hidden for
"Food preservation"Please download to view full document