FTPC 109-M2

• The frozen food industry had a humble beginning in the early part of the twentieth century, limited to freezing fruits, vegetables, meats, and fish. Today, the range of frozen foods includes: bakery goods, ice cream, desserts, consumer and catered packaged products, and juices.
• Frozen foods are valued for their superior sensory and nutritional quality when compared with foods preserved by other methods. The quality attributes of a frozen food can be maintained with a properly designed freezing process, and a carefully monitored handling and storage practice. Frozen foods are convenient to cook in the home (or institutional kitchen) prior to consumption.
• Chilling


  Storage of food between 15℃ (59℉) to 1℃, just above the freezing point of water. In chilling, all the water content of the food remains in liquid state.
• Freezing


  A low temperature preservation method where most of the water in the food is converted to ice. Freezing temperatures are much lower than 0 ℃, typically never more than -10℃, the usual freezing temperatures in the freezer section of most household refrigerators.
• Chilling/Refrigeration


  • Minimum adverse effects on the taste, texture, and the nutritional value of foods
  • Short-term method of preserving food
• Refrigeration


  • Does not kill microorganisms nor inactivate enzymes, but only slows down their deteriorative effects
• Refrigeration temperature is a key factor in predicting the length of the storage period. For example, meat will last 6-10 days at 0℃, one day at 22℃ and less than one day at 38℃.
• The preservative action of refrigeration is attributed to


  • Retardation of the growth of microorganisms
  • Slow down post-harvest metabolic activities of intact plant tissues and post slaughter activities of animal tissues
  • Slow down chemical reactions like enzyme-catalyzed oxidative browning or lipid oxidation
  • Retard loss of nutritive value
• Chilling is used as an adjunct preservation method for cooked food, pasteurized products, and fermented products. It is also used as process operation to solidify gels, to ripen cheese or control yeast activity in baked products or as an in-process storage procedure.
• Chilling temperatures meant to control pathogens has been set at 4℃ (40℉), which is the designated lower limit of the temperature danger zone (TDZ). At this temperature the growth of pathogens are inhibited and those of many non-pathogenic spoilage microorganisms are slowed down considerably.
• For every 10 degree Celsius decrease in temperature from the optimum for microbial growth, there is a corresponding 50% reduction in rate of metabolic activity which directly translates to the same reduction in spoilage rate, conversely to extension of shelf life.
• Chilling effects on food

  • Slows down aerobic respiration and thus retard onset of senescence and decay in fruits and vegetables
  • Stops respiration in animal food sources, preventing the decaying process from starting
• Quality losses that can occur during chilling storage

  • Microbiological activity
  • Enzymatic and other physiological activities
  • Physical damage due to bruising, dehydration or wilting
• Control of relative humidity in chilling storage is essential to achieve maximum storage life. Relative humidity higher than optimum will encourage growth of microorganisms, while lower than optimum will result in wilting or shriveling.
• Adjuncts to chilling


  • Cooking
  • Pasteurization
  • Fermentation and curing
  • Waxing and oiling
  • Modified and controlled atmosphere storage
  • Chemical preservatives/additives
• Safe temperature for storing food in the home refrigerator is between 1 to 3℃/ 34℉ to 40℉.
• Institutional chillers have more uniform temperature if supplied with adequate air circulation device. Food in chillers should not be packed too tightly together. Space for air circulation should be provided to maintain the cold temperature in the food.
• Freezing


  A continuation of refrigeration where the temperature of the food is further lowered beyond its freezing point, causing the water in the food to convert to ice.
• Freezing temperatures can completely inhibit the activities of microorganisms without necessarily causing their destruction.
• Freezing


  1. Pre-freezing treatments

  2. Freezing

  3. Frozen storage

  4. Thawing
• Blanching


  Mild heat treatment by exposing the product to hot water or steam at 80-100°C for specific periods to inactivate enzymes, drive out cellular gases and reduce microbial load
• Pasteurization


  Preliminary treatment to freezing to reduce microbial load
• Freezing involves the change of water contained in the food from a liquid to a solid (ice)
• When water freezes it expands, and the ice crystals formed cause cell walls of food to rupture
• As a result, the texture of the product will be much softer when it thaws
• Textural changes are most noticeable in fruits and vegetables that have a high water content
• Vegetables with a high water content, such as celery and salad greens, are not usually frozen
• Frozen fruits such as mango halves are best served when ice crystals are still present, as complete thawing makes the fruit limp and unattractive
• Textural changes due to freezing are less noticeable in products that are cooked before eating or in high-starch vegetables
• The effect of freezing on fruit tissue is less noticeable when fruit is still partially frozen
• Freezing concentrates the non-water components in food, leading to changes in acidity, enzyme activity, and other properties
• The resulting thaw drip of previously frozen foods is a manifestation of this concentration of solutes
• Blanching


  Mild heat treatment by exposing the product to hot water or steam at 80-100°C for specific periods
• Preliminary frying


  Oil may be used instead of water or steam, as practiced for potato and sweet potatoes
• Blanching (in peanut processing)


  Short-term dry air heating to remove the test surrounding the cotyledon
• Pasteurization


  Preliminary treatment for freezing, equivalent to blanching, usually applied to liquids or semi-liquids like purees
• Some cooked foods like pasta do not lend itself to freezing because the pasta gets soggy, but many cooked meat dishes can be successfully frozen
• Common chemical additives


  • Sodium metabisulfite
  • Ascorbic acid
  • Citric acid
  • Combinations of citric acid and ascorbic acid
• Salt solutions


  1. 3% solutions used to prevent enzymatic browning
• In recent years, there has been a re-examination of chemical additives particularly sulfites, and some countries have set 0 limits to low limits of the residual sulfite in fruit and vegetable products