Food Processing 2 Chapters 5 & 6

• Drying


  The application of heat under controlled conditions to remove the majority of the water normally present in a food by evaporation
• Dehydration


  Also known as drying, defined as 'the application of heat under controlled conditions to remove the majority of the water normally present in a food by evaporation'

  
• Purpose of dehydration


  • To extend the shelf life of foods by a reduction in water activity
  • Inhibits microbial growth and enzyme activity
  • But the processing temperature is usually insufficient to cause their inactivation, so any increase in moisture content during storage results in rapid spoilage
  • Drying causes deterioration of both the eating quality and the nutritional value of the food
  • The design and operation of dehydration equipment aim to minimize these changes

  
• Dehydration


  1. Moisture must move from the interior to surface of the material (by capillary action or diffusion)

  2. Surface water must be evaporated into air

  
• Factors affecting drying rate
• Drying curve


  • Plots the drying rate versus drying time or moisture contents
  • Three major stages: transient early stage, constant or first period, falling or second period
• Psychometric chart


  Heating and humidifying: a psychrometric process that involves the simultaneous increase in both the dry bulb temperature and humidity ratio of the air
• The most common method used to determine the moisture content is by drying
• Drying can be done using hot air, vacuum or freeze-drying
• Hot Air Drying - uses heat transfer from heated air to remove water vapor from food products
• Near-infrared spectroscopy - measures the amount of light absorbed by different chemical bonds within a molecule; can measure moisture content without destroying the product
• Vacuum Drying - removes water vapor through sublimation at low temperatures (below freezing point)
• Microwave dielectric heating - uses microwaves to heat materials directly through dipole rotation; useful for measuring moisture content in solid products
• Freeze-Drying - also known as lyophilization; removes water vapor through sublimation at very low temperatures (-40°C) under high vacuum pressure
• Vacuum Drying - removes water through sublimation (directly from solid state to gas) at low temperatures
• Moisture migration occurs when there are differences in moisture concentration between two points on a surface
• Moisture migration - occurs when there are differences in moisture concentration between two points on a food surface
• Freeze-drying - removes ice crystals formed during cooling process; leaves behind dry solids with no residual liquid
• Freeze-Drying - also known as lyophilization; removes water vapor through sublimation at very low temperatures (-40°C) and high vacuum pressure
• Food preservation is important because it allows us to store foods longer than their natural shelf life.
• Freeze-Drying - also known as lyophilization; freezes the material then applies vacuum to lower pressure so that ice will sublime directly into gaseous form
• The goal of food processing is to preserve food quality while extending its shelf life.
• Dehydrated foods are more stable than fresh ones because they have lower microbial load and less susceptible to spoilage due to lack of oxygen
• Sun drying is commonly used for grains like rice, wheat, and corn.
• Preservation methods include drying, refrigeration, fermentation, smoking, salting, pickling, curing, and canning.
• Air drying is used when the final product must be dry, such as fruits or vegetables that will be stored for long periods.
• Water activity (a) is defined as the ratio of the partial pressure of water vapor above a substance to that of pure water at the same temperature
• Food dehydration reduces weight and volume, making it easier to transport and store
• Outline


  • Sugar Concentration
  • Salting
  • Curing
  • Smoking
• Sugar


  An organic compound in the form of carbohydrate
• Types of sugar


  • Simple sugars known as monosaccharides
  • A double sugar joined by a glycosidic link - 2 monosaccharides joined together are called disaccharides
• Sugar


  Involved in the preservation and manufacturer of wide of food products
• Common sugar products


  • Jams
  • Jellies
  • Fruit juice concentrates
  • Sweetened condensed milk
• Action of sugar


  • Binds to the water in the foods reducing the amount of water that is available for the growth of microorganisms
  • Has an osmotic effect
• Salting


  A process for preserving meat and vegetables, as old as using the sun to dry foods
• Salting


  • Salt draws out moisture from food to prevent spoilage
  • Certain types of bacteria and other spoilage microorganisms thrive in moist environments
• Freshening


  The process of rinsing and soaking meat or vegetables in cold water to remove as much salt as possible before cooking
• Curing


  Addition of salt, sugar and nitrite or nitrate to meats for purpose of preservation, flavor enhancement, or color development
• Curing


  • Prevalently done for flavor enhancement then for preservation
  • Shelf-life extension
  • Development of unique property
  • Controlling microbial growth
• Curing ingredients


  • Salt (NaCl)
  • Sugar (C12H22O11)
  • Nitrate (NaNO2) or Nitrate (NaNO3)