FST 141

• Membrane Concentration


  Unit operation where water and some solutes in a solution are selectively removed through a semipermeable membrane
• Membrane Concentration


  • Need pressure on the feed liquid as driving force for transport across the membrane
• Applications of Membrane Concentration

  • Clarification and concentration of vegetable juices
  • Concentration and purification of fruit juices
  • Meat brine clarification for bacteria removal and brine reuse
  • Clarification of wine and beer
  • Concentration of wheat starch
  • Egg white concentration
  • Concentration of whey from cheese manufacture
  • Demineralize and purify water
• Evaporation


  Also called "concentration by boiling", partial removal of water from liquid foods by boiling off water vapor
• Evaporation


  • Exploits the difference in volatility between water and solutes
  • Ideal: selectively remove water without changing the solute composition, so original product can be obtained on dilution
• Evaporator


  • Heat exchanger which transfers heat from steam to the food
  • A device to separate the vapor phase from the liquid
  • A mechanical or steam ejector vacuum pump
• Multiple effect evaporation


  Several evaporators (or "effects") are connected together, vapor from one effect is used directly as the heating medium in the next
• Arrangements of multiple effect evaporation

  • Forward
  • Reverse
  • Parallel
  • Mixed
• Forward arrangement


  • Least expensive
  • Simple to operate, no feed pumps required
  • Lower temperatures with subsequent effects = less risk of heat damage
  • Rate of evaporation decreases with each effect
• Reverse arrangement


  • No initial feed pump
  • Best quality steam used on most difficult material to concentrate
  • Interstage pumps necessary
  • Higher risk of heat damage and fouling
• Parallel arrangement


  • For crystal production, allows greater control over crystallization
  • Prevents need to pump slurries
  • Most complex and expensive arrangement
• Mixed arrangement


  • Simplicity of forward feed and economy of backward feed
  • Useful for very viscous foods
  • Complex and expensive
• Food Properties and Evaporator Performance


  • Viscosity and consistency
  • Fouling
  • Foaming
  • Corrosion
• Viscosity and consistency


  • Viscosity affects the rate of heat transfer
  • Pumping consideration
  • Longer contact of viscous foods with hot surfaces, greater heat damage
• Fouling


  • Formation of deposits during evaporation
  • Proteins and polysaccharides are capable of forming deposits
  • Difficult to remove
  • Adversely affect heat transfer
• Foaming


  • Caused by proteins and carbohydrates
  • Causes inefficient separation of vapor and concentrate
  • Causes "entrainment" = production of fine mist of concentrate during violent boiling = goes out with vapor
  • Can be remedied by using antifoam agents
• Corrosion


  • Acidic food like fruit juices can cause corrosion
  • Can damage equipment
  • Result in transfer of metals to the evaporated product
  • Can be reduced by anti-corrosion chemicals or surfaces
• Types of sugar concentrates

  • Jams
  • Jellies
  • Preserves
  • Conserves
  • Marmalades
• Jam

  Thick, sweet spread made by cooking crushed or chopped fruits with sugar
• Jelly

  Made by cooking fruit juice with sugar
• Preserves

  Spreads containing small whole fruit or small uniform pieces in a clear, slightly gelled syrup
• Conserves

  Jam-like products made from a mixture of fruits; may contain nuts, raisins or coconut
• Marmalades

  Soft fruit jellies containing small pieces of fruit or peel; often contain citrus
• Principle of sugar concentrate technology

  1. Adding sugar to augment osmotic pressure and prevent microorganism development

  2. Partially removing water (by boiling) to increase sugar concentration
• A food concentrated to 65% or more soluble solids (sugar) and which contains substantial acid may be preserved with relatively minor heat treatment provided that food product is protected from air
• Sugar and pectin bind or tie-up the moisture sufficiently to lower the aw to about 0.848 where only molds can grow
• Hermetic sealing protects the product from moisture loss, mold growth and oxidation
• Factors Affecting Gel Formation

  • Pectin
  • Acid
  • Sugar
  • Fruit
• Pectin

  Major binding component in cell wall of fruits, concentrated in the skin and cores, primarily composed of poly-D-galacturonic acid in which some of the galacturonic acid residues are methyl esterified
• Degree of methylation (DM)

  Has a profound effect on pectin functionality
• High methoxyl pectins (HM)

  Have a DM of >50%, form thermally irreversible gels in the presence of sugars (soluble solids >55%) at pH < 3.5
• Low methoxyl pectins (LM)

  Have a DM <50%, form thermally reversible gels in the presence of Ca2+ ions, function over a broader pH range and at lower soluble solids content
• How gel formation works

  1. With assistance from acid, pectin precipitates out and forms insoluble fibers

  2. The insoluble fibers produce a mesh-like structure that traps the fruit juice or other liquid
• Combination of ¼ under ripe and ¾ fully ripe fruits are recommended
• Fruits high in pectin

  • Strawberries and pineapple
  • Papaya, guava, santol, apple and citrus
• Reasons for using commercial pectin

  • Fully ripe fruit can be used instead of a mixture of ripe and unripe fruit
  • Cooking time is shorter and set, so there is no question when the product is done
  • Yield from a given amount of fruit is greater
• Acid

  Examples: lemon juice or citric acid, assists gel formation by lowering pH for pectin to precipitate, provides flavor, may be added in fruits which are low in acid
• Sugar

  Helps gel formation, serves as a preserving agent, contributes flavor, has a firming effect on fruit, granulated sugar is commonly used, part may be replaced by light corn syrup or light mild honey, artificial sweeteners cannot substitute for sugar in regular recipes
• Fruit

  Gives jams and jellies their characteristic flavor, furnishes at least part of the pectin and acid required for successful gels
• Jellied Products without Added Sugar

  • Special modified pectins
  • Recipes using gelatin
  • Long-boil methods
  • Regular pectin with special recipes