Food Science and Processing

FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 29 : Processing and Preparation of Sugar and Related Products

Properties

• Solubility
  In the natural state of foods, sugars are in solution. Crystallisation of sugar occurs from a sufficiently concentrated sugar solution, and use of this is made in the commercial production of sugar from sugarcane and beets. The most-soluble sugar is fructose, followed by sucrose and lactose. The sugar that is the most soluble such as fructose is most difficult to crystallise than that the least-soluble sugar, lactose.


• Absorption of moisture
  Sugars are hygroscopic. Fructose is more hygroscopic than the other sugars. Cakes made with honey, molasses remain moist for a long time.


• Fermentation
  Most sugars, except lactose, may be fermented by yeasts to produce carbon dioxide gas and alcohol. This is an important reaction in making bread and other baked products. The carbon dioxide leavens the product and the alcohol volatilises during baking.


• Acid hydrolysis
  Sucrose is easily hydrolysed by acid but maltose and lactose are slowly acted on. The end products of sucrose hydrolysis are a mixture of glucose and fructose. This mixture is commonly called invert sugar. The monosaccharides are not appreciably affected by acids. Heat accelerates the action of acid.


• Enzyme hydrolysis
  The enzyme sucrose also called invertase is used in the candy industry to hydrolyse some of the sucrose in cream fondant to fructose and glucose. This is done to produce soft, semi fluid centres in chocolates. The enzyme is commonly added to the fondant layer around the fruit in chocolate coated cherries.


• Melting point and decomposition by heat


1. Caramelisation
   With the application of sufficient dry heat, sugar melts or changes to a liquid state. Heating beyond the melting point brings about a number of decompositional changes. As sucrose melts around 160oC, a clear liquid forms that gradually changes to a brown colour with continued heating. At about 170oC, carmelisation occurs with the development of a characteristic caramel flavour along with the brown colour.
   Caramelisation is a complex reaction, involving the removal of water and eventual polymerisation. Caramel has a pungent taste, is often bitter, is much less sweeter than the original sugar from which it is produced, and is non-crystalline. It is soluble in water. Fructose caramelises at 110oC, and maltose caramelises at about 180oC, galactose at 170oC.


2. Decomposition by alkalies
   The monosaccharides are markedly decomposed by alkalies and flavour may become strong and bitter. Sucrose is least affected by alkalies.


3. Sweetness
   Of the sugars, lactose is the least, followed by maltose, galactose, glucose and sucrose with fructose being the most sweet. A maximum sweetness from fructose is most likely to be achieved when it is used slightly with acid, cold foods and in beverages.