W5 Sugar, browning and caramlisation

Question 1

1. Describe the main sugars in food

Answer 1

Glucose, fructose, galactose
- all carbohydrates with the general formula Cn(H2O)n
- sucrose
- In nutrition: any of the mono or di-saccharides
- Important sources of sucrose are sugar cane and sugar beets. Sugar maple tree and date palms are minor sources
- High fructose corn syrup mainly added to foods however not common in Australia

Question 2

2. Explain enzymatic browning and its uses

Answer 2

• Phenolic compounds are responsible for the browning & bruising that often occurs in ripening fruit.
• Enzymatic browning can give a bitter taste and astringent feel
• Cell disruption and oxygen are needed to start enzymatic browning
  Stage 1: Monophenols  (Polyphenoloxidase + O2) Diphenols  Quinones
  Stage 2: Quinones Melanins * note At pH between 5 & 8
• Enzymatic browning can be desirable (coffee, tea, cacao, some dried fruit) or undesirable (multiple fresh fruits (like brown banana), prawns, lobster)

Question 3

2. ways to minimise enzymatic browning

Answer 3

• Denaturing/deactivating enzymes e.g. through heat/high pressure
• Adding acid to lower pH &/or chelate copper e.g. lemon juice
• Lowering the storage temperature
• Blocking exposure to oxygen through the use of coatings (e.g. sugar syrup)
  those used by the food industry e.g. Ascorbic acid reduces quinones to colourless diphenols OR inhibits PPO??
• Removal of metals (polyphenoloxidase contains Cu)
• Sulphites
• Genetic modification

Question 4

3. Outline the Maillard reaction, caramelization and dextrinisation and conditions required for each reaction to occur

Answer 4

what it is, factors influencing it:
A series of reactions between a reducing sugar (sugars that have a free carboxyl group which can react with a free amino group) and amino acids which results in the formation of brown complexes in food
- Maillard browning is the browning of food as a consequence of the Maillard reaction

Maillard Reaction results:
- Brown pigments called melanoidins
- Volatile compounds – often potent aromas
- Flavour compounds – bitter substances
- Desirable - aroma and colour of browned baked goods, cooked meat, chocolate flavour, roasted coffee, production of compounds that can stabilize food
- Undesirable – off odours and browning with long storage of multiple foods e.g. dried egg whites, milk powder, instant mashed potatoes, reduction in availability of digestible essential amino acids during storage due to glycosylation, compounds with potential mutagenic properties

Question 5

3. Factors that influence the Maillard reaction

Answer 5

Factors Influencing the Maillard Reaction:
1. The sugar: Reducing sugars are needed. These include glucose, fructose, galactose, lactose or maltose. Sucrose is not a reducing sugar but participates after being broken down to glucose and fructose (e.g. through heat &/or addition of acids).
2. The amino acid: Sugars react with the nitrogen in the amino group of amino acids. Therefore amino acids with amino groups in their side chains (e.g. lysine, arginine) are better substrates. Different amino acids results in different end products. Free amino acids are more reactive than peptide chains.
3. Water: The reaction peaks at a water activity (aw) of ~0.6
4. pH: The reactions are accelerated at pH ≥6
5. Temperature: Proceeds more quickly at ~140-160°C although can occur (slowly) at room temperature

Question 6

3. what is caramelisation

Answer 6

CARAMALISATION: sugar + heat (accelerated with high or low pH)

• Breakdown of sugars due to Heat or High or low pH
• Involves dry sugar or sugar syrup with most water evaporated
• No single compound is identified as caramel
  Steps involved (Caramelization involves a complex series of reactions which are not well understood):
  1. Sucrose (if used) breaks into glucose and fructose
  2. Monosaccharides are rearranged to give enediol
  3. Enediol converts to α-dicarbonyl compounds through dehydration or β- elimination
  4. Further degradation to multiple products e.g. caramelan, caramelen or caramelin groups
  5. Specific products formed depends on the type of sugar, pH and temperature

Question 7

3. what is dextrinisation

Answer 7

-starch + heat
-Occurs when starch is heated without water being added
- Temperature rises rapidly beyond that possible with water
- High energy → chemical degradation of starch through a chemical reaction with the water in starch
→ The starch molecule is split at 1 or more linkages between the glucose units
→ Dextrins: molecules of varying lengths derived from the breakdown of starch.
- Dextrins taste sweeter than starch

Question 8

4. Give examples of sweets and the sugar syrup required for their production

Answer 8

SUGAR CONFESTIONERY:
- Sugar with added flavour
- Confectionery production is highly sensitive to: 1) timing, 2) temperature, 3) skill of the preparer
- Important aspect of production is controlling crystallisation !!

• Crystalline confectionery = sugar syrup + heating &
  evaporation then cooling then beating
• Non-crystalline confectionery = sugar syrup + heating & evaporation then cooling without beating
• From the syrup solution: Rapid cooling & beating results in CRYSTALLINE confectionery e.g. fondant, fudge
• From the syrup solution: Slow cooling without agitation results in NONCRYSTALLINE confectionery e.g. hard lollies, caramels, peanut brittle, toffee