Lecture 7 - Part 2 Flashcards
What are the examples of browning reactions?
1) Non-Oxidative
Caramelization:
Suga> Caramel
Heat (160oC)
Acid/Basic Catalyst
Maillard Browning
2) Oxidative
Enzyme
What is the schematic of Maillard browning?
Sugar plus AA leads to a complex sugar amine compound and produces an uncoloured intermediates and finally produces a brown compounds/flavouring substances
What are melanoids?
Complex mixture of compounds giving colour/flavour
What are the impacts of Maillard browning?
Nutritional loss of Lysine
Colour and Flavour > Undesirable
When does browing occur in the Maillard browning rxn?
Browning can occur during both heat treatment and food storage at room temperature
What are the factors affecting the rate of rxn in the Maillard browning?
Reactivity of sugars: Glu > Lac > Mal
Water activity: Max. At: aw = 0.6-0.7
pH: Max. at higher pH
How do you inhibit Maillard browning?
pH: Low
Aw: High
Sugar: Non-Reducing
Other Reactants : Sulfite
What are enzymes roles in Maillard browning?
Proteins Increase reaction rate Catalysts Not Consumed Specific Minimal variety of undesired side products Some mediate unidirectional reactions A > B Some capable of encouraging both forward and reverse reactions A<>B
Where are the enzymes used in food processing derived from?
Non-toxic/edible plants + animals
Non-pathogenic microorganisms
What is oxidative (enzymatic) browning process?
Initial Reactions
Oxidative
Enzyme Catalyzed
Subsequent Reactions
Non-Enzymatic
What is phenolase?
Phenolase oxidize phenolic compounds into O-Quinones in oxidative (enzymatic browning)
How does plant tissue turn brown?
Phenolic and phenols in food are exposed to to oxygen.
Rapid oxidation of phenols to O-quinones
Rapid Polymerization
Rapid Polymerization
How do you prevent enzymatic browning?
Remove Enzyme:
- Reduce pH <3
- Heat
Remove Oxygen:
- Vacuum
- Brine/Syrup
What are the effects of browning?
Undesirable
-On cut surface of fruits and vegetables
Desirable
- Tea
- Cocoa
- Cider
