Thermal Modification of Food Flashcards
Browning Reaction: What is enzymatic browning? What do these reactions affect? How can you counter it?
Enzymatic browning is one of the most important reactions that takes place in most fruits and vegetables as well as in seafood
These reactions affect the taste, color, and value of such foods.
- Phenols react with oxygen through the enzyme polyphenol oxidase to form quinone.
The addition of lemon juice or through GMO with Arctic Apple can reduce the enzymatic oxidation of apples
What are the two forms of Non-enzymatic Browning Reaction? What are the consequences of cooking food?
Caramelization
Used in cooking for the desired nutty flavour and brown colour
As the process occurs, volatile chemicals are released producing the characteristic caramel flavour.
Maillard Reaction
The main chemical events during cooking
Positive Aspects → Flavours and melanoidins
Negative Aspects → The toxic Maillard products: Acrylamide & the others
Consequences of cooking food Softer Food Easy to digest Long term food storage Modification of human physiology Humankind co-evolved with cooked foods
What is the Maillard Reaction? Is it able to create new compounds? With which systems does it occur? What happens to the colour of the food?
Roasted and Baked food volatiles are formed during cooking through a well known chemical reaction named Maillard Reaction
In many cooked foods more than 50% of the compounds were not present in the raw material
MR occurs in all systems containing reducing carbohydrates (glucose, fructose) and free amino groups (proteins, amino acids, ammonia)
MR is always accompanied by colour development: non enzymatic browning reaction
Which factors influence MR (4)?
Concentrations of reactants
Time/Temperature & way of cooking (steaming, roasting, boiling, frying , deep-frying, microwave)
Water activity
pH
Why would we want to control or encourage MR?
In some food MR is not desired
In other foods we want to have colour and aroma formed during the MR
Some MR products are potent antioxidants and can increase food shelf life
Some MR products might be toxic and their formation should be limited
What is the first stage of the Maillard Hodge Scheme?
First stage of the reaction: from an amino acid and a reducing sugar to the Amadori compounds
What is the second stage of the Maillard Hodge Scheme? What is the product?
Second stage of the reaction: Strecker degradation between amino acids and dicarbonyls
The product is Pyrazine: A flavouring agents
What is the third stage of the Maillard Hodge Scheme?
Third stage of the reaction: The production of melanoidins.
What are melanoidins? What is its effect on the body? Source? RDI?
Melanoidins are the brown polymers formed in all the thermally processed foods
Not digested and used by gut microflora
→ Prebiotics
Coffee, bread crusts, roasted nuts, roasted potatoes, soy sauces, black beer, snack
The estimated daily intake is 5-10g
What is relationship between coffee and melanoidins?
20% of the coffee dry weight
Coffee drinkers consume up to 2g per day which is physiologically relevant
Special composition of polysaccharides, proteins and polyphenols
Color and taste role
Acts as prebiotic dietary fibre → Role in preventing colorectal cancer
What are the 4 toxic products produced by MR?
Acrylamide, Heterocyclic Amines (HCA), Furan, 3-MPCD
What is Acrylamide? How is it made? How is it carcinogenic?
Byproduct of heating asparagine, an amino acid found in carbohydrate rich food.
In the body acrylamide is converted to glycidamide, which is carcinogenic.
Epidemiological studies do not show a correlation so far
How can you reduce the production of Acrylamide or concentration of asparagine in food?
- Use Raw material with low asparagine and sugar content
- Modify time-temperature conditions during cooking
Soak raw potato slices in water for 15 to 30 minutes before frying or roasting to reduce acrylamide formation during cooking - Lower pH by addition of acid e.g. citric acid
Use Additives Antioxidants, Amino acids, and especially:
Asparaginase(Acrylaway), which converts asparagine to aspartic acid.
What are Heterocyclic Amines? How are they produced?
Formed by MR in roasted or fried meat or fish
Precursors are aminoacids and creatine
Researchers have identified 17 HCAs resulting from the cooking of muscle meats that may pose human cancer risk
How can you reduce the presence of Heterocyclic Amines in food?
Discard burned part of roasted products
Marinade → Olive oil, lemon juice, and garlic marinade cut HCAs levels in chicken by as much as 90%
Some spices are also very effective
