IUG Fall 2012 Dr Tarek M Zaida 1 Nonenzymatic Browning Background Brown colors often develop during 1 processing 2 storage and 3 preparation of foods and food ingredients ID: 230346
Download Presentation The PPT/PDF document "Lab Activity 1" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Lab Activity 1
IUG, Fall 2012Dr. Tarek M Zaida
1Slide2
Nonenzymatic
BrowningBackgroundBrown colors often develop during: 1. processing, 2. storage, and
3. preparation
of
foods and food ingredients.
2Slide3
Types of Browning
1. Enzymatic Enzymes (e.g. Oxidases) responsible for reactions that produce brown colors in food. Example: The enzyme polyphenoloxidase acts on phenols and oxygen in plant foods to form brown
colors.
It only occurs in fresh cut plants where the enzyme is still active and has access to its substrates
.
Note:Polyphenoloxidase
requires Cu as a cofactor, so copper chelators can limit enzymatic browning.
3Slide4
2.
Nonenzymatic In such browning cases, enzymes are not required for the production of brown colors in food.There three types of nonenzymatic browning:
Caramelization
Lipid Browning
Maillard
reaction
4Slide5
1. Caramelization
The process in which brown colors and pleasing aromas are resulted during the heating of sugars.Caramel colors are widely used to color cola beverages and other foods.Sugars in solution are quite stable to heat in the pH range of 3-7. Melting dry sugar or heating its solutions in the presence of acidic or basic catalysts, causes
the sugar to caramelize.
5Slide6
2.
Lipid BrowningThe polymerization of lipids after extensive heating (e.g., in old frying oils).6Slide7
3. Maillard
ReactionAlso known as the browning reaction,Is the phenomenon responsible for Turning
meat brown,
C
onverting bread to toast,
etc.,
The
Maillard reaction is named for Louis-Camille Maillard, a French chemist who studied the science of browning during the early 1900s.
7Slide8
Certain foods contain carbohydrates in the form of sugars, while others contain amino acids in the form of proteins.
Sugars and amino acids often exist side-by-side, as in the case of raw meats. They may also be blended together, as in the case of bread dough. As long as there is no outside catalyst, or cause for change, the meat remains red and the bread dough remains white.
8Slide9
The Maillard reaction is the catalyst for change, primarily by the addition of heat. When bread dough or meat is introduced to a hot oven, a complex chemical reaction occurs on the surface.
The carbon molecules contained in the sugars, or carbohydrates, combine with the amino acids of the proteins. This combination cannot occur without the additional heat source. The end result of this chemical recombination is the Maillard reaction. The surface of the heated bread dough is now brown, as is the outer layer of the roasted meat.
9Slide10
Everyday-life applications of
maillard reaction 1. Maillard reaction responsible for the brown color as well as for the change of flavor (meat & bread). 2. Recipes containing both eggs, which contain protein, and flour, which contains carbohydrates, benefit from the
Maillard
reaction to achieve a pleasing browned appearance
.
3. Self-tanning
products also rely on the reaction between amino acids and sugars to create a brown skin tone
. 4. The Maillard reaction is also used to create artificial flavorings, based on the hundreds of complex amino acid/sugar combinations formed after the process.
10Slide11
The
Maillard reaction occurs in three main steps: 1. The initial step: formation N glycoside
11Slide12
2. After formation of N glycoside the immonium
ion is formed and then isomerize, this reaction is called Amadori rearrangement and forms a compound called ketosamine:
12Slide13
3. The ketosamine products then either dehydrates into reductones
and dehydro reductones, which are caramel, or products short chain hydrolytic fission products such as diacetyl, acetol or pyruvaldehyde which then undergo the Strecker degradation.
13Slide14
Inhibition of Maillard
Reaction The Maillard reaction can be inhibited by: 1. keeping the temperature low, 2. reducing the accessibility of reagents or
3. adding
sulfite ions.
14Slide15
Sulfite ions are strong nucleophiles that can add to aldehyde groups to form an intermediate
that does not take part in browning. The mechanism of action of a sulfite is believed to be as follows: the browning intermediate DH reversibly binds a sulfite ion to form a sulfonated intermediate (DSH) which is not capable of
browning.
15Slide16
DH=
3-deoxyhexosulose 16Slide17
Because sulfite ion is readily volatile as sulfur dioxide gas
and sulfur dioxide gas can cause attacks in a proportion of asthmatics, the additive has been prohibited by the FDA in foods that are meant to be eaten raw. 17Slide18
Sulfites are allowed to a defined limit in some cooked foods because the additive escapes as gas during the cooking process. There is no widely accepted replacement for sulfites in foods although
deprotonated thiols (R-S-) are capable of acting as nucleophiles in a similar manner to sulfite and, if they react suitably with DH, may form the basis for an anti-Maillard browning additive if flavor problems can be overcome.18Slide19
Experiment
Materials 5% w/v solutions of the following: Sugar Amino Acid Fructose Lysine Galactose
Methionine
Glucose
Serine
Maltose Valine Sucrose
19Slide20
Procedure
1. Combine 3 mL of each sugar solution with 3 mL of each amino acid solution, in screw cap test tubes. 2
. Cap the tubes loosely.
3
. Autoclave at 121Âș C for 60 min (or
prepare
a boiling water bath by bringing a beaker of water to a boil on a hotplate), and heat the tubes for 60 min.
4. Remove tubes and allow cooling before handling. 5. Describe the aromas produced and the degree of browning for each solution. Record
the color as 0 = none, 1 = light yellow, 2 = deep yellow, and 3 = brown.
20