Function of Protein

Protein is formed when amino acids ( usually less than 50) linked together by peptide bonds in a quaternary structure.

Peptide Bond Formation :

                               R¹                                                                            H    R²

                                |                                                |      |

                  H₃N⁺ -  CN -  C - OH         +        H – N – CH – COO^-     

                                          || 

                                         O

                                                               ||(Remove H₂0)

                                                     R¹                 H     R²

                                                      |               |        |

                                       H₃N⁺ -  CN -  C – N – CH – COO^- 

                                                               ||

                                                              O

There is TWO main type of proteins can be found in food  

   v  Gluten

   v  Egg proteins

Figure 1: Gluten (Canadian Grain Commission  2016)

Figure 2: Egg (NCPTT 2016)

Gluten

Content:

  Ø  Found in the endosperm of mature wheat grain

Figure 3: Gluten in the endosperm of wheat( Canadian Grain Commission  2016)

Function:

    ü Use in dough formation :

    ü Contains gliadins and glutenins ( Canadian Grain Commission  2016)

•    Gliadins facilitate fluidity, extensibility, contribute to bread-loaf volume.
•    Glutenins is responsible for elasticity, cohesiveness and mixing tolerance of dough.

Egg Proteins

Content:

   ü  Egg white - Albumin Protein (NCPTT 2016)

Figure 4: Content of Egg white (NCPTT 2016)

      Ø  Ovalbumin - the most abundant protein in egg white

      Ø  Ovotransferin – act as a metal-chelating antioxidant , bind metallic ions

      Ø  Lysozyme – act as an antibacterial shielf for the egg

      Ø  Ovomucin – responsible for egg-white viscosity

   

   ü  Egg yolk

      Ø  Phosvitin- Emulsifying activity (Samaraweera et al. 2011).

     Ø Lecithin- Improve emulsification, texture and flavour.

EGG PROTEIN

Function of EGG PROTEIN:

Figure 5 : Function of Egg Protein (NCPTT 2016,Nii & Ishii 2005,American Egg Board 2016,Tarleton Academy 2016)

  ü Coagulation

   - Process that results in loss of solubility or a change from a fluid state to a solid state when it is exposed to heat or acid (NCPTT 2016).
               o   Egg white begins to thicken at around 62 °C

               o   Egg yolk begins to thicken at 65 °C

-   - Can affect the texture of food as it can act as a thickening agent due to the coagulation process (NCPTT 2016)

-   - Sugar can delay the coagulation process (NCPTT 2016)

             oIt can decrease the rate of heat denaturation and increase the coagulation temperature.

     - Salts promote coagulation

                                          

Figure 6: The process of protein coagulation(Socratic 2015).

   ü Emulsification

      - Egg yolk is a type of oil in water emulsion

      - Lecithin is an emulsifying agent (Nii & Ishii 2005) 

      - Important process in making salad dressings and whipped topping

                                  Figure 6: The process of emulsifier functions in oil and water.

   ü Foaming

      - Bubbles will be trapped by egg albumen and decrease in size, increase in number after whipping or beating (American Egg Board 2016)

              o Involve denaturation of protein at an air-liquid interface

              o then hydrophobic part of the protein will enter the air

              o the hydrophilic part of the protein remains in the water (Athaualpa 2006)

              o Globulins and ovomucin is responsible for foaming properties of the egg (NCPTT 2016)

      - Salts and lipids can reduce foaming performance by reducing its stability thus the  bubbles formed will collapse more easily

      - Sugar can improve stability of the food product.

      - It is important to dairy desserts such as ice-cream and custard (American Egg Board 2016).

               o Due to its foaming properties

               o It can increase its volume

Figure 7: The process of foaming (A Dash Of Science 2013).

ü ü Enrichment

       - To add colour and nutritional values in sauce (Tarleton Academy 2016).

Figure 8: The process of maillard reaction.

                        

Others function of Protein:

Figure6: Other Function of Protein ((Nii & Ishii 2005, Gorton 2012,British Nutrition Foundation 2016a,Tarleton Academy 2016, Food Info 1999 )

  ü  Emulsification

        - Protein is an amphiphilic substance which contains hydrophobic part and hydrophilic part (Nii & Ishii 2005) 

        - Protein can stabilize oil in water emulsion or air in water emulsion( Nii & Ishii 2005) 

               o by diffusing to interface,

               o unfold 

               o then exposing the hydrophobic group 

               o and interact with lipid

        - Prevent droplet coalescent ( separation of two immiscible phase)

        - It is important to salad dressing

  ü  Gelation
       - Involves denaturation of proteins

       - Gel is a continuous network of macroscopic dimensions immersed in a liquid medium and exhibit no steady-state flow due to water immobilization (Gorton 2012).

       - Gelation can make whey protein in the bakery product starts to bind water and lead to a better mouthfeel and palatability (Gorton 2012).

       - It is important to bakery products

  ü  Bulking  

        - Some Protein can mimic the sensory properties of meat

        - Form the main part of the filling of foods for vegetarians such as cottage pie (British Nutrition Foundation 2016a)

         - Eg. Texture Vegetable Protein

          

  ü  Glaze

         - Enhance the colour of the product

         - Give products a shiny glaze (Tarleton Academy 2016)     

     

  ü    Maillard Reaction
       - A type of non-enzymatic browning

           - Involve the reaction of simple sugars and amino acids

           - Form brown nitrogenous polymers which is called melanoidins (Food-Info 1999)

           - Gives a desirable colour to bread crust and cookies (Food Info 1999)

           - Give a desirable flavour to coffee , cocoa

 - 

Reference:

A Dash Of Science 2013, How do egg whites make a foam?, viewed 11 November 2016,
<http://adashofscience.com/2013/04/04/egg-white-foams/>
American Egg Board 2016, AERATION/FOAMING/STRUCTURE, viewed 8^th November, <http://www.aeb.org/food-manufacturers/eggs-product-overview/functional-properties/39-functional-properties/207-aeration-foaming-structure>

Athaualpa R. 2006, “ALBUMEN PROTEIN AND FUNCTIONAL PROPERTIES OF GELATION AND FOAMING”, viewed 7^th November 2016, < http://www.scielo.br/pdf/sa/v63n3/29835.pdf>.

      British Nutrition Foundation 2016a, Food Functions-Bulk, viewed 8th November 2016,http://www.foodafactoflife.org.uk/attachments/d12facea-6d5a-4f87b3289646.pdf

      British Nutrition Foundation 2016b, Food Functions-Glaze, viewed 8th November<2016,http://www.foodafactoflife.org.uk/attachments/7d85f595-53bd-450e90df0edc.pdf>.

Canadian Grain Commission  2016 ,Gluten's role in bread baking performance, viewed 8^th November 2016,<https://www.grainscanada.gc.ca/fact-fait/gluten-eng.htm>.

Eufic 2010, The Why, How and Consequences of cooking our food, viewed 7^th November 2016, <http://www.eufic.org/article/en/expid/cooking-review-eufic/>.

Gorton L. 2012, Protein's vital role in baking , viewed 7^th November 2016, <http://www.foodbusinessnews.net/articles/news_home/Supplier-Innovations/2012/12/Proteins_vital_role_in_baking.aspx?ID=%7B779890A3-9041-49F4-946A-7FDBB51FAE0D%7D>

NCPTT 2016, Protein Chemistry of Albumen Photographs , viewed 7^th November 2016, <http://albumen.conservation-us.org/library/c20/messier1991a.html>

Nii T., Ishii F 2005, “Dialkylphosphatidylcholine and egg yolk lecithin for emulsification of various triglycerides” ,viewed 7^th November 2016, <https://www.ncbi.nlm.nih.gov/pubmed/15748826>.
Samaraweera, H, Zhang, W,  Lee, EJ, & Ahn, DU 2011, 'Egg Yolk Phosvitin and Functional Phosphopeptides—Review', Journal of Food Science, vol.76, no.7, viewed 11 November 2016,
<http://www.aeb.org/images/Egg_Yolk_Phosvitin_and_Functional.pdf>
Socratic 2015, Can someone explain to me the chemistry of cooking an egg, and how amino acids, functional groups of proteins, and polymerization are used/completed?, viewed 11 November 2016,
<https://socratic.org/questions/can-someone-explain-to-me-the-chemistry-of-cooking-an-egg-and-how-amino-acids-fu>

Tarleton Academy 2016, FUNCTIONS AND PROPERTIES OF

INGREDIENTS, viewed 7th November 2016, <http://www.tarletonacademy.org/images/FUNCTIONS-AND-PROPERTIES-OF-INGREDIENTS.pdf>