Name: ______

The Chemistry of Cooking

1) Define chemical change/reaction (remember back to chapter 2).

2) Give 4 examples of lab observations that would give evidence that a chemical reaction occurred.

In this lab we will study the science of cooking to “taste” chemical changes. Studying food and cooking on a molecular level will not only give us insight into what we eat but also chemical reactions in general. Food is primarily made up of proteins, fats, and carbohydrates. Protein is the main component of muscle, tendons and organs. Proteins themselves are made up of long chains of amino acids. Fats consist of long chains of hydrocarbons with a carboxyl end. Lard, fish oil, olive oil, butter/ghee and whale blubber are all edible fats. Carbohydrates are often in the form of simple sugars (fructose, lactose “milk sugar”), complex sugars (sucrose “table sugar”) or complex carbohydrates such as starch. Starches and complex sugars are similar to proteins as they are chains of simple sugars that can be broken down by adding heat and water. You will notice the starch in a saltine cracker tastes sweet due to this reaction if you chew it long enough, try it! All three components of food can chemically come together to produce “browning.” Enzymatic browning, the maillard reaction and caramelization are all food reactions called “browning reactions.”

3) List and give examples of the three main molecules that make up the food you eat?

4) List three specific “browning reactions”? Why do you think these reactions are important?

5) Before reading the next section, do your best to scientifically answer the question, “Why do fried foods taste better than boiled food?”

When food is cooked, the heat added causes starches to break down into sugars and proteins to break down into amino acids. These sugars and amino acids then react in a complex process called the Maillard reaction. Products of the Maillard reaction are new flavor molecules and melanoidins (insoluble brown colored molecules). Melanoidins are what we see when a steak is seared or a potato is turned into a french fries at high temperature in oil. In foods with few starches, such as meat, the DNA itself breaks down to yield sugar and the meat protein supplies the amino acids. In food like potatoes, the carbohydrates produce sugars and the amino acids come from the protein present in the plant cells. Correct temperature conditions are also needed for the Maillard reaction to occur at an observable rate. Fats and oils used to sear and deep fry can exceed the temperature of boiling water reaching the necessary >300ºF range. When cooked in this way, water at the surface of foods becomes superheated steam creating a suitable environment for the maillard reaction and browning occurs. Since the superheated steam is only present at the surface that’s where the new flavor and color compounds are made. This creates a textural and taste difference between the inside and outside of foods cooked using this technique. 6-Acetyl-2,3,4,5-tetrahydropyridine and pyrazine are only two of many different compounds that are produced during the maillard reaction.

6-Acetyl-2,3,4,5-tetrahydropyridine is responsible for the biscuit or cracker-like flavor present in baked goods like breads and French fries. And pyrazine gives the rich flavors of roasted nut and chocolate to browned meats.

6) Explain (using 2 sentences) the Maillard reaction process.

7) What temperature is needed for the maillard reaction to occur?

8) Why are oils fats useful when cooking using this technique?

9) Why is there a taste/texture difference between the outside and inside of food cooked using the Maillard reaction?

This part of the lab is to be completed at outer lab benches; DO NOT EAT anything during this part of the lab; Make sure you wash your hands in the clean sink when done!
Step / Procedures / Comments, Observations, Errors and Data
1 / ·  Empty ½ of an l-lysine capsule into two different beakers
·  Add amount of glucose to equal the amount of l-lysine in each beaker / L-lysine:
Glucose:
2 / ·  Add 50mL of water to one beaker and stir to mix
3 / ·  Add 15mL of cooking to the other beaker and stir to mix
4 / ·  While stirring, heat both beakers on a hot plate set to med/high
·  Heat H2O beaker until it boils allow to boil for ~3 minutes
·  Heat the oil beaker till hot and “sizzling”
·  Allow reaction to occur until vigorous, and then take off heat.
(Be ware of hot oil “splatter”.
DO NOT allow mixture to burn.) / H2O beaker:
Water beaker:

10) Which part of this lab example was a chemical reaction? What evidence supports your answer?

ALL FOOD must stay on the center classroom tables at all times
Step / Procedures / Comments, Observations, Errors and Data
1 / ·  Potatoes are cut and boiled in water
·  Taste test
Use specific descriptors other than “like potatoes” to describe color, appearance, taste, mouth feel(or texture) and smell
2 / ·  Potatoes are cut into French fry strips and fried in hot oil
·  Taste test
Use specific descriptors other than “like potatoes” to describe color, appearance, taste, mouth fee (or texture) and smell

11) Which part of this kitchen example was a chemical reaction? What evidence supports your answer?

12) Compare the French fry to the boiled potato, which do you like better? Explain why?

13) Before reading the next section, answer the question, “Why does fruit turn brown?”

When fruits and vegetables are cut or peeled, they release enzymes found in the plant tissue. One of these enzymes is called polyphenoloxidase (PPO). PPO is very reactive when exposed to oxygen and will catalyze the biochemical reaction called enzymatic browning. This reaction occurs readily at warm temperatures when the pH is between

5.0 - 7.0. It converts the phenolic compounds present in foods to brown pigments called melanins. Iron and copper can increase this reaction rate. Which is easily observed when foods are cut with a rusty knife or mixed in a copper bowl. Enzymatic browning is detrimental to quality shortening shelf-life and accounting for up to 50% of all losses during fruit and vegetable production. However, it is essential for the color and taste of raisins, prunes, tea, coffee and chocolate. The food packing industry has developed many methods of controlling enzymatic browning to increase shelf-life of foods that are to be sold as “fresh.”

14) Summarize (using 2 complete sentences) the process that turns fruits and vegetables brown.

15) List two things that are necessary conditions for PPO to catalyze the enzymatic browning reaction?

16) On your own, think of and explain two ways to stop or slow enzymatic browning to increase shelf-life.

17) Why/when would enzymatic browning not be considered bad?

ALL FOOD must stay on the center classroom tables at all times; DO NOT use lab tools; specific food tools will be provided!!!
Step / Procedures / Comments, Observations, Errors and Data
1 / ·  Place slice of apple on a paper towel as a control
·  Observe apple every throughout testing time
(Don’t forget to document times) / Plain “unadulterated” apple:
3 / ·  Soak apple slice in water
·  Place treated apple on a paper towel
·  Observe apple every throughout testing time
(Don’t forget to document times) / Water treated apple:
·  Soak apple slice in vinegar (acetic acid)
·  Place treated apple on a paper towel
·  Observe apple every throughout testing time
(Don’t forget to document times) / Vinegar treated apple:
4 / ·  Soak apple slice in lemon juice (citric acid)
·  Place treated apple on a paper towel
·  Observe apple every throughout testing time
(Don’t forget to document times) / Lemon Juice treated apple:
5 / ·  After testing time has ended, taste the apple slices
Take turns so everyone gets a chance to eat!!! Document partners observations if you didn’t eat that part of the lab. / Plain:
Water treated:
Vinegar treated:
Lemon Juice treated:

18) List which part(s) of this lab showed chemical reaction? What evidence supports your answer?

19) Before reading the next section, do your best to scientifically answer the question, “What is caramel?”

Caramelization is a different chemical reaction than the maillard reaction. Technically it is cooking or browning sugar, a process used extensively to produce nutty flavors and brown color. When foods high in sugar like onions or carrots are cooked, sugars are released and undergo caramelization, thus, creating new flavor and aroma compounds that add complexity to food. Recipes often start by caramelizing vegetables before adding other ingredients of lower sugar content. The caramelization process starts with melting of the sugar at high temperatures and then boiling. Sucrose chemically decomposes into the smaller sugars glucose and fructose. This decomposition occurs at roughly 180oC (356oF). In the next steps of the reaction fructose and glucose decompose into smaller aromatic and flavorful compounds.

Diacetyl is an important flavor compound that’s produced and is responsible for a buttery or butterscotch flavor. In the final stages individual sugars combine to form polymers (large “sticky” chains of connected molecules). Then these polymers lose water to make a complex mixture of various high molecular weight components. These can be classified into three groups: caramelan (C12H12O9); caramelen (C36H18O24) ; caramelin (C24H26O13). Each group accounts for different sized molecules with darker brown colors. These polymers are often used as colors in commercial food products, from colas to soy sauce, confectionary and ice- cream and are labeled as E150.

20) Explain in your own words (using 2 sentences) how you make caramel from sugar.

21) Why would a recipe tell you to cook onions first before other ingredients?

22) What gives food a buttery or butterscotch flavor?

ALL FOOD must stay on the center classroom tables at all times
Step / Procedures / Comments, Observations, Errors and Data
1 / ·  Caramel sauce is made by caramelizing sugar and adding other ingredients

23) Was this example of cooking a physical or chemical change? What evidence supports your answer?

25) How does this homemade caramel compare to other caramel you have eaten?

26) Write a short (5 sentence) paragraph explaining what you learned in this experiment. Make sure you answer the question “Why/How is chemistry important to cooking/your life?”