Food Chemistry

MSPSummer 2009

What does Food Provide us With?

• Water (solvent, reactant)• Carbohydrates (starch, fructose, sucrose)

– monosaccharides, disaccharides, polysaccharides

• Proteins– amino acids

• Fats– fatty acids

}macronutrients

Micronutrients• Vitamins and Minerals – needed as

coenzymes for reactions in the body and antioxidants

“Catabolic” Processes

• “Catabolism” – breaking down large biomolecules into smaller biomolecules

• Carbohydrates, fats, and proteins can all be broken down to release energy

• Carbohydrates are the most common fuel• Simple sugars like glucose are broken

down to create ATP– or ATP equivalents

Stage I: Hydrolysis

The purpose of Stage I in catabolism is to degrade food molecules into component subunits:

Stage 1: Hydrolysis

• Polysaccharides degraded to monosaccharides– Begins in the mouth with amylase action on starch

• Proteins degraded to amino acids– Begins in the stomach with acid hydrolysis (pepsin)

• Fats broken into fatty acids and glycerol– Begins in small intestine with fat globules– Disperse with bile salts– Degrade with pancreatic lipase

Carbohydrates Overview

• Carbohydrates– larger sugars converted to glucose (6 carbon)– glucose converted to two pyruvate (3 carbon)– each pyruvate converted to two acetyl-

coenzyme A (2 carbons) + 2 CO2

– Each coenzyme A is eventually converted into 2 CO2 and ATP in the citric acid cycle

– Along the way other reduced coenzymes are made and converted into ATP during oxidative phosphorylation

21.7 Glycogen – Storage in Muscles

Glycogenesis

Glycogenolysis

• Glycogen degradation is controlled by: – Glucagon

• Pancreas responds to low blood sugar – Epinephrine

• Adrenal gland to stress/threat

Glycogenolysis

Insulin vs. Glucagon

Sources of Carbs?

• What are some common sources of carbohydrates?

Proteins Overview

• Proteins are broken down into amino acids• Amino acids can be metabolized and used

for fuel or• Used to build other amino acids

Amino Acids in the Diet• Essential amino acids – cannot be made in the

body and are required in the diet

• Nonessential amino acids – can be synthesized from other molecules in the body

• Complete dietary protein (usually from animals) contains all of the essential amino acids.

• Incomplete dietary protein (from plant sources like soy) do not contain all of the essential amino acids.

Fats Overview

• Provide energy• Animals store energy

as fat• Insulation, protection• Fats belong to the class

of biomolecules called lipids

Functions of Fats/Lipids

1. Energy source. 1 g of fat = 9 kcal (twice that of a carbohydrate)

2. Energy storage (fat cells or adipocytes)3. Free flowing structure in the cell membrane

(phospholipids)4. Hormones – regulatory molecules in the body5. Vitamins – Vitamins A, D, E, and K are lipids

Fat Soluble Vitamins

koagulations-vitamin

antioxidant

Functions of Lipids1. Energy source. 1 g of fat = 9 kcal (twice that of a

carbohydrate)2. Energy storage (fat cells or adipocytes)3. Free flowing structure in the cell membrane

(phospholipids)4. Hormones – regulatory molecules in the body5. Vitamins – Vitamins A, D, E, and K are lipids6. Vitamin absorption – dietary fat carries vitamins A,D, E,

and K into the body7. Protection – fat in the body is a shock absorber for vital

organs8. Insulation – fat in mammals keeps organs insulated from

the cold

Fatty Acids• Not “fats”• Saturated: Have the general formula

CH3(CH2)nCO2H. – Are solids at room temperature– think “Crisco”

myristic (C14) and palmitic acid (C16) correlated to heart disease

high melting point

Fatty Acids

• Unsaturated: Have one or more double bonds. Are often liquids at room temperature. (found in vegetable oil)– synthesized by plants, think “Wesson oil”

more trouble packing in solid state = lower melting points

Double Bonds

- double bonds can be cis or trans and are labeled based on the number of the carbon atom where the double bond occurs

- Chains can be named systematically or with common names cis-9-hexadecenoic acid

Melting Points

Lipid Metabolism

• Triglycerides are emulsified (dissolved) into fat droplets by bile salts from liver

– Bile: micelles of lecithin, cholesterol, protein, bile salts, inorganic ions, and bile pigments

lecithin

Hydrolysis of Fats

• Hydrolysis of triglyceride ester bonds is catalysed by pancreatic lipase

• Makes monoglycerides and fatty acids

Micelles

• Transport lipids

Bile SaltsHave steroid structure

From what common steroid lipid are bile salts sythesized in the body?

a. testosteroneb. lecithinc. cholesterold. estradiol

Fatty Acid DegradationOverview• Fatty acids are degraded into 2-carbon

fragments in a process called -oxidation• Step 1 of -oxidation : Activation• Steps 2 – 5 are a set of four reactions with a

basic outline similar to the last four reactions of the citric acid cycle– Each pass through the cycle releases acetyl CoA and

returns a fatty acyl CoA with 2 fewer carbons – One molecule of FADH2 and one molecule of NADH

are produced for each cycle of -oxidation

8 ATP per carbon!

16 carbon fatty acid

2 phosphate bonds!

Sources of Fats?

• What are some common sources of fats?

The Four Food Groups?

The Food Pyramid

Lesson 1: Venn Diagram

• What we eat for breakfast, lunch, and dinner. (on board)

Lesson 2: Identifying Healthy Foods

• Gather each of these in a cup and label:1. rice2. flour3. dried apple4. egg white5. peanuts6. granola bar7. freeze dried onion8. coconut flakes

Equipment

• Each Group:– 2 medium resealable plastic food bag– 2 ten section test trays (label sections 1-10)– 4 forceps– 2 hand lenses– 8 small spoons– 1 large resealable storage bag

Venn diagram

• Which of these foods are on our orginal Venn diagram?

• Write down some observations about each food (feel, smell, look, but NOT taste)

• Which foods have you eaten before?

• Store all of the foods for later.

Lesson 3, Testing Liquids for Starch (Carbohydrate)

Iodine by itself = brownIodine + starch = dark blue/black

Prep: brown bottle 10 mL I2, rest H2Ocornstarch, 5 mL cornstarch, 100 ml watercorn syrup, 5 mL syrup, 100 mL waterpour each liquid in a bottle to make set of 5 liquids per

groupwater, corn starch, corn syrup, corn oil, milk

Procedure: Add a few drops of I2 solution to a few mL of liquid

Class Test Table (on board)

liquid starch test

watercorn starchcorn syrupcorn oilmilk

Lesson 4 – Testing Foods for Starch

• Preparation: peel and crumble peanut, tear the apple, crumble granola bar

• Prodedure: Add two drops water to each food to help with test?? Add 2 drops I2 solution

• make observations

Class Data (on board)

Test Food I2 + foodriceflourappleegg whitepeanutgranolaonioncoconut

Lesson 5 – More about Starch

• Work out any differences in class data on liquids and solids.– are students using correct # of drops– are students measuring materials with greater

accuracy?– are students avoiding contamination (using

toothpicks, forceps)– Are students re-testing foods and re-

evaluating?

Lunch

• What types of food (liquid and solid) might be good to suggest students bring from home for testing?

Lesson 6 – Testing for Glucose

Preparation: prepare corn starch and corn syrup same way as with starch test

Procedure: Use glucose test paper to test the same liquids tested for starch.

Record results on board.

Lesson 7 – Testing for Glucose

Preparation: prepare peanuts, apple, and granola. Add 2 drops of water to each food. Stir well.

Procedure: Use glucose test paper to test the same foods tested for starch.

Record results on board.

Lesson 8 – More about Glucose

Make a Venn diagram for foods containing starch and foods containing glucose.

Work out any differences in positive and negative tests for glucose.

Lesson 9: Testing for Fats

Grease Spot Test! Paper bags.

Preparation: Prepare corn starch and corn syrup the same way. Cut a bag into rectangles (about 16). Keep 10 of them for lesson 10.

Procedure: Put two drops of liquid on. Blot extra liquid. Wait 10 minutes for appearance (or not) of a grease spot. [Check 2% milk also]

Record Class Data on board

Lesson 10: Testing Foods for Fats

• Preparation: shell and crush peanut• Put one small spoon of each food on the

test paper. (BE SURE TO WIPE FINGERS)

• Rub the food on the paper. Check after 10 min.

Lesson 11: More about fats

• More or less a useless lesson• Check any discrepancies?

Lesson 12: Testing for ProteinsTest papers (hold with forceps)blue color remains: contains proteinblue color fades: small amt. of proteinblue color disappears: no proteinPreparation: make corn starch and corn syrup

solutions. Make developing solution ( ½ liter of white vinegar and ½ liter of isopropanol)

Procedure: label test strip, test each liquid by dipping, develop in petri dish for 5 min.

(test the 2% milk too)

Lesson 13: Testing Foods for Protein

• Let’s split the labor:– Group 1: peanut and coconut– Group 2: egg white and onion– Group 3: rice and apple– Group 4: Flour and granola– Group 5: onion

• Preparation: use forceps to touch the foods. Shell the peanut. Tear apple, crumble granola.

• Two or three drops of water. Stir for 1 min. Mash damp food onto test strip (blue end).

[record class data (on board)]

Lesson 14: More about protein

• Venn diagram: carbs, fats, proteins

Lesson 15: Examine Labels

• Just practice checking labels for food contents. No real experiments.

Lesson 16: Marshmallow

• Test to see what is in a marshmallow (starch, glucose, fat, protein)

• record class data on board

• check marshmallow label!