Carbohydrates

Biopolymers

Large biological molecules: carbohydrates, nucleic acids, proteins

Monomer of carbohydrates

Monosaccharides (ex. glucose, fructose, galactose)

Condensation reaction

Connection of two monomers together, resulting in water leaving

Carbohydrate Condensation

2 monosaccharides → Disaccharide + H2O

Hydrolysis Reaction

Water is added to polymer, breaking it apart (consumes water instead of releasing)

Composition of Carbohydrates

C,H, and O; hydroxyl group and carbonyl group (ketone or aldehyde)

Formula for monosaccharides

C_x(H₂O)_x

Primary function of carbohydrates

Provide energy to organisms

2 types of carbs (sugars):

1. Simple - mono and disaccharides

2. Complex - polysaccharides

What is a carbohydrate with a ketone called?

Ketose (-ROR)

What is a carbohydrate with an aldehyde called?

Aldose (-ROH); glucose is an aldose

Ways of drawing carbohydrates:

1. Fischer projection (straight-chain)

2. Cyclic (how they are found in nature)

Stereoisomers of carbohydrates

1. Alpha - hydroxyl next to oxygen faces DOWN

2. Beta - hydroxyl next to oxygen faces UP

Common name for glucose

Hexose/dextrose

Photosynthesis

• Sunlight is used by plants to produce glucose

  • 6CO₂ + 6H₂O + Sunlight → Glucose + 6O₂

ATP Synthesis (Cellular Respiration)

• Used by animals to convert glucose into ATP (energy)

  • Glucose + 6O₂ → 6CO₂ + 6H₂O + ATP

Glucose

6-carbon sugar with alpha hydroxyl

Fructose

Isomer of glucose stored and metabolized into glucose in liver (STORED)

Stored form of glucose

Fructose; converted by liver into glucose

What foods contain fructose?

Fruit, honey, and syrup

Galactose

Isomer of glucose that ISN’T common in nature

Which monosaccharide can pass through the bloodstream?

ONLY glucose, all carbohydrates MUST be converted to glucose

Which organ converts fructose and galactose into glucose?

The liver

All monosaccharides:

1. Glucose

2. Fructose

3. Galactose

4. Ribose

5. Deoxyribose

Ribose

5-carbon sugar that forms RNA (rRNA); gain little in diet

Deoxyribose

5-carbon structure used for DNA formation; we CAN make this

All disaccharides:

1. Maltose

2. Sucrose

3. Lactose

Maltose

2 glucose molecules to form alpha bond; fermentation reaction

Sucrose

1 glucose and 1 fructose form alpha bond

Lactose

1 glucose and 1 galactose form beta bond

Why do people have a lactose intolerance?

Lactose has a beta bond needing to be broken by enzyme lactase, which some people don’t produce

Methods to start hydrolysis:

• Heat - would kill humans

• Acid - take too long

• Enzymes (-ase)

  • Ex. Lactase, maltase, sucrase (AKA invertase)

What is the other name for sucrase?

Invertase

Primary lactose maldigestion

• Inherited inability to produce lactase

  • Production stops after 3-5 years old

• The majority of people have this

• Mutation allows for production after loss

Secondary lactose maldigestion

Temporary decrease in lactose production that increases with age

Can lactose intolerant eat yogurt?

Yes, low amount of lactose because bacteria converts lactose into lactic acid

Cheese and lactose intolerance

• Lactose is in whey (water + lactose + protein) due to bacteria

• Hard cheese - less lactose

• Soft cheese - more lactose

Sugar beet/cane Preparation

1. Wash and cut

2. Extract juice

3. Evaporate and concentrate its syrup

4. Crystals fall from syrup, leaving molasses

Brown sugar composition

Sucrose + maltose

Honey

Contains mostly sugar (fructose and glucose) and phytochemicals

Functions of sugars in food preparation:

1. Sweeten foods

2. Preserve foods

3. Crystallization Agents (candies)

4. Caramelizing Agents

5. Fermentation (bread-making)

Which sugar is the most sweet?

Fructose

Which sugar is the least sweet?

Lactose

How do sugars preserve foods?

60% of sugar kills bacteria by osmosis (loss of water from cell)

How can you make milk sweeter?

Add lactase enzyme to break lactose into glucose and galactose

Sugar alcohols

• Instead of carbonyl, a sugar has an extra hydroxyl group (making it an alcohol)

• -ol ending

  • Ex. Sorbitol

Benefits of sugar alcohols

• Not metabolized by bacteria, preventing tooth decay

• Cooling sensation due to endothermic reaction (heat-absorbing)

  • Xylitol

• Less calories

Side effects of sugar alcohols

• Bloating, diarrhea, flatulence (laxative effect)

• Not absorbed by small intestine

Oligosaccharides

3-10 monosaccharides (raffinose and stachyose)

What foods contain oligosaccharides?

Beans and legumes (high in fiber foods)

Digestion of oligosaccharides

• CAN’T be digested, no enzyme

  • Fibers

• Metabolized by bacteria, resulting in gas in large intestine

Polysaccharides

10+ monosaccharides that can be digestible or non-digestible

Digestible polysaccharides

• Starch from plants

• Glycogen from animals

Non-digestible polysaccharides

Fibers (soluble and insoluble) - definition is non-digestible polysaccharides

Starch

(Glucose)_x, many glucose molecules connected by alpha bonds

2 types of starch:

1. Amylose (straight chain)

2. Amylopectin (branched)

Glycogen

Highly branched stored form of glucose in liver and muscles; holds more water

Why don’t we want to store so much glycogen?

It has more water, which would make us fat and give us less energy

Cellulose

Polysaccharide found only in plant cell wall, not digestible by humans (fiber)

Pectins

Polysaccharide in cell walls of fruits called “sugar acids”; fibers to humans

Use of pectins in food:

Used to make jams because they form strong gels in sugar due to dehydration

What makes fibers indigestible?

They all contain beta bonds which we don’t have enzymes for

Insoluble Fibers

Not fermented (Cellulose, hemicellulose, lignin)

Soluble Fibers

Can be fermented, giving calories (Gums and pectins)

Carbohydrate gums

• Soluble polysaccharides from plants that thicken and stabilize food

  • Traps color and flavor

• Used as additives

  • Salad dressing, candies, agar

Uses of complex polysaccharides in food:

• Structure

• Binding (bringing 2 things together that usually wouldn’t)

• Thickening (gelatinization)

Carageenan

Carbohydrate for binding casein to cocoa powder

Gelatinization

• Thickening a liquid with starch (amylose)

  • The more amylose, the thicker

• Increasing temperature swells the granules

Gelatinization Point

Temperature when maximum granule swelling occurs (most water is held)

Jam-making

Use pectins (at least 60% to preserve), fresh fruit or juice, and lower pH with lemon juice’s citric acid

Which carbohydrates have to be digested?

Disaccharides and starches (polysaccharides)

What carbohydrates can be absorbed without being digested?

Monosaccharides, they can be converted to glucose in liver

Path of Carbohydrate Digestion

1. Amylase in saliva converts starches into smaller sugars via hydrolysis

2. Stomach acid inhibits amylase, no digestion

3. Pancreatic juice breaks down oligosaccharides

4. Intestinal cells release maltase, lactase, sucrase

Carbohydrate Absorption

Monosaccharides go to liver through the portal vein, where they are converted to glucose or store as glycogen

How much energy do carbohydrates give?

4 kcal/g

Protein Sparing

Consuming carbs saves proteins for other functions instead of making glucose with protein

Normal Blood Glucose

70-100 mg/dL

Pancreatic Enzymes for Glucose Regulation

Insulin and glucagon

Insulin

Secreted by beta cells during high blood sugar to begin uptake of glucose into cells from blood

Glucagon

Released by alpha cells during low blood sugar to start glycogenolysis

Glycogenolysis

Breaking down glycogen in the liver into glucose

Fight or Flight Response

• Sympathetic response = cortisol and adrenaline released

  • Liver release glucose for muscles

  • More energy (glucose) needed

  • Increased blood sugar

Dietary Fiber Functions

• Regular stools, no constipation

• Reduce hemorrhoids, diverticulitis, colon cancer

  • Less pressure on inflammation

• Weight control, feeling of fullness

• Reduce cholesterol

• Slow glucose absorption (good for T2 Diabetes)

Recommended Intake of Carbohydrates

Majority of kcal (45-65%); fiber requirement is lower for women than men

Where do most carbs come from in the US?

Bread, soda, baked goods; too much lipid intake

When is insulin mostly secreted?

Between meals

Type 1 Diabetes

• Sudden onset usually when younger

• Not as prevalent as Type 2

• Result of autoimmunity to beta cells, no insulin production

• Ketoacidosis is common

Type 2 Diabetes

• Gradual onset from lifestyle choices, often in the obese

• Insulin resistance, can produce but need more than normal

• More prevalent than Type 1

Side Effects of High Sugar Intake

1. Empty calories

2. Dental caries from bacteria on enamel decaying tooth

Glycemic Index

• Blood glucose response to certain foods

  • Lower index is healthier (less increase in blood sugar)

• Uses glucose as standard

Glycemic Load

• Amount of carbohydrate in food times index divided by 100

  • Better because it compensates for serving size

• GI x grams of carb/100

High Glycemic Load Foods

• Stimulates insulin, resulting in resistance and feeling hungry quicker

  • High LDL, more fat/triglycerides

  • Diabetes, and risk of cardiovascular disease

Why should diabetics have many small meals?

Small meals cause less insulin secretion, preventing resistance

Symptoms of diabetes

• Fatigue, hunger, impotence, infection, frequent urination, poor wound healing, poor vision

• Peripheral nerve dysfunction (amputation is common)

• Cardiac arrest and death if uncontrolled

Managing Diabetes

• Diet to decrease calories, fats, salt intake, and weight loss

• Exercise to increase energy consumption

• Stop smoking

Sugar and Cancer

• Sugar (not fibers) linked to breast cancer

• Polyphenols in coffee/tea can fight cancer

  • Antioxidants and without creamer/sugar

Issue with high fiber intake

• Need more fluid intake

• Fibers bind vitamins and minerals (can’t be used)

• Lack of nutrients for young children (makes them feel full)

Nutritive Sweeteners

Give calories; sugars and sugar alcohols

Alternative Sweeteners

• Saccharin

• Aspartame

• Neotame

• Sucralose

• Acesulfame-K

• Stevia

• Polydextrose

Saccharin

Sweeter but with an aftertaste; cancer in rats, but safe