carbohydrates

Question 1

similiraties between glucose, fructose and galactose

Answer 1

Glucose, fructose and galactose all have the same molecula formula (C6H12O6) but have different molecular structures caused by differences in their physical properties (melting point, solubility in water..)

Question 2

cyclic form vs open-chain

Answer 2

• When dissolved in water, the CYCLIC STRUCTURE is in equilibrium with the OPEN-CHAIN FORM: in this form, one of the hydroxyl groups become a CARBONY (CO) group (either an ALDEHYDE OR KETONE)
  
  • These open-chain forms are highly reactive and readily undergo cyclization
  • The percentage of molecules in the open-chain form at any moment in time is ver small (1%)
  • However, the open-chain form is responsible for many of the IMPORTANT REACTIONS that sugars unedrgo during food processing

Question 3

composition of maltose, sucrose and lactose

Answer 3

Maltose= glucose+glucose
Sucrose= glucose + fructose
Lactose= glucose + galactose

Question 4

oligosaccharides and GI

Answer 4

• Oligo: 3-10 monosaccharide units
  
  • Present in fruits, vegetables and plants
  • They are POORLY DIGESTIBLE or NOT DIGESTED in the human gastrointestinal tract (GI), making them available as food to the intestinal microflora (bacteria residing in the human intestines)
  • Bacterial metabolism of oligosaccharides is a fermentation process: produces ORGANIC ACIDS AND GASES
  • These organic acids are the only source of calories from indigestible oligosaccharides

Question 5

FOS and GOS + probiotic vs prebiotic

Answer 5

• FOS: fructo-oligosaccharides: fructose subunits
  
  • GOS: galacto-oligosaccharides: galactose subunits
  • FOS and GOS are commercially produced as food ingredients, mainly in Japan where they have been widely used as LOW-CALORIE SWEETENING AGENTS and europe
  • Methods of production include extraction from natural sources (ex; FOS from the jerusalem artichoke) or synthesis from more abundantly available carbohydrates such as sucrose
  • FOS and GOS have been found to FAVOR THE GROWTH OF GOOD BACTERIA over the growth of bad ones
  • Substances having this property are termed PREBIOTICS
  • PROBIOTICS: GOOD BACTERIA that are ingested to promote health
  • Both prebiotic yougurts and probiotic yogurts are examples of popular functional foods
  • As is the case with many functional foods, their specfic health benefits remain speculative (as opposed to clinically proven)

Question 6

starch (what is it)

Answer 6

• Starch is found as WATER-INSOLUBLE GRANULES in the ENDOSPERM of wheat, cron, tapioca….The size and shape of the granules are specific to the starch source
  
  • Granule size varies by a factor of 50, ranging from 2um (rice) to 100um (potato)
  • Most common polysaccharide!
  • Granules are made up of polymers of glucose (vary in chain length and degree of branching
  • 2 polymeric forms: amylose and amylopectin
  • The relative proportions of amylose and amylopectin differ in starch granules from DIFFERENT PLANT SOURCES
  • The starch granules are INSOLUBLE IN WATER AND FUNCTIONALLY USELESS as is
  • However, when HEATED IN THE PRESENCE OF WATER, starch undergoes the unique phenomenon termed GELATINIZATION to form a viscous solution or a gel (a 3D network)
  • This phenomenon is the basis for the very important functional roles of starch in food system: THICKENING AND TEXTURE MODIFICATION

Question 7

amylose and amylopectin

Answer 7

AMYLOSE: linear chain of a-D-glucose units (n=250-300 units on average)
AMYLOPECTIN: branched-chain polymer of glucose units; branch points every 15-25 units
Total number of glucose units:commonly on the order of 1,000

Question 8

gelatinization of starch, effect of different temp. on starch

Answer 8

• COLD WATER: starch is insoluble and forms a suspension of starch granules (when stirred)
  
  • Within each granule, the starch has an EXTENSIVELY HYDROGEN-BONDED STRUCTURE
  • When a starch suspension is heated, hydrogen bonding within the granules is disrupted due to the increased thermal energy of the molecules
  • Granules start to absorb water and swell
  • At a certain temperature (gelatinization temp.) there is a marked INCREASE IN VISCOSITY (formation of a paste)
  • As the temp. Is raised beyond the gelatinization temp.: granules swell more and viscosity continues to increase
  • Some starch molecules (particularly amylose) are leached from the granules into the water
  • If heated is continued beyond a certain point, the viscosity begins to decrease owing to exudation of more starch molecules from the granules, which eventually rupture

Question 9

after gelatinization

Answer 9

• The pasting properties of starch are important in the cooking as well as the processing of foods
  
  • In addition, when gelatinized starch is cooled and if the starch concentration is sufficiently high, the starch chains re-associate (hydrogen bonds re-from) in an ordered structure, trapping water molecules: formation of a gel
  • The formation of a gel when wheat starch gelatinize during the BAKING OF BREAD is a key contributor to the texture of freshly baked bread
  • Over time, starch gels may become firmer due to the continued formation of hydrogen bonds between starch chains: RETROGRADATION (ex: staling of bread)
  • In freeze/thaw cycles, water molecules may be forced out of the gel: SYNERESIS (ex: appearance of water droplets on the surface of a thawed pie , the pie filling is a starch-based gel)

Question 10

% amylopectin and tempé f gelatinization in maize, wheat, rice, potato, amylomaize, waxy maize

Answer 10

MAIZE: 75% amylopectin, 70-75 degre
WAXY MAIZE: 100% amylopectin, 65-71degree
AMYLOMAIZE-7: 30% amylopectin, more than 100degrree
WHEAT: 77% amylopectin, 52-54degree
RICE: 81%amylopectin, 68-75degree
POTATO: 78% amylopectin, 56-69degree

Question 11

chemical modifications of starch

Answer 11

1. Pregelatinized starch
   
   2. Hydrolyzed starch
   3. Cross-linked starch
   4. Derivatized starch

** used as a raw material for production of syrup and sugar

Question 12

role of MCC (microcrystalline cellulose)

Answer 12

ITS A FOOD ADDITIVE

1. Anti-caking agent and flavor carrier in grated and shredded cheese
   
   2. Stabilize foams
   3. Stabilize emulsion
   4. Replace fat and oils, is used in low fat hot dogs, reduced fat ice cream
   5. Forms gels, improve adhesion (cling) of sauces, salad dressing
   6. Modify texture-thickens with favorable mouthfeel
   7. Improves quality of low-solids tomato sauces
   8. Freeze thaw stability, retards ice crystal growth
   9. Suspending agent in ice cream
   10. Vegetable fat whipped toppings - impoves body/texture/stability
   11. Other foods uses: barbecues sauces, frozen cheese lasagna, frozen guacamole, marshmallow topping, liquid diet products, sanswich spreads, low calorie mayonnaise
   12. Tabletting agent

Question 13

functions of carboxymethylcellulose (CMC)

Answer 13

** chemically modify cellulose to increase solubility in water

FUNCTIONS:

1. Increases viscosity without adding calories
2. It forms weak gels that trap water
3. It is used in ice cream to improve texture, prevent drip and retard formation of ice crystals during frozen storage

Question 14

other functional polysaccharides

Answer 14

1. VEGETABLES GUM polysaccharide are derived from various shrubs or trees
   
   • Have the ability to hold water and often act as THICKENERS, STABILIZERS, OR GELLING AGENTS in various food products.
   • Ex: guar gum (improves the consistency of gluten free baked goods), gum arabic, gum karaya, gum tragacanth
   2. PECTINS:
      - Found in plant cells and made of sugar acids (a key component in jams and jellies)
      - It substitues gelatine in vegan products

Question 15

nutritional of starch and insoluble fiber

Answer 15

• Starch is a source of glucose
  
  • INDIGESTIBLE FIBER:
    1. Called fiber, bran or bulk on food labels
    2. Gives crispiness and motuhfell to many foods
    3. Aids in digestion and the elimination of waste
    4. Helps maintain a feeling of fulness
    5. Is added to commercial bread products to slow staling and improve loaf volume

Question 16

6 functional roles of sugars

Answer 16

Functional properties of sugar:

1. Have sweetening power
2. Are fermentable
3. Agents for flavor and color production (caramelization/maillard reaction)
4. Contribute mouthfeel (viscosity)
5. Preservatives 
6. tenderizers

Question 17

From the higher relative sweetness to the lower

Answer 17

From the higher relative sweetness to the lower

1. Aspartame (not a carbohydrate)
2. Fructose
3. Sucrose
4. Xylitol (not a carbohydrate)
5. Glucose
6. Lactose

** sucrose = very sensible to heat and acid so used inverted sugar to stabilize its sweetnedd (use enzyme invertase that catalyze the splitting into glucose and fructose)

Question 18

maillard reaction

Answer 18

• Involves the reaction of the OPEN-CHAIN FORM OF SUGARS with PRIMARY AMINE (RNH2) groups, present in AA and proteins
  
  • Color and flavor produced associated with specific due are due to this reaction
    1. Coffee flavor, color and aroma - formed during roasting
    2. Popcorn - aroma/flavor
    3. Roasted peanuts
    4. Baked bread aroma

Question 19

preservatives of sugar 4 functions

Answer 19

VISCOSITY:
- SUGAR ALCOHOLS may be added to diet soft drinks to increase viscosity

PRESERVATIVES

1. Help prevent food spoilage by drawing water away from bacteria
2. The only preservatives needed for candies, jams, jellies and syrup is sugar
3. Sugar maintains moisture in cakes
4. Invert sugar is most effective in maintaining freshness of baked goods