Carbs Lecture Flashcards
What are carbohydrates?
- Compounds of Carbon, Hydrogen, and Oxygen
- Hydrogen & Oxygen are usually in ratio 2:1
- Synthesized in plants during photosynthesis
- metabolized by animals to produce energy
Functional Roles
- Bulk
- Viscosity
- Water holding capacity, etc.
Classification of CHO’s
1) Monosaccharides: Simple sugar (glucose, fructose, galactose)
2) Disaccharides
3) Oligosaccharides: 3 - 10 sugar units (ex. raffinose)
4) Polysaccharides
Oligo- and polysaccharides
Must be digested first before absorption
Only polysaccharide to be digested by humans?
Starch
Note: Non-digestible polysaccharides & lignin make up dietary fiber
: Non-digestible oligosacchs are important “prebiotics”
Total carbohydrate =
100% - (%Moisture + %Ash * %Lipid + %Protein)
Note: Always calculated, not actually measured
Total sugars =
Sum of all free monosaccharides and disaccharides
Added sugars =
Sugar added to foods
Other carbohydrate =
Total carbohydrate - (Dietary fiber + Sugars)
Which color test?
Hexose or Pentose
Bial Test
Which color test?
Aldose or Ketose
Seliwanoff
Which color test?
Reducing sugars
1) Benedict’s test
2) Barfoed’s test
Which color test?
Starch or Glycogen
Iodine test
Quantitative methods?
- Chemical methods
- Chromatography
- Enzymatic methods
How do you prepare your samples for CHO analysis?
- Dry the sample (except beverages)
- Mill sample to fine powder (increase surface area)
- Extract lipids (makes carb extraction easier and more complete)
Extraction of mono- & oligosaccharides
- Extract dry, lipid-free sample with hot 80% ethanol
- Repeat extraction to ensure completion
- 80% ethanol extract obtained
Why use 80% ethanol for mono and oligosacc extraction?
Mono, di and oligosacchs are shorter chain which leads to a lower molecular weight making them soluble in 80% ethanol
Principle of rotary evaporator
Evaporate the ethanol (solvent) from the extract
How is starch extracted as glucose?
- After extraction of sugars (with 80% ethanol)
- Residue is hydrolysis with acid - perchloric acid
- Extraction is done greater than or equal to 2x and pooled together
- Extracts are stored for starch analysis
Bial’s test for pentose:
- Pentose dehydrates to form furfural which reacts with bials reagent to give a blue colored product - positive for Pentose
- Furfural is a natural dehydration product of Pentose sugar
Principle of Seliwanoff’s test
Distinguishes between aldose and ketose sugars
Benedict’s Test
Tests for reducing sugars
Barfoed’s Test
Used for detecting the presence of reducing monosaccharides
Principle of Total sugars by Phenol-Sulfuric acid Method
Principle: carbohydrates when treated with strong acid/heat form furan derivatives
- The furans condense with phenolic compounds to form a colored product
- Absorbance measured at 490nm
- Glucose used as reference
