Lecture 11 - Carbohydrates 1 Flashcards
how is CHO measured?
by difference of the measured other ocmponents
%CHO = 100 - (%H2O + Ash + Pro + Fibre + Fat)
why is carbohydrate generally not included in proximate analysis?
because it exists in differentforms
what are the components in a proximate analysis?
moisture ash protein fibre fat
what are 2 major forms of CHO in food?
- digestible CHO
2. non-digestible CHO
what is the function of digestible CHO?
metabolic energy
what is the function of non-digestible CHO?
provides:
- bulkiness, body, viscosity, stability to emulsions and foams
- water holding capacity
- stability to freezing and thawing
- browning (generation of flavors and aromas)
- textures (crispness to smooth, soft gells)
- lower water activity (inhibits microbial growth)
how does WHO/FAO classify carbohydrates?
based on molecular size (Degree of polymerization (DP))
- sugars (DP 1-2)
- oligosaccharides (DP 3-9)
- polysaccharides (DP>9)
what is DP?
degree of polymerization
how are CHO classified in international nomenclature rules?
- oligosaccharide as CHO composed of 2 to 10 (or 2-20) sugar units
- polysaccharides contain 30-60,000 or more monosaccharides
what is generally considered a monosaccharide?
glucose fructose galactose arabinose xylose
what is generally considered a oligosaccharide?
2-10 monomers
eg disaccharides such as sucrose and lactose
trisaccharides such as raffinose
what is generally considered a polysaccharide?
what are the 2 types?
> 10 monomers
2 types:
- homopolysaccharide (starch, cellulose, glycogen)
- heteropolysaccharide (pectin, hemicellulose, gums)
CHO in foods may be present as…
- unbound molecule
- physically associated to other molecules (Starch and ganules)
- chemically bound to other molecules (Glycolipids and glycol-proteins)
what is the relevance of determining food CHO?
- nutritional labelling
- detection of adulteration
- food quality: ie sweetness, appearance, stability and texture depends on CHO present
- food processing: efficiency depends on type and conc of CHO present
how can the method of calculating CHO content (by subtracting % of all other components) in a food be erroneous? how can you measure the CHO content accurately?
subtracting % of all other components can be erroneous due to experimental errors
it is better to measure CHO content directly
in sample preparation, what can drying raw material be separated into?
drying raw material will separate it into: water and dehydrated material
in sample prep, what will grinding and extracting with CHCL3-MeOH result in?
- lipids and lipid soluble components
2. residue
in sample prep, what happens when you extract the residue with 80% ethanol?
- mono and disaccharides
2. residue
what are 5 methods of CHO analysis?
- chemical methods: colorimetric, titration, gravimetric
- physical methods: polarimetry, refractometry and density
- enzymatic methods
- instrumental methods: chromatography, NMR, electrophoresis, IR
- immunoassays
what are chemical methods of analysis?
colorimetric (phenol-sulfuric acid, anthrone, somogyi-nelson)
titration (lane-enon)
gravimetric (munson-walker)
what are physical methods of analysis?
polarimetry
refractometery
density
what are instrumental methods of analysis?
chromatograph
NMR
electrophoresis
IR
what is the procedure for the phenol-sulfuric acid method? what does it measure?
- measures TOTAL carbohydrates
- apply heat and H2SO4 to sample containing CHO (mono, oligo, poly..)
- condense furan components with phenol
- product: yellow-gold coloured compounds
the extent of reaction of the phenol-sulfuric acid method is a function of ____? What kind of curve is used?
the structure of the sugar
a standard curve must be used
in the phenol-sulfuric acid method, what is used to prepare the standard curve if there are different sugars?
glucose
what is the basic principle and procedure behind the anthrone method?
- measures total CHO (including reducing and non-reducing CHO)
1. CHO are dehydrated by strong acids to produce furan
2. furan reacts with anthrone reagent to yield a blue-green color solution
describe the Fehling’s test.
What 2 solutions are needed?
- detects aldehydes by reducing copper II (blue) to insoluble copper oxide (red precipitate)
- commonly used to reduce sugars
solutions:
- Fehlings A: 7g CuSO4.5H2O dissolved in distilled water w/ 2 drops of dilute sulfuric acid
- Fehlings B: 35g potassium tartrate and 12g of NaOH in 100mL distilled water
What are Fehling’s solutions? What is Fehlings A and B?
- bis tartrate complex of Cu2+
1. Fehlings A: 7g CuSO4.5H2O dissolved in distilled water w/ 2 drops of dilute sulfuric acid
2. Fehlings B: 35g potassium tartrate and 12g of NaOH in 100mL distilled water
What is the somogyi-Nelson method?
what is the reagent used?
- method for quantification of reducing sugars (oligo and polysaccharides)
- an improvement on Fehling’s method
- enzymes are used before the addition of reagent
principle:
- aldehydre groups of reducing sugars reduces Cu2+ to Cu+ in basic solution
- Cu+ reduces arsenomolybdate to a stable blue product
reagent: arsenomolybdate complex produced from ammonium molybdate with sodium arsenate
what is the procedure of the somogyi nelson method?
- Cu2SO4 and NaOH are added to the reducing sugar solution
- mixture is heated in a boiling water bath (reducing sugars reduce Cu(II) to Cu(I)
- arsenomolybdate complex reagent is added
- Cu (I) reduces arsenomolybdate complex. Reduction of the arsenomolbydate complex produces a stable blue color solution
are ketoses reducing sugars?
yes b/c ketoses (Eg. fructose) enolizes to aldoses in basic solution
the titration method is a ____ method
chemical
what is the titration method based on?
based on the reducing action of CHO towards certain metallic salts
reducing sugars reduce copper sulfate (CUSO4) from CU (II) to Cu (I) in alkaline tartrate system (potassium sodium tartrate) with NaOH
what is another name for the titration method?
lane and eynon
what is the procedure of the lane and eynon method?
- CHO are titrated against CuSO4 in alkaline condition
- methylene blue is used as the indicator
- once all CuSO4 is used up, reducing sugar will reduce methylene blue to form a colorless solution
what are disadvantages of the lane and eynon (titration) method?
- results depend on precise rxn times, temp and reagent concentrations used(they must be carefully controlled)
- method can’t distinguish between different types of reducing sugars
- method can’t directly determine conc of non-reducing sugars
- it is susceptible to interference from other types of molecules that act as reducing agents
the munson & walker method is a ____ method?
chemical
what kind of method is the munson & walker method?
gravimetric method
what does the munson and walker method determine?
concentration of reducing sugars in a sample
what is the principle of the munson and walker method?
what rxn occurs?
- CHO are oxidized in presence of heat and excess copper sulfate and alkaline tartrate
- formation of copper oxide precipitate
reducing sugar + Cu2+ + base –> oxidized sugar + CuO2 (precipitate)
in the munson and walker method, the amount of precipitate formed is directly related to the _____?
how is the amount of precipitate determined?
conc of reducing sugars in the sample
determined gravimetrically (by filtration, drying and weighing)
what are the disdvantages and advantages of the munson and walker method?
disadvantages:
- same as lane-eyon method
1. results depend on precise rxn times, temp and reagent concentrations used(they must be carefully controlled)
- method can’t distinguish between different types of reducing sugars
- method can’t directly determine conc of non-reducing sugars
- it is susceptible to interference from other types of molecules that act as reducing agents
advantages: more reproducible and accurate than lane-eynon
is the munson and walker method or the lane-eynon method more accurate and reproducible?
munson and walker is
oxidation is ___ of e
reduction is ___ of e
loss
gain
are reducing sugars reducing agents?
yes, reducing sugars can give up electrons to an oxidizing agent
