Bio 1510: Carbohydrates Lab (Moti
Nissani)
The Oxidation/Reduction concept: Let’s look, e.g., at the chemical reaction:
This can be thought of as two rxns: OXIDATION (losing electrons):
and REDUCTION (gaining electrons): 
Two reducing parts of sugars:
Aldehyde group: 
and Ketone: 
Mono-1; Di-2; Poly-many. Saccharide=sugar.
Mono-S: glucose (Greek, glykys, sweet; suffix ose, sugar), fructose, galactose (all: C6H12O6 in ring form; C6H10O5 in chain form), reducing
Di-S: Reducing: Maltose, lactose; Non-reducing: Sucrose
Glycogen: Poly-S, non-reducing, energy storage in animal cells; highly branched, some 60,000 glucose residues
Starch (non-reducing): 1. Amylose (coiled) and amylopectin (branched). Found, e.g., potatoes.
Honey: >70% Mono-S
Benedict’s Test: Named after Stanley Benedict. Test for reducing sugars (all Mono-S and some other sugars with free aldehydes or ketones). You first heat the solution, to convert the sugars from a linked to a chained form. If a reducing sugar is available (that is, it has a free aldehyde or a ketone group), the sugar reduces the copper (donates an electron to copper--C++ changes to C+), which gradually colors the solution. Depending on number of reaction sites, the resultant color of the solution will be green (few sites), yellow, orange, or red (many sites).
Barfoed’s Test: Tests for the presence of M-S. It is again based on the reduction (electron gain) of copper to copper oxide, forming a brick-red precipitate within 5 minutes at the bottom (sometimes the precipitate sticks to the sides of the glass tube). Owing to the acidity of the solution, only Mono-S can reduce the blue C++ to red C+.
Iodine test: The iodine solution is amber in
color. In the presence of some poly-S
molecules, color changes are seen.
Water, Mono-S, Di-Sàno color changes; Glycogenàweak brown color; Amylopectin (branched, shorter
helices)àorange/yellow;
Amylose (straight chain, highly coiled, allowing the accumulation of iodine
molecules)à
dark blue/black.