Carbohydrates-Lab 7 - Purdue University College of … 1 Carbohydrates-Lab 7 NUTR 45300 Food...
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6/20/2013 1 Carbohydrates-Lab 7 NUTR 45300 Food Chemistry Exp 1 Fehling’s test Uses a copper salt To be reducing the sugar must be able to open it’s ring and produce an aldehyde group Like this Reducing sugars If the oxygen attached to the anomeric carbon is part of an OH (hydroxyl) group, this is a reducing sugar O OH H H H O H OH H OH H OH alpha-D-glucopyranose
Transcript of Carbohydrates-Lab 7 - Purdue University College of … 1 Carbohydrates-Lab 7 NUTR 45300 Food...
6/20/2013
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Carbohydrates-Lab 7
NUTR 45300
Food Chemistry
Exp 1 Fehling’s test
Uses a copper salt
To be reducing the sugar must be able to open it’s ring and produce an aldehyde group
Like this
Reducing sugars
If the oxygen attached to the anomericcarbon is part of an OH (hydroxyl) group, this is a reducing sugar
O
OHH
HH
OHOH
H OH
H
OH
alpha-D-glucopyranose
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Non-reducing sugars
If that oxygen atom bears any group other than H (such as alkyl, aryl, etc.), then it is a non-reducing sugar
O
OH
HH
OHOH
H OH
H
OH
CH3
methyl alpha-D-glucopyranoside
Image courtesy of Engelsen (newton.foodsci.kvl.dk/engelsen/poster/mgms_poly.html#Disordered)
Ring equilibriums
openchain
Reducing andnon-reducing sugars
Non-reducing Reducing
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Fehling’s test
2Cu(OH)2 + RCHO
RCOOH + Cu2O + H2O
Bluesolution
Redprecipitate
Reducingsugar
Control Glucose
Fehlings vs Benedicts
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The Tollen’s test and other reducing sugar oxidations
Silvermirror
Tollen’s test Fehling’s test
Exp 2 Microscopic appearance of starch
Use of iodine to stain starch
Amylose gives a blue color
Amylopectin gives a more purple color
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Iodine staining (wheat starch)
Positive for amylose, blue
Negative for amylose,positive for amylopectin,more reddish-purple-brown
Other starches
(Magnification =1000x)
Corn Oat
Potato Rice
Tapioca Wheat
Starch gelatinization
+
Heat and waterRaw starch
Swollen starch Amylose
Amylo-pectin
Also see www2.hawaii.edu/lynn/main.html
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Gelatinization micrographs
Unmodified cornstarch
Corn starch, 65 C
Images courtesy of www2.unl.ac.uk/~hx14marshar/cho.htm#Starch gelatinisation
Gelatinization micrographs
Corn starch, 70 C Corn starch, 85 C
Images courtesy of www2.unl.ac.uk/~hx14marshar/cho.htm#Starch gelatinisation
Starch gelation
swollencollapsed amylose
cool
water
water
water
Junction zone
Starch gel
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Exp 3 Starch gels
Wheat and corn– High proportion of low molecular weight
amylose
– Tighter packed granules
– Higher gelatinization temps
– Lower gel clarity
Exp 3 Starch gels
Waxy corn starch– 100% amylopectin
– Highly branched, loosely packed
– Swells easily
– Lower gelatinization temps
Exp 3 Starch gels
Root and tuber starches– Higher proportion of high molecular weight
amylose
– Contains more amylopectin that cereals
– Loosely packed
– Swells easily
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Exp 3 Starch gels
Polar gel– Good freeze-thaw stability
Sucrose– Competes for water
– Inhibits granule swelling
– Increases gelatinization temp
– Decreases viscosity
– Decreases final gel strength
Exp 3 Starch gels
Fat– Decreased hydration of starch– More tender, less sticky gel
Glycerol monosterate– Polar, same effect as sugar but not for the
same reasons
Acid and diastase (amylase)– Hydrolyzes starch– Decreases gel strength
RapidViscoAnalyzer
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Ideal RVA graphs
Viscosity
Time/temperature
Peakviscosity
Breakdown Setback
Cooled pastestability
RVA graphs of different starches (idealized)
Viscosity
Time/temperature
Corn
Waxy corn
Cross-linked
RVA of grain starches-what they actually look like
