Carbohydrate Analysis Flashcards
Carbohydrates contribute to
bulk, body, viscosity, stability to emulsions and forms, water holding capacity, browning, flavors, aromas, etc
Ingested carbohydrates come from
plant origins with milk lactose being an exception
The only carbohydrate that can be absorbed in the small intestine
Monosaccharides
Humans can only digest
+ Sucrose
+ Lactose
+ Maltooligosaccharides/maltodextrins
+ Starch
Dietary fibers regulate
normal bowel function,
reduce the postprandial hyperglycemic response, and may lower serum cholesterol
Qualitative analysis ensures
that ingredient labels present accurate compositional information
Quantitative analysis ensures
added components are listed in the proper order ingredient labels and that amounts of specific components
For labeling purposes sugars are defined as
the sum of all free monosaccharides and diasaccharides
Examples of sugar alcohols
Sorbitol and xylitol
Sample Preparation
1) Drying
2) Grinding
3) Extraction (lipids)
Extraction is done with
hot 80% ethanol
Reducing sugars are
those mono- and oligosaccharides that contain a free carbonyl
Methods for Total Carbohydrate
Phenol-Sulfuric Acid Method
Phenol-Sulfuric Acid Method reagents are
inexpensive
readily available
stable
Phenol-Sulfuric Acid Method: Absorbance is measure at
490 nm
Method for Total Reducing Sugar
Somogyi-Nelson Method
Oxidation of the aldehyde group produces
carboxylic acid group
The Somogyi-Nelson method is based on the
reduction of Cu (II) to Cu (I) ion by reducing sugars
The Somogyi-Nelson method: Absorbance is measured at
520 nm
Dinitrosalicylic acid method will measure
reducing sugars naturally occurring in foods or released by enzymes
Munson-Walker Method
Oxidation can determined gravimetrically, titration with sodium thiosulfate or potassium permanganate or in the presence of methylene blue
Other methods for total reducing sugars
+ Dinitrosalicylic acid method
+ Munson-Walker
+ Lane-Eynon
+ Electrolytically
Keto groups cannot be _____ thus ketoses are not ________
Oxidized; reducing sugars
Under alkaline conditions ketoses are
isomerized to aldoses
Method for specific analysis of mono and oligosaccharides
High-Performance Liquid Chromatography (HPLC)
HPLC give both
qualitative analysis and quantitative analysis
HPLC analysis is
rapid, can tolerate a wide range of concen. and provides high accuracy and precision
HPLC does not require
prior derivatization of carbohydrates
HPLC does require
micron-filter filtration prior to injection
Important parameters/principles of HPLC
the stationary phase
the mobile phase
the detector
Stationary Phases (HPLC)
1) Anion-exchange chromatography
2) Normal-phase chromatography
3) Cation-exchange chromatography
4) Reversed-phase chromatography
Detectors
1) Refractive index detection
2) Electrochemical detection
3) Postcolumn derivatization
4) Precolumn derivatization
Gas Chromatography (GC) gas-liquid chromatography GLC provides both
qualitative and quantitative analysis of carbohydrates
A flame ionization detector is detector of choice for
peracetylated
carbohydrate derivatives.
Two preparation steps for gas chromatography
1) reduction of aldehyde groups to primary alcohol groups
2) conversion of the reduced sugar into a volatile ester
The basic principles/important parameters (GC)
1) Stationary phase
2) Temperature programming
3) Detection
Method of choice for determination of starch employs a combination of
enzymes in sequential enzyme-catalyzed reactions
Sample preparation for enzyme method
Carrez treatment
1) breaks emulsions
2) precipitates proteins
3) absorbs some color
Resistant Starch
Composed of starch and starch-degradation products that escape digestion in the small intestine
Hydrocolloids/Food Gums
Added polysaccharides along with the protein gelatin
(Nonstarch polysaccharides)
Physical Method
1) Microscopy
2) Mass and NIR Transmittance Spectrometry
3) Specific Gravity
4) Refractive Index
Major components of dietary fiber
1) Cellulose
2) Hemicelluloses
3) Lignin
4) Other nonstarch plant polysaccharides
Dietary Fiber
the sum of the nondigestible components of a foodstuff or food product