Carbohydrates –
food composition tables and labelling
SAFOODS Symposium
9 November 2011
Beulah Pretorius
University of Pretoria
Carbohydrates in food
 Carbohydrates – source of energy
 Carbon, Oxygen, Water: Cn(H2O)n
 Chemical Classification
 Molecular size
 Degree of polymerisation
 Type of linkage (-, β-)
 Character of individual monomers
Chemical Classification
 Monosaccharides
 Single sugars in structure
 3 most important
glucose
 glucose, fructose, galactose
 Disaccharides
 Pairs of two monosaccharides
maltose
 sucrose, maltose, lactose
 Sucrose  glucose + fructose
 Maltose  glucose + glucose
 Lactose  galactose + glucose
 Oligosaccharides
 3-9 monosaccharides
 Cereals (FOS), some vegetables
stacchyose
Chemical Classification
 Polysaccharides
 >9 monosaccharides (complex)
 Subdivided  starches + non-starch
polysaccharides (NSP’s)
Sugar alcohols (polyols)
 Reduced form of mono- or disaccharides
 Ketone or aldehyde group is replaced by an
alcohol group
 This means that polyols are carbohydrates
but not sugars
 Sweeteners
 Advantage: do not cause tooth decay,
contribute less energy
sorbitol
Polysaccharides
1) Starch
Polymer of glucose




Seeds, grains, roots
Amylose & Amylopectin
Some starch (raw potatoes)  crystalline
structure
Resistant starch after food processing
Polysaccharides
2) Non-starch polysaccharides (NSP)
 Polysaccharides other than starch
 Cellulose, hemicellulose, pectin
 Insoluble in 80% ethanol
 Most nutritional NSP in cell walls 
dietary fibre
Cellulose
Summary – chemical classification
Free sugars
Monosaccharides
Disaccharides
Sugar Alcohols
Glucose
Fructose
Galactose
Sucrose
Maltose
Lactose
Xylitol
Sorbitol
Mannitol
3-9 monomers
>9 monomers
Polysaccharides
Oligosaccharides
Stachyose
Maltotriose
FOS
Starch
NSP
Other
Amylase
Amylopectin
Pectin
Cellulose
Hemicellulose
Glycogen
Regulations relating to labelling
(Guideline 1, R.146 of 1 March 2010)
The major carbohydrates
Class (DP*)
Sub-Group
Components
(Examples)
Sugars (1-2)
Oligosaccharides
(3-9)
Polysaccharides
(>9)
Monosaccharides
glucose, galactose, fructose
Disaccharides
sucrose, lactose, trehalose,
maltose
Polyols
sorbitol, mannitol, xylitol,
lactotol
Malto-oligosaccharides
maltodextrins
Other
oligosaccharides
raffinose, stacchyose,
fructo-oligosaccharides
Starch
amylose, amylopectin,
modified starches
Non-starch
Polysaccharides
Cellulose, hemicellulose,
pectins, hydrocolloids
Nutritional Classification
 Available carbohydrates
 Digested in small intestine
 Glycaemic carbohydrates
 Unavailable carbohydrates
 Resist digestion in small intestine
 Non-glycaemic carbohydrates
 Deliver energy via fermentation in the
colon
 Energy calculation??
Summary - available/unavailable
Free sugars
Monosaccharides
Disaccharides
Glucose
Fructose
Galactose
Sucrose
Maltose
Lactose
Maltotriose
Xylitol
Sorbitol
Mannitol
Polysaccharides
Oligosaccharides
Stachyose
FOS
Sugar Alcohols
Starch
NSP
Amylase
Amylopectin
Pectin
Cellulose
Hemicellulose
Other
Glycogen
Stachyose + FOS + NSP + Lignin = Fibre
lignin is not a carbohydrate because it does not consist of sugar units
Food Composition Tables
Country
Term used
Expanded description
Standardised value
for wheat bran
(dry matter basis)
Standardised value
for maize flour
(dry matter basis)
USA (USDA
1975-94)
Carbohydrate
Total
Total carbohydrate by
difference
75 g/100g
85 g/100g
UK (Holland et
al., 1991)
Carbohydrate
Available carbohydrate
(summation) in
monosaccharide
equivalents
42 g/100g
93 g/100g
Eats Asia (US
Dept HEW/FAO,
1972)
Carbohydrate
Total carbohydrate by
difference
75 g/100g
85 g/100g
Australia
(English et al.,
1990)
Carbohydrate
Total
Available carbohydrate
(summation) not in
monosaccharide
equivalents
40 g/100g
85 g/100g
New Zealand
(Burlingame et
al., 1994)
Available
Carbohydrate
Available carbohydrate
(summation) in
monosaccharide
equivalents
42 g/100g
93 g/100g
Malaysia
(ASEAN, 1988)
Carbohydrate
Available carbohydrate
by difference
40 g/100g
85 g/100g
Monro, J and Burlingame, B. J of Food Comp and Analysis 9, 100–118 (1996)
SA Food Comp Tables (2010)
 SA Food Comp Tables (2010)
 Carbohydrate = available carbohydrate
(ie sum of free sugars, dextrins, starch & glygogen)
(incl added sugar)
 Added sugar = mono- or disaccharides added to a
food, also incl honey
 Total carbohydrate = available carbohydrate plus
dietary fibre
Breakfast Cereal WeetBix
Fruit roll dried,
mixed
Macaroni cheese,
white sauce
Carbohydrates by diff
75.3
85.7
18.5
Carbohydrates
(available)
63.2
74.5
17.5
6.2
15.4
0.0
Total Fibre
12.1
11.8
0.9
Total carbohydrates
75.3
86.3
18.4
Added sugar
Regulations relating to labelling
(Guideline 1, R.146 of 1 March 2010)
 Glycaemic carbohydrates
 Summation of individual carbohydrates
glucose, fructose, galactose, sucrose, lactose, maltose, trehalose,
maltodexrins and starch
Codex
(Guidelines on nutrition labelling CAC/GL 2-1985
The presence of available carbohydrates should be declared on the label as
“carbohydrates”. Where the type of carbohydrate is declared, this declaration
should follow immediately the declaration of the total carbohydrate content in the
following format:
“Carbohydrate ... g, of which sugars ... g”.
This may be followed by the following: “x” ...g
where “x” represents the specific name of any other carbohydrate constituent.
How to determine carbohydrates:
 Carbohydrate by difference:
 Total carbohydrates
 100 - (%moisture +%fat + %prot + %ash)
 %DM – (%fat + %prot + %ash)
 Incl  fibre, lignin, organic acids, polyols
 Refer to both available and unavailable carbohydrates
 Available carbohydrates
 100 - (%moisture +%fat + %prot + %ash + TDF)
•Single value does not reflect diverse nutritional properties
•Carb’s by diff combines uncertainties of macronutrient analysis
 Carbohydrate by direct analysis:
general approach
Hot aqueous
alcoholic solvent
(70-80%)
Enzymatic
Reductiometric
HPLC/GLC
Density
Refractive Index
Optical rotation
•Available carbohydrates
•Extraction and hydrolyses mimics intestinal digestion
•Cellulose and pectin not hydrolysed
Methods of analysis
 Enzymatic
 Specific enzymes react with specific sugars
 Method highly specific
 Kits
 Reductiometric
 Free monosaccharides can reduce alkaline
solutions of metal oxides
 Fehlings reagent + monosacch = copper oxide
 Calibration tables
 Replaced by enzymatic or HPLC
Methods of analysis
 High Performance Liquid
Chromatography (HPLC)
 Separate sugars
 Stationary phase (column – 25cm)
 Mobile phase (organic solvents, buffers)
 Detector (Refractive Index, UV, Fluorescence)
 Gas Chromatography (GC)
 Stationary phase (column – 100m)
 Mobile phase (carrier gas – helium, nitrogen)
 Detector (FID)
Methods of analysis
 Density or specific gravity
 High concentration of a single sugar
 Sucrose syrup
 Hydrometer – bulb and graded cylindrical
stem
 Floats in liquid – note the level – calibration table
 Brix – fruit juices
 Plato scale – beer-making
 Refractive index
 How much the speed of light is reduced inside
the medium
 Standard Curve
 Coupled with HPLC
Methods of analysis
 Optical Rotation
 Optical rotation is the rotation of linearly
polarised light as it moves through certain
materials
 Polarimeter
 Simple solutions of a few sugars
Glycaemic Index
 Glycaemic Index (GI) = measurement used to
classify foods according to their potential to
raise blood glucose levels
The GI of a foodstuff is generally
measured by determining the
increment in blood glucose
concentration after the consumption
of a test meal over a set period of
time and comparing it with a control
meal (normally white bread or
glucose) and expressed as a
percentage within a group of
individuals (in vitro)
Source: GI Foundation of SA
Glycaemic Load (GL)
 Expression of how much impact the food will have in
affecting blood glucose levels
CHO content per portion x GI
100
 Incorporates both the quantity and quality of the dietary
carbohydrates consumed
GL =
 Some fruits and vegetables have high GI values, but the
low GL -- effect on blood glucose levels is minimal
Watermelon (5 mm thick slice)
GI = 72 (high)
%CHO per 150g = 8.9
GL = 6.4
Source: GI Foundation of SA
Apples (one apple)
GI = 38 (low)
%CHO per 104g = 13.52
GL = 5.1
Discussion
Trehalose
 ,-1,1-glucoside bond between two -glucose units
 Trehalase
 FSANZ Final assessment report application A453 trehalose
as a novel food
 Similar to maltose
http://www.foodstandards.gov.au/_srcfiles/A453%20Trehalose%20FAR.pdf
 British Sugar
 Similar to isomaltulose, GI = 40-45
 Purdue University, America
 GI = 100 (http://www.accessmedicine.com/content.aspx?aID=5229721)
 Lower glycaemic response (British Journal of Nutrition (2009), 102, 1395–1399)
Discussion
 Energy calculation
 Variations:
 Uncertainties of prox methods in calculating carb’s by difference
 Proportions of mono-, di- & polysaccharides
 Unavailable carbohydrates & dietary fibre
 Energy conversion factors:
General factor – 17 kJ/g
Organic acids – 13 kJ/g
Alcohol – 29 kJ/g
Fructo-oligosaccharides – 11 kJ/g
Polyols – 10 kJ/g
Maize bran fibre – 1.3 kJ/g
Dietary fibre – 8kJ/g (recommended)
 Where a compound represents a substantial source of energy in a
product, use of a more specific factor for that compound may be
desirable
Food energy – methods of analysis and conversion factors, FAO, 2003
Livesey, et al.; 2009, Food Control, 11: 249-289
Thank you
Beulah Pretorius
University of Pretoria