Carbohydrate values in McCance and Widdowson (M&W) series of publications are expressed as monosaccharide equivalents.
These values can exceed 100g per 100g of food because on hydrolysis 100g of a disaccharide, such as sucrose, gives 105g monosaccharide (glucose + fructose).
Thus white sugar appears to contain 105g carbohydrate (expressed as monosaccharide) per 100g sugar.
For conversion between carbohydrate weights and monosaccharide equivalents, the values shown in Table 1 below (adapted from M&W introduction) should be used.
In trying to explain this to students (depending on the age) you could explain this using chemistry and molecular weights:
Sucrose + water → glucose + fructose
C12H22O11 + H2O → C6H12O6 + C6H12O6
342g + 18g → 180g +180g
So in this example you can see 342g of the disaccharide sucrose gives 360g monosaccharides.
| Table 1
|
Conversion of carbohydrate weights to monosaccharide equivalents
|
||
| Carbohydrate | Equivalents after
hydrolysis g/100g |
Conversion to
monosaccharide equivalents |
|
|
Monosaccharides e.g. glucose, fructose and galactose |
100 |
no conversion necessary |
|
|
Disaccharides e.g. sucrose, lactose and maltose |
105 |
x 1.05 |
|
|
Oligosaccharides e.g. raffinose (trisaccharide) stachyose (tetrasaccharide) verbascose (pentasaccharide) |
107 108 109 |
x 1.07 x 1.08 x 1.09 |
|
|
Polysaccharides e.g. starch
|
110
|
x 1.10 |
|
