McCance and Widdowson shows 100g sugar containing 105g sugar – why?

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).

sugar

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

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