Fibre – NSP or AOAC

ANALYSIS OF DIETARY FIBRE 

A number of methods of analysis for Dietary Fibre has been used in the UK over the years for the purpose of food nutrition labelling and these methods have changed as the definition of DF has evolved.

The Southgate method (1969) was used for many years and the results are included in standard works on nutrition information such as McCance and Widdowson. A method developed by Englyst et al (1992), which determined NSP only, was accepted by MAFF and it remained the recommended UK method for nutrition and labelling purposes until 1999.

Cereals are good sources of fibre

In August 1999, the Joint Food Safety and Standards Group (JFSSG – the precursor of the Food Standards Agency) accepted the role of resistant starch and lignin in DF and recommended the adoption of AOAC method 991.43 as the official UK method for DF. The further method, AOAC 997.08, determines fructans since these are also accepted as DF components (Hignett, 1999). This was confirmed in 2000 by a Food Standards Agency Guidance note.

In November 2005 the Institute of Grocery Distribution published a new Table of Guideline Daily Amounts (GDAs) for nutrients, in which the GDA for dietary fibre was 24g, and this Table carried the endorsement of the FSA.

The UK is now in line with the United States and continental Europe in the methodology for the analysis of DF.

However, the methods previously in use in the UK gave rise to different results and the user of these results must be aware of the differences. For example, Englyst determines NSP and can be split into insoluble and soluble DF. Southgate figures are normally higher than Englyst, particularly in the case of starchy foods. The AOAC method,

Sources of dietary fibre include vegetables, wheat and most other grains.

Foods rich in soluble fibre include fruits, oats, barley and beans.

Source of Dietary Fibre (DF)

The food must contain at least 3g DF per 100g or per 100ml or ‘the reasonably expected daily intake of the food’.

Increased Dietary Fibre

The food must contain at least 25% more than similar food for which no claim is made and must meet the criterion for a source claim

High in Dietary Fibre

The food must contain at least 6g DF per 100g or per 100ml or ‘the reasonably expected daily intake of the food’.

This FSA Guidance Note gives no Dietary Reference Value (DRV) for DF determined by the AOAC method but states that the value of 18g (which is based on analysis by the Englyst method) should not be used. A DRV related to the AOAC method is not proposed but will form part of harmonised EC legislation for nutrient claims

The RDA for Dietary Fibre as determined by the AOAC method should be 24g.

In the case of some processed cereal products, the differences between DF (AOAC) and DF (Englyst) could be greater than those shown above, due to the presence of variable amounts of resistant starch.

This is an interesting report on dietaryfibre comparing NSP and AOAC fibre measurement

LEVEL OF DIETARY FIBRE IN FOODS
A comparison of Dietary Fibre  found in food using the AOAC and the Englyst methods is given in the following table:
Product AOAC (g/100g)* Englyst (g/100g)
Apples (with skin)2.0 1.6
Bananas 1.9 1.1
Carrots (boiled) 3.1 2.5
Baked Beans 4.2 3.7
Cabbage 2.0 1.8
White Bread 2.0 1.5
Brown Bread 4.5 3.5
Wholemeal Bread 7.4 5.8

Dietary fibre consists of one or more of:

• Edible carbohydrate polymers naturally occurring in the food as consumed,
• carbohydrate polymers, which have been obtained from food raw material by physical, enzymatic or chemical means,.
• synthetic carbohydrate polymers.

Properties:

• Dietary fibre generally has properties such as:
• Decrease intestinal transit time and increase stools bulk fermentable by colonic microflora
• Reduce blood total and/or LDL cholesterol levels

Reduce post-prandial blood glucose and /or insulin levels.

 

With the exception of non-digestible edible carbohydrate polymers naturally

occurring in foods as consumed where a declaration or claim is made with respect to

dietary fibre, a physiological effect should be scientifically demonstrated by clinical

studies and other studies as appropriate. The establishment of criteria to quantify

physiological effects is left to national authorities.