Sources of resistant starch

RS is a natural part of our diet but the quantity of RS consumed in foods can vary depending on the amount and type of starch present, how the food was processed, how it was stored before consumption and how it was ingested. RS can constitute as much as 18% of the dry mass of a food (Englyst et al., 1992). However although some foods are relatively high in RS, these foods are not typically consumed on a large scale, hence the need for RS-enriched foods. RS levels present in some common foods range from as low as 1% of the dry matter in white bread, to 5% in hot boiled potatoes (Table 8.5).

Intakes of RS are estimates only due to a lack of internationally agreed methodologies and limited RS values for commonly consumed foods. There are no national food composition databases that contain an exhaustive list of the RS content of starchy foods. However, irrespective of these sources of variation the estimated levels of RS intakes in Western countries are consistently lower than for traditional and less-processed diets. For example in Western countries RS intakes could range between 3 and 9 g/day (see

Table 8.5 RS content of common foods (from Englyst et al., 1992)

Food

Dry matter (%)

RS (g/100 g dry matter)

White bread

54.5

1

Wholemeal bread

52.0

1

Cornflakes

95.8

3

Porridge oats

90.7

2

Ryvita crispbread

94.3

3

Boiled potato (hot)

22.8

5

Boiled potato (cold)

23.8

10

Spaghetti (freshly cooked)

28.3

5

Spaghetti (cooled)

34.7

4

Peas (frozen, boiled 5 min)

18.3

5

Lentils (boiled 20 min, cold)

28.3

9

Haricot beans (boiled 40 min)

41.4

18

Table 8.6), with the largest source of RS being from cereals; in contrast, in China estimated RS intakes could reach closer to 20 g/day. Recent research has demonstrated a rationale for increasing RS intakes, particularly for designing foods for weight management. Even though some food processing techniques form RS, e.g. cooking/cooling processes, most RS has been removed from the diet by ingredient and food processing techniques. Commercial RS ingredients are an ideal choice for enriching RS intake in the diet. Currently, RSs from all four classes are commercially available. Each type of RS has different physiological properties, so supporting evidence should be independently evaluated for each individual ingredient. The RS ingredients prepared from high-amylose corn are currently the best characterized, both physiologically and for food functionality, of those commercially available.

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