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NutrInsight • Slow-release carbohydrates: Growing evidence on metabolic responses and public health interest

Limiting starch gelatinization can preserve SDS content in foods

During food processing, starch granules can undergo dramatic structural changes. For example, when heated in
the presence of water, the semi-crystalline granular structure is disrupted, causing starch molecules to disperse
outside the granule. This phenomenon, which is called starch gelatinization, increases the accessibility of the
starch substrate to digestive enzymes [Bornet, 1993].

The results shown in Figure 2 suggest that starch gelatinization is responsible for the loss of SDS that occurs
during food processing. Indeed, the combination of high moisture levels and the presence of yeast in white
bread production or the application of high pressure levels during extruded cereal production promote starch
gelatinization. In contrast, rotary-molded biscuits are baked under low-moisture conditions, which limits the
extent to which starch granules are gelatinized.

This relationship between SDS and starch gelatinization has been confirmed by Englyst et al., who measured
the SDS content of different cereal products (breakfast cereals, bakery products and crackers, and biscuits),
and used differential scanning calorimetry (DSC) to determine the starch gelatinization index of the same
products (see Figures 3a and 3b). This study showed that cereal products with the highest SDS levels had the
lowest degree of starch gelatinization [Englyst et al., 2003].

This means that the control of processing conditions to limit the extent of starch gelatinization can preserve
SDS content during food processing.

(a) * (b) (c)
BP&C
100 * 14 100
90
SGI80 12 90 *
SDS (g ingested)70 *
60 10
GI5080
40 8
BC 70
6
† 60
4† BP&C
2 50

0 40 Bi
Bi BC Bi BC BP&C

Figure 3: Starch gelatinization index (SGI) (a), Slowly Digestible Starch (SDS) content (b), and glycemic index (GI) (c) of
three products from each of three cereal groups (BC, breakfast cereals group; BP&C, bakery products and crackers group;
Bi, biscuits group). Values indicate means; standard deviations are shown with vertical bars. Mean values that differed
significantly from the Bi group are indicated as follows: * P<0.05, † P=0.08. In the original publication, SDS is referred to as
Slowly Available Glucose (SAG).
Source: Adapted from Englyst et al., 2003

SDS content varies greatly within a food category

The cereal products described in the literature exhibit a wide range of SDS contents, from 0 g/100 g for puffed
wheat to 23 g/100 g for plain biscuits [Englyst et al., 1996; Englyst et al., 1999; Englyst et al., 2003; Garsetti
et al., 2005; Lintas et al., 1995]. The SDS content varies between cereal food categories, and even within a
same category, ranging for instance from 0 g/100 g to 14 g/100 g in breakfast cereals and from 4 g/100 g to
23 g/100 g in biscuits. This large variability that is observed even between products belonging to the same
cereal food category shows that the SDS content is more related to the ingredients used and the food processing
conditions applied than to the food category itself.

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