What is heattreated flour and how can it be used

The modification of wheat to produce heat-treated flour or the direct heat treatment of flour may be used to achieve a number of different changes in the final flour properties. We can broadly classify the type of heat treatment as wet (steam) or dry.

Steam treatment of wheat is commonly used to inactivate the enzymes present so that the subsequent flour may be used as a thickening agent, for example in the production of soups. Without inactivation any cereal a-amylase that is present would act on the damaged starch and the subsequent release of water would cause thinning of the soup.

Steam treatment of both wheat and flour may be used to induce a degree of gelatinisation in wheat flour which helps with its potential function as a thickening agent. Steam treatment may also have a small reducing effect on the numbers of viable microorganisms present in the flour but the treatment is usually insufficient to sterilise the material.

Dry heat treatment of wheat and flour has a long history. In the earlier years of the 20th century it was used to modify the extensibility of gluten from some wheat varieties (Kent-Jones, 1926) but such uses are no longer in common practice. The main application of dry heat treatment to wheat and flour is in the preparation of high ratio cakeflours as an alternative to chlorination (see 2.10). A number of patents were developed that established the necessary heating conditions required to achieve the necessary modification of flour properties (Doe and Russo, 1968; Cauvain et al., 1976). The cakes illustrated in Fig. 5(a) use an untreated flour (left) and a flour from a heat-treated semolina (right), while the graph (Fig. 5(b)) shows the effect of the relationship between oven (heat) temperature and heating time (Cauvain et al., 1976). Treatment temperatures normally exceed 100°C, rising to around 140°C as the treatment temperature increases the residence time required to achieve the modification decreases from several hours to a few minutes.

The mechanism of the improving effect from dry heat treatment is not clear but is likely to be associated with some modification of the surface properties of the starch present in the final flour. At the end of the treatment process the flour

Fig. 5 Effect of flour heat treatment on cake quality.

Heating time (min)

Fig. 5 Continued.

is very dry and it is clear that the loss of moisture is associated with achievement of the necessary changes in the flour (Cauvain et al., 1979), but the low moisture content of the flour is not part of the mechanism of improvement. When the dry flour is rehydrated considerable heat is given off - known as heat of hydration -and unless compensatory steps are taken, this may lead to undesirable increases in cake batter temperatures and premature release of carbon dioxide gas.

Continue reading here: References

Was this article helpful?

0 0