There are many factors that influence flour whiteness, such as wheat variety, technical process, additives, temperature, storage time, etc; but the following factors mainly accounts for flour whiteness:
a. Flour storage temperature
For the same wheat and additive, flour whitening requires different periods in summer and in winter. This is mainly because the bleaching effect of benzoyl peroxide (BPO) is related to ambient temperature. When the adding volume of BPO is 60mg, the bleaching reaction can be finished in 24 hours under the temperature of 30℃, while the bleaching reaction can be finished in 6 hours under the temperature of 50℃. However, in winter it may require 48 hours or even longer.
b. Moisture content
The optimum moisture content for additive using is approximately 15%, especially for Grade 1 and Grade 2 flour. Excessively high or low moistures are neither ideal for whitening. When the moisture content is too high, BPO resolves fast and the resultant reactive oxygen flows out participating in the reaction completely; when the moisture content is too low, BPO hasn’t resolved completely when being sold and so it cannot give full play to its whitening effect. Therefore, excessively high and low moisture contents influence BPO’s whitening effect.
c. BPO’s flowing property
Flour additive’s flowing property is related to the inorganic salt when diluting BPO. The better the BPO’s flowing property is, the evener the additive is. Meanwhile additive’s flowing property has a great bearing on its fineness. The finer the additive is, the evener it is in the flour, the better the whitening effect is. Otherwise, there may be “zebra stripes” phenomenon which affects flour quality seriously and pose a hidden problem.
d. Flour fineness
Flour particle size has a great influence on its whiteness. Shading coefficient test indicates that fine particle appears whiter than coarse particle; fine particle flour appears especially whiter if additive has been added.