In flour milling, a common issue is the yellowish color and insufficient whiteness, which can negatively impact consumer preferences, especially for steamed and boiled foods that require high whiteness.

The main whitening agents are benzoyl peroxide（BPO）, calcium peroxide, chlorine dioxide and so on.

Benzoyl Peroxide (BPO):

The pigment chromophore group in wheat flour is derived from carotenoids. Benzoyl peroxide, as a free radical, causes the release of singlet oxygen, oxidizing the unsaturated double bonds in carotenoids, destroying the pigment chromophore group and making flour fade. The maximum amount of benzoyl peroxide added to flour should not exceed 0.06g/kg.

In addition ‚ because BPO is a strong oxidizing agent ‚ in the process of making flour white, it destroys the vitamins in the flour ‚ and reduces the nutritional value of the flour. If used in excess ‚ will also make the flour livid gray ‚ excess added to the flour products present an unpleasant benzaldehyde smell.

Lipase:

This enzyme catalyzes the hydrolysis of oils to produce glycerol diesters, monoglycerides, and glycerol. Flour contains about 1.4% to 2.0% fat, which, when oxidized, forms disulfide bonds, improving the three-dimensional structure of the dough. The oxidation of lipophilic pigments like carotenoids also enhances flour whiteness.

Azodicarbonamide

When azodicarbonamide is added to wheat flour, the pigment can be destroyed by oxidation and fade, making wheat flour and its products white and shiny.

Polyphenol oxidase (PPO) was the main enzyme that had adverse effect on the color of flour. In wheat, PPO mainly distributed in the outer layer of the kernel, and the activity of PPO in aleurone layer was the highest. With the increase of flour yield, the content of PPO in flour increased, and the enzymatic Browning was also intensified. Mercaptoethanol, EDTA, saturated NaCl and sodium dodecyl sulfonate (SDS) have certain inhibitory effects on PPO in whole wheat flour. By adjusting the appropriate temperature, pH and adding a certain concentration of inhibitors (citric acid, ascorbic acid, cysteine, etc.) to effectively prevent the occurrence of PPO enzymatic Browning.

Physical methods also play an important role in flour bleaching. For example, through physical processes such as screening, decontamination, and grinding, wheat bran and other impurities in flour can be removed, improving the purity of flour and making it look whiter.