Bleach refers to  inhibit  food color  or material  make  it fade .Bleach  can  be  divided into  two categories , reduced  bleach and oxidizing bleach .Reduced bleaching agent  is  mainly  produced   by sulfur  dioxide   reduction  faded ,the material  such as sodium sulfite , sodium bisulfite ,etc .This type  oxidation bleaching  agent is the oxidation coloring  matter decomposition  after  bleaching,  mainly  used in flour ,its  usage  and  dosage  are  limited .The  bleach  hydrogen peroxide (used  to noodles ,grilled fish ,cakes ,etc ,).

The Browning of plant-based foods is associated  with the activity  of  oxidase ,and  sulfite  is  a kind of strong reducing agent,  has a  strong  inhibitory  effect of  oxidase activity.

They   play a role by reducing  sulfur  dioxide  generated .Sulfur  dioxide  in water   to  form  sulfurous acid ,its bleaching ,corrosion  protection  mainly has a reducing. In acidic  conditions   because  of  the sulfur  dioxide has the strongest  antimicrobial.,  and  therefore not free  of  sulfurous  acid  is thought to inhibit yeast, mold  and  bacterial .Bleach in general  as well as  bleaching  has   significantly  inhibitory effect on microorganism   and  antioxidant   effect . So  the   sulfite  can   through the decomposition  of  normal  metabolic pathways  in the  body , it is generally believed in the  specified  usage  under the  use  is safe .

Bleach   in  use  should   pay  attention to the  following  points ：

1.the  food is  mixed  iron ,copper  and  other  metals .

2.Sulfites  classes  does not apply to meat.