Browning reaction prevention

Many fruit and vegetable juices darken in color with time due to enzymic browning. The phenolic compounds involved in the reaction complex with cyclodextrin. Thus, the browning reaction can be prevented, either by passing the juice through a crosslinked cyclodextrin polymer to remove the phenol, or by adding cyclodextrin to the juice, since polyphenoloxidase, the enzyme responsible for oxidizing the phenolic compounds, is unable to act on the phenolic compounds while they are complexed with the cyclodextrin.98,99... 

This enzyme mixture can also remove glucose from eggs before drying to prevent Maillard type browning reactions in the dried product. 

Real-World Question How can the chemical reaction that turns apples brown be prevented ... 

Tyrosinase inhibition may be a potential approach to prevent and control the enzymatic browning reactions and improve the quality and nutritional value of food products [20]. Tyrosinase also plays a major key role in the developmental and defensive functions of insects. Tyrosinase is involved in melanogenesis, wound healing, parasite encapsulation, and sclerotization in insects [21-23]. For these reasons, in recent years the development of tyrosinase inhibitors has become an active alternative approach to control insect pests [20]. Additionally, it is now well-recognized that tyrosinase inhibitors are important for their potential applications in medical and cosmetic products [24-26]. 

The addition of sulfites during the predrying step is the only effective means available at present controlling NEB in the dried fruit and vegetable product. Sulfite is considered to be a safe additive to incorporate into fruit and vegetable products up to certain permissible limits. However, recently there are reports on the hypersensitivity of a few individuals to the ingested sulfite. Numerous attempts are therefore made to find alternative means to prevent browning reactions. 

The Maillard reaction (non-enzymic browning) is prevented by the addition of sulphur dioxide, either as the gas or as sulphite. Packaging that reduces the loss of SO2 due to oxidation or permeation (Davis et al., 1973) can decrease the need for this additive. 

Losses during the cooking of root vegetables are usually around 25% and in leafy vegetables are about 40%. The addition of sulfites, used to prevent enzymatic browning reactions in peeled potatoes or dried fruits and vegetables, results in extensive or total destruction of thiamine. 

Enzymatic browning reactions, which have been known for almost 100 years, are complex enzyme catalysed reactions involving the oxidation of phenohc compounds by some oxidoreductases in the presence of air oxygen. Oxidation products are quinones that are transformed by subsequent enzymatic and spontaneous (non-enzymatic) reactions into various coloured pigments. Quinones and other reaction products in plants have microbistatic effects and are able to prevent the spread of microbial and viral infections. Polymeric insoluble reaction products are an effective mechanical barrier against further erosion at the injury site of a plant. 

The enzymatic browning reaction is an important technological problem, especially in the case of subsequent cold or freezing storage. Therefore, in addition to the reaction mechanisms, considerable attention is paid to its possible prevention. Prevention should begin early by selection of materials suitable for the given method of processing. 

Erythorbic acid and sodium erythorbate may be used for preserved and semi-preserved fish products and frozen and deep-frozen fish at a concentration of 1500 mg/kg. The amount of these antioxidants allowed for preservation of cured and preserved meat products is only 500 mg/kg (expressed as erythorbic acid). The use of 4-hexylresorcinol (4-hexyl-1,3-benzenediol) is permitted up to 2 mg/kg as a colour retention agent for treatment of crustacean meat (fresh and frozen), namely to prevent black spots arising by enzymatic browning reactions, known as shrimp melanosis. 

Methanol is included to prevent the further reaction of py SO3 with water. The titration s end point is signaled when the solution changes from the yellow color of the products to the brown color of the Karl Fischer reagent. 

---