Sulfur-containing compounds heated under alkaline condition: antibrowning, antioxidative activities, and their effect on quality of shrimp during iced storage.

Sulfur-containing compounds heated under alkaline condition (pH 10) were determined for inhibitory activity toward polyphenol oxidase (PPO) from Pacific white shrimp (Litopenaeus vannamei) and for antioxidative activity. Cysteine and glutathione (GSH) (20 mM) heated at 100 degrees C at pH 10 strongly inhibited PPO activity. Heated alkaline cysteine showed the greater 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging activity, copper-chelating activity and reducing power than cysteine and glucose-cysteine Maillard reaction products (P < 0.05). Effect of heated alkaline cysteine at different concentrations (0, 20, and 100 mM) on the quality changes of Pacific white shrimp during iced storage was investigated. Shrimp treated with 100 mM heated alkaline cysteine had the lowest melanosis score, thiobarbituric acid-reactive substances (TBARS) value and total viable count (TVC), compared with those without treatment and treated with 20 mM heated alkaline cysteine, throughout the storage of 12 d (P < 0.05). Therefore, heated alkaline cysteine can be used as a novel additive to retard melanosis and extend the quality of postmortem shrimp.