Indole production and deepwater pink shrimp (Parapenaeus longirostris) decomposition

Abstract

Indole levels have been used to confirm the sensory evaluation of shrimp decomposition and a limit of 250 μg/kg has been used in several countries to differentiate passable shrimp from shrimp in the first state of decomposition. However, no data exist on the correlation between sensory quality and indole content in deepwater pink shrimp (Parapenaeus longirostris) which validate the use of this defect level. The sensory, microbiological and biochemical changes were determined in microbiologically contaminated (4 and 7 log cfu/g ) deepwater pink shrimp stored at 0, 5, 10 and 15°C. Indole, TMA-N, TVB-N, pH, TVC, Enterobacteriaceae and Pseudomonas spp. increased with time and temperature. At low temperature storage, final indole levels in severely decomposed shrimp (TVB > 60 mg/kg) were much lower than the suggested defect level of 250 μg/kg shrimp. Increased microbiological contamination (7 log cfu/g) induced faster and higher indole production at all temperatures. At higher storage temperatures, indole formation was greatly accelerated resulting in very high indole levels. High indole levels indicate decomposition; however decomposed shrimp may not necessarily contain indole. The shelf life of shrimp ranged from 15 h at 15°C to 6 days at 0°C. An indole defect level >90 μg/kg shrimp should be used for deepwater pink shrimp.