Indole levels in deepwater pink shrimp (Parapenaeus longirostris) from the Portuguese coast. Effects of temperature abuse

Abstract

Deepwater pink shrimp (Parapenaeus longirostris) is an important commercial species in Portugal with a catch volume over 1000 tons and a high market value, estimated in 2000 as being equivalent to 11 million Euros. 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 stage of decomposition. No data exist on indole levels in this species and taking into account that a considerable amount of the catches are exported as fresh to Spain, it was necessary to evaluate the indole production in order to identify the usefulness of this index as an indicator of temperature abuse in this species. Biochemical, physico-chemical, microbiological and sensory changes were evaluated in fresh deepwater pink shrimp stored at 2 °C and at room temperature (22 °C). Cooked deepwater pink shrimp chill-stored was studied too. The results indicated that indole was produced at levels of 167 µg/kg when raw shrimp was chill-stored for 7 days, while levels around 7400 µg/kg were produced after 32 h in raw shrimp stored at room temperature. Indole production of deepwater pink shrimps, showed a close parallel with microbiology data, mainly with Enterobacteriaceae production. We concluded that, in the conditions studied, the indole could be considered a useful indicator in assessing the history of shrimp if high temperature is suspected or bad hygiene conditions have been applied. Nevertheless, a low content of indole does not necessarily imply good quality.