Aterações químicas e microbiológicas em PACU (piaractus mesopotamicus) armazenado sob refrigeração a 5°c
This research was conducted with the objective of evaluating the shelf life and the spoilage process of "pacu" (Piaractus mesopotamicus) stored under refrigeration at 5°C. Fish samples, just after capture, were stored and evaluated at 0-7-14-21 days intervals, concerning chemical analysis (volatile nitrogen basis-, non protein nitrogen, total free aminoacids, free histidine and histamine) microbiological analysis (standard plate count, histamine producing bacteria in Niven agar, gelatinase and H2S producers, always with incubations at 35°, 20° and 5°C), and also sensorial evaluations. The results showed that as occurs with other fresh water tropical fishes, the "pacu" showed a high stability during the cold storage, with spoilage evidence only after 14 days storage, and based only in sensorial aspects because the chemical and microbiological parameters did not show a definitive evidence of spoilage. It was also noticed that the spoilage products appeared to be concentrated in the surface mucus since the chemical parameters of muscle tissue did not show remarkable changes even after 21 days storage under refrigeration. Histamine was not confirmed in the examined samples and the detected free histidine levels do not suggest that this fish species could be a potencial vehicle of histamine poisoning. However, his+ bacteria were isolated from the original samples being identified strains of Plesiomonas shigelloides and Vibrio fluvialis. The surface initial microbiota was reduced, prevailing mesophilic/psychrothropic species with lower counts at 5°C. During the storage at 5°C the microbiota showed a slow increase, only reaching high populations ( log 7,0CFU/cm2) after 14 days storage.