Microbiological and chemical quality of fresh and frozen whole trout and trout fillets

Abstract

The rainbow trout (Oncorhynchus mykiss) is considered as an important fish in the freshwater aquaculture and play a significant role in the human diet. The final quality of fish depends on the chemical and microbiological quality of fish at the time of freezing as well as on other factors including storage temperature and processing. The purpose of the study was to determine the microbiological status of 30 samples cooled and frozen trouts collected from approved farm in the Turiec region, territory of middle Slovakia. Total viable counts (TVCs), psychrotrophic bacteria, Pseudomonas spp. and also total volatile base-nitrogen (TVB-N) and pH were measured in samples of fresh (1. and 7. day of storage at 0 - 2 °C) and frozen whole trout and trout fillets. Frozen samples were stored at -18 °C during 1, 3, and 6 months. Samples were collected from the skin, muscles (sterile) and muscles after filleting. The microbiological quality of samples varied between fresh and frozen (6th month of storage) regarding TVCs and also between samples taken from the skin and muscles after filleting compared to muscle samples collected sterile regarding all tested bacteria. A large number of bacteria (pathogens and spoilage bacteria) enter with the raw material and in particular the skin contamination had a negative impact on the increase of microbial load in fillets. All processing techniques and procedures including filleting therefore must be designed and aimed to minimise contamination and growth of microorganisms in fish. However, based on the results of TVB-N analysis, differences between fresh and frozen samples were found, but all the samples were suitable for human consumption.

Keywords

• total viable counts
• psychrotrophic bacteria
• Pseudomonas
• total volatile base-nitrogen, rainbow trout