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.

Determination of Biogenic Amine Formation and Microbiological Changes in Carp (Cyprinus carpio L., 1758) Frozen Storage

“…In the FWF and FGF samples, it was detected that the TVB-N values increased throughout the storage period and were 13.38±1.39 and 12.87±0.81 on average at the end of the storage. The TVB-N values detected this study were found to be similar to the findings detected in the silver carp (Hypophthalmichthys molitrix) mince [59], while they were found to be higher than the values found in the whole trout and trout fillets (Oncorhynchus mykiss) samples [32].…”

“…The freezing process, to be applied for protecting the appearance and texture, smell and taste, and extending the storage period of fish that are hunted/harvested freshly and are not subjected to any technological process provides advantages to consumers [32]. In the food safety of seafood, it is known that aquatic environment and relevant processes during hunting/harvesting and various production phases have a very close relationship with the hygienic quality of products [12].…”

“…(PS) increased in the FWF and FGF samples throughout the storage, and they were found to be 3.33±0.02 and 3.26±0.10 log10 cfu/g, respectively, at the end of the storage (Table 2). Popelka et al [32] found that the number of PS increased throughout the storage and was 2.85±0.57 log10 cfu/g on average at the end of the storage in the whole trout and trout fillets (Oncorhynchus mykiss) samples, which were stored at -18 ºC for 180 days. They also reported that the number of PS remained at a lower level in the freezing method.…”

A new cost‐effective process for limitation of microbial growth in fish fleshes: Wrapping by aluminum foil coated with electrospun nanofibers

“…In the mentioned studies, the amount of the used materials in food preservations was determined to be higher than as compared with the materials obtained from nanotechnology applications. Psychrophilic bacteria that are the major group of microorganisms responsible for the spoilage of fresh fish at cold storage temperatures (Gram & Huss, ) could mostly reach a high level in the fish fillets within 7 days under cold storage conditions (Popelka, Jevinová, & Marcinčák, ). Already, as can be seen from the results, nisin and curcumin‐loaded nanofibers (0.0432 g nisin and 0.72 × 10 −4 g curcumin) as a coating material efficiently limited the rapid increase in psychrophilic bacteria growth, particularly, in this cold storage period.…”

“…In the mentioned studies, the amount of the used materials in food preservations was determined to be higher than as compared with the materials obtained from nanotechnology applications. Psychrophilic bacteria that are the major group of microorganisms responsible for the spoilage of fresh fish at cold storage temperatures (Gram & Huss, 1996) could mostly reach a high level in the fish fillets within 7 days under cold storage conditions (Popelka, Jevinová, & Marcin cák, 2016).…”