Histological, Physicochemical and Microbiological Changes in Fresh and Frozen/Thawed Fish

Abstract

The production and supply of fish as food is constantly growing worldwide. Various methods are applied to extend its shelf life, one of them being freezing. According to European Union legislation, the state of the food and its treatment must be indicated on the label. If the food had been frozen prior to marketing and then sold thawed, this information must be provided to the consumer by labelling it. Otherwise, this is considered a fraud to the consumer since freezing significantly degrades the quality of fish. Histological, physicochemical and microbiological changes in the muscle tissue of frozen fish occur. Different methods may be applied to distinguish between fresh and frozen and them thawed fish, of which histological examination is a reliable method.

Differentiating between fresh and frozen-thawed fish fillets by mitochondrial permeability measurement

“…The size of crystals is largely responsible for the alteration of cells within the tissue. Ice crystals are formed and an alteration of osmotic pressure is also observed, inducing denaturation of proteins (Li, Zhu, & Sun, 2018;Strateva & Penchev, 2020). A faster speed of freezing reduces the formation of ice crystals and indirectly significantly increases the quality of the fish (Sone, Skåra, & Olsen, 2019).…”

Evaluation of histological post‐mortem changes in farmed Atlantic salmon (Salmo salar L.) at different time intervals and storage temperatures

“…Freezing cause depolymerization and destruction of the cell membrane, damages to tissue and cellular structures and changes in osmotic pressure (Li et al, 2018). Tissue changes caused by freezing can histologically be recognized as empty vacuoles, causing histological sections to appear punctured such as a Swiss cheese (Love, 1958; Popelka et al, 2014; Strateva & Penchev, 2020), which consequently complicate the histological evaluation.…”