Structure of fish proteins as modified by salting procedures: A rheological and ultrastructural analysis of hake ( Merluccius hubbsi ) fillets

Abstract

Salting is a technique used for preserving fish meat and allows obtaining added value products. The salting process provokes several structure modifications, which in turns cause changes in the fish texture. Thus, the objective of this study was to investigate the effect of three salting procedures (dry salting [DS], mixed salting [MS] and brining [BS]) on the rheology and structure of Merluccius hubbsi (Argentine hake). Rheological properties were evaluated using dynamic oscillatory and thermorheology tests, and the structure changes by scanning electron microscopy. DS samples showed the highest values of salt concentration referred to liquid phase (zNaCl), while BS showed the lowest ones. In all cases, elastic (G′) and loss (G″) modulus increased with salting time. G′ values exceeded G″ values, indicating a predominant solid behavior. DS samples presented the greatest increase in rheological parameters (G′, G″ and η*). Thermomechanical spectra allowed to identify an increase in denaturation temperature (Td) of proteins (myosin and actin) for DS and MS, and to a lesser extent for BS (Td = 46.7 ± 0.4°C, Td = 50.3 ± 0.8°C, Td = 58.8 ± 0.6°C and Td = 58.2 ± 0.9°C for fresh, BS, MS and DS, respectively). Ultrastructural images evidenced conformational changes on the myofibrillar proteins and the connective tissue (collagen). BS caused the least superficial damage to hake tissue. Based on the results, BS could be the method recommended for the industrial production of salted M. hubbsi.