Effects of temperature prior to high-pressure processing on the physicochemical and structural properties of raw grass carp

Despite the effective microbial inactivation of high pressure processing (HPP), too intensive pressurization can cause undesirable quality changes in fish muscle. Combination treatments can be applied to retain sensory attributes after HPP for ready-to-eat fishery products. This present study thus investigated the impacts of different initial sample temperatures (- 18, 2, 20, and 55 C-degrees) on raw grass carp slices under 300, 400, and 500 MPa, followed by microbiological, sensorial, chemical, and structural analyses. Increasing the pressure level at 20 C-degrees led to whitening, hardening, and decreases in water holding capacity of grass carp. For example, 400 MPa induced a L* increase from 59.6 to 80.7, loss in muscle transparency, 5.1% of weight loss, and a hardness increase from 390.2 to 540.5 g. Correspondingly, fiber shrinkage and the compaction of tissue structure were observed in pressurized fish muscle. When grass carp were pressurized at a low initial temperature (2 C-degrees), the appearance remained semi-transparent under 300 MPa, and the changes in physicochemical quality were similar to the treatments at 20 C-degrees. HPP treatments at a subzero (- 18 C-degrees) or mild-heated (55 C-degrees) initial temperature caused greater quality changes when compared to other temperature conditions, e.g., L* > 70 under 300 MPa, and hardness > 700 g under 400 MPa. The myofibrillar protein contents dropped more significantly as the initial temperature increased. Overall, a better understanding of the impacts of pressurization temperatures would thus help to monitor fish quality and develop appropriate means for novel ready-to-eat fish-based products.