Combination Of High-Pressure Processing With Other Treatments And Its Impacts On The Safety And Quality Of Aquatic Products

Raw aquatic products have been favored in many regions throughout the world,because of fresh flavor and taste they present.High pressure processing?HPP?,as a novel non-thermal treatment,can improve safety and maintain raw attributes,but pressure-induced quality changes vary among species.Aquatic foods sensitive to pressure should be performed at a lower pressure,or combined with other treatments to alleviate quality changes.However,there is still limited information regarding combination effects.In this study,typical aquatic foods were selected to investigate the laws and underlying mechanisms of quality changes after HPP.Combination treatments were further used for safety control and freshness retainment at the best extent,with thermal treatment as control.The results were shown as followed:?1?In order to study HPP suitability of different aquatic foods,quality comparison between16 species usually for ready-to-eat production was done at 200-500 MPa.Results showed that higher pressure induced more microbial inactivation.HPP showed much superiority in retaining raw properties,in comparison to the cooked samples with more weight loss,whiter appearance,worse texture and weaker water-holding capacity?WHC?.The extent of overall quality changes after HPP ranged from high to low in the following sequence:fishes>crustaceans&mollusks>shellfishes.Too intense treatment caused whitening and decline in raw properties of fish meat.Quality of basa changed in the range 400-500 MPa,whereas qualities of grass carp,tilapia and other pressure-sensitive fishes,200-300 MPa.HPP caused less changes and efficient shucking effect in crustaceans and mollusks:particularly,nearly no changes occurred in shellfishes at500 MPa.Revealed by five aquatic foods of different pressure-resistance as representatives,pressure induced higher level of weight loss,lightness L^*,hardness and chewiness.WHC of grass carp and basa increased respectively below 200 MPa and 300 MPa but dropped at upper pressure,while those of abalone,white shrimp and squid dip as pressure rose.Four principle components extracted from these fourteen quality traits indicated correlation between quality changes,protein composition and microstructural property.Pressure-induced decrease in myofibrillar protein and fiber compression/aggregation resulted in whitening and hardening.The more compact the microstructure was,the less quality changed after pressurization.?2?As a common ingredient for Cantonese-style sashimi,grass carp fillets were chosen for deeper studies and pressurized at 300-500 MPa under different initial core temperatures?-18?,4?,20?,55??.Quality of cooked samples were shown the worse.Upper and lower temperature helped in bacterial reduction.Treatment at 4?caused less quality changes:pressurized fillets?300 MPa?still appeared semi-transparent,whereas mild heat and freezing resulted in aggravation of quality changes:complete whitening was observed in fillets at 300MPa.Then,pressurization at 4?witnessed less fiber shrinkage and protein structure changes:for example,the inter-filament spacing area ratio?62.5%?was larger than those at 55??43.7%?and-18??52.8%?;?-helix content?35.9%?was more than those at 55??27.6%?and-18??24.8%?;I₈₅₀/I₈₃₀ value?1.029?,which indicated exposure of amino acid residues,was larger than those at 55??1.224?and-18??1.128?.Therefore,at lower temperature,fillets showed less weight loss,more tender texture and stronger WHC.?3?Meanwhile,commonly-used salting/drying treatments were selected to process fillets till different salt/water contents before HPP at 300-500 MPa.It was shown that cooked samples still had the worst quality.As Na Cl rose and moisture dropped,effective bacterial inactivation and a significant reduction of weight loss can be seen.Pre-salting/drying,if conducted alone,showed little,even negative,impact for alleviating quality changes after HPP,which might be relevant with salting-induced fiber swelling and drying-induced fiber compression/aggregation that led to a more compact microstructure.A phenomenon can be observed in fillets containing1.71%salt,that dehydration lowered ascent of L^*and hardness after HPP,along with stronger WHC.Semi-dried salted fillets?1.71%salt,72.3%water?at 300 MPa appeared raw-like and those at 400 MPa even looked semi-transparent,suggesting that alleviation of quality changes might result from the synergetic effect of salting and drying.Further,fibers of semi-dried salted fillets complexly connected with enough spacing in between caused less structural compression after HPP.Raman spectra revealed an increase of?-helices from 36.1%to 44.4%after synergetic pre-treatment and dropped to 43.1%after HPP at 400 MPa,which indicated that pre-salting and pre-drying enhanced WHC and lower its change after pressurization.