Thermal Effect During Ultra-high Pressure Food Processing And Texture Profile Analysis

Ultra-high pressure food processing technology is an innovatory technology in the food science and engineering. Compared with the thermal treatment, it keeps food’s intrinsical quality characters such as colour, aroma, flavor, nutrition and so on immensely, and attracts wide attention from the scholars and food manufacturers.As a newly developing product, there’re still some quality control and process control problems for the commercialized production, including the heat effect induced by the compression and its effect on the result of enzymes inactivation and its uniformity; the relation between technological parameters like operation pressure, sample sizeand the percentages of ice instaneously formed, plateau time and thawing time; the effect of ultra-high pressure on the texture of seafood. In light of this, some basic research is done in this paper, base on the summary of the predecessors’s work. The work and result are as follows:(1) The effect of the compression heat induced by compression and natural convection on the temperature distribution in the pressure vessel chamber is studied by the numerical and simulation method, based on agar gel and Bacillus Subtilis-a Amylase (BSA). Coupling with the kinetics equation of the inactivation of enzymes, the distribution of the relative activity retention is obtained. The effect of the filling ratio of food in the pressure vessel chamber on the enzymes inactivation A/A0is studied with the model. The result shows that the heat effect and convection currents in the pressure medium affect the uniformity of the enzymes inactivation greatly. But when the filling ratio is more than75%, the effect of convection currents can be ignored. High level of enzymes inactivation is obtained by the high filling ratio, but it gets more nonuniform. As for the multi-packs processing, the difference between the samples becomes smaller. The model agrees well with experimental result.(2) Pressure shift/assisted freezing (PSF/PAF) processes and pressure induced/assisted thawing processes (PIT/PAT) of a long cylindrical sample in the water-ice I range are modeled with the enthalpy method and shift method dealing with the latent heat release and the thermophysical properties respectively, based on tylose agel.The plateau time and the percentages of ice instaneously formed under different operation pressure during the PSF process is calculated, and the impact of pressure and sample size on the ultra-high pressure thawing time is investigated. The result shows that, compared with atmosphere pressure freezing, the plateau time is shorter and the ice nucleates uniformly. The percentage of the ice instaneously formed and the plateau time contraction effect increase with pressure, with the maximum percentage of ice instaneously formed32.4%and the maximum plateau time contraction effect43.27%at the triple phase point. PAT and PIT can shorten the thawing time, and the effect increases with pressure. But when it extends to the PIT range, the change is small when pressure keeps on increasing.(3) The effect of pressure and time on the texture of sea cucumber and scallop is studied by the texture profile analysis, and is compared with the samples by the thermal treatment and vacuum freezing drying treatment. The result shows that hardness, springness, cohesiveness, fracture, gumminess and chewiness of scallop increase with. pressure, and there’s some interaction between holding time and pressure.Compared with thermal treatment, sea cucumber and scallop processed by ultra-high pressure are tender and of small hareness and good chewness. In other word, the taste of sea cucumber and scallop processed by ultra-high pressure is better than thermal treatment.