Microstructural and Physiological Changes in Plant Cell Induced by Pressure: Their Role on the Availability and Pressure-Temperature Stability of Phytochemicals
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© 2017, Springer Science+Business Media New York.High pressure processing (HPP) is the most widespread nonthermal food pasteurization technology. The stability during HPP treatments of chemical compounds with health-enhancing properties found in plants has been intensively studied. A rising research interest is the elucidation of the mechanisms by which HPP may enhance their biosynthesis and bioavailability. Pressure levels under 100 MPa appear to induce oxidative stress in plant tissue leading to the activation of metabolic pathways related to the biosynthesis of secondary metabolites. Likewise, treatments at ~150¿200 MPa result in cellular membrane rupture, increased cell wall permeability, and nearly complete cell viability loss while metabolic activity gradually ceases at higher pressure. Major structural changes occur during treatments at higher pressure levels influencing the bioavailability of phytochemicals. Carotenoids attached to polymeric structures on cell walls, or entrapped inside cellular organelles, are released into the media by pressure treatments at 200¿400 MPa, which may also initiate their degradation. Depending on the food matrix, phenolic compounds and vitamin C are released, degraded, or remain unaffected by 200¿600 MPa treatments. At high pressure, phenolics are highly susceptible to oxidation and enzymatic reactions, whereas ascorbic acid stability depends largely on the dissolved oxygen concentration. Future work should focus on pressure come-up time (CUT) effects, development of kinetic models coupling the biosynthesis and/or release of phytochemicals with its pressure-temperature stability, and determinations of their in vitro and in vivo bioavailability.