High hydrostatic pressure induced physiological changes and physical damages in asparagus spears

• CO2 production of asparagus increased after high pressure treatment below 200 MPa.
• Metabolism shifted from respiration to fermentation after high pressure treatment.
• A pressure of 200 MPa is suggested as threshold for severe cell damage to occur.
• Firmness recovery might be related to cell wall polysaccharide modification.

High hydrostatic pressure (HHP) has been applied as a postharvest treatment in fresh fruits and vegetables for certain purpose, e.g. as a phytosanitary approach to control quarantine insect pests. However, detailed information on HHP-induced physiological changes of plant tissues in a broad range of pressure is limited. In this context, asparagus spears were treated by HHP at mild (10–200 MPa) and high pressure (400–600 MPa) for 0.5 to 30 min. At pressure lower than 200 MPa, the CO2 production rate of asparagus spears increased with raising pressure and extending treatment times, while no sign of respiration was found at treatment pressures higher than 400 MPa. A shift from aerobic respiration to fermentation was noticed in the sample treated at mild pressure, which might be attributed to the HPP-induced hypoxia stress, enzyme activation, and cell damage. Generally, HHP treatment resulted in a decreasing firmness; however, slight but substantial recovery in firmness was observed in the treatments at pressure higher than 100 MPa for 20 min, which might be caused by fortification of intercellular adhesion through formation of new ionic linkages in cell wall pectic polysaccharides. Overall, it was suggested that 200 MPa could be a threshold for causing instant lethal metabolic disorder and severe physical damage in asparagus spears.