ABSTRACT
Recently, high hydrostatic pressure (HHP) processes have been used in food preservation because they are able to inactivate many microorganisms and minimize the loss of color and nutrients to a greater degree than those that occur during heat treatments. High pressure affects protein structure, and, therefore, enzymes are also affected. High pressure has been applied in the manufacture of jams from different fruits (Horie et al., 1981). Asaka and Hayashi (1991) found that Bartlett pear samples treated under pressures from 200 to 500 MPa grew dark quickly, so it would seem that Bartlett pear jams manufactured by HHP wouldn’t be adequate for commercialization. The darkness of these samples is due to the action of polyphenoloxidase (obiphenol: oxygen reductase, EC 1.10.3.1) (PPO) on natural substrates in the fruit. However, Knorr (1993) showed that pressure ranging from 100 to 400 MPa produced a decrease in potato PPO activity. Also, Eshtiaghi et al. (1994) showed that PPO from potatoes in a phosphate buffer solution (pH 7) was inactivated when pressurized under 900 MPa for 30 min at 45°C. Likewise, Seyderhelm et al. (1996) obtained similar results for their experiments with PPO inactivation. Gomes and Leward (1996) found that PPO activity extracted
from mushrooms in a buffer solution at pH 7 decreased when pressurized in the 100 to 800 MPa range and was completely inactivated at the latter pressure. These authors also discovered that non-purified PPO from mushrooms pressur ized under 400 MPa for 10 min showed a 40% increase in activity, while at 800 MPa, there was a 60% decrease. The PPO potato extract, from potato pressurized at 800 MPa for 10 min, showed a 40% residual activity compared to non-treated samples.
