After HHP treatments, the concentration of
ascorbic acid significantly diminished (P≤0.05) when
the pressure levels increased (Table 3). Ascorbic
acid degradation could be induced by enzyme
activation during pressurization. Nagy (1980)
revealed two of the main reasons for ascorbic acid
degradation, namely oxidative reactions by enzymes
such as cytochrome oxidase, ascorbic acid oxidase,
polyphenol oxidase and peroxidase available in the
juice; and aerobic and anaerobic non-enzymatic
reactions. High pressure affects the secondary,
tertiary and quaternary structures of proteins; such
conformational changes can enhance enzyme activity
by uncovering active sites and consequently facilitate
catalytic conversion. Patras et al. (2009) found that
the ascorbic acid content in strawberry pureé was
reduced by around 19% after being treated at 400-600
MPa/20°C/15 min. Similar findings were observed
by Barba et al. (2010) and Landl et al. (2010) with
vegetable beverages and apple purees, respectively.