2.4.2. Determination of ascorbic acid oxidase (AAO) activity
Spectrophotometric analysis was undertaken to measure the enzyme
activity of AAO as described in the previous work (Leong & Oey,
2012) using L-AA as substrate. One unit of AAO activity was defined as
the amount of enzyme AAO required to catalyse the oxidation of
1 μmol of L-AA to dehydro-L-ascorbic acid (DHAA) per minute at 25 °C
and pH 6.0. The reaction mixture consisted of 2500 μl phosphate buffer
(0.1 M NaH2PO4, pH 6.0 containing 0.5 mM EDTA), 100 μl of dailyprepared
5 mM L-AA substrate solution (dissolved in 0.1 M NaH2PO4
buffer, pH 5.6) and 400 μl of carrot extract mixed in a 4 mL quartz
cuvette (path length of 1 cm) (Starna, NSW, Australia). For the blank solution
used as reference, the substrate solution was replaced by 100 μl of
phosphate buffer solution (0.1 M NaH2PO4, pH 6.0 containing 0.5 mM
EDTA). Each measurement was conducted at 265 nm in triplicates
using a UV/vis spectrophotometer (Ultrospec 3300 pro, Amersham
Biosciences, Sweden).
(a)
(e)
(c) (d)
(b)
Fig. 1. Vertical (a) and parallel (b) position of carrots inside the PEF chamber (d) placed in the ELCRACK-HVP 5 equipment (c) and carrots before PEF treatment (e).
S.Y. Leong et al. / Innovative Food Science and Emerging Technologies 26 (2014) 159–167 161
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