3. Result and discussion
3.1. Purification of amylase from pitaya peel
A single protein with amylase activity was purified from red
pitaya peel using ammonium sulphate precipitation, gel filtration
chromatography with a Sephadex G-200 and ion exchange chromatography
with a DEAE-Sephadex column. Table 1 summarises the
purification of amylase from pitaya peel. The crude extract was
precipitated with ammonium sulphate (0–20%, 20–40%, 40–60%
and 60–80% saturation). The results indicated that 40–60% saturation
achieved the highest purification fold of 8.4 and a yield of
88.7% among the other concentrations of ammonium sulphate. An
ammonium sulphate fraction of 40–60% was then loaded onto the
affinity chromatography column (Sephadex G-200). The enzyme
was eluted from the column with a salt concentration of 1 M NaCl.
After elution, amylase activity and proteins were found in one
peak (Fig. 1a). Amylase from pitaya peel was purified more than
102.5-fold with 75.3% yield, and its specific activity equalled
1455.5 U/mg proteins (Table 1). The active fractions of obtained
from the above step were subsequently separated using DEAESephadex
ion exchange chromatography (Fig. 1b). After this step,
the amylase was purified 234.2-fold with a recovery of 72.1% and
a specific activity of 3325.6 U/mg of protein (Table 1). The gel filtration
chromatography technique and ion exchange chromatography
used in this study has also been used successfully for amylases purified
from Vigna mungo cotyledons, Arabidopsis thaliana leaves, corms
of Colocasia, millet of malt, and roots and cotyledons of Pisum
sativum. These results are in accordance with similar purification