MAE of pectin was performed according to the methods
described by Wang et al. (2007) in an ordinary household
microwave oven (LG, MH-3948 WB) at working frequency of
2450 MHz with adjustable microwave power and time. A flow
chart for the extraction of pectin is depicted in Fig. 1. About
1 g of dried orange peel powder was weighed and placed into
a 250 ml Pyrex beaker and different amount distilled water
(10–20–30 ml) containing different pH values (1–1.5–2) was
added. The pH of the solvent was adjusted with the help of sulfuric
acid (0.05–0.016–0.005 mol/l). According to the experimental
design (Table 1), the extraction was performed under different
MAE conditions. The beaker was placed in the middle of the oven
over a rotating dish and was exposed to microwave radiation at
different powers (160–320–480 W) for the selected irradiation
time (60–120–180 s). After microwave heating, the mixture in the
Pyrex beaker was allowed to cool down to room temperature and
filtered using filter paper (Whatman no-1). The filtered extract
was centrifuged and the supernatant was precipitated with an
equal volume of 95% (v/v) ethanol. The coagulated pectin mass
was washed with 95% (v/v) ethanol for three times to remove the
mono and disaccharides (Minkov, Minchev, & Paev, 1996).