The second extraction process was employed in CHE and three
selected UAHE conditions (10.18, 12.22 and 14.26 W/cm2 at 70 C
for sonication 30 min) according to Panchev et al. (1988) with
minor modifications. After the first centrifugation, hot distilled
water (150 mL) of the same temperature with the first extraction
was mixed with the residue, and held without sonication for
30 min. Then the extraction mixture was cooled and centrifuged
(9000 rpm, 30 min), the filtrate was coagulated and dried. The
dried pectin was labeled as Pectin II. The flow chart of the extraction
and purification of pectin from grapefruit peel was shown in
Supplementary Fig. S2.