Ultrasonic and heating extraction of pistachio by-product pectin: physicochemical, structural characterization and functional measurement

In this study, Box-Behnken design was applied to optimize the ultrasound-assisted extraction (UAE) and heating extraction (HE) conditions for pectin production from pistachio green hull (PGH). The pectin extraction yield at optimal condition for UAE (ultrasound power of 150 W, pH of 1.5 and time of 24 min) and HE (temperature of 70 degrees C, time of 90 min and liquid to solid ratio of 40 v/w) methods was about 12.0 and 10.3%, respectively. In these conditions, the galacturonic acid content of UAE-pectin and HE-pectin was about 59.33 and 75.11%, respectively. Both pectin samples showed good emulsifying activity, water holding capacity and oil holding capacity. In addition, total phenol content, antiradical and surface activities of HE-pectin were higher than UAE-pectin. The degree of esterification of pectin produced by the HE method was higher than the UAE method, which was confirmed by FT-IR and H-1-NMR analysis. The results of XRD patterns showed an amorphous structure with several crystalline portions for PGH pectin. The rheological properties of pectin solutions illustrated that in high frequencies, both pectin samples had a similar behavior (elastic), while in low frequencies, HE-pectin showed a viscous behavior. In the final, it should be stated that the UAE method significantly increased pectin yield using a lower processing time and consumed solvent, however, HE-pectin presented a better quality in comparison to UAE. Graphic abstract