*3.6. Extraction of Pectins*

Recently, advanced technologies have been developed to improve the yield and to decrease the time of pectin extraction. The "so-called" green methodologies are nonthermal processes that apply, in place of the heat, the acoustic energy of ultrasounds (ultrasoundassisted extraction), or microwave radiation (microwave-assisted extraction) to increase the release of the target material [35,36]. Nevertheless, the employed process for the pectin extraction from walnut husks was the traditional method which involved hydrolysis of protopectin with citric acid and extraction from the primary cell wall of plant tissue using water under reflux, because preliminary extraction tests using ultrasounds resulted in lower yields. Citric acid, compared with mineral acids, had a lower environmental impact and it was cheaper [37].

The obtained results showed that the pectin content of husks from Montalto (PM, 69.8 ± 0.1 g/100 g DM) was about three times higher than that extracted from Zumpano hulls (PZ, 27.1 ± 0.3 g/100 g DM), which indicated that different pedoclimatic areas influenced fibre content.
