The increasing interest of pectin derived compounds as functional additives in the
pharmaceutical and food industries demands new sources and eco-friendly
extraction approaches. In this regard, onion peel wastes (OPW) hold great potential,
with over 450,000 tons of OPW being discarded annually [1], despite their
remarkable pectin content. Pectins are commonly extracted acid hydrolysis (pH 2,
>85 °C), that yield mainly the HG domain, due to complete hydrolysis of the
branched domains or enzymatic hydrolysis, which is time consuming, but yields
branched pectin rich in RG-I and RG-II domains. As an alternative to the
conventional process for producing pectin derived compounds (PDC),
hydrothermal hydrolysis based on subcritical water (SubW) is emerging as an eco-friendly technique. SubW refers to water at temperatures ranging from 100 °C
(boiling temperature) to 374 °C (critical temperature), which remains in a liquid state
due to the application of pressure. SubW can facilitate the extraction of pectin from
natural matrices, and by controlling the operational parameters, pectin can be
tailored into smaller units with varying degrees of polymerization to produce PDC.
However, in practice, accurate control of experimental conditions has emerged as
the primary challenge of the SubW extraction process, which can lead to the
formation of undesired degradation products, and uncontrolled molecular weight
reduction of the pectin.
