Multiscale comparative study of pectin extraction from broccoli stalk using alkaline and enzymatic modifications: Structural characterization and gelling properties.

To promote the application of high methoxyl pectin (HMP) extracted from broccoli stalk waste as a novel, healthy, and gelling food additive, low methoxyl pectins (LMPs) with different degrees of esterification (40-45 %, 25-30 %, and 10-15 %) were prepared from broccoli stalk pectin (BSP) using enzymatic (E-pectin) and alkaline (A-pectin) de-esterification methods. The results demonstrated that the de-esterification method and degree of esterification led to distinct structural and functional differences among the LMPs. As the degree of esterification decreased, both the molecular weight (Mw) and apparent viscosity of the LMPs gradually decreased. However, pectin obtained via enzymatic de-esterification (E-pectin) exhibited higher Mw (208.2-229.3 kDa), apparent viscosity (1.6514-8.9394 Pa·s), and thermal stability (243.9-248.5 °C) compared to pectin obtained via alkaline de-esterification (A-pectin) and commercial apple pectin (CAP). The negative charge and the proportion of rhamnogalacturonan I (RG-I) domains increased as DE decreased, with E-pectin containing a higher RG-I content (20.55-25.41 %). FTIR analysis confirmed that de-esterification treatment primarily caused the cleavage of glycosidic bonds and methoxyl groups without altering the main backbone structure of pectin, while X-ray diffraction (XRD) analysis indicated that E-pectin exhibited a lower degree of crystallinity. With decreasing DE, both E-pectin and A-pectin showed enhanced gel hardness and water-holding capacity (WHC). At comparable DE levels, E-pectin exhibited superior gel strength, WHC, and gelation temperature, with E-3 showing the highest thermal stability and gelation performance. These findings suggest that broccoli stalk-derived pectin is a promising gelling and thickening agent, with LMPs having potential for application in food products.