Gelation of Nicandra physalodes (Linn.) Gaertn. polysaccharide induced by calcium hydroxide: A novel potential pectin source

Abstract

In this study, a novel gelling polysaccharide with a yield of ~6.7% (dry basis) was obtained from Nicandra physalodes (Linn.) Gaertn. seeds, and subsequent structural analysis suggested that Nicandra physalodes (Linn.) Gaertn. polysaccharide (NPGP) was composed of galacturonic acid (87.8%), rhamnose (3.7%), glucose (3.6%), arabinose (1.8%), galactose (1.8%), and a small amount of xylose (1.3%). The weight average molar weight (Mw) and number average molecular weight (Mn) of NPGP were determined as ~ 79.6 kDa and ~23 kDa, respectively. Also, it was found that NPGP had a low methoxylation degree (DM) of ~28%. These results indicate that NPGP can be grouped into the family of low methoxyl pectins (LMP). Subsequently, we further investigated the gelling properties of NPGP, and found that NPGP exhibited varying sensitivities to different types of calcium sources, with Ca(OH)2 being especially effective in inducing NPGP gelation. At a fixed NPGP concentration (0.5%, w/v), an increased amount of Ca(OH)2 addition induced a stronger gel, with the greatest gel hardness being observed at 0.06% (w/v) of Ca(OH)2 concentration. However, further Ca(OH)2 addition decreased the gel hardness. Furthermore, it was also observed that NPGP gels had relatively good heating stability but poor freeze-thawing stability, which could be greatly enhanced by incorporating appropriate amounts of sucrose. Overall, these findings highlight the potential commercial value of developing NPGP as a novel pectin resource.