Citrus or apple inks for the 3D printing - the influence of the low methylated pectin structure and the standardized sugar type on their printability

In this study, the potential use of low methylated amidated pectin for the preparation of hydrogel bioinks was investigated. The pectins used were derived from various fruits and were characterized by differences in molecular weight, monosaccharide composition, degree of esterification, degree of amidation and the type of sugar additive (sucrose or glucose). The focus was on analyzing the influence of polymer structure and sugar type on the 3D printability and thermal properties of the developed formulations. The results showed that the type and amount of sugar seem to be the most crucial factors. It was observed that in the presence of sucrose, pectin crosslinking occurs not only through ionic and hydrogen interactions (sugar-pectin-metal ion), but also through chemical crosslinking, most likely as a result of the Millard reaction between amidated pectin and fructose formed via sucrose hydrolysis. This phenomenon is not observed in the presence of glucose in the system, where the polymer forms reversible gels. Printability tests indicated that using biopolymer standardized with glucose and optimizing its amount in the system is beneficial to obtain inks based on amidated pectin with a low degree of esterification.