Linseed pectin: gelling properties and performance as an encapsulation matrix for shark liver oil

Fully de-esterified Na-pectate with excellent gelling properties was isolated from linseed (Linum usitatissimum) using an alkaline extraction procedure aided with a sequestering agent. The gelling behavior of this material was studied as a function of amount of Ca2+ added and temperature by dynamic oscillatory rheology. Calcium cross-linking adjusted at varying stoichiometric ratios, (R=2[Ca2+]/[COO−]), resulted in unequivocal gel network formation with mechanical spectra characteristic of permanent gel structure. Crude shark liver oil (SLO) was encapsulated into a composite matrix comprising linseed Na-pectate, alginate and chitosan. To this end, SLO was loaded into a linseed pectin–alginate solution at 2% (w/v), and gel beads were formed by dropwise addition into a CaCl2 bath and further coated by chitosan. Three different formulations were evaluated by varying the ratio of pectin to alginate (in % of the total equivalent concentration), while keeping constant the total polymer concentration at ∼4% (w/w). As the proportion of linseed pectin in the formulae increased, the gel beads lost mechanical strength, sphericity and swelled more rapidly in water by a transport mechanism controlled only by diffusion of the solvent. Loading efficiency was greater in the capsules in which pectin contributed to 28% of the negatively charged polymer species (P28), which retained 73% of SLO, while capsules of pure alginate (P0) and those with a higher amount of pectin (P71) retained 65 and 67% of SLO, respectively. The observed differences between the three types of capsules were a direct consequence of the strength of linseed pectin gels, weaker than those of alginate.