Rheological analysis of hydrocolloidal Basil seed mucilage in the context of seed physiology

Hydration of the seeds of the Ocimum basilicum develops a translucent mucilage around the seed that plays a vital role in its germination, adhesion and dispersal. This functionality stems from the structure of the mucilage, which comprises of adherent and non-adherent layers, that have varying concentrations of complex polysaccharides such as pectin, cellulose, and hemicellulose. Pectin crosslinks in the presence of Ca⁺² ions to form hydrocolloidal gels. The interplay between the pectin and calcium concentrations and degree of esterification determines the nature and extent of crosslinking. However, the extent to which it contributes to the gel structure, its rheology and the resulting seed physiology is not completely understood. This work uses Large Amplitude Oscillatory Shear (LAOS) rheology as a tool to estimate the factors that affect crosslinking in the Basil seed mucilage. We observe that the mucilage behavior is gel-like, with a constant modulus plateau at low strains and shear thinning at higher strains. The non-linear signatures such as the loss modulus overshoot and strain stiffening observed for mucilage gels are compared with those of the pectin-Ca gels to estimate the extent of Ca⁺² crosslinking and the degree of esterification of the pectin present in the mucilage.