The influence of locust bean gum on native and alkali-modified agar gels

Native (NA) and alkali-modified (AA) agars from Gracilaria vermiculophylla, cultivated in integrated multi-trophic aquaculture (IMTA) systems, were mixed with locust bean gum (LBG) at different mass ratios (i.e. 100/0, 75/25, 50/50, 25/75, 0/100 agar/LBG) to prepare hydrogels with a final polymer concentration of 1% wt. The rheological properties of pure and mixed systems were studied under small (SAOS) and large amplitude oscillatory shears (LAOS). NA and AA interacted differently when mixed with LBG. Chemically, NA was poorer in 3,6-anhydro-α-L-galactose (LA; gelling) and richer in sulfated and methylated (non-gelling) units. Gels prepared with AA were more rigid (higher G′ and gel strength) than the ones made with NA. Under SAOS, addition of LBG led to a gradual decrease in gel rigidity (G′ decrease) and for gels made with NA, to a significant decrease in elasticity (tan δ increase). For both agars, the gelation point moved to lower temperatures and the thermal hysteresis was progressively widened upon increase of LBG content in the gels. This matched with less coarse networks imaged through cryoSEM, particularly for AA. In LAOS experiments (strain sweeps), differences observed in the shapes of the curves for NA and AA gels, in the non-linear region, seemed to suggest stronger interactions for the former, probably reflecting the very different microstructures of both type of gels. Agars from sustainably grown G. vermiculophylla can yield gels with various rheological profiles when mixed with LBG. This can be very appealing to manufacture new products with interesting textures and mouth feel for consumers.