Synergistic gelation between yellow mustard gum and κ-carrageenan1GRDC, Agriculture and Agri-Food Canada
2University of Guelph, Canada
Yellow mustard gum (YMG) has been included in the newest version of the Handbook of Hydrocolloids (2021) as emerging gums that “have commercial potential and can be considered to have credentials as natural gums for clean labeling”. In addition to its functionality (thickening, emulsifying and gelling) as hydrocolloids, YMG has been found to synergistically interact with κ-carrageenan to form a firm and elastic gel. Our recent study described an overall synergistic gelation process (heating, cooling, and curing) of YMG-κ-carrageenan mixtures by a rheological approach. Based on the gel characteristics and gelling process, a primary interaction mechanism was proposed as a combination of polymer interactions (both association and segregation) and ion migration.
However, the contributions of the above two factors have not been demonstrated with direct evidence at a molecular level. A further investigation of the interaction mechanism is needed to validate the proposed mechanism using more techniques.
In this study, a differential scanning calorimeter (DSC) and stress relaxation tests were used to illustrate the synergistic gelation mechanism of YMG- κ-carrageenan. DSC evaluated the thermal properties of the gels that indicate the changes in polymer conformation in the synergistic gel system during gelling and melting. The shifts of exotherm/endotherm peaks were observed in the synergistic binary gel compared with the pure κ-carrageenan gel suggesting new polymers formed through an association between YMG and κ-carrageenan. Stress relaxation tests were applied to the YMG-C mixtures of different blending ratios at different temperatures (10°C to 60°C). A concept of entanglement network numbers was applied to provide a quantitative measurement for the viscoelastic characteristics of the binary gels. The effects of the blending ratio on the synergistic gelation were concluded based on the quantitative determination.
The results confirmed the early proposed gelation mechanism. YMG-C (3:7) mixture formed a single-phase gel on cooling. The gelation was ascribed to the conformational transitions of the “new” polymers developed by YMG and κ-carrageenan. The new polymer could be a complex of linear β-glucan chain and κ-carrageenan polymer chain. Double helical chains were bound on the smooth regions of the linear glucan chain on mixing at a high temperature. The new complex then went through the “coil to helix” and the helix aggregation to form a gel network on cooling, which resulted in the gel network with thicker strands than the double helix chain alone, thus leading to higher gel strength.