Preparation of Food-grade Ultrastable Foam via Multi-dimensional Assembly of Natural Saponin Glycyrrhizic Acid Nanofibers
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Abstract:
In this work, ultrastable foams were prepared by using the naturally occurring saponin glycyrrhizic acid (GA) as the foam stabilizer. In the process of homogenization at high temperature, the self-assembled GA fibrils could be rapidly adsorbed onto the the surface of the bubbles and form a multilayered interfacial fiber film. Then, rapid cooling enabled the unadsorbed fibrils were further self-organized into a hydrogel network through hydrogen bonding in the continuous phase, by which the bubbles were trapped and fixed (thereby forming stable foams). The stability tests showed that when the GA nanofibril concentration was greater than 4 wt%, ultrastable foams could be formed (which remained unchanged at room temperature (25 ℃) over 3 months. Microstructural observations revealed that with the increase of nanofibril concentration, the size of bubbles became smaller and more uniform and the fiber layers on the surface of the bubbles were more compact. The rheological results also showed that with the increase of GA nanofibril concentration, the foams exhibited a stronger viscoelastic respond, and the foam prepared at a high fiber concentration had higher viscoelastic moduli (G′ and G?): At 1 wt% and 8 wt% GA, respectively, G′ and G″were 5.954 and 4.084,. 1.6098×104 and 5.995×103, respectively, whereas, the yield stress were 8.087 and 8.982×102 respectively. These results indicated that the naturally occurring saponin GA could be used as a new type of foaming agent for the preparation of ultrastable foams with high formability. The preparation method was simple and uses mild conditions thus may have a broad prospective applications in food, pharmaceutical, cosmetic and other fields.
