The properties of alginate-cyclodextrin hybrid bubble hydrogel for ethylene gas encapsulation and storage

In this study, a novel alginate-cyclodextrin hybrid bubble hydrogel was developed for the stable encapsulation of ethylene gas. Ethylene gas was introduced into aqueous bubble systems prepared using sodium alginate (SA), α-cyclodextrin (α-CD), SA + α-CD, β-cyclodextrin (β-CD), or SA + β-CD. Among these, the α-CD bubble system demonstrated the highest ethylene-loading ability (0.88 mL/g_carrier). However, over 50 % of the encapsulated ethylene was released from all bubble systems within 60 h due to cavity disintegration, demonstrating that these bubble systems were unstable for gas storage. Therefore, to enhance gas storage stability, the bubble systems were converted into bubble hydrogels. The gas contents of SA, SA + α-CD, and SA + β-CD bubble hydrogels significantly decreased to 0.31, 0.23 and 0.18 mL/g_carrier, respectively. This phenomenon could be attributed to bubble rupture and coalescence induced by mechanical stress during gelation. Regarding storage stability, 70-80 % ethylene was retained in the bubble hydrogel systems at room temperature after 28 days storage, indicating that the hydrogel structure significantly improved gas-storage stability. This can be ascribed to the hydrogel film coating and the water layer around the surface of cavities. Therefore, the bubble hydrogel represents a promising encapsulation matrix for fruit ripening applications.