Effect of hydrogel:oleogel ratio on technological properties of vitamin D-loaded bigels

Vitamin D deficiency is a public health concern, highlighting the need for innovative delivery systems for food fortification [1]. Bigels, biphasic systems composed of a mixture of hydrogel and oleogel, have potential to protect and deliver lipophilic bioactive compounds [2]. This study aimed to develop vitamin D-loaded bigels and characterize their swelling capacity and liquid loss, which are important technological properties for evaluating their behavior as vitamin D delivery systems. Three bigel formulations were prepared by varying the hydrogel (H) and oleogel (O) ratios (70H:30O, 50H:50O, and 30H:70O, w/w). The oleogel phase consisted of soybean oil and glycerol monostearate (95:5, w/w), while the hydrogel phase was prepared with pea protein, NaCl, pectin, and water (15:2:2:81, w/w) [3]. Vitamin D was incorporated to provide 6,650 IU per 100 g of bigel during the homogenization of the oleogel into the hydrogel using an ultra-turrax disperser. Swelling capacity was determined by immersing the bigel samples in an aqueous medium for 120 min at 25 °C [4], and liquid loss analysis by filter paper capillary absorption over 24 h at 25 °C and 5 °C [5]. After 120 min, the control hydrogel completely disintegrated, whereas the control oleogel exhibited a swelling capacity of 22.6%. Among the bigels, the 50H:50O formulation showed the highest swelling capacity (50.8%), indicating that the balanced proportion between the two phases stabilized the system and prevented dissolution of the protein network while allowing water diffusion, which may contribute to the gradual release of vitamin D from the bigel matrix [6]. The 70H:30O and 30H:70O formulations exhibited swelling capacities of 10.6% and 29.1%, respectively. For liquid loss, both the hydrogel:oleogel ratio (p < 0.0001) and storage temperature (p < 0.0001) significantly affected the physical stability of bigels. Refrigeration reduced liquid loss in all samples, including the hydrogel and oleogel controls. The 70H:30O formulation showed the lowest liquid loss (7.1% at 25 °C and 3.5% at 5 °C), similar to the control hydrogel (2.7% at 5 °C), followed by the 50H:50O formulation (32.1% at 25 °C and 20.5% at 5 °C). The 30H:70O bigel exhibited the highest liquid loss (39.7% at 25 °C and 25.7% at 5 °C), a behavior likely associated with its higher oleogel content, which showed liquid loss similar to the control oleogel (38.3% at 25 °C). Therefore, considering both swelling capacity and liquid retention, the formulation with a 50:50 (w/w) hydrogel-to-oleogel ratio showed the best overall performance as a potential vitamin D delivery system.

Acknowledgments: The authors acknowledge CAPES [001] and FAPERJ [E-26/204.497/2025] for financial support and the Federal Fluminense University (UFF) for providing the infrastructure of the LABIOTEC.