3.6. Leaching Study
A leaching test was performed to assess the physical stability of the
bigel formulations (Table 2). It was found that for all formulations,
the amount of liquid lost remained below 10% with greater than 90% of
leached liquid coming from the aqueous phase. In NMR T2-relaxation, the
aqueous phase was found to have a more mobile population than the lipid
phase. The observation that the aqueous phase accounts for most of the
liquid leached from the system, is consistent with the fact that the
aqueous phase is more mobile within the bigel and, therefore, water
tends to percolate more than the oil from the bigel matrix. Data from
the leaching study also found that formulations with the highest
concentrations of MDG had a significantly lower amount of overall liquid
leached from the matrix. Specifically, the amount of water that leached
from the system reduced by 34% and 23% when comparing the highest and
lowest MDG concentrations for OG:HG ratios 60:40 and 70:30,
respectively. This may be the result of MDG interacting with the
aqueous-lipid interface or the co-crystallization of MDG preventing the
movement/leaching of water from the matrix. Additional studies are
needed to confirm which mechanism is at work in the system. Although
texture analysis showed a decrease in hardness, this does not
necessarily correspond to a loss of physical stability.
4. Conclusion
The effect of mono-diglycerides (MDG) on a rice bran wax oleogel –
gelatin hydrogel biphasic system was explored to improve its physical
stability and tailor its mechanical and textural properties. MDG had the
most significant impact on the 60:40 OG:HG bigel formulations, where
CSLM images confirmed a phase inversion from oleogel-in-hydrogel to
hydrogel-in-oleogel at 3% (w/w) MDG. These microstructural changes were
reflected in FTIR to show that as the MDG concentration increased, the
interactions within the oleogel phase increased and the interactions
within the hydrogel decreased. The textural hardness of the bigel
formulations also significantly decreased with the increase of MDG
concentration while maintaining greater physical stability. Through the
available evidence, it appears MDG serves as both a lipid modifier and
emulsifier in this biphasic system and can be used to both tailor the
mechanical properties and increase physical stability.