Determination of the fate of vitamin D and E in the Pickering emulsions stabilized with microgel particles obtained by protein-polyphenol complexation during in vitro digestion

Although pickering emulsions stabilised by whey protein microgels are often associated with a low levels of lipid digestion properties and thus reduce caloric intake, it should be more acceptable that this is not the case for bioactive fat-soluble vitamins that may be used in such emulsions. A Pickering (o/w) emulsion was formed and stabilized by microgel obtained by thermal cross-linking of whey protein isolate (WPI) and polyphenol (tannic acid, TA; oxidized tannic acid, OTA) at 90 °C for 30 min. To determine the behaviour of vitamins during in vitro digestion, Pickering emulsions containing WPI microgels (1% protein in final emulsion) complexed with different amounts of TA and OTA (0.1, 1 and 3%) and flaxseed oil with fixed vitamin D and E content of 0.25% were prepared separately by ultrasonication. According to free fatty acid release (%), both vitamin D and vitamin E containing emulsions showed an increasing trend due to the increase in polyphenol concentration. Particle size and charge values were compared to evaluate the physical stability during the digestion process. All TA samples showed significant decrease in mean particle size after digestion. In contrast, this phenomenon was reversed after digestion in OTA-containing samples. There was a dramatic decrease in particle charges for both TA and OTA containing samples after digestion. The highest particle charge value before digestion (-46.6 mV) was found for the sample containing 3% OTA, while the lowest value after digestion was -24.4 mV. However, after digestion, it was shown that emulsions containing vitamin E reached bioaccessibility value of 88.18±2.35 % (for 3 % TA). For vitamin D, this value was found to be 76.37±3.42 %.
The results of the study show that pickering emulsions with high physical stability and higher bioaccessibility of fat-soluble vitamins pickering (o/w) emulsions can be successfully produced by utilizing stabilised protein-polyphenol microgels.