Dear Naveen Edirisinghe ;

the encapsulation efficiency determined based on the following formula:

EE (%)=100− ( P2∕P1 ×100)

where

P2 is the surface of phenolic compounds

P1 is theoretical total polyphenol content, as detailed in the following references;

• Incorporation of the nanoencapsulated polyphenolic extract of Ferula persica into soybean oil; Assessment of oil oxidative stability. https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC7300055&blobtype=pdf
• Robert, P., Gorena, T., Romero, N., Sepulveda, E., Chavez, J., & Saenz, C. (2010). Encapsulation of polyphenols and anthocyanins from pomegranate (Punica granatum) by spray drying. International Journal of Food Science and Technology, 45(7), 1386–1394.

Check your phenol contents before NPs formation in the formulation recipe ready for NPs to be prepared and dialyze/separate out your freshly prepared NPs from the to be formulated recipe you are using, and check your phenols contents of the extract, this will only tell the ratio of the phenol contents encapsulated if encapsulation of all the constituents of the extract follows similar, and hopefully equal proportions of encapsulation, you will have some idea! You are encapsulating an extract containing multiple constituents! Else, separate the prepared NPs, hydrolyze them, and quantitate the contents, if the quantitation technique correctly represents the extract's components, otherwise use a chemical marker which may be internal or an external marker added from outside and whose detection behavior is similar in pre and post encapsulation.