In this study, sea buckthorn polyphenols (SBP) were successfully nano-encapsulated in casein and whey proteins via nano-emulsification in order to improve their bioactivity upon simulated gastro-intestinal digestion. Encapsulation efficiency of 69 % and 75 % were observed for CPM and WPM nanoparticles, respectively. FESEM images revealed spherical particles with some cavities where sea buckthorn polyphenols were embedded. Based on FTIR and FESEM results, SBP appeared to be protected inside the nanoparticles. The results of DLS showed that CPM and WPM nanoparticles had narrow dispersibility and thus more uniformity in particle size. DSC results revealed decreased thermal stability of nanoparticles. SDS-PAGE revealed very lighter peptide bands in CPM and WPM after in vitro digestion, suggesting their improved digestibility as compared to the control proteins. Bioactivity retention of nanoparticles and free SBP upon simulated digestion was accessed in terms of antioxidant, antidiabetic and antiobesity and anticancerous activities. Results revealed high bioactivity in CPM and WPM compared to free SBP. These findings provide new insights into bioactivity 6 enhancement of polyphenols upon gastro intestinal digestion, thereby confirming that the casein and whey protein nanoparticles can act as an effective oral delivery vehicle for sea buckthorn polyphenols. In the second part of study, cow milk was fortified with WPM nanocapsules (sea buckthorn polyphenols encapsulated in whey protein) for the development of functional milk powders. The developed functional milk powders were studied for techno-functional, structural and nutraceutical properties. All the milk powder samples exhibited less than 6 % moisture content which guarantees their better stability and prolonged shelf life. Rehydration indices of developed functional milk powders were measured in terms of solubility and dispersibility index. The functional milk powders presented ˃ 95% solubility, thus incorporation of encapsulated polyphenols in milk does not affect its solubility. The functional milk powders obtained presented higher dispersibility values (> 95%) indicating their good dispersibility. However fortification of milk with 1.5% WPM (M5) showed only 89.97 % dispersibility index which was due to the slight clumping of particles. Differential scanning calorimetry (DSC) showed that the thermal properties of functional milk powders were almost similar to that of the control milk powder which might be due to the fact that the sea buckthorn polyphenols were used in encapsulated form. This prevented their interaction with other milk constituents, which could have otherwise affected the thermal properties. Chemical structure of functional milk powders was characterized by ATR-FTIR which showed the presence of polyphenolic compounds in milk powders. Bioactivity retention of functional milk powders upon simulated digestion was accessed in terms of antioxidant, antidiabetic and antiobesity and anticancer activities. Functional milk powders showed significantly high (p≤0.05) antioxidant, antidiabetic and antiobesity activities as compared to the control milk powder after in vitro digestion. Moreover, significant reduction (p ≤ 0.05) in cell viability (%) of HEPG2 cancer cell lines was seen upon treatment with functional milk powder samples. Therefore, retention of bioactivity in simulated gastrointestinal conditions indicates that sea buckthorn polyphenols loaded nanoparticles (WPM) prepared in this study can be used for development of functional milk products.