Stability of α-tocopherol in amorphous freeze-dried carbohydrate-protein systems

Encapsulation of sensitive compounds in amorphous, glassy wall materials may protect them from environmental factors causing their loss during storage of food ingredients and foods. The stability of αtocopherol (2.5%, w/w, based on non-fat solids) in freeze-dried lactose-milk protein isolate-olive oil (3:1:2), lactose-soy protein isolate-olive oil (3:1:2), trehalose-milk protein isolate-olive oil (3:1:2), and trehalose-soy protein isolate-olive oil (3:1:2) systems was studied. The oil-in-water emulsions were prepared and freezedrying was carried out at <0.1 mbar for >48 h. The particle size distribution of fresh emulsions, thawed emulsions, and reconstituted materials were analyzed by laser diffraction. The encapsulation efficiency of the freeze-dried materials (encapsulated oil divided by total oil) and the glass transition in these dehydrated systems, Tg, were measured using differential scanning calorimetry (DSC). The retention of α-tocopherol in dehydrated materials at various temperatures (20, 30, 37, 45, and 60 oC) over time was measured spectrophotometrically. The reconstituted materials showed different droplet size distributions compared with the fresh and thawed emulsions, suggesting oil migration in the dehydrated matrices. The anhydrous Tg in dehydrated systems ranged from 101 to 116 oC. Approximately 82% of the retained α-tocopherol was encapsulated in trehalose-soy protein isolate-olive oil system while about 68% was encapsulated by the lactose-milk protein isolate-olive oil system. About 80% of α-tocopherol was retained in trehalose-soy protein isolate-olive oil system after 10 d of storage at temperatures from 20 to 60 oC but no temperaturedependence was observed. At 60 oC, milk protein isolate-containing systems showed better protection of αtocopherol than soy protein isolate-containing systems during 40 d storage. Better encapsulation efficiency in soy protein isolate-containing systems did not result in better stability of α-tocopherol.The stability of αtocopherol in dehydrated systems had little difference depending on the components of the matrices. The glassy wall matrices, however, protected α-tocopherol at elevated temperatures.