ISOMERISATION AND STABILITY OF LUTEIN AND BETA CAROTENE ENCAPSULATED IN FREEZE-DRIED TREHALOSE

Bioavailability and retinol (vitamin A) activity equivalent of β-carotene depend on its state and isomeric form. β-carotene and lutein exist in several isomeric forms and amorphous and crystalline states. We investigated lutein and β-carotene stability in freeze-dried materials prepared using whey proteins (WPI) as an amphiphilic emulsifier with or without gum Arabic, a polyelectrolyte used to form a double-layered oil-water interface with WPI at pH 3.5 (LBL emulsion). An emulsion with 50:1 sunflower oil:WPI with 0.1% of dissolved carotenoids in oil (β-carotene:lutein, 1:1) and 1:4 oil:water ratio was produced using a two-stage high pressure homogenizer at 240 bar (200 and 40 Bar) for three cycles. This emulsion was diluted to 1:9 oil:water ratio using a trehalose solution to achieve 20% (w/w) trehalose in the aqueous phase. Citric acid (10% w/w in water) was added until pH 3.5. The LBL emulsion contained 1:100 of 0.5% (w/w) aqueous solution of gum Arabic. Emulsions were freeze-dried in glass vials, water activity was adjusted at 0.33a_w, and samples were stored at 25, 37 and 45°C prior to a_w, colour and carotenoids analyses. Carotenoids in 0.5g of solids were extracted using 2 ml water, 3.9 ml ethylacetate:methanol (50:50 with 0.2% BHT), 1 ml of 2 mol KOH in methanol, 1ml dichoromethane and 3.8 ml of hexane, and 10 μL injections of the organic phase were analysed using HPLC with a C30 analytical column. An eluent gradient used acetonitrile, methanol:ethyl acetate (1:1) and 0.5% acetic acid in water and carotenoids were detected at 450 nm using a photodiode-array detector. A rapid isomerization and decrease of the initial lutein and β-carotene occurred at all temperatures. The total carotenoids decreased during storage, but the loss of carotenoids was significantly increased above the glass transition of trehalose. There were no significant differences in the carotenoids stability at the individual storage temperatures. The results indicated the significance of isomerisation of dissolved carotenoids and concomitant matrix and temperature dependent loss during storage of food materials.