Stability and loss kinetics of lutein and β-carotene encapsulated in freeze-dried emulsions with layered interface and trehalose as glass former

- Freeze dried single-layer (SL) and layer-by-layer (LBL) systems were prepared.
- Systems were stored below, around and above glass transition temperature.
- Stability and loss kinetics of carotenoids in dehydrated emulsions were examined.
- Loss of lutein and all-trans-β-carotene followed first order kinetics.
- LBL showed slower carotenoid losses during storage compared to SL.

Dehydration and subsequent storage of food materials may result in physicochemical changes and losses of bioactive substances. The purpose of the present study was to determine the stability and loss kinetics of carotenoids in dehydrated emulsions, and to compare the ability of freeze dried single-layer (SL) and layer-by-layer (LBL) emulsions with trehalose as wall material to protect the carotenoids. WPI (2%, w/w, in oil) was used as an emulsifier and homogenised with sunflower oil containing β-carotene (0.05%, w/w) and lutein (0.05%, w/w). Gum Arabic was added to obtain LBL emulsion. Trehalose (20%, w/w) was used as the wall material. Citric acid solution (10%, w/w) was used to adjust the pH of emulsions to pH 3.5. The emulsions were then freeze-dried, humidified at 33% RH, stored at low oxygen (25 °C, 37 °C and 45 °C) in closed containers, and analysed using HPLC with C30 column and photodiode-array detector. The loss of lutein and all-trans-β-carotene followed first order kinetics and was more rapid in the SL system compared to the LBL system. Carotenoid losses increased with increasing storage temperatures especially in the SL systems. The activation energy of all-trans-β-carotene in SL was 62.1 kJ/mol compared to 43.9 kJ/mol in LBL and 58.9 kJ/mol in SL compared to LBL with 45.9 kJ/mol for lutein. The total β-carotene retention upon storage for 70 days was higher in LBL at all storage temperatures. However, the utilisation of LBL increased isomerisation. LBL gave better protection towards carotenoid losses during storage and is highly applicable to formulated materials to control the stability of oil soluble bioactive components.