Warburg's method as a simple tool for measuring oxygen uptake in spray-dried emulsions

Lipid oxidation is usually responsible for oil downgrading of spray-dried powders and it is strongly dependent on the storage conditions. Direct measurements of the oxygen uptake using cost-effective methods combined with the study of water adsorption of the powders allow evaluating their barrier properties against oxidation. Therefore, a low-cost and simple apparatus based on the Warburg's manometric technique was built, and its results were compared to Rancimat and Oxipres methods. Firstly, free unsaturated oil (fish oil) was evaluated and data showed a strong positive correlation between the oxygen uptakes for the new apparatus (0.015 mL O-2/h) and Oxipres method (Pearson's coefficient = 0.97). After, different surface-active compounds (SAC) (whey protein isolate - WPI, gelatin - GE, or modified starch - MS) mixed to maltodextrin (MD) were used to encapsulate the fish oil via spray drying. The lowest oxygen uptake was obtained by MD + WPI (0.0018 mL O-2/h), followed by MD + GE (0.0103 mL O-2/h) and MD + MS (0.0291 mL O-2/h), with similar behavior obtained by Rancimat method. The lowest protective barrier of MD + MS-powders was confirmed by the comparatively higher susceptibility to water adsorption, and consequently the lower glass transition temperature (similar to 58.7 degrees C at water activity = 0.3 - 0.4). This study presented a successful creation of an apparatus to provide useful, fast and effective information about oxygen consumption by fish oil and encapsulated fish oil, allowing the understanding of the protection of SAC against oxidation in spray-dried emulsions. The proposed apparatus can be easily implemented in laboratories, with potential application for other oxygen-sensitive products.