Polyphenolic compound stability and antioxidant capacity of apple pomace in an extruded cereal

The effect of extrusion temperature and feed moisture content on the phenolic content of apple pomace was evaluated to obtain an extruded cereal high in antioxidants. Mixtures of oat flour, apple pomace and potato starch were conditioned at different moisture contents (23-29 g/100 g) and extruded at different temperatures (115-165 °C) in a single screw extruder. Total phenolic content, individual phenolic compounds, antioxidant activity and lipid oxidation index were determined in extruded products. Compared with the unprocess mixture, a retention between 79.9 and 97.1% of total phenolic content was observed whereas individual phenolic compounds were retained between 57 and 71% for chlorogenic acid, 55-64% for caffeic acid, 38-51% for p-coumaric acid, 25-28% for ferulic acid, 56-70% for rutin, and 46-76% for phloridzin. Most of the individual phenolic compounds showed higher stability at 140 °C with intermediate feed moisture content. Antioxidant activity of the extruded products did not show significant changes compared to the unprocessed mixture. Thus, despite the use of high temperatures in the extrusion-cooking it is possible to minimize the loss of bioactive compounds to achieve products, such as ready-to-eat cereals, that contain important antioxidant capacities.