Effect of extrusion cooking process parameters on the retention of bilberry anthocyanins in starch based food

• Anthocyanin retention during extrusion cooking depends on barrel temperature, moisture content, screw speed and flow rate.
• Improved anthocyanin retention at high screw speed and increased flow rate.
• Lower activation energy of anthocyanins degradation during extrusion than in batch heating.
• Total phenolics and antioxidant activity not affected by heating method.
• Extruded samples show a long-term stability of anthocyanins.

The aim of this research was to investigate the influence of extrusion cooking on the retention of bilberry bioactives. Maize starch was mixed with 2% of bilberry extract and extruded using a twin screw extruder. The effects of screw speed (180–720 1/min), moisture content (18–28%, wet base) and barrel temperature (100–160 °C) on the retention of anthocyanins, total phenolics and antioxidant activity in extruded samples were investigated. While total phenolics and antioxidant activity were unaffected by extrusion cooking, anthocyanin retention was depending on barrel temperature, moisture content, screw speed and flow rate. The highest retention was observed at the lowest barrel temperature (100 °C, c/c0 = 0.82), the highest moisture content (28%, c/c0 = 0.90), the lowest screw speed (180 1/min, c/c0 = 0.75) and the highest flow rate (30 kg/h at 360 1/min, c/c0 = 0.77), respectively. Even at the highest screw speed of 720 1/min investigated, the anthocyanin retention could be enhanced by increasing the flow rate. The addition of a flow channel extended the exposure time and decreased anthocyanin retention. A comparison between offline heating of bilberry extract solutions and extrusion cooking indicated that the rate constant of anthocyanin degradation depends on moisture content and interactions with mechanical energy. Extruded samples showed a high retention of color and anthocyanins up to 82% even after 40 months of storage. Extrusion cooking offers thus the chance to produce products rich in total phenolics and antioxidants while anthocyanins retention can be adjusted.