Retention of β-carotene as a model substance for lipophilic phytochemicals during extrusion cooking

Incorporation of phytochemicals, such as lipophilic bioactives, into starch based food products via extrusion has become a very attractive process in the last decades. However during extrusion cooking, phytochemicals are exposed to high temperatures and high mechanical stresses accelerating oxygen or light induced as well as other chemical reactions or structural changes (i.e. isomerisation). In order to investigate processing losses due to the sensitivity of phytochemicals, oil-dispersed β-carotene as a model for lipophilic phytochemicals (e.g. carotenoids, tocopherols) was incorporated into an extrusion cooked cereal based product. Process induced stresses were varied by using different dosing points, screw speeds and barrel temperatures. An initial loss of about 30% β-carotene due to oxidative/thermal degradation was found for all process conditions investigated. Maximum retention was achieved, if the β-carotene was incorporated at the end of the extruder. Increasing the melt temperature from 135 °C to 170 °C didn't show any influence on the β-carotene retention. Increasing the screw speed from 300 to 500 1/min increased the retention significantly (P < 0.05) by about 25%. These results suggest that β-carotene losses are mainly affected by the generated mechanical stress in extrusion rather than by thermal stress.

► The β-carotene incorporated at the end of the extruder shows the maximum retention. ► Increasing the temperature (135-170 °C) shows no influence on the retention. ► Increasing the screw speed (300-500 min−1) increases the retention about 25%. ► The β-carotene losses are mainly driven by the generated mechanical stress.