Thermal and Mechanical Effects on Retention of Food-Grade β-carotene during Extrusion Processing

To determine the separate thermal effects of extrusion, nonisothermal experiments were conducted by heating wheat flour mixed with 0.46% (w/w) food-grade beta-carotene in an oil bath nonisothermally at 149 degrees C at 28% (w/w) moisture content. To determine the total (thermal plus mechanical) effects of extrusion on retention of trans-beta-carotene, the same mixture was extruded at 30/50/70/90/110 degrees C and 50/70/90/110/130 degrees C (barrel temperatures feed to exit) at screw speeds of 200, 250, 300, and 400 rpm on two separate days with a dough moisture content 30% (w/w). The rate constant at 100 degrees C, 3.56 x 10(-4)s(-1), and activation energy, 18.82 kJ/gmol, obtained from the nonisothermal experiments were used to calculate trans-beta-carotene retention due to thermal effects during extrusion. For both temperature profiles, total trans-beta-carotene retention ranged from 58-97%. Thermal effects accounted for le than 5% of the lo, showing that mechanical effects were the predominant cause of trans-beta-carotene degradation. A linear statistical model worked well for separate days of extrusion; however, an exponential model was more effective for combined days of extrusion. Overall, food-grade beta-carotene was more stable than that of pure trans-beta-carotene.