Dielectric Roasting Induced Physical, Mechanical, and Grinding Characteristics of Black Pepper (Piper nigrum)

Abstract

The present study was focused on microwave (dielectric) roasting (300-600 W, 5-15 min) on the physical, textural, color, and grinding of black pepper. The microwave roasting is a volumetric heating that causes rapid removal of moisture, and internal pressure generated inside the seed tends to change the physiology and physical attributes. An increase in roasting power and time increased the geometric mean diameter (5.216 to 6.283 mm), sphericity (0.883 to 0.927), aspect ratio (0.853 to 0.914), and surface area (85.560 to 124.262 mm2) of black pepper. Whereas the significant ( $p<0.05$ ) reduction was observed in 100 grain weight (7.55 to 5.63 g), bulk density (500.97 to 251.38 kg/m3), fracturability (72.99 to 1.78 N), and hardness (63.65 to 1.61 N). Roasting led to browning, and a significant reduction was observed in the color parameters, $L^{\ast }$ (22.82 to 17.76), $a^{\ast }$ (2.47 to 0.56), and $b^{\ast }$ (2.41 to -0.75) with a significant ( $p<0.05$ ) increase in total color difference (0.96 to 5.30). Roasting also increased the particle size distribution in grounded power, and the mean particle size increased from 121.72 to 146.14 μm.