Impact of drying and micronization on the physicochemical properties and antioxidant activities of celery stalk

BACKGROUND: The influence of convective drying and ball-mill treatment of celery stalk on particle size distribution, physicochemical properties, bioactive compounds and antioxidant activities were analyzed in this study. RESULTS: Ball-milling of celery stalk dried at temperatures of 50, 75 and 100 °C resulted in decreased average particle sizes of 48.8, 10.5 and 7.2 µm, respectively. Bulk density was increased with reduced particle size. Darker (L*) and reddish (a*) powders were formed at higher temperatures, while ball-milling increased greenness (-a*) of powders dried at 50 and 75 °C. Total content of phenol compounds increased with increasing temperature. 2,2-Diphenyl-1-picrylhydrazyl radical scavenging activity and reducing power were affected by ball-milling for 24 h and drying at elevated temperatures. Iron chelating ability was unaffected by increasing temperature or reduced particle size. CONCLUSION: Increasing drying temperatures not only decreased the average particle size of powders, but also increasingly reduced particle size after ball-milling. Micronization of celery stalk dried at the highest temperature had the best antioxidant activities. Drying and ball-milling were not highly deleterious to the major phenolic structures.