Effect of pretreatments and drying conditions on drying rate and colour retention of basil (ocimum basilicum)

Abstract

The effects of steam blanching, surfactant pretreatment and drying conditions on the drying rate and on the chlorophyll and colour retention of air-dried basil were studied. Colour was monitored by recording the L*, a*, b*values. Chlorophyll and pheophytin levels were assayed by HPLC. Temperature was the main factor in controlling the rate of drying. The influence of air velocity and air humidity were less pronounced and significant only at the beginning of the drying period. Steam blanching and surfactant pretreaments increased drying rates by a factor of 10 and 14, respectively. Both pretreatments resulted in a better retention of the overall green colour of the basil leaves. Higher chlorophyll retention confirmed the protective effect of steam blanching. In order not to impair quality, low air drying temperatures were necessary for non pretreated samples while high air drying temperatures were acceptable for steam blanched and surfactant pretreated samples. © 1993 Academic Press, Inc.