Optimization of spray drying conditions for production of Achillea millefolium extract powder

In this study, a spray drying process of yarrow (Achillea millefolium L.) liquid extracts was optimized by using the response surface methodology. The study aimed to determine the influence of temperature (120-195?C), liquid flow rate (3-16.5 cm3 min-1) and dry matter content in the liquid extract (0.3-1.5 %) on the yield of the drying process, the total polyphenols content and the antioxidant activity of the dry powder. Under the tested conditions the yield varied dramatically and ranged from 8 to 75%, while the effects on the polyphenol content and antioxidant activity were lower. The optimized conditions for the maximum antioxidant activity and maximal yield of the dried extract were as follows: temperature of 130?C, liquid flow rate of 7.5 cm3 min-1 and dry matter content of 1.2%. Under the optimal conditions, the yield was 66 %, while there was a slight decrease in the polyphenol content in the dried extract as compared to that in the liquid extract (145 mg of gallic acid equivalents [GAE] per g of the total dry matter vs. 152 mg GAE g-1, respectively). Consequently, antioxidant activity of the dry powder was only slightly reduced as compared to that of the liquid extract (DPPH neutralization was 58 vs. 64 %, respectively). The dried yarrow powder preserved its antimicrobial activity against pathogenic bacteria Staphylococcus aureus (MIC value of 10 mg cm-3) and Pseudomonas aeruginosa (MIC value of 20 mg cm-3).