Spouted bed dried rosmarinus officinalis extract: A novel approach for physicochemical properties and antioxidant activity

In this study, a conical-cylindrical spouted bed dryer with Teflon  beads as spouting material
was used for producing powdered rosemary (Rosmarinus o cinalis L.) extract. The influence of the
inlet drying gas temperature (Tgi) and the percentage ratio between the feed rate of concentrated
liquid extract by the maximum evaporation capacity of the spouted bed (Ws/Wmax) on selected
physicochemical properties of the finished products were investigated. Antioxidant properties of the
concentrated liquid extract and dried extracts were also evaluated by the 2.2-diphenyl-1-picrylhydrazyl
radical scavenging (DPPH•) and lipid peroxidation induced by Fe2+/citrate (LPO) methods; and
compared with the values obtained for a lyophilized extract (used as a control). Colloidal silicon
dioxide (Tixosil  333) and maltodextrin (DE 14) at a 2:1 ratio was added to the concentrated extract
before drying (4.4% w/w) to improve the drying performance. The drying variables Ws/Wmax and Tgi
have statistically significant influence on total polyphenols and total flavonoid contents of the dried
powders. The concentrated extract (on dry basis—being absolute solid content) showed superior
antioxidant activity (AA) compared to both the spouted bed dried and the lyophilized extracts;
exhibiting IC50 values of 0.96   0.02, 2.16   0.04 and 3.79   0.05 μg mL−1 (DPPH• method) and
0.22   0.01, 1.31  0.01 and 2.54   0.02 μg mL−1 (LPO method), respectively. These results of AA
are comparable to values obtained for quercetin, a flavonoid compound often used as a reference
standard due to its potent antioxidant activity; with IC50 of 1.17 μg mL−1 (DPPH•) and 0.22 μg mL−1
(LPO). However, the dried rosemary extracts are about 13.5 times more concentrated than the
initial concentrated extract (dry weight), with a concentration of total flavonoids and polyphenols
compounds ranging from 4.3 to 12.3 and from 1.2 to 4.7 times higher than the concentrated extract
values (wet basis). The AA per dry product mass was thus significantly higher than the values
measured for concentrated extractive solution, irrespective of some losses of AA apparently due to
the drying process.