Plant Part and Extraction Temperature Affect Cilantro (Coriandrum sativum) Biomarker Compounds

This study was conducted to evaluate the influence of plant parts (flowering tops and basal leaves) and two extraction temperatures (60⁰C vs. 90⁰C) on total phenols (TP) and flavonoids (TF) contents, and a main biomarker compound in cilantro, quercetin.  Cilantro (cv. Slow Bolt) was grown as a fall/winter crop in Charleston, SC.  Four replicates, each replicate from at least 10 plants, were sampled in late October and separated into floral parts and basal leaves and kept at 0⁰C.  After 3 months of storage, all plant materials were air-dried at 32⁰C for 4 days and ground to a powder.  Each replicate powder was acid hydrolyzed to extract the phenolic compounds in 60⁰C or 90⁰C water bath for 2 hrs and the supernatants were collected after centrifugation. The supernatants were used to determine the TP and TF contents using colorimetric assays, and the quercetin content as aglycone using a HPLC.  The results showed that the choice of plant part significantly affected quercetin content and the temperature significantly affected all the variables measured.   Plant part had significantly interacted with temperature affecting quercetin contents.  Overall the flowering tops had greater TP, TF, and quercetin contents compared to the leaves, and extraction at 90⁰C temperature increased all the biomarker contents as compared to those of 60⁰C.  The TP, TF, and quercetin contents in flowering tops at 90⁰C were about 24 mg gallic acid equivalents (GAE), 92 mg quercetin equivalents (QE), and 0.31 mg quercetin per g dw powder, respectively.   The values for the flowering tops at 60⁰C were 18 mg GAE, 71 mg QE, and 0.061 mg quercetin per g dw powder, respectively. The greater biomarker contents in the flowering tops may be due to the accumulation of those compounds in forming seeds.  The higher temperature may have increased the acid hydrolysis of flavonoid glycosides into free aglycones.  In conclusion, these data indicated that plant part and the extraction temperature play a role in determining the biomarker contents present in cilantro.