Pharmacognostic specification and rosmarinic acid content of mentha cordifolia leaves and stems in Thailand

Abstract

Mentha cordifolia Opiz ex Fresen. is one of the popular Thai kitchen herbs due to its unique aroma and benefits to human health such as helping to relieve colds, fever, motion sickness and poor digestion problems. This study aimed to specify the quality parameters of M. cordifolia dried leaves and stems with special reference to rosmarinic acid (RA) contents. The pharmacognostic specifications of leaf and stem crude drugs were investigated including microscopic cross-sectioning of leaf and stem as well as leaf constant numbers; physico-chemical contents i.e. acid-insoluble ash, total ash, loss on drying, moisture, extractive matters and volatile oil. The chemical constituents of the volatile oil were analyzed by GC/MS. TLC fingerprints of these crude drugs were demonstrated. The ethanolic extracts were prepared exhaustively using Soxhlet apparatus. RA quantitative analysis was made by reverse phased high performance liquid chromatography (RP-HPLC) using intentsil® ODS-3 column as stationary phase and methanol: 0.2% phosphoric acid (45% : 55%) as mobile phase. The results demonstrated the anatomical characters of leaf and stem cross-sections. The stomata (diacytic type) were found in upper and lower sides of leaf. The microscopic leaf constant numbers were found to be as follows: upper stomatal index 2.85 ± 0.64, upper trichome index 045 ± 0.44, upper oil gland index 3.09 ± 0.89, upper epidermal cell area 2128.64 ± 182.80 µm2, palisade ratio 4.63 ± 0.35; lower stomatal index 19.95 ± 2.65, lower trichome index 0.46 ± 0.33, lower oil gland index 5.97 ± 1.75 and lower epidermal cell area 1793.52 ±262.45 µm2. The physico-chemical specification demonstrated the contents of acid-insoluble ash, total ash, loss on drying and moisture in leaf should not be more than 1.98, 9.41, 7.06 and 10.50 % by weight respectively; the ethanol-soluble extractive matter, water-soluble extractive matter and volatile oil in leaf should not be less than 5.04, 15.23 and 0.36 % by weight respectively. The main chemical compound in the volatile oil was piperitenone oxide (73.22%). The specification contents of acid-insoluble ash, total ash, loss on drying and moisture in stem should not be more than 1.63, 8.41, 7.04, 10.01 % by weight respectively; the ethanol-soluble extractive matter and water-soluble extractive matter in stem should not be less than 5.20 and 16.60 % by weight respectively. RP-HPLC analysis revealed the RA content in leaf as 1.92 ± 1.26 and in stem as 0.99 ± 0.41 g/100 g by dry weight.