Harvesting and Drying Effect On Oil Yield and Composition of Four Mint Genotypes Grown In Mississippi

A field experiment was conducted in Mississippi to evaluate the effect of harvest time and drying on biomass yields and oil composition of peppermint (Mentha X  piperita L. ‘Black Mitchum’ and ‘B-90-9’), Japanese mint  (Mentha arvensis L. ‘Arvensis 2’ and ‘Arvensis 3’), Scotch spearmint (Mentha gracilis L. ‘Scotch’), and Native spearmint (Mentha spicata L. ‘Native’).  Drying of peppermint biomass prior to oil extraction tended to increase the concentration of (-)–menthol in ‘Black Mitchum’ but not in ‘B-90-9’.  Drying of ‘Black Mitcham’ increased (-)-menthone and eucalyptol concentration in the oil in harvest 5, whereas drying of ‘B-90-9’ increased only eualyptol in harvest 3.  The concentration of (-)–menthol in ‘Black Mitchum’ increased slightly until harvest 3, 4, and 5, and then slightly decreased in harvest 6.  In ‘B-90-9’, (-)–menthol concentration in freshly distilled biomass was lower in harvest 1 and higher in the other harvests. The concentration of (-)–menthone in both cultivars of peppermint was highest during harvest 1 and decreased with every subsequent harvest time to reach the lowest values in harvest 6.  In Japenese mint, (-)-menthol concentration in freshly distilled oil of Arvensis 2 tended to increase with later harvest dates.  However, this trend was not apparent in ‘Arvensis 3’or in dry distilled ‘Arvensis 2’.  Drying of Japanese mint biomass did not significantly alter (-)-menthol concentration in either cultivar.  Drying of Scotch spearmint biomass before extraction reduced (-)-carvone only in harvest 3 and did not change it in other harvesting times.  Also, drying reduced the concentration of (R)-(+)-limonene in harvests 1 and 2 but increased it in harvest 6. In most instances, harvesting time did not alter the concentration of carvone. In native spearmint fresh biomass, (-)-carvone concentration was lowest in harvest 4 and higher in the oils from the other harvests.  Harvesting time did not significantly affect carvone concentration in the oil from the dried biomass.  Generally, (R)-(+)-limonene concentration in native spearmint oil was high in harvest 1, then decreased in harvest 2 and 3 and then tended to increase again.  Drying of the biomass before extraction of the essential oil did not affect (R)-(+)-limonene concentration. Our results indicate that the four mint species could grown in Mississippi and could provide relatively good yields and oil composition comparable to the values reported in the literature.  Hence, these mints may be viable crop alternatives for Mississippi and the Southeastern USA.