Physiological postharvest response of peppermint (Mentha x piperita L.) herbs

Freshly harvested peppermint herbs (Mentha x piperita L.) have a considerable respiration rate according to 552+/-155 W t(-1) [watts ton(-1)] at 10degreesC, 1181+/-325 W t(-1) at 20degreesC and 2209+/-523 W t(-1) at 30degreesC, on average of 6 trials. This respiration rate showed a clear senescence-related decline immediately after harvest in accordance with the course of the regression function (y) over cap = alpha + beta . e(c(x-z)) (c < 0; x = storage time in hrs). During 80 hrs of storage the senescense-caused decrease reached 60.1% of its initial rate at 10 degrees C, 51.1% at 20 degrees C and 44.4% at 30 degrees C, respectively. The consequence of the metabolism on the loss of fresh weight, dry matter and external quality traits were quantified for temperature levels of 10, 20 and 30 degrees C, respectively. With consideration of the changes in mass by respiration and transpiration, the calculated balanced content of essential oil increased - especially in the second cut of the plants - by 7.77 %/24 hrs. The single essential oil components underwent the following typical changes, also estimated and calculated on the basis of balance calculation: Decreases were recorded for menthone (first cut) by -3.76 %/24h, for pulegone (first cut) by -4.05 %/24 h and for carvone by -3.95 %/24 h. Increases occurred with menthol by +10.21 %/24 h, menthofuran by +9.06 %/24 h, menthylacetate by +23.05 %/24 h, isomenthone (2(nd) cut) by +4.61 %/24 h and cineole by 0.83 %/24 h. No clear response could be found for limonene. These increases can be explained by a biosynthesis of the components during the post-harvest period. The best maintaining of external quality traits could be found by storing the harvested plant material at 10 degrees C.