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Freshly harvested Common Saint-John's wort, variety “Topaz” has a relatively high rate of respiration, which is clearly influenced by the crop temperature at the time of harvest. In an average of six experiments, the rate reached 670±69.7 W t −1 at 10 °C, 1744±234 W t −1 at 20 °C and 3371±398 W t −1 at 30 °C. The Q 10 was estimated to be 2.60 over the range 10–20 °C and 1.93 over the range 20–30 °C. The senescence-related decrease depended on storage time according to a function with a declining negative exponent. The mean decrease in respiration rate over an 80 h postharvest period relative to the baseline value at the time of harvest was 39.9% at 10 °C, 45.5% at 20 °C and 50.4% at 30 °C. The rate of respiration influenced the transpiration rate noticeably and led to high losses in fresh weight (2.18%/24 h) and dry matter (1.44%/24 h on a dry basis) at 10 °C. Exterior quality of the stored plants was well maintained for 70 h at ≈10 °C. Levels of the principal therapeutic ingredients, hypericin and flavonoids, calculated on balance trials, remained generally stable over the 80 h postharvest period at the temperatures examined, except that physiologically young plants (first year of cultivation, first cut) showed a pre-mortal increase caused by new synthesis, which reached 88% in some cases during 80 h of postharvest time. In practical terms, for quality to be maintained, it is essential to ensure effective ventilation and cooling after harvesting. |
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