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A study of some factors affecting the yield and composition of peppermint oil (mentha piperita L.)

Clark, Robert John 1981 , 'A study of some factors affecting the yield and composition of peppermint oil (mentha piperita L.)', PhD thesis, University of Tasmania.

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This study attempted to define some of the factors or groups of
factors which together determine the yield and composition of
peppermint oil. By investigating the effect of these factors on
plants under glasshouse-growth room conditions, an attempt was made
to understand the factors influencing oil yield and composition
under field conditions. The manipulation of the field situation to
increase oil yield without adversely affecting oil composition was
The oil content of peppermint leaves increased from basal to
midstem leaves and decreased from midstem to apical leaves. Oil
accumulation corresponded to the period of leaf expansion, during
which glandular trichomes were observed to fill with oil. Midstem
leaves accumulated maximum amounts of oil at the time inflorescences
were observed on plants growing under long day-low night temperature
(LD x LNT) conditions. Basal and apical leaves reached their maximum
oil content prior to and following the appearance of inflorescences,
respectively. Oil accumulation was favoured by LD x LNT conditions
relative to SD x HNT (short day-high night temperature) conditions.
The decreased oil accumulation under SD x HNT conditions did not appear
to be associated with a deficiency of photosynthate, since oil
maturation occurred to the same extent under both LD x LNT and SD x HNT
conditions. The results presented support previous reports of a true photoperiodic
effect on dry matter, oil yield, growth habit and flowering.
Furthermore, it appeared that there exists a true photoperiodic effect
on the monoterpene composition of peppermint oil. Day length, night temperature, day temperature and light intensity were also important
interacting factors determining oil yield and composition, under
glasshouse-growth room conditions. The photosynthate model proposed
by Burbott and Loomis (1967) explained the effect of environmental
factors with respect to pulegone, menthone and menthofuran. Factors
favouring the maintenance of high levels of photosynthate resulted in
high concentrations of menthone and low concentrations of pulegone and
menthofuran. The photosynthate model did not explain the effect of
environmental factors on several other monoterpenes of peppermint oil.
An investigation of the net CO 2 exchange characteristics of
peppermint indicated that light saturation occurred between 400 and
500 pEM- 2s -1 in attached fully expanded leaves of peppermint. Maximum
rates of 'apparent' photosynthesis occurred at 20°C. The important
determinants of 'apparent' photosynthesis were an increase in 'true'
photosynthesis when temperature was increased to 25° C, a steady
increase in dark respiration with increased temperature, and a rapid
increase in photorespiration between 15 ° C and 30°C. Such net CO 2
exchange characteristics of peppermint support the photosynthate model
proposed to explain environmental effects on oil composition.
With respect to the field situation in Tasmania, provided that
areas with reasonably high plant densities were considered, oil yield
per unit area reached a maximum early in the growing season. Oil yield
per unit area remained at the maximum level for a considerable period
(5 to 6 weeks) with the only significant change being a final decrease
in yield towards the end of the growing season. During the period of
maximum otl yield the percentage menthol increased from approximately
40% to 45%. Delaying harvest once the percentage menthol reached the
required 45%, resulted in further increases in the percentage menthol,
but at the expense of increased percentage menthofuran and decreased
oil yields. In addition to the above study of harvest date, the relationship
between nitrogen application and irrigation rate and timing, on the
yield and composition of peppermint oil and the possibility of obtaining
two harvests of peppermint in one season, were investigated. High
yields of oil were associated with high applications of nitrogen and
high levels of irrigation, particularly throughout the last half of
the growing season. The composition of oil extracted from herb at the
commercial harvest date (approximately 45% menthol) was not significantly
affected by either nitrogen or irrigation treatments. The oil yield
from regrowth within the same growing season was significantly affected
by irrigation and nitrogen treatments applied prior to the first
harvest. When 300kg N/ha and 50mm of irrigation weekly (during the
last half of the growing season) were applied, the oil yields from
regrowth approached the yield normally obtained at the commercial
harvest date. Oil from regrowth contained high concentrations of
menthol, menthyl acetate, menthofuran and limonene, and low
concentrations of menthone and cineole, relative to peppermint oil
typical of Tasmanian production areas. In a subsequent trial involving the manipulation of harvest date,
nitrogen and irrigation, the first harvest was timed to coincide with
maximum oil yield per unit area (40% menthol) and the second harvest
occurred when the concentration of menthol exceeded 50%. In this way
the total yield of oil per unit area was increased significantly
without adversely affecting oil quality. By comparing the composition
and yield potential of peppermint oil under Tasmanian conditions with
that reported for other world production areas, it is concluded that
Tasmania is well suited to the production of high yields of high
quality peppermint oil.

Item Type: Thesis - PhD
Authors/Creators:Clark, Robert John
Copyright Holders: The Author
Copyright Information:

Copyright [Published Date as found in Millennium record] the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1981. Bibliography: l. 263-274

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