Evaporation of Spearmint (Mentha spicata var. viridis L.) Herb Oil during One Year of Storage under Semi-Arid Condition
El Rasheed Ahmed Salim1*, Abu-Bakr Ali Abu-Goukh2, Hassan El-Subiki Khalid3 and Gaffar Mohamed El
1Food Industry Institute, Industrial Research & Consultancy Centre, Ministry of Industry, Sudan
2Department of Horticulture, Faculty of Agriculture, University of Khartoum, Sudan
3Medicinal and Aromatic Plants Institute, National Centre for Research, MOST, Sudan
Submission: October 06, 2016; Published: October 24, 2016
*Corresponding author: El Rasheed Ahmed Salim, Food Industry Institute, Industrial Research & Consultancy Centre, Ministry of Industry, Khartoum North, Sudan.
How to cite this article: El Rasheed A S, Abu-Bakr A A-G, Hassan El-S K, Gaffar M El H. Evaporation of Spearmint (Mentha spicata var. viridis L.) Herb Oil during One Year of Storage under Semi-Arid Condition. Agri Res & Tech: Open Access J. 2016; 2(4): 555594. DOI: 10.19080/ARTOAJ.2016.02.555594
The experiment investigated evaporation of essential oil of stored spearmint herb under ambient temperature during one year of storage, in Sudan semi-arid conditions to study oil content per year months, seasons and evaporation rate. Spearmint herb samples were dried under shade for seven days and kept in polyethylene bags and stored at ambient room temperature. Spearmint oil was extracted by water distillation using the technique of British Pharmacopoeia; the oil determined initially after seven days of drying before storage and then every month for 12 months. Losses of oils under Sudan semi-arid seasons recorded and the rate of evaporation calculated with respect to changes per month. The results showed that the essential oil content progressively decreased during storage of spearmint herbs from 1.3 ml/100g initially and end by 0.1 ml/100 g after 12 months of storage. The oil content rate show a decreased by 0.1 ml/100 g every month during the first five months (January-May) of winter season; then decreased by 0.2 ml/100 g per month during hot summer (May-June); and negligible decease during rainy autumn season (July-August), after which the oil decreased by 0.1 at late hot dry summer (September – October) and the experiment end by a decreased of 0.05 ml/100g every month during the last storage period at beginning of winter (November -December).
Spearmint (Mentha spicata) is considered as one of the most important and valuable source of essential oils. The highest growth and yield can be obtained from 20 cm spacing . Early morning harvest yielded high oil content , from fresh leaves to yield good oil physic-chemicals . And 40°C air-forced oven drying temperature is the best for high oil Carvone content . The fresh and dried leaves are used as spice, flavoring agent and in folk medicine [5,6]. The oil is used in pharmaceutical, antiseptic, perfumery and food industries [5,7,8]. The major commercial form of spearmint is still the shelf-stable dried product, since it can be transported easily and stored well under proper conditions , Oil extracted during the first months of storage contain high Carvone content . It can result in loss of essential oils, changes in color and texture and decrease in nutritive value [11,12]. Storage leads to gradual evaporation of essential oil from stored herbs, the major source of loss being
due to oxidation and resinification of the essential oils  which can be recovered by not more than two redistillation process . Therefore, investigating the effect of storage on oil content and composition under Sudan conditions is recommended. The objectives of this study were to evaluate the effect of storage period of spearmint herb on oil content per month during a year, oil content reduction during different seasons and evaporation rate of essential oil from stored herb.
Field experiment was conducted at ‘Halfaya’ area and storage at Shambat, Khartoum North, Sudan (15° 40/ N, 32° 22/E). The climate was a semi – arid, tropical, with seasonal annual rainfall
of 120 mm during the period mainly between July to September.
The mean maximum and minimum temperatures are as high
as 47.5 °C during summer (March – June) and as low as 7.5 °C
during winter (Nov – Feb) . The soil was an alluvial type
with high content of silt; slightly alkaline. Land preparation and
cultural practices were carried out as recommended. The land
was divided into 48 plots of 4.5 X 6 mm each and 30 x 30 cm
spacing. At harvested the whole plot was covered with spearmint
aerial herb (stem and leaves) due to spread of underground
runners, which gives good aerial shots at rhizome’s nodes.
Spearmint (Mentha spicata var. Viridis) plants were raised
from underground runners (rhizome-like rootstock). They were
obtained from fully mature plants grown in spearmint growing
area at ‘Halfaya’, Khartoum North, Sudan. The underground
and surface runners were transplanted into new well prepared
beds. Pre-transplanting irrigation was applied followed by the
first irrigation immediately after transplanting. Irrigation was
carried out every 7 during the experiment period.
The samples were arranged in a completely randomized
design of 12 treatments and four replicates. The treatments were
namely: M0, M1, M2, M3, M4, M5 M6 M7 M8 M9 M10 M11 and
M12; (where M: mean month, M0 at the beginnings, M1 for the
end of January harvest till M12 that mean the end of December).
About two kilograms of herb; during each harvest from well
established 60 days plants; were harvested. The aerial parts
of the plants (main aerial stem, branches and leaves) were cut
about 5 cm above the ground level. Foreign materials and weeds
were removed immediately from the harvested material.
The aerial parts of cut plants (main aerial stem, branches
and leaves) were kept for further investigations. The herb was
subjected to open shade air drying for seven days. Foreign
materials and weeds were removed immediately from the
harvested materials. The dried herb samples were kept in
polyethylene bags and stored at ambient room temperature
at Shambat area, Khartoum North, Sudan. Samples were taken
every month for oil determination.
Spearmint oil content was 1.3 ml/100g dry weight before
storage (Figure 1); this agrees with reports that mentioned mint
oil content is in the range of 0.75 - 2.00 ml/100g dry weight
[18,19]. Oil content progressively decreased during storage of
spearmint herbs at ambient conditions from 1.3 ml/100g initially,
oil content decreased with successive significant decrease and
end by 0.1 ml/100 g after 12 months of storage. Because drying
decreases oil content on dry weight basis significantly in contrast
to the highest oil in the fresh harvested herb . Also agree with
Ram et al. who reported that drying and storage of herbage of
rose – scented geranium (Pelargonium sp.) for five days prior
to distillation significantly reduced the essential oil recovery as
well as oil quality .
The decrease in oil content during storage of plant material
at ambient conditions was also well demonstrated in medicinal
plants such as; mint , caraway (Carum carvi L.) , French
tarragon (Artemisia dracunculus L.) leaves , black, green and
white pepper (Piper nigrum L.) , lavender flower (Lavandula
intermedia) and funnel fruits (Foeniculi fructus) .
Seasonal effect of Sudan semi-arid climate Appendix 1-3
condition on spearmint herb was illustrated in Figure 2, the
result showed that slight decreasing in the curve of losing
during winter from 1st January to May, then the curve drastically
decreased during hot summer season for high losses of essential
oil due to high evaporation during hot weather. At autumn the
curve stays horizontal due to negligible decrease or stoppage
of essential losses due to high humidity and low temperature
of Sudan semi-arid zone; and lastly slightly the curve decreased
with decrease of humidity and increase of temperature after
the rainy seasons; this period represent the send hot summer
season in Sudan after the rainy one. At the last there is very slow
decrease due to winter season. This gives an overall conclusion
that the spearmint herb essential oil content was decreased by
storage period under ambient room temperature except autumn
season. These result due to that after drying; the essential oil stay in the oil secretary organ; oil glands; and evaporate without any
replacement; since during the plant life there is compensation
between the evaporated oil through stomata and the oil obtained
by the biosynthesis process in the living cells. After the death of
the living cells of spearmint herb the plant lost stomata and oil
glands flexibility, and the oil content subjected to microclimate
conditions; therefore oil losses is a factor that positively increase
in temperature and negatively with decreasing of humidity in the
surroundings, this finding agree with Salim who postulate that
high temperature during the day results in reduction in essential
oil content . Lastly the climate condition; such as temperature,
evaporation rate, humidity speed of wind and rainfall; of the area
of study changed during the year in Appendix 1-3 are associated
with the evaporation rates.
The oil content of stored spearmint was decreased by 0.1 ml
per 100g every month during the first five months (January –
May) (Figure 3), and then it decreased by 0.2 ml per 100 g every
month during the successive hot months (May-July), which
characterized as a hot season in Sudan semiarid condition. The
high rate of evaporation is due to high temperature during this
period (Appendix 2) which leads to high rate of evaporation
(Appendix 3). During autumn season (July- August), the decrease
was stopped and oil content remained constant at 0.0 ml/100g;
these decreases were due to that high rain during this period lead
to saturation of the surrounding microclimates consequently
increase humidity and temperature which resulted in oil
evaporation; also during this period high cloud, rain (Appendix 3)
and saturated air with humidity leads to reduce the temperature.
The decreased after autumn is by 0.1 ml every month during the
last storage period (September – December) (Figure 3); this is
due to the slight increase of temperature. Essential oils possess
high level of unsaturation and are unstable due to many factors,
such as light, heat, oxidation and dehydration [26,27]. Choi and
Sawamura reported that most essential oils are thermolabile
or heat-sensitive and are subjected to oxidative changes in the
presence of air and light, and during storage . The degree of
change is usually a function of both temperature and time. Other essential oil crops acts the same behavior; oil content declined markedly during storage of black pepper in low density and
high density polyethylene packages  and the major loss of
essential oil in chamomile drug was reported to be due to high
storage temperature .
Oil content of spearmint herb progressively decreased
during storage period at ambient conditions in Sudan semi-arid
conditions and after 12 months of storage the essential oil will be
near to zero percent. The highest decrease during hot summer
season is due to high temperature, low rain and low humidity.
Evaporation and stopped during autumn season are due to high
rain fall, humidity and low temperature which they decreased
the evaporation rate and then losses of stored herb essential oil.
I wish to express my thanks to the staff in the Department of
Horticulture (Faculty of Agriculture, U. of K., Sudan), Medicinal
and Aromatic Plants Institute (NCR, Sudan), Institute of Food
Research Industries at (IRCC, Sudan) and Mr. Mohammed
Damona in Pharmaceutical Industries (IRCC) for their generous
help in conducting extraction. My thanks are also due to IRCC
for financing this research and contribution of everybody who
directly or indirectly shared the help.