Citation
Zainuddin, Noorul Jannah
(2019)
Development of nanoemulsion containing Parthenium hysterophorus L. crude extract for pre-emergence herbicide formulation.
Doctoral thesis, Universiti Putra Malaysia.
Abstract
A nanoemulsion containing Parthenium hysterophorus crude extract (PHCE)
was developed with the aim to introduced nanoemulsion as delivery system for
PHCE in pre-emergence herbicide formulation. Parthenium hysterophorus is a
noxious plant containing allelochemical parthenin with an ability to inhibit the
growth of neighbouring plants. The study on herbicidal activity of P.
hysterophorus was widely reported however, the study on development of PHCE
in herbicide formulation was less explored. Nanoemulsion was proposed as the
delivery system for PHCE to increase the efficiency and stability of plant crude
extract. The use of natural-based active ingredients and adjuvants in
nanoemulsion herbicide formulation was thought to be more environmental
friendly compared to conventional synthetic herbicide.
In the initial stage of the study, the local invasive weed known as Rumput Miang
Mexico (RMM) was genetically identified as P. hysterophorus by using Internal
Transcribes Spacer (ITS) region-based. The collected DNA sequence was
registered in NCBI GenBank® under accession number of KY249559. The
amount of the main allelochemical (parthenin) was determined to be 26.74 mg
g-1 of dry plant by using UPLC-MS spectroscopy analysis.
In the development of P. hysterophorus nanoemulsion (PHNE) formulation,
several oil were tested to solubilize PHCE. Form the result, palm kernel oil ester
(PKOE) was chosen as the oil phase due to the highest concentration of
parthenin (2.43 ± 0.07 mg mL-1) was solubilized as compared to the other tested
oils. Phase behaviour of P. hysterophorus crude extract (PHCE) was studied by
construction of ternary phase diagrams using different surfactants. High solubilisation capacity (isotropic region) was obtained by mixture of surfactants
Tensiofix and Tween 80 (ratio 8:2) compared to the other mixture of surfactants.
One spot was selected as pre-formulation from the isotropic region of PKOE:
PHCE (3:1)/ Tensiofix: Tween 80 (8:2)/ water system and further become the
starting point for composition optimization of PHNE.
Mixture Experimental Design (MED) modelling was used to determine the
optimal composition of PHNE. From the optimization process, analysis of
variance (ANOVA) showed a fit quadratic polynomial model for four independent
variables (PKOE, Tensiofix: Tween 80 (8:2), PHCE and water) in relation to
particle size. The model suggested an optimal formulation composition which
contained 30.91 % of PKOE, 28.48 % of mixed surfactants (Tensiofix and Tween
80, 8:2), 28.32 % of water and 12.29 % of PHCE with the smallest particle size
(140.10 nm) was obtained. The reading of both experimental and predicted
particle size in the verification experiment was acceptable with a residual
standard error (RSE) less than 2 %.
Under the optimal condition, the particle of final formulation was clearly shown
by morphology analysis to be spherical in shape and demonstrated an average
particle size which is in agreement with dynamic light scattering analysis. The
optimized nanoemulsion demonstrated a good stability (no phase separation)
under centrifugation and different storage conditions (25 ± 5 °C and 45 °C).
Manipulating time as parameter, nanoemulsion stored for 60 days exhibit
monodisperse emulsion with narrow distribution of polydispersity index values
(0.07 to 0.08), stable zeta potential values (± 25 mV) and slight increase of
particle size (143.0 nm to 218.5 nm). The increase in particle size over time
might have been contributed by Oswald ripening phenomenon which was shown
by a linear graph from Oswald ripening rate analysis.
In the efficiency test, PHNE was compared with PHCE in terms of surface
tension and phytotoxicity against Diodia ocimifolia seed. PHNE displayed lower
surface tension in comparison to PHCE which suggested that nanoemulsion
might have enhanced the ability of the plant crude extract to penetrate through
plant seed coat. In addition, PHNE was shown to cause total inhibition of D.
ocimifolia seed at lower concentration (5 g L-1) than PHCE (10 g L-1). The ability
of PHCE to inhibit D. ocimifolia seed was almost doubled after being formulated
in nanoemulsion system by having half effective dose (ED50) value for PHNE
(1.93 g L-1) and PHCE (3.60 g L-1). Similarly to the seed germination, PHNE
shown to be more efficient in reducing the growth of radicle and shoots of D.
ocimifolia in compared to the plant crude extract. The finding of the research
could potentially serve as a platform for development of a natural herbicide
formulation from crude plant extract for green weed management.
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