Parametric optimization of microwave reflux extraction of spice oleoresin from white pepper (Piper nigrum)
© The Author(s). 2017
Received: 16 October 2016
Accepted: 8 April 2017
Published: 27 April 2017
White Piper nigrum is an important commodity crop containing a number of essential bioactive components with nutritional and medicinal properties when sufficiently extracted. Microwave refluxation is therefore a novel technique employed in the extraction of bioactive components from natural products of plant origin. This method doubled as classical and traditional solvent extraction techniques with reduced extraction time, higher selectivity, low solvent consumption, and higher extraction rate.
The Taguchi L9-orthogonal design was employed to determine a combination of extraction factors that jointly optimized the extraction yield. The use of this para metric design was due to its ability to mitigate inherent noise factor with minimal experimental trials.
The optimal extraction condition was attained at 90 min of irradiation time, 300 W of microwave power, 0.105 mm of particle size, and 10 ml/g of molar ratio. Under this condition, the corresponding optimum extraction yield of 4.278 (v/w)% was obtained. Moreover, the percentage contribution of each extraction factor on the response settings resulted in the decreasing order: irradiation time > molar ratio > power level > particle size. Phytochemical screening was condcuted on the oleoresin extracts and a total number of 26 bioactive compounds were identified. Also, the Fourier Transform Infrared Analysis (FTIR) and the Scanning Eectron Microscopy (SEM) confirmed the presence of seven presence of seven functional groups with an observable structural transformation.
The result of optimum design, phytochemical screening, and structural characterization therefore provided a better understanding on the potential of microwave refluxation in extracting spice oleoresin from white Piper nigrum.
The medicinal property of white pepper is due to the presence of an active compound called piperine with a molecular formula of C17H19NO3 (Rmili et al. 2014). Vasavirama and Upender (2014) reported that white pepper is made up of 4.6–9% piperine, 6% pungent resin, 2.5% essential oil, and starch. The oleoresin extracts from white pepper possess a characteristics anti-inflammatory (Mustapa et al. 2015), antidepressant (Madhu et al. 2009), analgesic (Sabina et al. 2013), anti-rheumatic (Nahak and Sahu 2011), and adiabatic (Peña-Alvarez et al. 2009) properties. Due to its ability to demobilize cancer, it is used as bio-enhancer when combined with other drugs in cancer treatment. This is because it increases the bioavailability and efficacy of other drugs (Janakiraman and Manavalan 2008). Raman and V. G. Gaikar (2002) reported that oleoresin extracts does not have pharmacological activity of its own but enhances the assimilation of other drugs.
Many researchers had reported the conventional way of extracting bioactive compounds from white pepper and these include cold percolation (Vittal, 1990) maceration (Singh et al. 2013), soxhlet extraction (Vasavirama and Upender 2014), hydrotropic solubilization (Raman and Gaikar 2002; Mageed 2011), and hydro-distillation (Rmili et al. 2014; Abdurahman and Olalere 2016a). However, several limitations in the used of this method include high solvent consumption, low extraction yield, solvent contamination, higher cost of extraction, and longer extraction time. These setbacks necessitated the use of an improved extraction method involving lower solvent consumption, shorter irradiation time, higher yield, higher selectivity, and environmental friendly. Microwave reflux extraction is a method that provides an efficient way of extracting spice oleoresins from plant matrix (Abdurahman and Olalere 2016b). It works on the principle of ionic conduction and dipole interaction of electric and magnetic field. The ionic conduction offers stiff resistance to the movement of ions which generates an heating effect on the irradiation medium (Abdurahman and Olalere 2016b). An effective extraction is therefore achievable through the use of a multi-directional heating in relation to surface area of the plant matrix. According to Mohan et al. (2013), the reflux microwave extraction is the most appropriate method for extracting samples from plant origin. Therefore, the aim of this study is to determine a combination of operating conditions for an optimum extraction yield of spice oleoresin from white pepper using taguchi orthogonal design.
A standard grade white pepper was purchased from Malaysian Pepper Board (MPB), Sarawak, Malaysia. The initial moisture content was 3–4% and was then oven dried at 60 °C for 2 h. The pepper seeds were then crushed and sieved into five different powdered sizes of 0.105, 0.154, 0.30, 0.450, and 0.90 mm. These were neatly packed inside a sealed nylon for subsequent extraction.
Microwave water-reflux extraction
The extract was analyzed using GC-MS (Agilent 5973-model, USA) equipped with C-18 column (30 mm tubular column diameter, 0.25-mm internal diameter and 0.25-μm film thickness). The column initial oven hold was operated at 50 °C for 5min and then allowed to rise to 250 °C at 3 °C per minute with an additional 300 °C for 5 min. A small portion of clear golden-colored supernatant solution was filtered using the 0.45 μm PTFE micro filter and diluted with analytical grade acetone to 1:10. One microliter of the diluted solution was then injected into the gas chromatography column at 280 °C at a helium gas velocity of 1 ml/min. The peak area fragmentation fingerprints for different components were matched with the NIST05a.Library database.
Characterization of residue and oleoresin extract
Fourier transform infrared spectroscopy (FTIR) was carried out to determine the bonding structures and functional group characteristics of the liquid extracts. This was performed using a Thermo-Nicolet 6700-IR spectrometer equipped with a DTGS detector and KBr Beam-splitter. The analysis was executed using the conventional KBr standard procedure with wave number ranging from 4000–500 cm−1. Under this study the spectral from the oleoresin extract with characteristics bond and group frequencies were compared with the table of expected absorption bands of different functional groups (Chupin et al. 2015). SEM-images of dried residue were analyzed before and after extraction, to determine the morphological transformation occassioned by the microwave radiation.
Results and discussion
Effect of irradiation time
Effect of microwave power
Effect of feed particle size
Effect of molar ratio
Determination of factor range
Extraction factors and levels
Level 1 (−1)
Level 2 (0)
Level 3 (+1)
Feed particle size
where y is the response value, and n is the number of observation.
L9 (3^4) experimental matrix, response and SN-ratio
Irradiation time (min)
Extraction yield (v/w)%
0.49 ± 0.02
0.62 ± 0.01
1.83 ± 0.04
0.17 ± 0.07
0.21 ± 0.08
0.92 ± 0.01
0.26 ± 0.05
4.28 ± 0.04
1.87 ± 0.32
Average mean effects
Main effect of response means
Irradiation time (min)
Chemical composition of the oleoresin extracts
GC-MS analysis of various components inside the oleoresins
Composition (% mass)
Functional groups from the FTIR-analysis
C = O ketone
C = O stretching
=C-O-C asymmetrical stretching
O-H alcohol-strong and broad
The optimum operating condition for the extraction of spice oleoresin from white pepper was attained at 90 min of irradiation time, 300 W of microwave power, 0.105 mm of particle size, and 10 ml/g of molar ratio. Under this condition, the optimal extraction yield of 4.278(v/w)% was obtained. The decreasing order of significance of the four extraction factors was given as irradiation time > molar ratio > power level > particle size. This study therefore suggests that for an optimized extraction of spice oleoresin from white pepper, the irradiation time must be properly monitored being the most significant factor in the extraction process. The phytochemical screening and FTIR analyses on the extracts confirmed the presence of a total of 26 bioactive chemical compounds and seven functional groups. The SEM images further elucidated the structural transformation of the white pepper matrix as a result of microwave heating. The results established the potential of microwave reflux extraction as an efficient and productive extraction technique.
The authors wish to acknowledge the financial support and sponsorship from the Doctoral Scholarship Scheme of the Malay sian Ministry of Education (MOE), and the PGRS-160320 research grant from Universiti Malaysia Pahang (UMP), Malaysia.
OOA conducted the experiments and developed the robust experimental design. AHN supervised the experimental and provided useful insight into the project. AOR conducted the GC-Ms analysis and typesetting of the manuscripts. OAH helped in the statistical analysis of the experimental data. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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