Development of various green extraction techniques and water extraction online particle formation for Moringa oleifera
Date
2019
Authors
Nuapia, Yannick Belo
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Abstract
Moringa oleifera is an excellent source of bioactive compounds which exhibit several nutritional and medicinal properties. Different parts of the plant are used as source material of these compounds. This thesis provides data on: (i) pressurized hot water extraction of vitamin C, polyphenols and other nutrients from Moringa oleifera leaves and, (ii) ultra-high supercritical fluid extraction and characterization of oil compounds from Moringa oleifera and peregrina seeds. In addition, data on water extraction with on-line particle formation developed for drying aqueous extract is also given. The details of the current work are described as follows:
The first part of the work involved the optimization of pressurized hot water extraction for producing Moringa oleifera extract rich in vitamin C and polyphenolic compounds mainly kaempferol and quercetin. This work has been published in South Africa Journal of Botany and it is presented in this thesis as Paper 1. Response surface methodology (RSM) and artificial neural network (ANN) were used to understand the influence of main parameters such as temperature, time and flow rate in the extraction process. The optimal conditions for an efficient pressurized hot water extraction were found to be 91°C for temperature, 60 min for extraction time and 0.3 ml min-1 for flow rate. The predicted concentrations of kaempferol, quercetin and vitamin C was found to be 3.92 ± 0.30 (with a recovery of 94.23%), 4.74 ± 0.32 (with recovery of 93.55%) and 0.357 ± 0.19 (with a recovery of 85.02%) g per 100 g of dry powder, respectively.
Also, macro and micro-nutrients were extracted using pressurized hot water extraction from Moringa oleifera leaves. This work has been submitted to Food Chemistry Journal and it is presented in this thesis as Paper 2. Response surface design of the experiment was applied to investigate the influence of two independent factors which are temperature (50 - 200°C) and time (5 – 60 min) on the behavior pattern of macro and micro-nutrients from the leaves of Moringa oleifera. The obtained results showed that the macro-elements such as Ca, K, Mg, and Na, were less influenced by the extraction temperature while, the micro-nutrients like Al, Co, Cr, Cu, Fe, Ni and Zn depended on the extraction temperature.
The recovery of macro-nutrients ranged from 89±2 to 99±1% while that of micro-nutrients ranged from 23±2 to 37±4%. Therefore, at optimum conditions, more macro-nutrients than micro-nutrients were extracted. This study showed that pressurized hot water extraction was successfully used to extract metal species from Moringa oleifera leaves just like organic compounds.
Pressurized hot water hot extraction was used for the recovery of polyphenol compounds, vitamin C, macro and micro-nutrients from the Moringa oleifera leaves (Paper 1 and 2). The technique uses water as a green solvent and has emerged as a sustainable alternative for the extraction of bioactive compounds from the plant. The main disadvantage of using water as a solvent, compared to organic solvents, is the difficulties to concentrate the obtained extracts. The presence of water might be detrimental to the stability of the extract and increases the cost of transportation of a final commercial product since the amount of bioactive compounds per mass of water extract is low. Drying the water extracts involves extra process steps to obtain a commercial product. Thus, in Paper 3, pressurized hot water extraction of antioxidants and other essential chemicals from Moringa oleifera leaves combined with one-step on-line drying technique, based on the use of supercritical carbon dioxide, was optimized. This extraction process is also called WEPO (water extraction with on-line particle formation). A full factorial design was applied to investigate the influence of three qualitative such as CO2 pressure, CO2 flow rate and nitrogen pressure and five quantitative factors including nitrogen position, use of vacuum, length of the tubing, the internal diameter of the nozzle and additional nitrogen on the particle size and distribution (nm), water content (%) and the amount (mg) of powder collected. These factors were first screened, and qualitative factors were found to be the most important parameters for the optimization of the WEPO technique. The obtained optimum conditions for fine and dried particles were found to be 90.95 bars CO2 pressure, 16 ml min-1 flow rate of CO2 and 26 bars nitrogen pressure. With these conditions, the amount of powder collected, water content and the average size of particles were 150 ± 10 mg, 3.58 ± 0.56% and 384.33 ± 21.36 nm, respectively. Results were compared with those from extracts obtained by continuous flow PHWE followed by a freeze and spray drying techniques. The results showed that the WEPO process gave fast results with well-defined particles and uniform particle sizes and exhibiting high water solubility as compared with other techniques. Ultra-high-pressure supercritical fluid extraction method was optimized and applied to the extract, and characterized oil from two Moringa species namely, Moringa oleifera and peregrina seeds (Paper 4). A full factorial design was used to investigate the influence of pressure and temperature (40 to 80 MPa and 40 to 70ᵒC, respectively), on the amount of oil extracted from crushed seeds. The results revealed that pressure has significant positive influence on the amount of oil extracted. The optimum conditions were found at 80 MPa and 57ᵒC. The extracted amounts obtained at optimum conditions were 396 ± 23 and 529 ± 26 mg per sample mass, for Moringa oleifera and peregina seed oil, respectively. The extraction kinetics study revealed a mainly solubility-controlled extraction of oil; and 28 g of CO2 was required to extract 400 mg of oil per gram of seeds using the developed method. Addition of ethanol into the extraction vessel prior to the extraction increased the polar fraction in the oil extracted. The developed method increased the extracted oil by two folds compared to a sonication method. The obtained oil consisted mainly of glycerolipids, sterol esters and phospholipids. Phospholipids, campesterol and stigmasterol esters were found higher in Moringa oleifera while cholesterol esters were more abundant in Moringa peregrina.
Description
A thesis submitted to the Faculty of Science, University of the Witwatersrand in fulfilment of the requirements for the degree of Doctor of Philosophy WITS University, Johannesburg, 2019